NOTES ON CV 102 BASIC CIVIL ENGINEERING (for internal circulation only)
DEPARTMENT OF CIVIL ENGINEERING NATIONAL INSTITUTE OF TECHNOLOGY TIRUCHIRAPPALLI – 620 015
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CV 102 BASIC CIVIL ENGINEERING
Properties Properties and uses of construction materials such as stones, bricks, cement, concrete and steel. Site Site select selection ion for buildi building ng – Comp Compone onents nts of Build Building ing-- founda foundatio tions ns – Shallo Shallow w and De Deep ep foundations – brick and stone masonry – plastering – lintels, beams and columns – roofs.
Roads – Classification of rural and urban roads – pavement materials – Traffic signs and road markings – Traffic signals.
Surve Surveyin yingg- Class Classifi ificat cation ion – Chain Chain surve survey y – Rangi Ranging ng – Comp Compass ass survey survey – Exhib Exhibiti ition on of different survey equipments. equipments.
Water supply – Quality of water – wastewater treatment unit – their functional utility – Need for conservation of water.
Text Books:
1. Build Building ing Cons Constru tructi ction on by Sushi Sushill Kumar Kumar 2. Building Building Materials Materials by S.C. S.C. Rangw Rangwala ala
Reference:
Lecture Notes prepared by the Department of Civil Engineering/ NITT
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TABLE OF CONTENTS
I Building Materials Stones Brick Cement Concrete Steel II Building Components Site Selection for Building Foundation Masonry Plastering Lintels Columns Slabs Beams Roofs III Services Roads Surveying Environmental Engineering
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UNIT I BUILDING MATERIALS STONES
Stone is a naturally available material of construction and is obtained from rocks. Classification of Rocks Rocks are classified in following three ways 1. Geological Classification 2. Physical Classification 3. Chemical Classification 1. Geological Classification Based on the mode of formation, the rocks are classified as: i. Igneous Rocks ii. Sedimentary Rocks iii. Metamorphic Rocks i. Igneous Rocks: These rocks are formed by the cooling of molten rocky material called magma which is inside the earth's surface. If the magma cools at a considerable depth from earth's surface then it is called Plutonic rock. The cooling is slow and hence these rocks possess coarsely grained crystalline structure. eg. Granite.
If the magma cools at a relatively shallow depth from earth's surface then it is called Hyperbyssal rocks. The cooling is quick and hence these rocks possess finely grained crystalline structure eg. Dolerite. If the magma cools at earth's surface than it is called volcanic rocks. The cooling is very rapid and hence these rocks possess extremely fine grained structure. eg. Basalt. ii. Sedimentary Rocks: Sedimentary rocks are formed by the deposition of products of weathering on the pre-existing rock. All the products of weathering are u1timately carried away from their place of origin by the agents of wind, rain, frost, etc. eg. Sandstone, Limestone, Gypsum, Gravel etc iii. Metamorphic Rocks: When the pre-existing rocks (i.e. Igneous and Sedimentary rocks) are subject to great heat and pressure, they are changed in character and forms metamorphic rocks. eg. Slate, Marble, Gneisses. 2. Physical Classification Based on general structure the rocks are classified as i) Stratified Rocks ii) Un Stratified Rocks iii) Foliated Rocks. i) Stratified Rocks: These rocks possess planes of stratification and such rocks can easily be split up along these planes. eg. Sedimentary Rocks.
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ii)Unstratified Rocks: These rocks do not exhibit any definite layers or strata. The structure of these rocks may be crystalline, granular or compact granular. eg. Igneous rocks. iii) Foliated Rocks: These rocks have a tendency to be split up in a definite direction only. eg. Metamorphic Rocks. 3. Chemical Classification Based on chemical constituents, the rocks are classified as i) Silicious Rocks ii) Argillaceous Rocks iii)Calcareous Rocks. i) Silicious Rocks: In these rocks, Silica is the main constituent. eg. Granite Quartzites etc. ii) Argillaceous Rocks: In these rocks, clay or argil is the main constituent. eg. Slates, Laterites etc. iii) Calcareous Rocks: In these rocks, Calcium Carbonate is the main constituent eg. Lime stones, Marbles etc. Tests for Stones The following are the tests conducted on stones to decide construction work
1. 2. 3. 4. 5. 6. 7. 8.
Impact test Crushing strength test Attrition test Hardness Test Water absorption test Freezing and thawing test Microscopic test Smith's test
1. Impact test: In this test, a cylinder of diameter 25 mm and height 25 mm is taken out from the sample of stone. A steel hammer of wt 2 Kg is allowed to fall axially on the cylinder from 1cm height for first blow, 2 cm height for second blow etc. Blow at which the specimen breaks is noted. If it is nth blow, n represents the toughness index of stone. 2. Crushing Strength test: In this test, a cube of stone is tested in a compression testing machine. The rate of loading is 4.0 N / mm2 per minute. The maximum load at which the stone crushes is noted.
Crushing Strength of the stone = Max load / Area of bearing face of the stone 3. Attrition test: In this test, some known weight of stone pieces are taken and put in the Deval's attrition test cylinder. The cylinder is rotated about its horizontal axis for 5 hrs at the rate of 30 RPM. Then the contents in the cylinder are sieved by 1.5 mm sieve. The quantity of material which is retained on the sieve is weighed.
Initial Weight Percentage of Wear =
Loss in Weight
6
x 100
4. Hardness Test: In this test, a cylinder of stone diameter 25 mm and height 25 mm is placed in Dorry’s testing machine and pressed with a pressure of 12.5 N. The annular steel disc of the machine is rotated at a speed of 28 RPM. During rotation coarse sand of standard specification is sprinkled on the top of disc. After 1000 revolutions, the specimen is taken out and weighed. The coefficient of hardness is given by the formula
Loss in weight in g Coefficient of hardness = 20 -
3
5. Water absorption test: In this test, a stone of known weight is immersed in water for 24 hrs. Then it is weighed again after 24 hrs and the percentage absorption of water should not exceed 0.6 6. Freezing and thawing test: In this test specimen of stone is placed in freezing mixture at12°c for 24 hours and it is then warmed at atmospheric temperature. The procedure is repeated for several times and the behavior of stone is noted. 7. Microscopic test: In this test, thin sections of stone are taken and they are examined in a microscope to study various properties like grain size, mineral constituents etc. 8. Smith’s test: In this test, clear water is taken in a test and pieces of stones are placed in it. The tube is vigorously stirred. If the water becomes dirty it indicates the stone contains earthy matter. Qualities of Good Building Stone
A good building stone should have the following qualities: 1. The crushing strength of stone should be greater than 100 N/mm2. 2. Stones must be decent in appearance and be of uniform colour. 3. Stones must be durable. Their natural bed must be perpendicular to the direction of pressure. 4. Stones should be easily carved and dressed. 5. Fracture should be sharp and clear. 6. For a good building stone, co-efficient of hardness should not be below 14. It should be hard enough to resist wear and tear. 7. It must have a wear less than 3 percent. 8. It must be fire resistant. 9. It should not contain quarry sap which is nothing but moisture present in the stones. 10. It must have a specific gravity of greater than 2.7. 11. It must have a compact, fine, crystalline structure, strong and durable. 12. The toughness index must not be less than 13. 13. It must be acid resistant and free form any soluble matter. 14. When a stone is immersed in water for 24 hrs, the percentage absorption by weight should not exceed 0.6
Uses of Stones
7
1. Stones are used as basic material for concrete, moorum of roads, calcareous cements etc. 2. Stones are used in the construction of foundation, walls, columns, lintels, arches, roofs etc. 3. Stones are used to cover floor of buildings of various types such as residential, commercial, industrial etc. 4. Stones are adopted to form paving of roads and foot paths. 5. Stones are converted to form basic materials for concrete, moorum of roads, artificial stones, hollow blocks, etc. 6. Stones are also used as ballast for railway track. 7. Stones are used as flux in blast furnace. 8. Stone blocks are used in the construction of bridges, piers, abutments retaining wall, dams etc. 9. In modern days, polished stone panels are used as cladding for architectural purposes and also polished stone slabs are replacing the dining table tops in residential houses and restaurants.
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BRICKS
Bricks are artificial blocks manufactured from tempered clay into standard sizes. They are extensively used for building construction. Bricks are very popular because of their easy availability, economy, strength, durability, reliability and insulating properties. Bricks are manufactured from Earth containing alumina (20 to 30%) Silica (50 to 60%), Iron Oxide (5 to 6%) and small quantities of lime and magnesia. Manufacture of Bricks
Manufacture of bricks involves the following operations 1. Preparation of brick earth 2. Moulding 3. Drying 4. Burnings 1. Preparation of Brick Earth Clay to be used for the manufacture of the bricks has to be prepared carefully. This includes the following operations Removal of loose soil: The top layer of loose soil should be removed for a depth of 20 cm. It should not be used for preparation of bricks as it contains lot of impurities. Digging, spreading and cleaning: The earth removed from below 20 cm is spread on a level ground. All undesirable materials like grass, roots, gravel etc are removed. Weathering: The spread earth is left as such for a few weeks to allow the clay to mellow Blending: This consists of mixing the clay with suitable ingredients by turning up and down many times. Tempering: This is done to make the whole mass of clay, homogenous and plastic. This is done by trampling under feet by men or cattle in a Pug mill when bricks are required on large scale.
A Pug Mill is a conical iron tub provided with a vertical iron shaft. Numbers of horizontal arms with several cutting blades are attached to this shaft. The brick earth is put inside the pug mill and the shaft is revolved by bullocks or steam, diesel or electric power. The rotation of the shaft causes the breaking up of lumps and clods of clay. The clay gets pugged and tempered. 2. Moulding The pugged brick earth is then moulded into shape in moulds. Moulding can be done on the ground or on top of a table, either by hand or machine.
Ground Moulding: A piece of ground is selected, levelled and plastered. Fine sand is sprinkled and then the mould is placed on top of it. The tempered clay is taken in hand and dashed into the mould till the mould gets filled with clay. Excess earth is removed. Then the mould is removed slowly and carefully leaving the moulded brick on the ground.
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Table Moulding: In this the moulder stands near a table and the moulding is done on top of the table. The moulder can mould 500 to 1000 bricks per day. Machine Moulding: Hard, Strong clay can be moulded by this method. This is adopted when a large number of bricks have to be moulded. There is a variety of moulding machine in the Western Country. In India the Central Building Research Institute, Roorkee has developed a hand operated earth moulding machine. The thoroughly pugged brick earth is pushed under pressure through an opening whose length and breadth is equal to the length and breadth of brick.
The pushed out p1astic bank is cut to the desired thickness of bricks by wires, fitted in a frame at distances equal to the brick thickness. The machine moulded bricks have sharp edges and corner, smooth external surface and uniform texture. 3. Drying After the bricks are moulded, they are, dried. This is done on specially prepared drying beds which must be higher than the surrounding ground. Bricks are dried for a period of 7 to 14 days. During drying this must be protected from wind, rain and direct sun. 4. Burning After drying the bricks area burned in kilns of clamps to make them harder, stronger, denser, less absorbent and more durable. Burning in Clamps: A clamp is an arrangement where the bricks and fuel are arranged in alternate layers. A floor is prepared and the fuel is first spread at slope of 15°. The fuel consists of wooden piece, cow dung, straw, waste paper etc., On top of this layer the raw bricks are placed. Then another layer, of 75cm. thick fuel is spread. Thus alternate layer of brick and fuel are arranged to a height of 3 to 4 cm. Then entire clamp is plastered on all the sides and top and filled with earth cover to conserve the heat. The bricks are burnt for a period of one or two months and then cooled for the same period. After cooling the burnt bricks are removed. Burning in Kilns: When large number of bricks have to be burnt Kiln are adopted. Kilns are of two types
1. Intermittent Kilns and 2. Continuous Kilns In intermittent Kilns the loading firing cooling and unloading are done one after the other and not simultaneously whereas in continuous these operations are carried out without any interruptions. A kiln is an enclosure made of thick walls and provided with doors for loading and unloading operations. Arrangements are made to carry and circulate hot air and gases through the body of the kiln by providing flues. The kiln is provided with a roof. Among the various types of kilns adopted the Hoffman’s Kiln is very popular, it can produce about 2,000 to 25,000 burnt bricks per day. Merits and demerits of Clamp and Kiln burning of Bricks
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Clamp Burning: 1. It is a temporary structure 2. Initial cost is low 3. Amount of fuel used is low and hence economical 4. Continuous supervision is not necessary 5. Quality of bricks is poor. Only 60% is of First Class variety. 6. Firing cannot be regulated 7. It takes a long time for burning and cooling the bricks (3 to 6 months). 8. Used when small number of bricks required at a time. Each clamp can turnout one lakh bricks at a time. 9. There is large amount of wastage of heat from the hot gases. Kiln Burning: 1. It is a permanent structure 2. Initial cost is higher 3. Fuel cost is higher 4. Constant supervision is necessary 5. Quality of bricks turned out is good. 90% first class bricks 6. Time of firing is only 24 hours and cooling is 12 days. 7. It is yielding about 25,000 bricks per clay 8. Heat of hot gases is utilized in heating bricks to be burnt. Size and Weight of Bricks The Indian Standards Institution, New Delhi has specified, standard bricks of 19cm x 9cm x 9cm with 1cm thick mortar joints. This standard brick weight is 3kg. Classification of Bricks Bricks are classified as under 1. First class bricks: Table moulded edges are clear, square straight. Used for superior works. 2. Second class bricks: Ground moulded burnt in kilns surface not smooth and edges not regular used where the bricks work will be plastered. 3. Third c1ass bricks: Ground moulded not hard rough surface and edges are also not sharp and regular. Used for unimportant and temporary constructions. 4. Fourth class bricks : These are over burnt bricks dark in colour and irregular. Used as aggregates for concrete foundations, floors, roads etc. Characteristics of Good Bricks A good brick should satisfy the following essential qualities 1. Colour should be uniform. Colour should be red. Well burnt and sound bricks have these colours. 2. The bricks should have even surfaces free from flaw or cracks and should have sharp well defined edges. 3. These should be so hard that no impression should be left when scratched with finger nails. 4. These should produce clear ringing sound when struck against each other. 5. No brick should absorb more than 15% of its weight of water when kept immersed in for 24 hours. 6. No brick should have a crushing strength less than 3.5 N/mm2. 7. On breaking the surface it should show a bright homogeneous and compact surface
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free from voids 8. A brick soaked in water should not show any deposit of white salts on drying in shade. 9. When dropped flat from a height of 1m the brick should not break. 10. Bricks should not conduct most heat and they should be sound proof. Testing of Bricks For deciding the suitability of bricks the following tests are to be conducted. 1. Absorption test: A brick is taken and it is weighed dry. It is then immersed in water for a period of 16 hours. It is weighted again and the difference in weight indicates the amount of water absorbed by the brick. It should not, in any case, exceed 20 percent of weight of dry brick. 2. Crushing strength test: Crushing strength of a brick is found out dry by placing it in compression testing machine. It is pressed till it breaks. Minimum crushing strength of bricks is 3.5 N/mm2and for superior bricks; it may vary from 7.0 to 14.0 N/mm2 3. Soundness test: In this test, two bricks are taken and they are struck with each other. Bricks should not break and a clear ringing sound should be produced. 4. Hardness test: In this test, a scratch is made on brick surface with the help of a finger nail. If no impression is left on the surface then the brick is treated to be sufficiently hard. 5. Test for presence of soluble salts: Soluble salts, if present in bricks, will cause efflorescence on the surface of bricks. For finding out the presence of soluble salts in a brick, it is immersed in water for 24 hours. It is then taken out and allowed to dry in shade. Absence of grey or white deposits cover about 10 percent surface, the efflorescence is said to be slight and it is considered as moderate, when the white deposits cover about 50 percent of surface, the efflorescence becomes heavy and it is treated as serious, when such deposits are converted into powdery mass.
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CEMENT
It is the product which is obtained by burning and crushing to powder a well proportioned mixture of calcareous and argillaceous materials. It was introduced in 1824 by Joseph Asp Din a brick layer of Leeds, England. After hardening it resembles in colour to the stone quarried near Portland in England, so it is named after that as Portland cement. It is available in different varieties and the selection of variety depends upon the condition, strength and the type of structure. Raw materials required for manufacture of cement are: 1. Calcareous and 2. Argillaceous material Calcareous Materials: Calcareous materials are those materials which contain calcium or lime as their main constituents such as lime stone, chalk etc. Argillaceous Materials: Argillaceous materials are those materials which contain alumina as their main constituents such as shale, laterite etc. It provides the required proportion of silica, clay, oxide of iron to the cement. Proportion of mixing
The ingredients are generally mixed in the ratio of two parts of Calcareous materials and one part argillaceous material. Limestone and shale are first crushed and then they are mixed either in wet state or in dry state by grounding them together. The mixture is then burnt in a rotary kiln at a temperature between 1400°C and l500°C. Pulverized coal, gas or oil being used as the fuel. The clinker so obtained is first cooled and then gypsum (3 to 4%) is added and it is grounded to the required fineness. Main chemical Ingredients of Cement (Raw Stage) Sl. No.
Ingredient
Composition
Percentage
1
Lime
CaO
60 to 67
2
Silica
Sio2
17 to 25
3
Iron Oxide
Fe2O3
0.5 to 6
4
Alumina
Al2O3
3 to 8
5
Gypsum or Calcium Sulphate
CaSO4
3 to 4
6
Magenisum Oxide
MgO
0.1 to 4
7
Sulphur Trioxide
SO3
1 to 3
8
Alkalies such as soda
NaOK2O
0.1 to 1
Functions and Effects of Various Ingredients Lime: It makes the cement sound and provides strength to the cement. Excess of it in original form causes the cement to expand and disintegrate.
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Silica: It provides strength to the cement. In excess it slows down the setting of cement. Alumina: It provides quick setting property to the cement. In excess it weakens the strength of cement. Calcium Sulphate (Gypsum): It helps in increasing the initial setting time of cement. Iron Oxide: It provides colour, hardness and strength to the cement. Magnesium Oxide: It provides colour and hardness to the cement. Excess of it in free state makes the cement unsound. Sulphur Trioxide: In small quantity it makes the cement sound and in excess it makes the cement unsound. Alkalies: In excess it causes efflorescence. Final compounds of Cement Sl. No. 1
Formula
Abbreviation
Range
Dicalcium silicate
2(CaO)SiO2
C2S
21 to 45%
2
Tricalcium silicate
3(CaO)SiO2
C3S
25 to 50%
3
Tricalcium Aluminate
3(CaO)Al2O3
C3A
5 to 11%
4
Tetra Calcium Aluminum Ferrite Other Constituents and Gypsum
4(CaO)Al2O3 Fe2O3
C4AF
9 to 14%
5
C2S 1. 2. 3. 4.
Compound
-
-
8%
It hydrates slowly. It hardens more slowly It provides ultimate strength to the cement. It has more resistance to chemica1 attack.
C3S 1. It hydrates more rapidly. 2. It develops early strength. 3. It generates heat more rapidly and has less resistance to chemical attack. C3A 1. It is fast reacting with large amount of heat generation. 2. It causes initial setting of cement. 3. It is weak against sulphate attack.
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C4AF 1. It is comparatively inactive. 2. It has poor cementing value. 3. It is slow in reaction with small heat generation.
Properties of Cement Fineness: It is the degree of grinding of cement. The rate of reaction depends upon the fineness of grinding i.e. it increases with the fineness and vice versa, causing early setting and greater heat which is the main cause of cracks due to expansion and contraction. A coarser particle settles down in concrete causing bleeding. It is measured in terms of percentage weight retained, on BIS Sieve No.9 after 15 minutes sieving. For accurate measurement it is measured by surface area, air permeability method and the unit is cm2/gram of cement. Setting Time: Setting of cement is the phenomenon by virtue of which the green cement changes into hard mass. Initial setting is a stage in the process of hardening after which any crack that may appear will not reunite and the completion of this process is, known as final setting time. The time between water is added in cement and initial setting takes place is known as Initial Setting Time.
In order that the concrete may be placed in position conveniently, initial setting time of cement should be sufficient and after lying the hardening should be rapid so that structure can be available for use early in time. Cement should not loose its plasticity till the various operations of mixing, transporting and placing are complete. Hence this time is generally kept not less than 30 minutes. Strength: The quality of concrete and cement is always judged by strength and that is only by compressive strength because cement is weak in tension and for it steel reinforcement is always provided. For this purpose cement and standard sand are mixed in the ratio of 1:3 and sand should be as per BIS 650 -1966 i.e. Standard Leighton Buzzard sand. It is light greyish white in colour. Soundness: Free lime and magnesia present in cement makes the cement unsound by increasing the volume after setting. Because when water is mixed with free lime it disintegrates. So these compounds should be present within limits. It is generally measured by Le-Chatelier method or by Autoclave method. Heat of Hydration: Setting of cement is due to chemical reactions between cement and water and this process is known as Hydration. As, this reaction is exothermal process, so sufficient heat is generated and this process continues for an indefinite period at a diminishing rate. This heat causes unequal expansion in mass concrete structure such as dams, retaining walls etc. For such works low heat cement is always recommended. It is always measured in calories/gram unit. Different Types of Cement
1. Ordinary Portland cement. 2. Rapid Hardening Portland cement 3. Low Heat Portland cement 15
4. Portland Blast Furnace slag cement 5. Portland Sulphate resistant cement 6. Air entraining portland cement 7. White and coloured cement 8. High Alumina cement 9. Pozzoana cement 10. Oil well cement 11. Quick setting cement 12. Expanding cement 1. Ordinary Portland Cement: It is also known as Normal setting cement. It is general purpose cement suitable for all purpose. It is used in Road pavements, buildings, culverts, water pipes etc. In the other sense it is used every where except in places where special properties of other types are required. Out of the total consumption of different types of cement 90% of this type is used.
2. Rapid Hardening Cement: Its manufacturing process is same as that of ordinary cement except chemical composition, degree of grinding and temperature of burning. It contains less quantity of C2S and more quantity of C3S. It is generally used where high early strength is required and so it is some times called as High Early Strength Portland cement.
It is used by concrete product manufactures, highway pavements which are to be opened early for road traffic and in cold weather concreting due to its high heat of hydration development. 3. Low Heat Portland Cement: This cement is so called because it develops low heat at the time of hydration. It contains C3A and; C3S in less quantity because they develop early heat. It develops strength quite late and so not advised to concrete structures as it requires shuttering and curing, for a longer period. It is generally used in massive concrete structures such as dams, bridge, abutments, retaining walls etc. 4. Blast Furnace Slag Cement: As the name indicates in this cement granulated blast furnace slag is grained along with cement clinkers. Percentage of slag varies from 25 to 65%. It is cheaper as compared to ordinary cement because waste product is used in it. It can also be used in massive concrete such as dams, bridges etc. It has a1so the capacity to resist sulphate bearing soils, and water. Hence good for use in marine structures and construction in marshy areas. 5. Sulphate Resistant Portland Cement: It contains very low percentage of C3A and C4AF. Because when C3A and C4AF come in contact with sulphates they form sulpho aluminates causing swelling and disintegration. It is used in canal lining, construction of pipe lines and culverts etc. 6. Air Entraining Portland Cement: It is ordinary Portland cement mixed with small quantities or air entertaining materials during grinding. The diameter of air bubbles varies from 0.075 mm and 1.25 mm. On account of air bubbles the strength of cement is reduced. Air bubbles are permitted only up to 3 to 4 percentage, as these reduce 10 to 15% strength of cement. Air entraining materials are Dorex Resin, Vinsol, Resin, oils and Fats etc. These should be 0.01% to 0.05% by weight of cement. This cement is more plastic and workable causing less segregation and bleeding in concrete. It makes the concrete more resistant to freezing. It. also reduces the water requirement and has high resistance to weather. This cement
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is generally used in making insulated walls, roof slabs, and light weight concrete and the concrete which is subjected to freezing and thawing.
7. White and Coloured Cement: In it white chalk and china clay are used instead of lime stone and clay as these are having low percentage of Iron Oxide i.e.1 %. Oil is used as fuel to avoid contamination o£ coal ash. It is 3 to 4 times costlier than ordinary cement. It is used for decorative floorings. Bridge railings, traffic curbs and aerodrome markings.
For coloured cement suitable pigments varying from 5 to 10% free from soluble salts are added during grinding. Iron oxide gives Red, Yellow and Brown colour. Chromium dioxide gives green and cobalt Blue gives blue coloured cement is used for decorations only such as Terrazzo Floor finishes swimming pools etc.
8. High Alumina Cement: It contains 35% to 45% of aluminates Bauxite and chalk or lime stone are mixed dry and heated till they melt and on cooling they form clinkers. These clinkers are then grounded to the required fineness. It is dark in colour and initial setting time varies from 3 to 6 hrs and final setting takes place with in 2 hours of the Initial set. Its setting times are controlled by the rate of cooling of the fused product. It is highly resistant to heat and the strength is more. It is high resistant to attack of sulphates. It gives h igh heat of hydration and, is also costlier than ordinary Portland cement. It is used in structures subjected to the action of sea water, chemical and sulphate bearing water. It is generally used for chemical plants and in lining of furnaces. It can also be used in cold weather concreting. 9. Pozzolana Cement: Pozzolana is a naturally occurring material such as volcanic ash or Pumice stone or an artificial product such as burnt clay or shale containing siliceous and aluminous mineral substances. As per BIS 1489-1967, the proportion of pozzolana material varies from 10 to 25% by weight of cement. It increases the workability, reduces heat of hydration, and increases the water tightness. It also offers greater resistance against sulphatic action and sea water. It is used in the construction of massive concrete structures such as dams, bridge abutments and retaining wall etc. This cement has been also used in Bhakra Nangal Dam. 10. Oil Well Cement: As the name indicates, it is used for cementing; oil wells. It is used at greeter depth under high temperature and pressure. As approximately 3 hrs are required to, pump the cement to fill the space between steel tube lining and wall of the well, so it should not set during this period. Iron Oxide is so adjusted that all the alumina is converted into C4AF and sc proportion of C3A is very small, high increases the setting time of cement and also hardens quickly after setting. It protects the oil well causing from corrosion and also help in supporting the oil well casing and thus reduce the tension, in steel pipes. It also fills up the porous strata preventing water or gas from gaining access in the oil bearing strata. 11. Quick Setting Cement: It has less proportion of CaSO4 (Gypsum) or a small % of aluminium sulphate is added at the time of grinding. It is grounded much finer than ordinary Portland cement. Its initial setting time is 5 minutes and final setting time is 30 minutes. It is used for concreting under or in running water and only in special circumstances as it gives very little time for mixing .
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12. Expanding Cement: As per the name, its volume increases on hardening. It takes about 15 days-for the expansion to occur fully but the time can be controlled by curing. The upper limit of expansion is 1%. The agent which causes expansion is Calcium Sulpho Aluminate (3CaOA12O33CaSO4) which is formed by the presence of calcium sulphate with Calcium Oxide present in cement in sufficient quantity. Field Tests on Cement:
1.The colour of cement should be uniform gray with light greenish shade. 2.Cement should feel smooth when touched. 3.If hand is inserted in a bag of cement it should feel cool not warm. 4.If a small quantity of cement is thrown in a bucket of water, it should sink and should not float on the surface. 5.Cement should be free from any hard lumps. A sample meant for testing shall be drawn from at least 12 different bags or barrels or containers or from 12 different positions in a heap if cement is loose. Chemical composition of cement should be checked for B. I. S. specifications. Laboratory Tests on Cement: 1. Fineness of Cement: 100 gm of cement is weighed accurately and placed on IS: sieve No. 9 (90 micron). Any air lumps are broken using fingers. Now gentle sieving is done continuously for fifteen minutes. The residue left is weighed. This shall not exceed 10% by weight of the sample of cement special methods have been devised in which it is possible to estimate the particle size distribution. This is estimated in terms of the specific surface, i.e., the surface area per unit weight. 2. Consistency: This is a test conducted to estimate the quantity of water to be mixed in cement to form a paste of normal consistency for use in other tests. 300 gms of cement should be weighed. To this about 25% of water should be mixed. The paste obtained should be filled in the mould of the Vicat apparatus. The interval of time between the instant of adding water to the dry cement and the instant of commencement of filling the mould is called the time of gauging.
The plunger, the biggest of the three needles 10 mm. diameter, is lowered gently on to the paste in the mould. Now the settlement of the plunger is noted. If the settlement is between 5 and 7 mm from the bottom of the mould the amount of water added is correct. If this condition is not satisfied, the test must be again repeated changing the percentage of water until the stipulated extend of penetration of the plunger is reached. Let
W1 = Weight of cement taken for the test. W2 = Weight of water added corresponding to the condition of the stipulated extent of penetration of the plunger. Percentage of water,
=
Pa
=
W2 W1
X 100%
3. Test for Setting Time: The object of this test is to make a distinction between normal setting and quick setting types of cement end also to detect deterioration due to storage.
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Weigh 300 gm of cement and add Pa percentage of water (which is the percentage of water required to have normal consistency. See test for consistency.) The paste obtained after mixing is filled in the mould.1. In the Vicat apparatus, attach the needle of square section, i.e. 1 mm X 1 mm to the Vicat rod. Lower the system so that the needle just touches the surface of the paste and gently release. Find out if the needle pierces into the paste fully. If it does, again release the needle on the paste after a few seconds and again observe whether the needle pierces fully into the paste. This is repeated till the needle does not pierce into the paste completely. Now the interval of time between this instant and the instant at which water was added to the cement is called the initial setting time.
Fig.1.1 Vicat Apparatus
Now change the needle to the third one which has a projecting sharp point in the centre with an annular attachment. Now release this needle as before on the same paste. The needle as well as the attachment will make their impressions on the paste. Repeat this process till only the needle makes the impression but not the attachment. The interval of time between this instant and the instant at which the water was added is called the final setting time. Vicat Apparatus is shown in figure.1.1.
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CONCRETE
Concrete is the most versatile material for all types of construction works and has been used for innumerable construction works, either as plain concrete or as reinforced cement concrete or as precast concrete, or prestressed concrete or in many other forms. In building industry, the concrete is mainly used for purposes, viz., foundations, columns, beams, slabs, stair cases, lintels, doors, window frames, sun-shades, storage tanks, etc. The various constituents of concrete are cement, water, fine aggregate, and coarse, aggregates. In Reinforced Cement Concrete Steel is also used.
Cement: Properties and various types of cement have already been discussed previously
Aggregate: These are the inert or chemically inactive materials which form the bulk of cement concrete. These aggregates are bound together by means of cement. The aggregates are classified into two categories, Fine and coarse.
The material which is passed through 4.75mm size sieve is termed as fine Aggregate. Usually natural river sand, issued as a fine aggregate. But at places where river sand is not available crushed stone may be used as a fine aggregate. The material which is retained on 4.75 mm size B. S. test sieve termed as a coarse aggregate. Broken stone is generally used as a coarse aggregate. The nature of work decides the maximum size of coarse aggregate. For thin slabs and walls the maximum size of coarse aggregate should be limited to one-third the thickness of the concrete section. The aggregate to be used for cement concrete work should be hard, durable and clean. The aggregate should be completely free from lumps of clay, organic and vegetable matter, fine dust etc. The presence of a11 such debris prevents adhesion of aggregates and hence, reduces the strength of concrete. Water: Water which is used for making concrete should be clean and free from harmful impurities such as oil, alkali, acid etc. In general water which is fit for drinking should be used for making concrete. Grades of Concrete
Concrete as per IS 456 2000 is classified into three groups as ordinary concrete, Standard concrete and High strength concrete. M10, M15 and M20 are ordinary concrete, M25, M30, M35, M40, M45, M50 and M55 are grouped as Standard concrete and M60, M70, M75 and M80 are grouped under High strength concrete. The letter ‘M’ refers to the mix and the number indicates the specified compressive strength of that mix at 28 days expressed in N/mm2. For lean concrete bases and simple foundations for masonry walls M5 and M7.5 grades of concrete may be used. These mixes need not be designed. Grades of concrete lesser than M20 are not to be used in RCC work. For general guidance, the nominal mix proportions (volume ratio) correspond approximately to the different grades as follows:
M 5 - 1:5:10 M 7.5- 1:4:8
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M 10 - 1:3:6 M 15 - 1:2:4 M 20 - 1:1.5:3 M 25 - 1:1:2 Gain of strength with age
The concrete develops strength with continued hydration. The rate of gain of strength is faster to start with and the rate gets reduced with age. It is customary to assume the 28 days strength as the full strength of concrete. Actually concrete develops strength beyond 28 days also. The variation of strength with age is shown in Figure.1.2. Minimum Age of member with full
Age Factor
design stress is expected (months) 1
1.00
3
1.10
6
1.15
12
1.20 N E M I C E P S D R A D N A T S F O H T G N E R T S
Rapid hardening
40
30
20 Ord. portland or PBFS
10
1
3
7
14
DAYS
Fig.1.2 Gain in compressive strength with age
Strength of Concrete
Strength of concrete is its resistance to rupture. It may be measured in number of ways, such as strength in compression, in tension, in shear or in flexure. All these indicate strength with reference to a particular method of testing .The compressive strength of concrete is generally determined by testing cubes or cylinders made in laboratory or field. The size of the mould should be 150mm x150mm x150mm.Based on the compressive strength only the concrete is graded. The strength of the concrete is mainly depend on the following factors 1. Quality of materials and grading of the aggregates 2. Water
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3. 4. 5. 6.
Water cement ratio Cement content Age of concrete; and Methods of mixing, placing, compacting and curing.
Workability of concrete
The concrete should have sufficient workability. The workability of concrete indicates the ease with which it can be mixed, placed and compacted. The degree of workability (decided by slump test) for different forms of concrete work is specified. Generally, the strength decreases with increase in degree of workability and vice verse.
Slump Test
Slump test is the most commonly used method of measuring workability of concrete which can be employed either in the laboratory or at site of work. It is not a suitable method for very wet or very dry concrete. The slump cone is as shown in Fig.1.3. The mould is placed on a smooth, horizontal, rigid and non absorbent surface. The mould is then placed in four layers, each approximately ¼ height of the mould. Each layer is tamped 25 times by the tamping rod taking care to distribute the stroke evenly over the cross section. After the four layers are filled in side the cone, mould is removed from the concrete immediately by raising it slowly and carefully in a vertical direction. This allows the concrete to subside. This subsidence is referred as slump of concrete.
All dimensions in Centimeters Fig 1.3 Slump Cone Durability of Concrete
The concrete possesses a high durability value, it is not much affected by atmospheric actions. On the contrary, with the age, the concrete goes on hardening, there by increasing in strength. It is this property, which gives this material a distinct place among the building materials.
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Water Cement Ratio
The strength of concrete depends upon the quantity and quality of its ingredients i.e. cement, aggregate and water. General assumption is that strength of concrete directly depends up on the quantity of cement. If cement is more, strength will be more but this assumption is not correct because strength strength of concrete concrete also depends depends upon water water cement cement ration.
Water cement ratio is generally defined as the ratio of volume or weight of mixing water to that of cement in a concrete mix. It is expressed in liters of water required per bag of cement 50 kg. The relation between strength and water/ cement ratio of concrete is as shown in Fig.1.4.
Fig.1.4 Relation between strength and water/ cement ratio
Operations in Concreting
The following processes are involved in making concrete to achieve desired strength and durability. 1. Storing of material (Cement, aggregate) 2. Batching of material (By volume, by weight) 3. Mixing of concrete (By hand, by machine) 4. Transportation of concrete. 5. Placing of concrete. 6. Curing of concrete
1. Storing of Material
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Cement: It is a fine powder and also hygroscopic in nature i.e. it absorbs moisture from air or free water and starts setting. So it should be protected from dampness. dampness. Hence the water houses constructed for its storage must fulfill the basic requirements.
Trying the level best and keeping all precautions, strength of cement reduces on long storage. Every effort should be made to store it for lesser time. Cement stored for long time should be checked before its use. It has also been observed that by the passage of time, stressed cement recapture its strength up to certain extent.
Aggregates: For achieving proper quality of concrete, it is essential that aggregate should be free from deleterious materials, organic matters such as tree leaves, vegetable wastes, animal refuse etc. It should also not be coated with mud, silt or clay as these reduces the bond between cement paste and aggregate particles. It should have uniform moisture content and proper grading of aggregates.
2. Batching of Materials
Batching means measurement of ingredients of concrete for proper mixing. Normally such a quantity is mixed in one batch, which can be transported, transported, placed and compacted compacted with in time i.e. before initial set takes place. Batching is of two types. 1. Volum olumee Bat Batch chin ing. g. 2. Weig eight Bat Batch chin ing. g. Measurement of Cement: Cement is always measured by weight. This is because its volume differs considerably by the way of container is filled in. A batch of concrete should always consume full number of bags. For this purpose weight, of cement bag is taken as 50 kg. Measurement of Water: Water is generally measured by volume because its weight can not be easily calculated. Measuring of water water by volume is easy and automatic. Measuring device can be easily made. Generally Generally water in the field is measured by buckets or tin, cans but this method is not accurate.
For these these purpo purpose se gener generall ally y woode wooden n boxes boxes of Measurem Measurement ent of Aggregat Aggregatee by Volume: Volume: For capacity equivalent or part of one cement bag i.e. 35 liters are used. These boxes are known as Petties or Farmas or Gauge Box. Weigh Batching: As per the name, ingredients of concrete are measured by weight. This is more accurate and is generally used where high quality concrete is required. As described earlier generally generally one cement bag or its multiple is the basic unit. In this system allowance allowance for water present in aggregate is made, but bulking has no effect. 3. Mixing of Concrete
i) Hand Mixing ii) Machine Mixing.
small works where quantity quantity of concrete required is small. small. In i) Hand Mixing: It is adopted for small it various ingredients of concrete are mixed by hand.
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ii) Machine Mixing: For producing large quantity of concrete at a faster rate and at lesser cost, machine machine mixing mixing is adopted. adopted. The machine machine used for mixing mixing concrete concrete is known as concrete concrete mixer.
1. Conti ontinu nuou ouss mix mixer er 2. Batch atch type type mixe ixer. Continuous mixer: It mixes and delivers delivers concrete just as a steady stream stream of concrete, till it is in operation. This type of mixers is not so common in use in India.
Batch type mixer : Mixes and discharge each loads of material separately. These are of two types.
1. Tilti ilting ng mixe ixers. rs. 2. Non-T Non-Tilt ilting ing or or Rota Rotary ry Mixe Mixers. rs. Tilting Tilting Mixer: Mixer: It has a conical drum which revolves about an inclined axis of 50 with horizo horizonta ntal. l. The The drum drum can be broug brought ht into into differ different ent posit position ionss for chargi charging, ng, mixin mixing g and discharging. In small mixers the materials are charged directly and in mixers of large capacities loading skips are used. The mixed concrete is generally discharged on iron sheets. Blades are fixed, in the internal surface of the rotating drum.
Non-Tilting Type: It is also known as rotary type mixer. It has a drum revolving about horizontal axis and cylindrical in shape. It has an opening on both sides one for charging and other for discharging. For charging loading skip is used which is fed with the help of wire ropes and for discharging chutes are used.
4. Transportation of concrete:
As the initial setting time of cement is generally 30 minutes, hence mixing, transportation, placing and compaction should be completed with in this time. In no case this time should not exceed one hour after initial setting time. When transportation time required is more, than it should be kept agitated and in summer seas season on it shou should ld be kept kept cool cool.. In no case case ther theree shou should ld be any any loss loss of water ater duri during ng transportation.
5. Placing of Concrete:
As for as possible concrete should be placed in single thickness. In case of deep sections, concrete should be placed in successive horizontal layers and proper care should be taken to devel develop op enoug enough h bond bond betwe between en succe successi ssive ve layers layers.. Concr Concrete ete should should be place placed d as soon soon as possible. But in no case, it should be placed after 30 minutes of its preparation. During During placing it should be seen that all edges and corners of concrete surface remain unbroken, sharp and straight in line.
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6. Curing of Concrete:
Concrete surfaces are kept wet for a certain period after placing the concrete. This is termed as Curing of Concrete. The period of curing depends on the type of cement and nature of work. For ordinary Portland cement, the curing period is 7 to 14 days. If rapid hardening cement is used, curing period can be considerably reduced. It can be done by spraying and ponding of water or covering the concrete with moist earth, sand, or wet gunny bags.
Types of Concrete
The following are the various types of concrete in use. 1. Plain Cement Concrete 2. Reinforced Cement Concrete 3. Pre Stressed Concrete 4. Light Weight Concrete 5. No-Fines Concrete 6. Pre-Cast Concrete 7. Fiber Reinforced Concrete 1. Plain Cement Concrete
It is a mixture of cement, sand pebbles or crushed rock and water. It possesses the following important properties. i)
It is free from corrosion
ii)
It has a high compressive strength
iii)
It blinds rapidly with steel
iv)
It forms a hard surface, capable of resisting abrasions.
v)
It has a tendency to shrink. It can be minimized by curing
vi)
It has a tendency to be porous.
2. Reinforced Cement Concrete
Plain cement concrete is strong in compression but weak in tension. To make this efficiency better steel bars known as reinforcement are embedded in concrete. This is known as reinforced cement concrete (RCC). 3. Pre-stressed Concrete
In this type of concrete, high tensile steel wires are used as reinforcement instead of mild steel bars. There are two types of prestressing namely
i) Pre-tensioning and ii) Post tensioning.
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i) Pre-tensioning: In pre-tensioning method, the wires are initially stressed and the concrete is cast in the moulds built around the wires. The wires released after the concrete attain its strength. The tendency of the wires to return to their original length sets up a compression in concrete, which helps the concrete to resists more tensile stress.
ii) Post-tensioning: In post tensioning the wires are placed inside the concrete and then stressed. The use of prestressed concrete results in saving of concrete and steel to the extent of 50% and 80% respectively compared to RCC.
4. Light Weight Concrete
They are produced from a wide variety of both natural earth substance and fly ash. It mainly consists of cement, aggregates of loose porosity, steel and water. The bulk density of this concrete varies from 500 to 1800 kg/m3 whereas the bulk density of ordinary concrete is about 2300 kg/m3. Advantages: i)
Its weight is less
ii)
It has better insulating and fire resisting properties
iii)
It saves the cost of material handling because of its lightness.
iv)
It has a high water absorption property
v)
Local industrial waste can be economically utilized to prepare this type of concrete.
vi)
The use of light weight concrete results in the reduction of cost to the extend of about 30 to 40% or so.
5. No-fines Concrete
It consists of cement, coarse aggregate and water. Thus fine aggregate or sand is eliminated. This concrete has been adopted for cast-in-situ external load bearing walls of single and multi storey houses, small retaining walls etc., The advantages are. i)
It possesses better insulating properties
ii)
The unit weight of no-fines concrete is about 2/3 of the unit weight of conventional concrete.
iii)
There is direct saving in material requirements as the concrete does not require sand.
iv)
The drying shrinkage is low
v) As there is absence of capillary passages, there is no transmission of water by Capillary action.
6. Precast Concrete
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Precast concrete is manufactured in a factory and the transmitted to the site. The advantages are: i)
The p re-cast articles m ay b e given t he d esired shape and f inish with accuracy.
ii)
The labour required in the manufacturing process of pre-cast units can be easily trained.
iii)
Concrete of superior quality is produced
iv) The pre-cast structures can be dismantled when required and they can then be suitably used elsewhere. v)
The work can be completed in short time.
7. Fiber Reinforced Concrete (FRC)
It mainly consists of cement, fiber, sand and water. Asbestos, glass, nylon or coconut fibers have been tried as alternative to steel. The advantages are: a)
It has thin sections
b)
Production rate is less
c)
More durable
d)
Less maintenance cost
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STEEL
Steel is probably the most versatile commonly used structural material. Steel is used to a large extent in modern multi-storied buildings. Steel is used as reinforcing bars/wires for concrete since concrete is weak in tension. Structural steel is available in various forms and shapes and it is being used for various structural components. Physical Properties of Mild Steel
1. 2. 3. 4. 5.
Mass density Young’s Modulus Modulus of Rigidity Poisson’s Ratio Coefficient of thermal expansion
= = = = =
7850 Kg/m3 2.04 x 105 N/mm2 0.785 x 105 N/mm2 0.25 – 0.3 12 x 10-6 per º c
Reinforcement Steel
Steel reinforcement is of following types 1. Mild Steel bars (MS) 2. High strength deformed bars / rolled twisted bars (HSD / RTS) 3. High tensile bars Normally in all types of structural elements High Strength Deformed bars are used as main reinforcement. For distribution bars mild steel is being used. Reinforcement steel is characterized by its yield strength and ultimate tensile strength. Stress strain behavior is studied by conducting simple tension test and various salient points are noted to determine the strength. Reinforcement bars are available in various nominal sizes. Mild steel (Grade I) and (Grade II) are available in the following nominal sizes 5,6,8,10,12,16,20 mm diameter which has the yield stress of 250 N/mm2 and minimum ultimate tensile stress as 410 N/mm2. Diameters 22, 25,28,32,36,40,45,50 are also available which has yield stress as 240 N/mm2. High strength deformed bars / wires are available in the following nominal sizes: 6,8,10,12,16,18,20,22,25,28,32,36,40,45,&50 with the characteristic strength 415 N/mm2 and 500 N/mm2. Structural Steel
Various shapes and sections are used for building works. Most of them are made by rolling. The common types of sections used in structural steel work are shown in Fig..1.5
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Fig.1.5 Sections in Steel Plates: Plates may be of any size or thickness. Common uses of plates in building construction are as webs and flanges of deep beams, column flanges, column base, etc. Flats: These are rolled as in the case of plate but are much longer in lengths and have shorter widths. The widths vary form 18mm to 50 mm. The minimum and maximum thickness vary from 3mm to 80 mm. Flats are costlier than plates but are put to a considerable use in building construction. Flat section may have one rounded side with greater thickness than the remaining section and this is called bulb ball. These are used only in specific instances. Angles: Angle sections are widely used in steel trusses. Most common types are angles with equal legs and with unequal legs and are designated by ISA width and height of legs of angles. The equal angles vary form 20 mm x 20mm to 200mm x 200mm in size and 3mm to 5mm in thickness. The term 20mm x 20mm denotes that the width of legs is 20mm overall. Unequal angles vary in size from 20mm x 30mm to 220mm x 100mm and thickness from 4mm to 20mm. Special angles with a square toe, round backed, acute, square root and bulb types are also available. These are used to a limited extent in special constructional features T-Sections:These are used for roof trusses and for certain built up columns. They are designated by the width of the stem, width of the table and by the thickness. The standard sizes vary form 40mm x 40mm to 150mm x 150mm with thickness from 6mm to 8mm. Special TSections with bulbs etc. are also used to some extent. Channels:Channels are mainly used for beams, columns and top and bottom chord members of
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truss. They are designated by the depth, flange width and weight per unit length. The size varies form 50mm x 75mm x 3kg to 420mm x 100mm x 30kg. Whenever stronger channels of lesser depth are required, these are specially cast with greater thickness than given by the standards. ISI handbook gives the following four series of channel sections. The only series that is available in India is ISMC. Indian Standard Junior Channels (ISJC) Indian Standard Light Channels (ISLC) Indian Standard Medium Weight Channels (ISMC) Indian Standard Special Channels (ISSC) Joists: Rolled Steel Joists or I-Sections are most commonly used for beams and columns. They are denoted by the flange with, overall depth and weight per meter run. The British Standard Joists Section varies in size form 7 cm x 4cm to 60 cm x 17 cm. In U.S.A. I-sections have vary wide flanges are used. ISI handbook gives the following five series of Beam Sections. The only series that is available in India is ISMB.
Indian Standard Junior Beams (ISJB) Indian Standard Light Beams (ISLB) Indian Standard Medium Weight Beams (ISMB) Indian Standard Wide Flange Beams (ISWB) Indian Standard H Beams (ISHB) Miscellaneous Sections: Z-Sections, rail-sections, troughs, bars etc. are used to a limited extent in steel work for a building.
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UNIT II BUILDING COMPONENTS SITE SELECTION FOR BUILDINGS
The following general principles should be borne in mind in the selection of a site: 1. The site should serve its purpose 2. The site should be located in a fully developed or a fast developing area with transporting facilities. 3. The plot should be in a locality where the various facilities like (a) Community services such as police and fire protection, clearing of waste and street cleaning; (b) Utility services such as water supply, gas, electricity and drainage; (c) Amenities such as schools, hospitals, libraries, recreation, telephone etc.; (d) shopping facilities and (e) means of transport; are available. 4. The proportions of plot to be built-up, vacant spaces to be left in front and sides, heights of buildings, etc., should be in accordance with local byelaws. 5. The site should not be irregular in shape or having any sharp corners. 6. The site should be situated on a elevated place. 7. The soil strata should be of good bearing capacity. 8. The situation of the site should be such as to ensure unobstructed natural light and air. 9. The site should be available in a locality where natural beauty and manmade environment create healthy living and working conditions. 10. The site should be away from quarries, kilns, factories etc., 11. The legal and financial aspects should be given due consideration before the purchase of the plot. 12. The site should be abandoned under adverse circumstances such as (a) unhealthy, noisy or crowded localities; (b) proximity to rivers carrying heavy loads, badly maintained drains and Nallahs; (c) Reclaimed soil or water lagged areas, subject to submergence or settlement; and (d) Industrial vicinities having smoke and obnoxious odour. Classification of Buildings
Buildings can be classified as 1. 2. 3. 4. 5. 6.
Residential buildings Educational buildings Institutional buildings Commercial buildings Assembly buildings Industrial buildings
The topography of the region, the hydrological conditions at site and the type of soil prevalent in the site are to be ascertained before selecting a site. Proximity to essential services and the presence of schools, hospitals and temples as well as recreation facilities such as libraries, parks and swimming pools, shopping areas are to be considered. Transportation facilities for passengers and goods should also be ascertained. For industrial buildings availability of raw materials in the nearby areas offers advantages.
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Residential buildings are to be planned considering the following points: 1. Orientation 2. Aspect 3. Privacy 4. Grouping 5. Circulation 6. Furnishing 7. Sanitation 8. Ventilation 9. Flexibility 10. Landscaping 11. Economy Maximum benefit is derived from nature if the buildings are properly oriented. The residential building should be oriented in the direction in which the wind blows most of the time. The orientation is also dependent on the layout of existing roads and buildings in the locality. Doors and windows should be positioned so as to get maximum lighting, breeze and view of the landscape. Privacy inside the house is achieved by proper placing of windows. Privacy outside the house is achieved by growing trees and creepers. The rooms should serve their utility. The surrounding area should be clean and also free from noise pollution. The doors and windows should be placed opposite to each other to ensure maximum ventilation. The rooms should be selected in such a way that rooms originally designed for a specific purpose can serve other purposes also. The floor space should be optimally used with lesser areas for circulation and staircase. Components of Buildings
Any building has two parts – the superstructure and the substructure. The various components of the superstructure are 1. Masonry units such as walls and columns 2. Floors 3. Doors, windows and other openings 4. Roof structures 5. Elevators, ramps and 6. Building finishes The various components of buildings are shown in Fig.2.1.
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Fig. 2.1 Components of Building
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FOUNDATION
Foundation is that part of the substructure or lower portion of the building which safely transmits the load of the superstructure to the soil beneath it and the sides of the wall. The bearing capacity of soil is defined as the maximum load per unit area, which the soil can support without yielding. Any foundation constructed, should be safe with respect to bearing capacity and settlement consideration. In designing the foundation, the safe bearing capacity of the soil which is the ultimate bearing capacity reduced by a factor of safety should be considered. Types of Foundations
Foundations can be broadly divided into two categories 1. Shallow foundations and 2. Deep foundations. Generally if the depth to width ratio of the foundation is less than 1, then it is known as a shallow foundation and if it is greater than 1, it is known as deep foundation. Shallow Foundation
The various types of shallow foundations are as follows: 1. 2. 3. 4. 5. 6. 7. 8.
Wall footing Isolated footing Combined footing Inverted arch footing Continuous footing Cantilever footing Grillage foundation Raft or Mat foundation
1. Wall Footing
This footing is provided throughout the length of the wall and may be either stepped or single. E.g. Load bearing walls. These are used for light structures. Wall Footing is as shown in Figure. 2.2. Plinth Level
Floor Level
G.L. Footings in Foundation
Wall Earth Filling Concrete in Foundation
Fig 2.2 Wall Footing
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Footing
2. Isolated or Column Footing
This footing supports individual columns. It may be simple, stepped or sloped footing. These are shown in Figures 2.3 and 2.4.
20cm
Column
15 cm offset
Distributors Concrete in Foundation Main rods
Fig.2.3 Simple Footing
Fig.2.4 Stepped and Sloped Footings 3. Combined Footing
A combined footing supports two or more columns in a row. If the columns carry equal loads, then a rectangular shaped footing can be provided. If there are unequal loads and if space limitations are present, then trapezoidal footing can be constructed. Generally, reinforced concrete is used to construct these footings. The shape of the combined footing is designed in such a way that the center of gravity of the resultant area coincides with the center of gravity of the loads. Combined footing is as shown in Figure.2.5.
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Columns
Columns Footing
Elevation
Elevation Footing
Plan
Plan
Rectangular Combined Footing
Trapezoidal Combined Footing
Fig. 2.5 Combined Footings 4. Inverted Arch Footing
Inverted arches (Figure 2.6) are constructed at the base between two walls. It is constructed on soft soils of low bearing capacity when the depth of foundation provided is less. The arch action causes outward pressure and hence the end columns must be strong enough. This type of foundation is suitable for bridges, reservoirs and tanks.
Piers
Inverted Arch Fig. 2.6 Inverted Arch Footing 5. Continuous Footing
This consists of a single continuous reinforced concrete slab supporting three or more columns in a row. This prevents differential settlement in the structure. Continuous Footing is as shown in Figure 2.7
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Columns
Footing
Columns Fig. 2.7Continuous Footing 6. Strap or Cantilever Footing
Strap footings (Figure 2.8) are also known as cantilever footings. These consist of two or more individual footing connected by a beam called as strap. When the distance between the columns is great, trapezoidal footings, if provided are narrow and hence strap footings are provided. The strap beam does not have any contact with the soil. The column loads are transferred into the soil uniformly.
External Column
Internal Column
Strap
Concrete Base Fig.2.8 Strap or Cantilever Footing 7. Grillage Foundation
The grillage footing transfers heavy loads from steel columns to the foundation, which transfers it to the soil of low, bearing capacity. Steel joints in single or double tress are provided. The steel joints are held in place by pipe separators and nuts are completely embedded in concrete of minimum 15 cm to prevent corrosion. This type of foundation can be constructed for a single column or more than one column. The grillage foundation is shown in Figure 2.9.
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Fig. 2.9 Grillage Foundation 8. Raft or Mat Foundation
In regions where the allowable bearing capacity is low and the soil is of a highly compressible nature and the loads from the superstructure on the columns is more, then the footing area is more than half the building area, it is economical and safe to use raft foundations covering the whole area. The use of raft foundation minimizes differential settlement. The weight of the soil excavated is almost equal to that of the raft. The raft consists of reinforced concrete beams with a relatively thin slab underneath. The hydrostatic uplift is also counteracted by the presence of raft foundations. Raft foundation is as shown in Figure 2.10.
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Main Beam Secondary Columns
Beam
Slab
S e c o n d a r y B e a m
Main Beam
Columns
Fig. 2.10 Raft or Mat Foundation Deep Foundation In such types of footings, the depth is very large compared to its width and these may be classified as pile foundations, piers and well foundations. Pile Foundations Piles are used under the following situations. 1. The live load and dead load coming from the structure is very heavy and the distribution of load on soil is uneven. 2. The Construction of grillage or raft foundation is not economical. 3. The subsoil water level fluctuates appreciably. 4. The structure is situated on sea-shore or river bed and there is scouring action of water (Marine Structures) 5. In places where canals, deep servers are to be constructed in future. Classification of piles Piles are classified based on function as below 1. End bearing piles 2. Friction piles 3. Compaction piles 4. Sheet pile 5. Batter pile 6. Fender pile 7. Under reamed pile 1. End bearing piles
They are penetrated through soft soil and rest on a hard bed. These piles can act as columns or piers. The friction component from the sides of the pile is less as compared to the end bearing capacity. End Bearing Piles are as shown in Figure 2.11.
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l i o S t f o S
Fig. 2.11 End Bearing Piles 2. Friction piles In this type of piles, the frictional resistance offered by the soil on the sides of the pile counteracts the load acting on the pile. The load from the superstructure is transmitted through the pile to the soil on the sides. Friction piles are as shown in Figure 2.12.
Fig. 2.12 Friction Piles 3. Compaction piles
These piles are used to densify loose granular soils. As the piles are driven, the soilsurrounding item gets compacted. Compaction piles are as shown in Figure 2.13.
Fig. 2.13 Compaction Piles
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Fender Pile e l i P t e e h S
e l i P r e t t a B
Fig. 2.14 Sheet, Batter and Fender Piles 4. Sheet piles
These piles are thin members of steel or timber used in waterfront structures. They can reduce sup age and uplift under hydraulic structures. These Piles are as shown in the Figure 2.14. 5. Batter piles
These are inclined piles existing lateral loads. These Piles are as shown in the Figure 2.14. 6. Fender piles These protect the structures against impact from ships and other floating objects. These Piles are as shown in the Figure 2.14. 7. Under reamed piles
The stem of such piles has one or more bulls known as under ream which increase the bearing capacity of the pile and also resist uplift. Under reamed Piles are as shown in the Figure 2.15.
Fig. 2.15 Under Reamed Piles
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Classification based on the materials and composition 1. Cement concrete piles
Cement concrete piles possess excellent compressive strength. These piles can be reinforced or prestressed. They can be divided into following two groups- pre-cast concrete piles and cast in-situ concrete piles 2. Pre-cast concrete piles
These piles are manufactured in factory. They may be tapered or parallel sided. They may be square, octagonal or round in shape. The precast concrete piles are generally used for a maximum design load of about 80 tons. They may be reinforced to withstand handling stresses. The concrete in the piles should be controlled concrete and should correspond to M20 grade. 3. Cast in-situ concrete piles
In this type a bore is dug into the ground by inserting a casing,. This bore is then filled with cement concrete after placing reinforcement, if any. They may be either cased cast in-situ concrete piles or encased cast in-situ concrete piles depending upon whether the casing is kept in position or is withdrawn. 4. Timber piles
Timber piles are prepared from trunks of trees. They may be circular or square. They are 30 to 50 cm in diameter with a length not exceeding 20 items its top width. At the bottom, a cast – iron shoe is provided and at the top, a steel plate is fixed. If a group of timber piles is driven, the top of each member of the group is brought at the same level and then a concrete cap is provided to have a common platform. They have small bearing capacity, and are not permanent unless treated. It is very difficult or even impossible to drive these piles into hard stratum. 5. Steel piles
Steel piles are used in the following three different forms. H Piles ; Box Piles and Tube Piles • 6. Sand piles These piles are formed by making holes in the ground and then filling them by sand. The top of the sand piles is filled with concrete to prevent the sand to come upwards due to lateral pressure. They are easy to construct and can be used irrespective of any position of water table. They are not suitable for loose or wet soils or where there is a danger of scour. They are also not suitable in regions subjected to frequent earthquakes. 7. Composite piles
A composite pile is formed when it is a combination either of a bored pile and a driven pile or of driven piles of two different materials. They are suitable where the upper part of a pile is to project above the water table. They are economical and easy to construct.
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MASONRY Brick Work In Cement Mortar
Masonry may be defined as the construction of building bounded together with mortar. The building unit known as in walls may be stones, bricks or precast blocks of concrete. Bricks are used as the building units or building blocks in brick masonry. Masonry is normally used for construction of foundations, walls, columns and other structural components of buildings. The basic advantage masonry construction lies in the fact that they are load-bearing structures. It performs a variety of functions, such as 1. 2. 3. 4.
Supporting loads Subdividing space Providing thermal and acoustic insulation Affording fire and weather protection etc.
Mortar
It is the pasty material formed by the addition of water mixture composed of fine aggregate (sand or surkhi) material (cement or lime), which may be handled with a trowel Mortar unites the individual bricks together. Generally the following types of mortar are in use: 1. Mud mortar 2. Lime mortar 3. Lime surkhi mortar 4. Cement mortar and 5. Cement lime mortar or lime- cement- mortar Terms Used in Brick Masonry Course: A complete layer of bricks laid on the same called a course and its thickness is equal to the thickness of one mortar joint. Frog : Depressions provided in the face of the brick. Bed: The bottom surface of the brick when it is laid flat is called bed. Stretcher: The side surface of bricks visible in elevation when the brick is laid flat is called the stretcher (19 cm x 9 cm). Header: The end face of the brick when it is laid flat is as header (9cm x 9cm) Bed joint: The horizontal mortar joints between two successive courses are known as bed joints. Perpend : These are the joints between bricks either in longitudinal or cross directions. Bat: The brick which is cut across its width is called as bat Closer: The brick which is cut across its length is called as closer. Principles in Brick Masonry Construction
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i) ii)
iii) iv) v) vi)
vii) viii) ix) x)
Good brick masonry should utilize bricks which are sound, hard, well burnt, and tough with uniform colour, shape and size. The brick should be compact, homogeneous and free from holes, cracks, flaws, air-bubbles and stone lumps. These bricks should be properly soaked in water for at least two hours before use. In the brick work, the bricks should be laid on their beds with the frogs pointing upwards. The brick courses should be laid truly horizontal and should have truly vertical, joints. As far as possible the use of brick-bats should be discouraged. As far as possible the brick walls should be raised uniformly with proper bond. Generally the height of brick masonry construction in a day should be less than l.5 m. The maximum difference in rise of the wall between the different portions should n ot be more than one metre. When the mortar is green, the face joints should be raked to a depth of 12 to 19 mm in order to have a proper key for plastering or pointing to be done. In order to ensure continuous bond between the old and the new, the walls should be stopped with a. toothed end. Finished brickwork in lime mortar should be cured for a period of 2 to 3 weeks. This period can be reduced to 1 to 2 weeks in case of brickwork with cement mortar. In order to carry out the brickwork at higher level single scaffolding is used.
Bonds in Brick Masonry
Bonding is a process of arrangement of bricks and mortars to tie them together in a mass of brickwork. It should have a minimum of vertical joints in any part of the work. It is a weak portion of brickwork and should not be continuous in two successive courses. A wall having continuous vertical joints shall act as independent column. Hence load on wall shall not be uniformly distributed. A more strong and durable brick masonry construction will not have continuous vertical joints. It shall distribute load on a wider area and thereby minimise the tendency to settle. The various types of bonds are explained. Types of Bond
1. 2. 3. 4.
Stretcher bond Header bond English bond Flemish bond
1. Stretcher bond
In this type of bond (Figure 2.16), all the bricks are laid with their lengths in the direction of the wall. This pattern is used for walls having thickness of 9 cm only. For greater thickness of walls, this arrangement is not at all practicable.
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Fig. 2.16 Stretcher bond 2. Header bond
In this type of bond (Figure 2.17) all the bricks are laid with their ends towards the face of the wall. This type of arrangement is suitable for walls, which are one brick thick. This is a1so suitable for the construction of curved wall and footings for better load distributions.
Fig. 2.17 Header bond 3. English bond
In this type of bond alternate courses of headers and stretchers are laid. It is necessary to place the queen closer after first header in the heading course for breaking the joints vertically as shown in Figure 2.18. English bond construction requires the following points to be kept in view. i) ii) iii) iv) v) vi)
A quoin closer must be provided after the quoin header. A header course should never start with a quoin closer. Each alternate header should be centrally placed over a stretcher. Continuous vertical joint should not be allowed except at stopped end. In case of the wall thickness equivalent to an even number of half bricks the wall shall present similar appearance of both the faces. In case of the wall thickness equivalent to an odd number of, half bricks, the same courses shall have stretchers on one and header on the other. Only headers should be used for the hearting of the thicker walls.
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vii)
The joints on the header course should be made thinner than those in the stretcher course. This is because of the fact that the number of vertical joints in the stretcher course are half the number of joints in the header course.
Fig 2.18 English Bond-One Brick Thick Wall
4. Double Flemish bond
In this bond alternate headers and stretchers are laid in each course. This type of bond: is better in appearance than the English bond. The facing and back are of the same appearance. The Brick bats are used in case of walls having thickness equivalent to odd number of half bricks. The queen closer is placed next to the quoin header in alternate, courses in order to break the continuity of the vertical joints. Double Flemish Bonds are as shown in Figure 2.19
Fig.2.19 Double Flemish bond
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Comparison between English Bond and Double Flemish Bond English Bond
Double Flemish Bond
More compact and stronger for walls having Less compact and stronger thickness more then 1 1/2 bricks. No pleasing appearance of the facing.
Better appearance of the facing
No strict supervision and skill required for its Good workmanship and careful supervision construction is required More costlier than double Flemish bond Cheaper in cost because number of brick bats are used
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STONE MASONRY
Stone masonry is made of stone units bonded together with mortar. Classification of Stone Masonry
Depending upon the arrangement of stones in the construction, it can be classified as follows:
Stone Masonry
Rubble Masonry
Ashlar Masonry Ashlar fine
Random rubble masonry Coarsed Uncoarsed
Ashlar rough tooled
Square rubble masonry Coarsed Uncoarsed
Ashlar rock or quarry faced
Polygonal rubble masonry
Ashlar chamfered
Flint rubble masonry
Ashlar block in course
Dry rubble masonry RUBBLE MASONRY
In this type of masonry, stones of irregular sizes and shapes are used. The stones, as obtained from quarry, are taken for use in the same form or they are broken and shaped in suitable sizes by means of hammer as the work proceeds. Random rubble masonry:
1. In this type of masonry, the stones used are of widely different sizes. This is the roughest and cheapest form of stone masonry. 2. In coarsed random rubble masonry, the masonry work is carried out in courses such that the stones in a particular course are of equal heights, as shown in figure. 3. In uncoarsed random rubble masonry, courses are not maintained regularly. The larger stones are laid first and the spaces between them are then filled up by means of spells as shown in Figure 2.20
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Uncoarsed Random Rubble Masonry
Coarsed Random Rubble Masonry
Fig. 2.20 Random Rubble Masonry Square rubble masonry
In this type of masonry stones having straight bed and sides are used. The stones are usually squared and brought to a hammer dressed or straight cut finish. In the coursed squared rubble masonry, the work is carried out in courses of varying depth. In the uncoursed squared rubble masonry, the different sizes of stones having straight edges and sides are arranged on face in several irregular patterns. Flint rubble masonry
In this type of rubble masonry, stones used are flints or cobbles. These are irregularly shaped modules of silica. The stones are extremely hard. But they are brittle and therefore they break easily. The face arrangement may be either coarse or uncoarsed as shown in Figure 2.21
Fig. 2.21 Flint Rubble Masonry Dry rubble masonry
In this type of masonry mortar is not used in the joints. This type of construction is the cheapest and requires more skill in construction. This may be used for non-load bearing walls such as compound wall etc.
ASHLAR MASONRY
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In this type of construction, no irregular stones are used. The stones used in this masonry are rectangular blocks and are all dressed finely with chisel. The courses are not necessarily of the same height. It may vary from 25 to 30 cm. Following are the different types of ashlar masonry as shown in Figure 2.22
Fig.2.22 Ashlar Fine Masonry Ashlar rough tooled masonry
In this type of ashlar masonry the beds and sides are finely chisel-dressed. But the face is made rough by means of tools. A strip, about 25 mm wide and made by means of a chisel is provided around the perimeter of the rough dressed face of each stone.
Ashlar rock or quarry faced masonry
In this type of ashlar masonry, a strip about 25 mm wide and made by means of chisel is provided around the perimeter of every stones as in case of rough-tooled ashlar masonry. But the remaining portion of the face is left in the same form as received from quarry. Ashlar chamfered masonry
In this type of ashlar masonry, the strip is provided as above. But it is chamfered or bevelled at an angle of 45 degrees by means of a chisel for a depth of about 25 mm. Ashlar Chamfered Masonry is as shown in Figure 2.23
Fig.2.23 Ashlar Chamfered Masonry Ashlar block-in-coarse masonry
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This is combination of rubble masonry and Ashlar masonry. In this type of masonry, the face work is provided with rough tooled or hammer dressed stones and backing of the wall may made in rubble masonry. Points to be observed in the construction of stone masonry
The following points should be kept in mind during the construction of stone masonry. 1. 2. 3. 4. 5. 6. 7. 8. 9.
Stones should be strong, rough and hard Each stone should be well watered before use All the stones should be laid on their natural bed Proper bond should be maintained; formation of vertical joints should be avoided. Small stone pieces should be used for facing. The wall should be raised uniformly throughout its length. Stones should be dressed properly according to the type of masonry. Mortar should be in proper proportion. After the construction is over the whole masonry work should be kept wet for at least 2 to 4 weeks.
Comparison between Stone Masonry and Brick Masonry
1. Cost of stone masonry work is more, as it requires more skilled labour. 2. Due to various sizes and shapes of stone, complicated lifting devices are required in the construction. But bricks having regular shape and uniform size, can be moved easily by manual labour. 3. In the case of brick masonry any mortar can be used, but in the case of stone masonry mortars other than cement will not be having any bond with the stone surface. 4. In the case of stone masonry, the dead weight is more because it is comparatively heavy, for the same reason, it is suitable for under water construction. 5. Stone work is stronger than brick work. 6. Thinner walls are not possible in stone masonry. 7. Bricks resist fire better than stones. In case of fire, stone easily disintegrates. 8. In the case of brick masonry, mortar joints are thin and uniform due to their uniform size and shape, and hence the structure becomes more durable with less consumption of mortar. But in the case of stone work, - pointing is necessary. 9. It is easy to provide connections and openings in case of brick work. 10. Brick work is less water tight than stone work, bricks absorb moisture from atmosphere and dampness can enter the building. Hence plastering is essential, as extra expenditure to brick work. 11.By stone masonry architectural and massive effects can be developed, hence it is used for constructing temples, monumental works, bridges etc. Bricks are used, due to their light weight, in residential and commercial building works.
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PLASTERING
Plastering is the process of covering rough surfaces of wal1s, columns, ceilings and other building components; with thin coat, of plastic mortars to form a smooth durable surface. The coating of plastic material mortar is termed as plaster. Plastering on external exposed' surface is known as rendering. Objects of Plastering
Plastering is done to achieve the following purposes 1. To protect the external surfaces against penetration of rain water and other atmospheric agencies. 2. To give smooth surface in which dust and dirt cannot lodge. 3. To give decorative effect. 4. To protect surfaces against vermin. 5. To conceal inferior defective workmanship. Requirements of Good Plaster
1. It should adhere to the background and should remain adhered during all variations in seasons and other atmosphere conditions. 2. It should be hard and durable. 3. It should possess good workability. 4. It should be possible to apply it during all weather conditions. 5. It should be cheap. 6. It should effectively check penetration of moisture. The type of plaster depends upon 1. Availability of binding materials 2. Durability requirements 3. Finishing requirements 4. Atmospheric conditions and variations in weather 5. Location of surface The types of mortars commonly used for plastering are 1. Lime Mortar 2. Cement Mortar 3. Lime Cement Mortar 1. Lime Mortar
Lime used for plastering may be either fat lime or hydraulic lime. However, fat lime is preferred since it yields good putty after slaking. Hydraulic lime contains particles which slake very slowly as it comes in contact with atmospheric moisture, slaking may even continue for 6 to 8 months. If unslaked particles remain in such a plaster, balusters are formed during the process of slow slaking. Thus the plastered surface gets damaged. Hydraulic lime yields harder and stronger surface.
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If hydraulic lime is used for plastering, it should be ground dry with sand. It is then-left for 2 to 3 weeks and then reground before use. Fat lime on the other hand, is slaked wet. The mix proportion varies from 1:3 to 1:4 for fat lime and 1:2 for hydraulic or Kanker lime. The binding properties of lime mortar can be improved by adding gugal at the rate of about 1.6 kg per cubic metre of mortar. The adhesive and tensile properties of lime mortar can further be improved by mixing chipped hemp at the rate of about 1 kg per cubic metre of mortar. Such a treatment prevents the formation of tensile cracks on the plastered surface. 2. Cement Mortar
Cement mortar is the best mortar for external plastering work since it is practically nonabsorbent. It is also preferred to lime plaster in bathrooms etc. and in damp climates. Cement mortar is much stronger than lime mortar. The mix proportion may vary from 1:4 to: 1::6. Sand used for plastering should be clean coarse and regular. Before mixing water, dry mixing is thoroughly done. When water is mixed, the mortar should be used within 30 minutes of mixing well, before initial setting takes place. 3. Lime Cement Mortar
Lime cement mortar contains properties of both the lime mortar as well as cement mortar. Cement mortar as such does not possess sufficient plasticity. Addition of lime to it imparts plasticity resulting in smooth plastered surface. Mix proportions generally used are 1: l: 6 (cement: lime: sand) 1: 1: 8 or 1:2:8. Generally, fat lime is used.
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LINTELS
A lintel is a horizontal structural member/spanning opening, to support the load of the structure coming over it. It is used to span the openings for doors, windows, and corridors. Its function is similar to that of an arch. As the construction of lintels is much simpler than the construction of arch it is becoming more popu1ar these days. The following types of lintels are commonly used. 1. Wooden lintel 2. Brick lintel (Arches) 3. Stone lintel 4. Steel lintel 5. RCC lintel 1. Wooden Lintels
Wooden lintels are the oldest type of lintels and now days, also they are used in hilly areas where timber is available. The sound and hard timber like teak is used over the opening and masonry is constructed over it. A timber is easily liable to catch fire. Only good quality timber with a coal of suitable preservative should be used as lintels. One piece of timber or a built up section may be used as a linte1. The ends of the lintels rest on a mortar on the walls for a minimum width of 15 cm. Wooden lintels are very strong and hence a relieving masonry arch is constructed over it when the load coming over it is, considerably more. If it is used in ill ventilated places, it is liable for decay. 2. Brick Lintels
Brick lintels are used for small openings, generally exceeding 1 metre span, and, light loads. They are built up, hard, well-burnt, copper-coloured, and free from cracks and straight edged bricks. The depth of the lintel varies from to 10 cm to 20 cm depending upon the span. A centering or timber supporting is required to construct brick lintel. When lintels are constructed to span over large opening, mild reinforcing bars are used with rich cement mortar. It is known as reinforced brick lintel. 3. Stone Lintels
Stone lintels are used in stone masonry structures and buildings faced with stones. It may be constructed of a single piece or more than one piece. Its use is restricted to monumental buildings or in hilly areas due to high cost and weakness in withstanding excessive transverse stresses. The least thickness of the stone lintel is about 7.5 cm and as a thumb rule the thickness is taken as at least 1 mm per one cm length of the opening. 4. Steel Lintels
Steel ang1es are used for spanning smal1 openings and rolled steel joints are used for heavy loading and large spans. Some times, a combination of two or more joists is used. Tube separators are used to keep the Rolled Steel Joists in the required positions. The system may be embedded in cement concrete to protect steel, from fire and corrosion.
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5. RCC Lintels
They are economical and simple in construction, and are commonly used these days. RCC lintels are more durable, strong and fire-resistant. It consists of a rectangular or square concrete section reinforced with mild steel bars. It can be pre-cast or cast-in-situ. Precast RCC lintels are preferred for small spans up to 2 m. Pre-cast lintels increase the speed of the construction and quality control is better in this case. The top of the precast lintels should be marked by paint to facilitate placing of the lintels in the correct position. For cast-in- situ lintels, a centering is erected. The reinforcement is placed and then concrete is poured, compacted and cured. Generally 1:2:4 concrete is used in the construction of lintels. The depth of lintel and the amount of the reinforcement is governed by the intensity of load, the type of support and the span. When RCC lintels are used, there is no need of providing any relieving arch. RCC Lintels are as shown in Figure 2.24
Fig.2.24 RCC Lintels Loads on Lintels
A lintel carries the weight of the wall constructed over it. It has been found that the weight of the wall enclosed in a triangle with a base equal to the effective span of the lintel and the side angle of 60°. This consideration is based on the assumption that if a lintel falls, the amount of brickwork which would collapse with it would probably be something between a semi-circular arch and an equilateral triangle. It can be a1so be assumed that the same effect will be produced if the loading of the lintel is evenly distributed over a length equal to the effective span and for a height equal to half the effective span of the lintel. The above contention is only valid when the lintel is placed in the middle of the wall.
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COLUMNS RCC Columns
Reinforced concrete columns may be constructed in square, rectangular, hexagonal, or circular shapes. Longitudinal reinforcements are provided to take up the major load coming over the columns. Lateral ties are provided to keep the main reinforcement in position and to take up the shrinkage and; temperature stresses. They also provide lateral rigidity which checks the buckling of the longitudinal bars. These ties may be provided in the form of spiral. The spiral lateral ties are advantageous as they provide extra strength to the column. Columns at the corner of buildings may have "L" shape. The longitudinal bars should not be less than 0.8 percent and not more than 8 percent of the cross sectional area of the column. Generally the diameter of the bar is not more than 6 mm and not less than 10 mm. The minimum concrete cover provided around the bar is 4 cm. The pitch of the letera1 ties is not more than 30 cm or the least dimension of the column or four times the diameter of the longitudinal bar. The volume of the lateral reinforcing steel should not be less than 4 percent of the total volume of column. Various types of RCC columns are shown in Fig.2.25
Fig.2.25 RCC Columns
First of all, the longitudinal bars and lateral ties are fixed in the position and then shuttering is erected. With the aid of suitable fillets, the gap between bars and the shuttering maintained so as to have suitable concrete cover. Concrete is poured into it and well compacted. Again the shuttering is provided for the second stage and concreting is done as usual. This process of casting is continued till the full column is complete but rate of casting is not more than 2 meters height per hour. The concreting in the column should be stopped a few centimeters below the level of the beams running into the columns. This portion of the column is concreted with the beam. Concrete should be placed carefully when the columns extend for several storey. The section of the columns in upper storey may be reduced as they have to carry lesser loads. But the centre lines of co1umns must coincide accurately for various columns of different storeys. This should
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be checked at each stage of the construction. The steel reinforcement from the column in the lower storey is bent such that they are accommodated in the column of the top floor. Steel Columns
Steel columns have many advantages over cast iron and other metal columns. They are more dependable and- safe. A steel column may be damaged in a collision badly bent out of 1ine and still support its load without collapsing if that load does not approach the critical load for the columns. Types of steel columns are illustrated in Figure 2.26. Struts of one or two angles are used for compression member in roof trusses, light towers and lattice girders. The two angles of a double angle strut riveted together by rivets driven through washers placed between the two angles at intervals of 1.2 to 2.0 meters, or at such, interval that the unsupported l/r of one angle does not exceed l/r for the whole strut. Two or four angles starred and connected by batter plates spaced at intervals of 1 to 1.3 meters are sometimes used to support light loads. Latticed columns made up of channel angles connected by, lattice bars are often used where light loads are to be supported on long columns. Rolled H-columns are available in depths ranging from 15 to 40 cm and are now commonly used instead of built-up columns in steel skeleton construction. Built-up columns are usually of H-shaped section although columns with two or more webs are not uncommonly used in building frames. Top chord sections of heavy trusses are usual unsymmetrical and are made up of two rolled or built-up channel sections and cover plate. The bottom side of the section is latticed. Columns for bents are sometimes made up of a pair channels and an I-beam with batten plates at intervals of 1.3 meters connecting the flanges of the channels. Columns made up of four angles and a web plate is commonly used in mill building bents. Battened columns in which two components of a column are connected only by batten plate are certainly inferior to latticed columns and should be avoided if a continuous plate or latticing can be used instead.
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Fig.2.26 Types of Steel Columns
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SLABS
A slab is a structural element with its thickness being small compared to the other two dimensions. Most of the slabs in construction are rectangular in plan and can be divided into two categories. •
•
One way slabs, simply supported, cantilevered or continuous bending in one direction only. Two way slabs, simply supported, cantilevered or continuous in two directions.
One Way Slab
One way slabs span in one direction only and may have simply supported or clamped edges or edges over which the slab is continuous. These edges are perpendicular to the direction of the span. Along the other two edges either the supports do not exist or are so far apart they carry practically no load from the slab and hence do not contribute towards the moment and shear in the slab in any significant measure. The assumption is that of unidirectional bending in the direction of the span. It is as shown in Figure 2.27
Fig.2.27 Simply Supported One Way Slab Two Way Slab:
The term two-way slab may be attributed to such cases in which the load is carried in more than one direction.
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BEAMS
A beam is a structural member subjected to a system of external forces at right angles to its axis. The various types of beams are shown in Figure 2.28 In general the beams can be classified as follows: 1) Cantilever Beam 2) Simply supported beam 3) Over hanging beam 4) Rigidly fixed beam 5) Continuous beam 1. Cantilever beam: A beam fixed in one end and free at the other is called as cantilever beam. 2. Simply supported beam: A beam supported or resting freely on walls or columns at it both ends, is known as simply supported beam. 3. Over hanging beam: A beam having its end portion extended beyond the support is known as an over hanging beam. 4. Rigidly Fixed Beam: A beam whose both ends, are rigidly fixed in walls is known as rigidly fixed beam or built-in beam. 5. Continuous Beam: A beam supported on more than two supports is known as a continuous beam. It mayor may not be an over hanging beam.
Fig.2.28 Types of Beams
Types of Loading
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1. Concentrated or point toad 2. Uniformly distributed load and 3. Uniformly varying load Span of the Beam
The horizontal distance between the supporting walls is known as clear span of the beam. The horizontal distance between the lines of action of the supporting walls is known as effective span.
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ROOFS
Roof may be defined as a covering provided over the top of a building with a view to keep out rain, snow, sun and wind and to protect the building from the adverse effect of these elements. A roof basically consists of roof covering materials supported on structural elements installed on the building top. The structural elements may be trusses, portals, flat slab, shell, dome or space frame whereas the roof covering material may be thatch, wooden singles, tiles, slates, A.C. sheets, G.I sheets etc. Roof is considered to be one of the important items of work in a building and due attention should therefore be paid in the matter of selection of the type of roof and the method of construction. Components and Details of lateral and vertical bracing are as shown in Figure 2.29 and Figure 2.30 respectively.
Fig.2.29 Components of a Roof Truss
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Fig.2.30 Details of Vertical and Lateral Bracings Classification
Roofs may classified as 1. Pitched or Sloping Roofs 2. Flat Roofs 3. Curved Roofs 1. Pitched Roof
It is the most common form of roof and is generally regarded as the cheapest alternative for covering a structure. Pitched roofs are almost always constructed in wood or steel. Wooden pitched roof consists of a system of joists, rafters and purlins arranged in the form of a triangular shaped support known as truss. The lower ends of the rafter rest upon the wall plates and at their upper end they are connected to a common ridge piece. In pitched roof a slope of less than 1 in 3 is generally not considered satisfactory from drainage point of view. In areas of heavy snow fall, steeper slopes of say 1 to ½ or 1:1 are provided to reduce the incidence of snow load on the roof. The slope of the roof varies according to the span, the climatic conditions of the site, the nature of the covering material and other similar factors. Roof Covering for Pitched Roofs
Roof covering is provided over the form-work of roof structure to act as a barrier for the rain, sun, wind or other such elements. The selection of covering material depends upon various factors such as availability of material, its initial cost and cost of maintenance, appearance and durability. The various types of roof covering are
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a. b. c. d. e. f.
Thatch covering Shingles Tiles Asbestos-cement sheets Galvanized corrugated iron sheets Slates
Of the above types of roof coverings the Asbestos-cement sheets (A.C.sheets) and Galvanized iron sheets are commonly used. Asbestos-Cement Sheets
Asbestos is a silky fibrous material found in veins in metamorphosed volcanic rocks. Asbestos cement roofing sheets are available as corrugated roofing sheets, wall boards. Rainwater gutters and felts. The A.C. sheets are fixed with smooth surface uppermost to wood or steel purlins. The purlins are placed at a maximum spacing of 1.375 meters by drilling holes on crowns. Galvanized Iron Sheets
Galvanized iron sheets are available in box, plain and corrugated forms. The purpose of corrugations is to impart additional strength to the tin sheets. The iron sheets are protected against fusing in wet weather by galvanizing with zinc. The sheets are fixed to purlins spaced at 2 ½ metre centre and are held in position by means of coach screws using bitumen washers. Steel Roof Trusses
Steel roof trusses are designed in such a way that the various members are in either tension or compression. The type of the truss depends on i) ii) iii)
Span Roof slope Covering material
The various types of steel trusses depending upon the span and arrangements of various members of truss are shown in Figure 2.31(a) and 2.31(b)
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Fig.2.31 (a) Various Types of Roof Trusses
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Fig.2.31 (b) Various Types of Roof Trusses
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2. Flat Roofs
Where the rainfall is low, flat roofing is preferred over sloping roof. A gentle slope is given to the surface for the free flow of rainwater. Madras Terraced Roof
This is a type of flat roof commonly used in Tamilnadu. The procedure of construction of this type of roof is as follows: 1. Teakwood joists are placed on Rolled Steel Joists with a furring piece between the joists and rolled steel joists. The furring is placed sloping and it gives necessary slope to the flat roof. 2. A course of specially prepared terrace bricks ism laid diagonally across the joists .The size of brick is generally 150 mm x 75 mm x 25 mm and they are placed on edge in lime cement mortar 3. After the brick course has set a course of brick bat concrete is laid. The thickness of this course is about 75 mm and it consists of three parts of brick bats, one part of gravel and sand and 50 % lime mortar by volume. 4. The concrete is well rammed for three days and allowed to set. 5. Flat tiles are then laid over the layer of concrete. The tiles are laid in two courses making the thickness of about 50 mm. Alternatively China Mosaic pieces may be used in place of place of flat tiles. 6. Finally the surface of the roof is finished by three coats of plaster as shown in Figure 2.32. The surface is rubbed and polished and it is given a slope of 1 in 30.
Fig. 2.32 Madras Terraced Roof
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In Madras Terrace Roofing as well as RCC. roofing 100% water tightness cannot be achieved. However on top of the roofing, about 10 cm. thick lime surkhi concrete is laid and two layers of flat tiles are laid to make the roof water tight. Advantages of Flat Roofs
1. The construction of roof is simplified. 2. It is easier to make a flat roof as fire proof than a sloping roof. 3. The roof area can be utilized for roof gardens, drying yards, etc. The terrace can conveniently be used for sleeping in hot season. 4. The construction work of upper floors can easily be started. In case of a pitched roof, the entire roof is to be removed and is to be replaced by a new floor under such circumstances. 5. A flat roof is found to be economical than a pitched roof. Disadvantages
1. Flat roofs cannot be used for long spans. 2. Cracks are developed on the surface of the roof, when the variation in temperature is high. 3. Pockets of water are formed on the surface of the roof, if slopes are not sufficient. This leads to the leakage of the roof. 4. At places where rainfall is heavy, flat roofs are not desirable. 3. Curved Roofs
These are just the modification of pitched roofs and are frequently used to cover large areas. Shell Roofs and Domes are the variety of Curved Roofs. They are used in factories, and monuments. They are constructed of timber or RCC. Shell roof are of two types. They are north light shell roof (Figure 2.33) and Barrel vault shell roof (Figure 2.34).
Fig. 2.33 North light shell roof
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Fig.2.34 Barrel vault shell roof
Dome is a rounded vault forming a roof. It is useful when then roof is to be provided on circular brickwork or regular polygon shape walls. Curved roofs pleasing in appearance and economical as less steel and concrete are required because of arch action.
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UNIT III SERVICES ROADS
Role of Transportation
Transportation contributes to the economic, industrial, social and cultural development of any country. Transportation is vital for the economic development of any region since every commodity produced whether it is food, clothing, industrial products or medicine needs transport at production and distribution stages. The inadequate transportation facilities retard the process of socio economic development of the country. Economic activity and Transport
Production or supply Consumption for human wants or demand
Social Effects of Transportation
Sectionalism and transportation Concentration of population into urban area Aspect of safety, law and order
Advantages of Transportation
1. Transportation is for advancement of the community. 2. Transportation is essential for the economic prosperity and general development of the country, and 3. Transportation is essential for strategic movement in emergency for defence of the country and to maintain better law and order. Different Modes of Transportation
Roadways or Highways Railways Waterways Airways Ropeways Pipelines Belt conveyors
Characteristics of Road Transport
The Characteristics of road transport are briefly listed here:
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(i) Roads are used by various types of road vehicles, like passenger cars, buses, trucks, two and three wheeled automobiles, pedal cycles and animal drawn vehicles trucks, etc. But railway tracks are used only by rail locomotives and wagons, waterways are used by only ships and boats. (ii) Road transport requires a relatively small investment for government. Motor vehicles are much cheaper than other carriers like rail locomotives and wagons, water and air carriers. Construction and maintenance of roads is also cheaper than that of railway tracks, docks, harbors an airports. (iii) Road transport offers a complete freedom to road users to transfer the vehicle from one lane to another and from one road to another according to the need and convenience. This flexibility of changes in location, direction, speed and timings of travel is not available to other modes of transport. (iv) In particular, for short distance travel, road transport saves time. Trains stop at junctions and main stations for comparatively longer time. (v) Speed of movement is directly related with the severity of the accident. The road safety decreases with increasing dispersion in speed. Road transport is subjected to a high degree of accidents due to the flexibility offered to the road users. Derailment of railway locomotives and air crash of air planes are also not uncommon. They are in fact more disastrous. (vi) Road transport is the only means of transport that offers itself to the whole community alike.
CLASSIFICATION OF ROADS Types of Roads
The different types of roads are classified into two categories depending on whether they can be used during different seasons of the year. 1. All-weather roads and 2. Fair-weather roads All weather roads are those which are negotiable during all weathers, except at major river crossings where interruption to traffic is permissible up to a certain extent. The road pavements which are negotiable only during fair weather are called fair weather roads; on these roads, the traffic may be interrupted during monsoon season at causeways where streams may overflow across the road. Based on the type of the carriage way or the road pavement, the roads are classified as:
Paved roads, if they are provided with a hard pavement course which should be at least a water bound macadam (WBM) layer Unpaved roads, if they are not provided with a hard pavement course of at least a WBM layer. Thus earth roads and gravel roads may be called unpaved roads.
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Based on the type of pavement surfacing provided, the road types are divided classified as:
Surfaced roads which are provided with a bituminous or cement
concrete surfacing Unsurfaced roads which are not provided with bituminous or cement concrete surfacing. The roads provided with bituminous surfacing are also called black-topped roads.
Methods of Classification of Roads
The roads are generally classified on the following basis: Traffic volume • Load transported or tonnage • Location and function • The classification based on traffic volume or tonnages have been arbitrari1y fixed by different agencies and there may not be a common agreement regarding the limits for each classification group. Based on the traffic volume the roads are classified as heavy, medium and light traffic roads. These terms are relative and so the limits under each class should be clearly defined and expressed as vehicles per day etc. Likewise the classification based on load or tonnage is also relative and the roads may be classified as class I, II etc. or class A, B etc. and the limits may be expressed as tonnes per day. The classification based on location and function should be therefore a more acceptable classification for a country as they may be defined clearly. Classification of Road System by Nagpur Road Plan
The Nagpur Road Plan classified the roads in India based on location and function into the following five categories 1. 2. 3. 4. 5.
National Highways (NH) State Highways (SH) Major District Roads (MDR) Other District Roads (ODR) Village Roads (VR)
1. National Highways
National Highways are main highways running through the length and breadth of India, connecting major ports, foreign highways, capitals of large states and large industrial and tourist centres including roads required for strategic movements for the defense of India. 2. State Highways
State Highways are arterial roads of a state, connecting up with the national highways of adjacent states, district head quarters and important cities within the state and serving as the main arteries for traffic to and from district roads.
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3. Major District Roads
Major District Roads are important roads within a district serving areas of production and markets and connecting those with each other or with the main highways of a district. The MDR has lower speed and geometric design specifications than NH/SH. 4. Other District Roads
Other District Roads are roads serving rural areas of production and providing them with outlet to market centres, taluk head quarters, block development head quarters or other main roads. These are of lower design specifications than MDR 5. Village Roads
Village Roads are roads connecting villages or groups of villages with each other to the nearest road of a higher category.
Modified Classification of Road System by Third Road Development Plan, 1981-2001
The roads in the country are now classified into three classes, for the purpose of transport plannings, functional identification, earmarking administrative jurisdictions on a road network viz: 1. Primary system 2. Secondary system 3. Tertiary system or rural roads The Primary system consists of two categories of roads: Expressways National Highways (NH) Express ways are a separate class of highways with superior facilities and design standards and are meant, as through routes having very high volume of traffic. The expressways are to be, provided with divided carriageways, controlled access, grade separations at cross roads and fencing. These highways should permit only fast moving vehicles. Expressways may he owned by the Central Government or a State Government, depending on whether the route is a National Highway or State Highway.
The Secondary system consists of two categories of roads:
State Highways (SH) Major District Roads (MDR)
The Tertiary system are rural roads and these, consist of two categories of roads:
Other District Roads (ODR) Village Roads (VR)
The definitions of NH, SH, MDR, ODR and VR are the same as given under classification of roads by Nagpur Road Plan. 74
Classification of Urban Roads
Urban roads, other than expressways are classified, as: 1. 2. 3. 4.
Arterial Sub-arterial Collector street Local Street
1. Arterial
An arterial is a street for through-traffic, usually on a continuous route. The arterial system connects existing or proposed expressway systems to provide for distribution and collection of through traffic from sub-arterial and collector-street systems. For efficient movement of through traffic, continuity of the arterials is essential. Parking, loading and unloading activities are restricted and regulated. Pedestrians are allowed to cross only at intersections. 2. Sub-arterial
A sub-arterial is a street primarily for carrying through-traffic, usually on a continuous route, but has less traffic mobility. 3. Collector Street
A collector street collects and distributes traffic from and to local streets and also provides access to arterial streets. These may be located in residential neighbourhood, business and industrial areas. There are few parking restrictions except during peak hours in collector streets. 4. Local Streets
A street primarily for access to residences and business areas is called a local street. Most of the streets in urban areas either originate from or terminate on these streets. Local streets may be residential, commercial or industrial, depending on the main use of the adjoining land. They allow unrestricted parking and pedestrian movement. HIGHWAY CROSS-SECTIONAL ELEMENTS
The cross sectional elements of roads are shown in the Figure. 3.1
Fig.3.1 Cross Sectional Elements of a Road Right of Way
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The right of way is the width of the land to be acquired for road purposes, keeping in view future requirements. The width of land depends on the class of highway as well as terrain.
Roadway Width
The width of roadway is the width of formation at the top and is equal to the width of carriageway plus the width of shoulders on either side of the carriage-way.
Width of Carriage-way
The central paved width of road for vehicular traffic is called carriage-way. In general, 3.75 m is considered desirable for a road having single lane for vehicles of maximum width 2.44 m. For pavements having two or more lanes, width of 3.5 m per lane is considered sufficient.
Shoulder width
The portions of the roadway between the outer edges and the edges of the carriage-way are called shoulders. They serve the following functions:
provide lateral stability provide parking space in emergency provide space for emergency repairs of vehicles provide additional space for vehicles while overtaking other vehicles
Camber
The rise given to the centre of carriageway with reference to its edge is called camber. It is provided to drain away the rain water from the surface of pavement as quickly as possible.
TYPES OF PAVEMENT STRUCTURE
Based on the structural behaviour, pavements are generally classified into two categories: 1. Flexible pavements 2. Rigid pavements Flexible Pavements
Flexible pavements are those, which on the whole have low or negligible flexural strength and are rather flexible in their structural action under the roads. A typical flexible layer consists of the following as shown in Figure.3.2
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Fig. 3.2 Flexible pavement Subgrade
It is the foundation layer, to support the load coming on the pavement. Since the entire load surface is ultimately transmitted to the subgrade, it should never be overstressed. Therefore it is desirable that the top layer of 0.5 m of the subgrade should be well compacted at optimum moisture content. Sub-base course
Purpose of the sub-base course is to permit the road of relatively thick pavement at a low cost. Economy is the essential item in the design. Locally available material should be used. eg. natural gravels, stabilized soil. If the soils and drainage conditions are good, the sub-base may be omitted. Purpose of sub-base are 1. 2. 3. 4.
Increase the structural support for the base & surface courses. Improve drainage Eliminate frost heave and salt heave Prevent the base and surface courses from being affected detrimentally by the poor qualities of the under laying soil. IRC recommends a minimum thickness of 10 cm for flexible pavements.
Base Course
That portion of the roadway superstructure which lies immediately under the wearing course or pavement. The purpose of the base course in flexible pavement is to provide a stress distributing medium which will spread the load applied to the surface so that shear and consolidation deformation will not take place in the sub-grade. It also increases load supporting capacity of the pavement. Rigid pavement
A rigid pavement may consist of concrete slab directly over a base course as shown in Figure.3.3. They have good flexural strength or rigidity. Example of the rigid pavement is the cement concrete road.
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Fig.3.3 Rigid pavement Wearing Course
The purpose of the wearing course are given below Wheels of vehicle are in actual contact. Purpose is to provide a smooth riding surface that will resist destructive pressure exerted by the traffic. Should prevent or minimize penetration of surface water into the road bed. Prope Properly rly desig designed ned we weari aring ng course course adds adds apprec appreciab iable le streng strength th to the entire entire road road structure materials - low cost surfaces - bituminous or cement
HIGHWAY MATERIALS
1. 2. 3. 4. 5.
Sub gr grade ade Soi Soill Ston Stonee Aggr Aggreg egat ates es Bitu Bitumi mino nous us Mat Mater eria ials ls Bitu Bitumi mino nous us Pavi Paving ng Mix Mixes es Portl Portland and Cem Cement ent and and Cement Cement Conc Concre rete te
1. Subgrade Soil
Soil mainly consists of mineral matter formed by the disintegration of rocks, by the action of water, frost, temperature, pressure or by plant or animal life. This subgrade soil is an integral part of the road pavement pavement structure as it provides the support to the pavement. pavement. Compacted soil an stabilized soil are often used in sub-base or base course of highway pavements Desirable Properties
The desirable properties of soil as a highway material are
Stability Incompressibility Permanency of strength Minim Minimum um change changess in volume volume and stabil stability ity under under adver adverse se weather conditions of weather and ground water Good drainage Ease of compaction
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2. Aggregates
Aggregates Aggregates are the major component component used in road making. It is used in granular bases and sub bases, bituminous courses and in cement concrete pavements. pavements. A study of the types of aggregates, their properties properties and tests is of great importance to a highway engineer.
Desirable Properties
The desirable properties of aggregates as a highway material are Strength: The aggregates to be used in road construction should be sufficiently strong to withstand the stresses due to traffic wheel load. Hardness: The aggregates should to hard enough to resist the wear due to abrasive action of traffic. Toughness: The aggregates should have sufficient resistance to impact or toughness due to moving wheel loads. Durability: The aggregates should resist disintegration due to the action of weather. The property of of the stones to withstand the the adverse action action of weather weather may be called soundness. soundness. Shape of Aggregates: The aggregates may be rounded, angular, cubical, flaky or elongated shape of particles. The flaky and elongated particles will have less strength and durability when compared compared with cubical, angular or rounded particles of the same stone. Adhesion with Bitumen: The aggregates must have less affinity with water when compared with bituminous materials; otherwise the bituminous coating on the aggregate will be stripped off in presence of water. Tests on aggregates
The common tests on road aggregates aggregates in India are: Aggregate Impact Test • Los Angles Abrasion Test • Aggregate Crushing Test • Water Absorption Test and Bulk Specific Gravity Test • Flakiness Index Test • Aggregate Polishing Test • Stripping Test • 3. Bituminous Materials
Bitumen is defined as a viscous liquid, or a solid, consisting essentially of hydrocarbons and their derivatives, which is soluble in carbon disulphide. It is substantially non-volatile and softens gradually when heated. It is black or brown in colour and possesses water proofing and
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adhesive adhesive properti properties. es. It is obtained by refinery refinery process process from petroleum petroleum,, in which which case it is known as “petroleum Bitumen”. It is also found as a natural deposit, in which case it is known as “native bitumen” or “natural bitumen”. The viscosity of bitumen is reduced some times by a volatile diluent; this material is called cutback. Properties of Bitumen
For satisfactory performance as a road material, bitumen should have the following desirable properties: properties: •
•
•
• •
•
It should be fluid enough at the time of mixing to coat all the surfaces of the aggregates evenly to a thin film. Fluidity is achieved either by heating or by cutting-back with a thin flux or by emulsifying the bitumen It should have low temperature susceptibility, or in other words, it should exhibit little change in viscosity with change in temperature. The bitumen should have a good amount of volatiles in it and is should not lose them excessively when subjected to higher temperature. This will ensure its durability The bitumen should be ductile and brittle The bitumen should be capable of being heated to the temperatures at which it can be easily mixed without any fire hazards The bitumen should have good affinity to the aggregates and should not be stripped off in the continued presence of water
TRAFFIC CONTROL DEVICES
The various aids and devices used to control regulate and guide traffic are 1. Traffi afficc sig signs ns 2. Markings 3. Signals Traffic Signs
The Traffic signs should be backed by law in order to make them useful and effective. They perform a number of of functions such such as
Give timely warning of hazardous situations when they are not self evident Are of great help in regulating traffic by imparting message to the drivers about the need to stop, give way and limit their speeds. Give information regarding highway routes, directions and points of interest
In view of the above, traffic signs occupy a significant place in traffic engineering. They are mounted on fixed or portable supports and are placed on the side of the loads. Importance of Traffic Signs
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Traffic signs are provided to warn, direct and guide road users. They are in- the form of symbols or inscriptions. They are mounted on fixed or portable supports and are placed on the side of roads.
The various traffic signs are classified as: 1. Warning or cautionary signs 2. Regulatory or mandatory signs 3. Informatory and guiding signs 1. Warning or Cautionary Signs
These signs are used to caution the drivers about certain hazardous conditions ahead shown in Figure.3.4. These signals warn the driver so that he can take the desired precaution.
` Fig.3.4 Warning signs
The boards on which the cautionary signs are displayed have been standardized by IRC. An equilateral triangular board of 450 mm side is supported on a post of height 2.75 m above ground level up to the base of the triangle. A rectangular plate of 450 x 400 mm is placed 150 mm below the base of the triangle on which the sign is written. 2. Regulatory or Mandatory Signs
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These signs are used to inform road users certain rules and regulations which have to be observed for safe and free flow of traffic. The violation of these signs is a legal offence. Some of the mandatory signs included are shown in Figure.3.5
Dead slow No turn Speed limit Over taking prohibited Sound horn prohibited Parking prohibited
Fig. 3.5 Mandatory signs
The size, shape and details of traffic signs have been standardized by IRC. A regulatory sign has to be displayed on a red disc 600 mm in diameter and installed at a height of 2.8 m above ground level up to the centre of the disc. It carries a rectangular definition plate between the circular discs. 3. Informatory or Guiding Signs
These signs are provided for route identification, direction to travelers and such other information a traveler requires in order to reach his destination. Examples of informatory signs are (shown in Figure.3.6)
Route marker sign Road junction approach End of speed limit Road name sign
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Fig.3.6 Informatory signs
Route marker signs are erected ahead of intersections and such other points that may be considered necessary to guide the through traffic. Road Markings
Road markings are used as a means of controlling and guiding traffic. They are highly important on roads and intersections as they promote road safety and bring about smooth and harmonious flow of traffic along guided paths of travel. They also serve to supplement the messages conveyed by road signals and signs. In some cases, they are used alone to convey certain regulation, information or warning that cannot otherwise be effectively made known to the road users Types of Road Markings
Road markings are basically of two types: Carriageway markings and Object markings.
As the name implies, the former type of markings are those that are applied to the carriageway itself. The latter type covers markings on objects such as abutment, piers, kerbs, traffic islands, culvert headwalls, etc. Carriageway Markings
1. Centre line 2. Traffic lane line 3. No-overtaking zone markings 4. Pavement edge lines. 5. Carriageway width reduction transition markings 6. Obstruction approach markings. 7. Stop lines. 8. Pedestrian crossings 9. Cyclist crossings 10. Route direction arrows etc. 11. Word messages. 12. Markings at approaches to intersections.
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13. Parking space limits, 14. Bus stops. A few markings are explained 1. Centre Lines
The purpose of the markings is to guide the driver and separate the stream of traffic moving in opposite directions. These markings may be solid lines or broken lines according to the type of the road. An example is shown below (Figure.3.7)
Fig.3.7 Centre line marking 2. Traffic Lane Lines
These markings divide the carriageways into separate lanes on either side of the centre line. This helps to regulate the traffic into proper lanes (Figure.3.8).
Fig.3.8 Traffic lane marking 3. Pedestrian Crossings
These markings are provided at important intersections to facilitate pedestrians to cross a road (Figure. 3.11).
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Fig 3.9 Pedestrian crossings
OBJECT MARKING
Objects within the carriageway Kerb marking for visibility Kerb marking for parking restriction Objects adjacent to the carriageway
Object Markings within the Carriageway
The object marking for obstruction within the carriageway shall be marked not less than five alternating black and white stripes of 100mm width. The stripes shall slope downwards at an angle of 45° towards the side of the obstruction on which the traffic passes. Where vertical clearance of an overhead bridge is less than the prescribed minimum, the available clearance is marked on the structure. Vertical stripes are also marked on the face of the wall. Objects Adjacent to the Carriageway
Some objects such as abutments and subway piers, which are adjacent to the carriageway, should be marked with alternate white and black diagonal stripes sloping downwards. Object Markings on Kerbs
Kerbs of all islands should be painted with alternate black and white stripes of 0.5m width or a chequered black and white design of the same width. The two designs are showed in Figure.3.10
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Fig. 3.10 Kerb marking Marking Indicating parking restrictions
Kerbs on carriageway marking shall be used to show where parking is prohibited. The marking should be continuous yellow line covering the top and face of kerb or the carriageway close to it. Details of road markings are available General Principles of Longitudinal Pavement Markings
1. Solid lines are restrictive in nature and it is an Offence to cross or straddle such a line. 2. Broken lines are restrictive in character, and vehicles can cross such a line provided this can be done with safety. 3. When a combination of a solid and broken lines is used: in countries where the traffic moves to the left (right), a vehicle should not cross the continuous line adjacent to and to the left (right) of a broken line on the right (left) of the lane in which it is moving. 4. Double lines indicate maximum restrictions Material and Colour
The material commonly employed for pavement, curb and object marking is paint. Alternative materials such as strips of steel, rubber or plastic, reflecting or non-reflecting studs, permanently fixed white or coloured stones, inlaid concrete blocks etc. are also used in certain situations. The commonly used colours for road are white and yellow. The usage of these colours in India is, summarised below Colour of Road markings as per Indian Practice
Colour White Yellow Alternate bands of white and black
Uses All carriageway markings except those intended for parking restrictions Markings intended for parking restrictions Continuous centre and barrier line markings Kerb and object markings
Traffic Signals
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Traffic signals are provided at road intersections. These signals are provided to control, warn and guide the traffic. Traffic signals serve the following purposes
improves safety and efficiency of movement of vehicular traffic and pedestrians maintains orderly flow of traffic reduces accidents in general provides nearly continuous movement of traffic more economical than manual control stops heavy traffic to allow slow moving traffic to cross the road safely
Generally a traffic signal is composed of three lenses, arranged vertically one above the other with red lens on top, yellow or amber in the middle and a green lens at the bottom. These lenses are illuminated by an independent light source from behind. The shape of traffic control signal is circular having 200 mm visible diameter. The height at which the signals are usually installed varies from 2.4 to 3 m. The signals are located on the left hand side of the road as near the stop-line as possible. This is the primary signal. If an additional signal is placed on the departure side of the intersection on the right side, it is called a secondary signal. The normal sequence of traffic signal is red, amber-green-amber- red and so on. Following are the indications given by colours of signal (Figure.3.11)
Red : Vehicle must stop Amber : Light about to change Green : Vehicle can proceed.
Fig. 3.11 Traffic signal
The time lapsed from the beginning of red to a particular side to the beginning of next red to the same side is called a cycle. Stopping or go signal will be given to a particular stream each time. Thus, in each cycle, different streams will have different times for being given green/red, based on the volume. The number of such operations in cycle containing red-amber-green is known as a phase. When
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there are series of signals on a city road, there should be a proper co-ordination of the signal system to provide a green wave.
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SURVEYING
Surveying is the art of determining the relative positions of points on, above or beneath the surface of the earth by means of direct or indirect measurements of distance, direction and elevation. It also includes the art of establishing points by predetermined angular and linear measurements. The application of surveying requires skill as well as the knowledge of mathematics, physics, and to some extent, astronomy. In surveying, all measurements of lengths are horizontal, or else are subsequently reduce to horizontal distances. The object of a survey is to prepare plan or map so that it may represent the area on a horizontal plane. A plane or map is the horizontal projection of an area and shows only horizontal distances of the points. Vertical distances between the points are, however, shown by contour lines, or some other methods. Vertical distances are usually represented by means of vertical sections drawn separately. Primarily, surveying can be divided into two classes: 1. Plane surveying 2. Geodetic surveying. Plane Surveying
It is that type of surveying in which the mean surface of the earth is considered as a plane and the spheroid shape is neglected. All triangles formed by survey lines are considered as plane triangles. The level line is considered as straight and all plumb lines are considered parallel. In everyday life we are concerned with small portions of earth’s surface and the above assumptions seem to be reasonable in light of the fact that the length of an arc 12 kilometers long in the earth’s surface is only 1 cm greater than the subtended chord and further that the difference between the sum of the angles is only one second for a triangle at the earth’s surface having an area of 195 sq.km. Geodetic Surveying
It is that type of surveying in which the shape of the earth is taken into account. All lines lying in the surface are curved lines and the triangles are spherical triangles. It, therefore, involves spherical trigonometry. All Geodetic surveys include work of longer magnitude and high degree of precision. The object of geodetic survey is to determine the precise position on the surface of the earth, of a system of widely distant points which form control stations to which surveys of less precision may be referred.
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CLASSIFICATION
Surveys may be classified under headings which define the uses or purpose of the resulting maps. a) Classification based upon the nature of the field survey 1. Land surveying (i) Topographical Surveys This consists of horizontal and vertical location of certain points by linear and angular measurements and is made to determine the natural features of a country such as rivers, streams, lakes, woods, hills, etc., and such artificial features as roads, railways, canals, towns and villages.
(ii) Cadastral Surveys Cadastral surveys are made incident to the fixing of property lines, the calculation of land area, or the transfer of land property from one owner to another. They are also made to fix the boundaries of municipalities and of state and federal jurisdictions. (iii) City Surveying They are made in connection with the construction of streets, water supply systems, sewer and other works. 2. Marine or Hydrographic Survey Marine or hydrographic survey deals with bodies of water for purposes of navigation, water the work consists in measurements of discharge of streams, making topographic survey of shores and banks, taking and locating soundings to determine the depth of water and observing the fluctuations of the ocean tide. 3. Astronomical Survey The astronomical survey offers the survey means of determining the absolute location of any point of the earth. This consists in observations to the heavenly bodies such as the sun or any fixed star. b)
Classification based on the object of survey
1. Engineering Survey This is undertaken for the determination of quantities or to afford sufficient data for the designing of engineering works such as roads and reservoirs, or those connected with sewage disposal or water supply. 2. Military Survey This is used for determining points of strategic importance. 3. Mine Survey This is used for the exploring mineral wealth. 4. Geological Survey This is used for determining different strata in the earth’s crust. 5. Archaeological Survey This is used for unearthing relics of antiquity.
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c) Classification based on instruments used An alternative classification may be based upon the instruments or methods employed, the chief types being
1. 2. 3. 4. 5. 6. 7. 8. 9.
Chain Survey Theodolite survey Traverse Survey Triangulation Survey Tacheometric Survey Plane table Survey Photographic Survey Aerial Survey and Remote Sensing
The accuracy of the survey depends its usefulness’., the degree of accuracy needed will vary with the purpose of the survey. Accuracy of a survey depends on several factors that may be grouped as personal, instrumental, climatic and celestial. Chain surveying
Surveying with the chain is the art of measuring portions of earth’s surface with the aid of chain alone and representing the same on a reduced scale so as to bring out the portion vividly under the eye. This type of surveying is suitable for surveys of small extent on open ground to secure data for exact description of the boundaries of a piece of land or to take some details. Chaining
Chaining is term which is used to denote measuring distance either with the help of a chain or tape and is the most accurate method of making direct measurements. For work of ordinarily precision, a chain can be used, but for higher precision a tape or special bar can be used. The distances determined by chaining form the basis of all surveying. No matter how accurately angles may be measured, the survey can be no more precise than the chaining. Instruments for Chaining The various instruments used for the determination of the length of line by chaining are as follows: 1. Chain or tape 2. Arrows 3. Pegs 4. Ranging rods 5. Offset rods 6. Plasterer’s laths and whites and 7. Plumb bob 1. Chain Chains are formed of straight links of galvanized mild steel wire bent into rings at the ends and joined each other by three small circular or oval wire rings. These rings offer flexibility to the chain. The ends of the chain are provided with brass handle at each end with swivel joint, so that the chain can be turned without twisting. The length of a link is the distance between the
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centers of two consecutive middle rings, while the length of the chain is measured from the outside of one handle to the outside of the other handle. Following are various types of chains in common use: (i) Metric Chains (ii) Gunter’s Chain or Surveyors Chain (iii) Engineer’s Chain (iv) Revenue Chain (v) Steel band or band Chain Metric Chains After the introduction of metric units in India, the metric chains are widely used. Metric chains generally available in lengths of 5,10,20, and 30 meters.IS:1492-1970 covers the requirements of metric surveying chains Fig 3.12 shows the details of a metric chain
To enable the readings of fractions of a chain without much difficulty, tallies are fixed at every meter length for chain of 5 m and 10 m lengths and every five meter length of chain of 20 m and 30 m lengths. In case of 20 m and 30 m chains, small brass rings are provided at every meter length, except where tallies are attached. To facilitate holding of arrows in position with the handle of the chain, a groove is cut on the outside surface of the handle. The tallies used for marking distances in the metric chains are marked with the letter ’m’ in the order to distinguish them from non – metric chains. The length of chain, 5 m, 10 m, 20 m, or 30 m as the case may be, are engraved on both the handles to indicate the length and also to distinguish the chains from non-metric chains.
Fig 3.12 Metric Chain 2. TAPES Tapes are used for more accurate measurements and are classed according to the material of which they are made, such as follows: (i) Cloth or linen tape (ii) Metallic tape (iii) Steel tape (iv) Invar tape Cloth or Linen Tape Cloth tapes of closely woven linen, 12 to 15 mm wide varnished to resist moisture, are Light and flexible and many be used for taking comparatively rough and subsidiary measurements such as offsets. A cloth tape is commonly available in lengths of 10 meters, 20 meters, 25
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meters , and in 33 ft.,50ft.,66ft., and 100 ft. The end of the tape is provided with small brass ring whose length is included in the total length of the tape. A cloth tape is rarely used for making accurate measurements, because of the following reasons: (i) it is easily affected by moisture or dampness and thus shrinks; (ii) its length gets altered by stretching (iii) it is likely to twist and tangle ; (iv) it is not strong . Before winding up the tape in the case, it should be cleaned and dried. Metallic Tape A metallic tape is made of varnished strip of waterproof linen interwoven with small brass, copper or bronze wires and does not stretch as easily as a cloth a cloth tape. Since metallic tapes are light and flexible and are not easily broken, they are particularly useful in crosssectioning and in some methods of topography where small errors in length of the tape are of no consequences. Metallic tapes are made in lengths of 2, 5, 10, 20, 30 and 50 meters.
In the case of tapes of 10, 20, 30 and 50 m lengths a metal ring is attached to the outer ends and fastened to it by a metal strip of the same width as the tape. This metal strip protects the tape, and at the same time inspector’s stamp can be put on it. In addition to the brass ring, the outer ends of these tapes are reinforced by a strip of leather or suitable plastic material of the same width as the tape, for a length of at least 20 cm. Tapes of 10, 20, 30 and 50 metre lengths are supplied in a metal or leather case fitted with a winding device. Steel Tape
Steel tapes vary in quality and accuracy of graduation, but even a poor steel tape is generally superior to a cloth or metallic tape for most of the linear measurements that are made in surveying. A steel tape consists of a light strip of width 6 to 10 mm and is more accurately graduated. Steel tapes are available in lengths of 1, 2, 10, 30 and 50 meters. The tapes of 10, 20, 30 and 50 metre lengths are provided with a brass ring at the outer end, fastened to it by a metal strip of the same width as the tape, The length of the tape includes the metal ring. It is wound in a well- sewn leather case or a corrosion resisting metal case, having a suitable winding device. Tapes of longer length more than 30 m are wound on metal reel. A steel tape is a delicate instrument and is very light, and therefore, cannot withstand rough usage. The tape should be wiped clean and dry after using, and should be oiled with a little mineral oil, so that it does not get rusted. Arrows
Arrows or marking pins are made up of stout steel wire, and generally, 10 arrows are supplied with a chain. An arrow is inserted into the ground after every chain measured on the ground. Arrows are made up of good quality hardened and tempered steel wire 4 mm in diameter and are black enameled. The length of arrow may vary from 25 cm to 50 cm. The most common length being 40 cm, one end of the arrow is made sharp and other end is bent into a loop or circle for facility of carrying. Arrow is shown in the figure 3.13.
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Fig.3.13 Arrow Pegs
Wooden pegs are used to mark the positions of the stations or terminal points of a survey line. They are made of stout timber, generally 2.5 cm or 3 cm square and 15 cm long, tapered at the end. They are driven in the ground with the help of a wooden hammer and kept about 4 cm projecting above the surface. Ranging Rods
Ranging rods have a length of either 2 m or 3 m, the 2 metre length being more common. They are shod at the bottom with a heavy iron point, and are painted in alternative bands of black and white or red and white or black, red and white in succession, each band being 20 cm deep so that on occasion the rod can be used for rough measurements of short lengths. Ranging rods are used to range some intermediate points in the survey line. They are circular or octagonal in cross –section of 3 cm nominal diameter, made of well-seasoned, straight grained timber. The rods are almost invisible at a distance of about 200 meteres; hence when used on long lines each rod should have a red, white or yellow flag, about 30 to 50 cm square, tied on near its top. Ranging Rod is shown in the figure 3.14.
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Fig.3.14 Ranging rod Ranging Poles
Ranging poles are similar to ranging rods except that they are longer and of greater diameter and are used in case of very long lines. Generally, they are not pointed, but in all cases they are provided with a large flag. Their length may vary from 4 to 8 meters and diameter from 6 to 10 cm. The foot of each pole is sunk about .5 m in to the ground, the pole being set quite vertical by aid of a plump bob. Offset Rods
An offset rod is similar to a ranging rod and has a length of 3 m. They are round wooden rods, shod with pointed iron shoe at one end, and provided with a notch or a hook at the either. The hook facilities provide pulling and pushing the chain through hedges and other obstructions. The rod is mainly used for measuring rough offsets nearby. It has also two narrow slots passing through the center of the section, and set right angles to one another, at the eye level, for aligning the offset line. Ranging out survey lines
While measuring the length of the survey line or ‘chain line’, the chain or the tape must be stretched straight along the line joining its two terminal stations. If the length of the line is less than the length of the chain, there will be no difficulty, in doing so. If, however, the length of the line exceeds the length of the chain, some intermediate points will have to be established in line with the two terminal points before chaining is started. The process of fixing or establishing such intermediate points is known as ranging. There are two methods of ranging (i) Direct ranging (ii) Indirect ranging.
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(i) Direct Ranging
Direct ranging is done when two ends of the survey lines are inter visible. In such cases, ranging either can be done by eyes or through some optical instrument such as a line arranger or a theodolite. (ii) Indirect Ranging or Reciprocal Ranging
Indirect or Reciprocal ranging is restored to when both the ends of the survey lines are not inter visible either due to high intervening ground or due to long distance between them. In such case, ranging is done indirectly by selecting two intermediate points M1 and N1 very near to the chain line (by judgment) in such a way that from M1, both N1 and B are visible and from N1 both M1 and A are visible. Two surveyors station themselves at M1 andN1 with ranging rods. The person at M1 then directs the person at N1 to move to a new position at N2 in line with M1b. The person at N1 in line with M1B. The persons at N2 then direct the person at M1 to move to a new position M2 in line with N2A. Thus, the two persons are now at M2 and N2 which are nearer to the chain line than the positions M1 and N1. The process is repeated till the points M and N are located in such away that the person at M finds the person at N in line with MB, and the person at N finds the person at N finds person at M in the line with NA. After having established M and N, other points can be fixed by directed ranging. This method is done as shown in the figure 3.15.
Fig 3.15 Reciprocal Ranging Error due to incorrect chain
If the length of the chain used in measuring length of the line is not equal to the true length or the designated length, the measured length of the line will not be correct and suitable correction will have to be applied. If the chain is too long, the measured distance will be less. The error
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will, therefore, be negative and the correction is positive. Similarly, if the chain is too short, the measured distance is more, the error will positive and the correction will be negative. Let L = True or designated length of the chain or tape. L’ = Incorrect (or actual) length of the chain or tape used (i) Correction to measured length Let l’ = measured length of the line l = actual or true length of the line. Then, true length of line = measured length of line x L’ L l = l’ [L’/L] …………..(3.1) (ii)Correction to area Let
A’ = measured (or computed) area of the ground A = actual or true area of the ground
Then, true area = measured area x [L’/L] 2 . A = A’ (L’/L)2
or
Alternatively, L’/L = L + ∆L --------------L Where ∆L = error in length of chain ∆ L/L = e Let Therefore
= 1+
∆L/L
A = (L’/L) 2 x A’= (1+e) 2 x A’
But (1+e)2
=1+2e +e2 =1+2e, if e is small
Therefore A = (1+2e) A’ Compass Surveying
Chain can be used when the area to be surveyed is comparatively small and is fairly flat. However, when large areas are involved, methods of chain surveying alone are not sufficient and convenient. In such cases, it becomes essential to use some sort of instrument which enables angles or directions of the survey lines to be observed. In engineering practice, following are the instruments used for such measurements. (a) Instruments for the direct measurements of directions
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(i) (ii)
(i) Surveyor’s Compass (ii) Prismatic Compass (b) Instruments for the measurements of angles sextant Theodolite Traverse Survey
Traversing is that type of survey in which a number of connected survey lines from the framework and the directions and lengths of the survey lines are measured with the help respectively. When the lines form a circuit which ends at the starting point, it is known as closed traverse. Units of angle measurement
An angle is the difference in direction of two intersecting lines. There are three popular system of angular measurement (a) Sexagesimal system : 1 circumference = 360 1 degree = 60 1 minute = 60 (b) Centesimal system : 1 circumference = 400 1 grad = 100 ( c ) Hours system
1 centigrade 1 circumference 1 hour 1 minute
= 100 = 24 = 60 = 60
The segmental system is widely used in united states, Great Britain, India and other parts of the world. More complete tables graduated according to the system. However, due to facility in computation and interpolation, the celestial system is mostly used in astronomy and navigation. BEARINGS AND ANGLES The direction of a survey line can either be established (a) with relation to each other, or (b) with relation to any meridian. The first will give the angle between two lines while the second will give the bearing of the line. Bearing: Bearings of a line is its direction relative to a given meridian. A meridian is any direction such as (1) True meridian (2) Magnetic meridian (3) Arbitrary Meridian. True Meridian: True Meridians through a point is the line in which a plane ,passing that point and the north and south poles, intersects with surface of the earth. It, thus passes through the true north and south. The direction of true meridian through a point can be established by astronomical observations.
True Bearing: True bearings of a line is the horizontal angle which it makes with the true meridian through one of the extremities of the line. Since the direction of true meridian through a point remains fixed, the true bearing of a line is a constant quality
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Magnetic Meridian: Magnetic meridian through a point is the direction shown by a freely floating and balanced magnetic needle free from all other attractive forces. The direction of magnetic meridian can be established with the help of a magnetic compass.
Magnetic Bearing: The magnetic bearing of a line is the horizontal angle. Which it makes with the magnetic meridian passing through one of the extremities of the line. A magnetic compass is used to measure it Arbitrary Meridian: Arbitrary meridian is any convenient direction towards a permanent and prominent mark or signal, such as a church spire or top of a chimney. Such meridians are used to determine the relative position of line in a small area.
Arbitrary Bearing: Arbitrary bearing of a line is the horizontal angle which it makes with any arbitrary meridian passing through one of the extremities. A theodolite or sextant is used to measure it Designation of Bearings
The common system of notaion of bearings are : (a) The whole circle bearing system (W.C.B.) or Azimuthal system (b) The Quadrantal bearing (Q.B.) system The whole Circle Bearing System : (Azimuthal System) In this system, the bearing of a line is measured with magnetic north in clockwise direction. The value of the bearing thus varies from 0 to 360 ˚. Prismatic compass is graduated on this system. In India and UK., the W.C.B. is measured clockwise with magnetic north.
Fig. 3.16 W.C.B. system Referring to the Fig 3.16 the W.C.B. of AB is Ө 1 of AC is Ө2, of AD is Ө 3 and of AF is Ө4. (a) The Quadrantal Bearing System : (Reduced bearing)
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In this system, the bearing of a line is measured eastward or westward from north of a line is measured eastward or westward from north or south, which ever is nearer. Thus, both North and south are used as reference meridians and the directions can be either clockwise or anticlockwise depending upon the position of the line. In this system, therefore the quadrant, in which the line lies, will have to be mentioned. These bearings are observed by surveyors compass. Referring figure. 3.17 the Q.B. of the line AB is α and is written as N α E, the bearing being measured with reference to north meridian (since it is nearer ), towards East. The bearing of AC is β and is written as SβE, it being measured with reference of south and in anticlockwise direction towards East. Similarly, the bearings of AD and AF are respectively S θ W and θ NØW. Thus, in the Quadrantal system, the reference meridians are prefixed and the direction of measurement (Eastward or Westward) is affixed to the numerical value of the bearing. The Q.B. of a line varies from 0˚ to 90˚. The bearings of this system are known as Reduced Bearings (R.B.)
Fig.3.17 Q.B. systems CONVERSION OF BEARINGS FROM ONE SYSTEM TO THE OTHER
The bearing of the line can be very easily converted from one system to the other, with the aid of a diagram. Referring to fig. 3.16 the conversion of W.C.B. into can be expressed in the following table:
Conversion of W.C.B. into R.B.
Line
W.C.B. between
Rule for R.B.
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Quadrant
AB AC AD AF
0˚ and 90˚ 90 ˚and 180˚ 180 ˚and 270˚ 270˚ and 360
R.B.=W.C.B. R.B.=180-W.C.B. R.B.=W.C.B.-180 R.B.=360-W.C.B.
NE SE SW NW
Similarly, referring to figure 3.17 the conversion of R.B. into W.C.B. can be expressed into the following table: Conversion of R.B. into W.C.B.
Line AB AC AD AF
R.B. NαE SβE SθW N ØW
Rule for W.C.B. W.C.B. =R.B. W.C.B.= 180 –R.B. W.C.B.=180 +R.B. W.C.B.=360-R.B.
W.C.B. between 0˚ and 90˚ 90 ˚and 180˚ 180 ˚and 270˚ 270˚ and 360
FORE AND BACK BEARING
The bearing of line, whether expressed in W.C.B. system or in Q.B. system, differs according as the observation is made from one end of the line or from the other. If the bearing of a line AB is measured from A towards B, it is known as forward bearing or Fore Bearing (F.B). if the bearing as backward bearing or Back Bearing (B.B), since it is measured in backward direction.
Fig 3.18 Fore and Back Bearings Considering first the W.C.B. system and referring to figure. 3.18.a the back bearing of line AB is Ø and fore bearing of AB is θ. Evidently Ø =180˚+θ. Similarly, from figure3.18.b the back bearing CD is Ø and fore bearing θ, hence, Ø = θ-180˚. Thus, in general it can be stated that B.B= F.B+180˚, using plus sign when F.B is less than 180˚ and minus sign when F.B is greater than 180˚.
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Fig 3.19 Fore and Back Bearings
Again, considering the Q.B. system and referring to figure3.19.a the fore bearing of line AB is N θ E and there fore, the bck bearing is equal to S θW. Similarly from figure 3.19.b the fore bearing of the line CD is S θW and back bearing is equal to N θE. Thus, it can be stated that to convert the fore bearing to back bearing, it is only necessary to change the cardianal points by substituting N for S, and E for W and vice versa, the numerical value of the bearing remaining the same. CALCULATION OF ANGLES FROM BEARINGS
Knowing the bearing of two lines, the angle between the two can very easily be calculated with the help of a diagram,
Fig.3.20 Calculation of angles from bearings
Ref. to figure 3.20, the included angle α between the lines AC and AB = Ө2 - Ө1 = F.B of one line –F.B. of the other line, both bearings being measured from a common point A. Ref. figure 3.21, the angle α=(180˚+ Ө1)- Ө2 =B.B. of previous line –F.B. of next line.
Fig.3.21 Calculation of angles from bearings
Let us consider the quadrantal bearing .Referring to figure 3.21(a) in which both the bearings have been measured to the same side of common meridian, the included angle α= Ө2- Ө 1. In
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figure3.21 (b), both the bearings have been measured to the opposite sides of the common meridian, and included angle α= Ө1+Ө2. In figure 3.21(c) both the bearings have been measured to the same side of different meridians and the included angle α=180˚( Ө2+ Ө1). In figure3.21 (d) both the bearings have been measured to the opposite sides of the different meridians, and angle α= 180-˚( Ө1- Ө2). CALCULATION OF BEARINGS FROM ANGLES
In case of a traverse in which included angles between successive lines have been measured, the bearings of the line can be calculated provided the bearing of the line is also measured.
Fig.3.22 Calculation of bearings from angle
Referring to figure3.22 let α, β, γ, δ are the included angles measured clockwise from back stations and Ө1 be the measured bearing of the line AB. Therefore The bearing of the next line BC =180˚( Ө2+ Ө1) The bearing of the next line CD = Ө3 = θ2 + β - 180˚ The bearing of the next line DE = Ө 4 = Ө3 + γ - 180˚ The bearing of the next line EF = θ 5 = θ4 +δ + 180˚ As is evident from Figure 3.22 ( Ө1 + α ) , ( θ 2 + β ), and ( Ө3 + γ) are more than 180˚ while ( θ4 + δ) is less than 180˚ . Hence in order to calculate the bearing of the next line, the following statement can be made. “Add the measured clockwise angles to the bearing of the previous line. If the sum is more than 180˚, deduct 180˚. If the sum is less than 180˚, add 180˚ “ In a closed traverse, clockwise angles will be obtained if we proceed round the traverse in the anti clockwise direction
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ENVIRONMENTAL ENGINEERING
Water supply subsystem
The nature of the water source commonly determines the planning, design, and operation of the collection, purification, transmission, and distribution works. The diagram of a water supply system is given in Figure.3.23. The two major sources used to supply community and industrial needs are referred to as surface water and groundwater. Streams, lakes, and rivers are the surface water sources. Groundwater sources are those pumped from wells. The source in each case determines the type of collection works and the type of treatment works. The pipe network in the city is called the distribution system. The pipes themselves are often referred to as water mains. Water in the mains generally is kept at a pressure between 200 and 860 kilopascals (kpa). Excess water produced by the treatment plant during periods of low demand (usually the night time hours) is held in a storage reservoir. The storage reservoir may be elevated or it may be at ground level. The stored water is used to meet high demand during the day. Storage
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compensates for changes in demand and allows a smaller treatment plant to be built. It also provides emergency backup in case of a fire. Population and water-consumption patterns are the prime factors that govern the quality of water required and hence the source and the whole composition of the water resources system. One of the first steps in the selection of a suitable water supply source is determining the demand that will be placed on it. The essential elements of water demand include average daily water daily consumption and peak rate of demand. Average daily water consumption must be estimated for two reasons: •
•
to determine the ability of water source to meet continuing demands over critical periods when surface flows are low or groundwater table at a minimum elevations for purposes of estimating quantities of stored water that would satisfy demands during these critical periods.
The peak demand rates must be estimated in order to determine plumbing and pipe sizing, pressure losses, and storage requirements necessary to supply sufficient water during periods of peak water demand. Many factors influences water use for given system. For example, the mere fact that water under pressure is available stimulates its use, often excessively, for watering lawns and gardens, for washing automobiles, for operating air conditioning equipments and for performing many other activities at home and in industry. The following factors have been found to influence water consumption in a major way 1. Industrial activity 2. Meterage 3. System management 4. Standard of living 5. Climate The following factors are also influence water consumption to a lesser degree: extent of sewerage, system pressure, water price, and availability of private wells.
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Fig.3.23 Water Supply Subsystem
The influence of industry is to increase per capita water demand. Small rural and suburban communities will use less water per person than industrialized communities. Industry is probably the largest single factor influencing per capita water use. The second most important factor in water use is whether individual consumers have water meters. Meterage imposes a sense of responsibility not found in residences and businesses. This sense of responsibility reduces per capita water consumption because customers repair leaks and make more conservative water-use decisions almost regardless of price. Because water is so cheap, price is not much of a factor. Following meterage closely is the aspect called system management. If the water distribution system is well managed, per capita water consumption is less than if it is not well managed. Well managed systems are those in which the managers know when and where leaks in the water mains occur and have them repaired promptly. Industrial activity, meterage, and system management are most significant factors controlling water consumption than are either the standard of living or the climate. The rational for the
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latter two factors is straightforward. Per capita water use increases with an increased standard of living. Highly developed countries use much more water than the less developed countries. Likewise, higher socio economic status implies grater per capita water use, where as areas of high rainfall experiences lower water use. Water Quality
Precipitation in the form of rain, hail, or select contains very few impurities. It may contain trace amounts of mineral matter, gases, and other substances as it forms and falls through the earth’s atmosphere. The precipitation, however, has virtually no bacterial content. Once precipitation reaches the earth’s surface, many opportunities are presented for the introduction of mineral and organic substances, micro organisms, and other forms of pollution (contamination). When water runs over or through the ground surface, it may pick up particles of soil. This is noticeable in the water as cloudiness or turbidity. It also picks up particles of organic matter and bacteria. As surface water seeps downward into the soil and through the underlying material to the water table, most of the suspended particles are filtered out. This natural filtration may be partially effective in removing bacteria and other particulate materials. However, the chemical character tics of the water may change and vary widely when it comes in contact with mineral deposits. As surface water seeps down to the water table, it dissolves some of the minerals contained in the soil and rocks. Groundwater, therefore, often contains more dissolved minerals than surface water. Standards of Purified Water
The physical, chemical and bacteriological standards for water is suggested by the following agencies 1. Indian Council of Medical Research (I.C.M.R) Committee. 2. World Health Organization (W.H.O) International. 3. United States Public Health Society (U.S.P.H.S). 4. American Water works Association (A.W.W. A). 5. Environmental Hygiene Committee. The physical and chemical quality of water should not exceed the limits shown in the table below as per WHO standards and as per IS:10500-1983. The bacteriological quality is given by MPN (Most Probable Number) index and in treated water supply system MPN index should be 0/100 ml. Physical and Chemical standards of potable water (IS: 10500 – 1983) S.No
Charecteristics
Acceptable
Cause for rejection
1
Turbidity (units on J.T.U scale)
2.5
10
2
2.5
3
Colour(Units of platinum Cobalt 5.0 scale) Taste and odour Unobjectionable
4
pH
6.5 to 9.2
7.0 to 8.5
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Unobjectionable
5
500
1500
6
Total dissolved solids (mg/l) Total hardness as CaCo3(mg/l)
200
600
7
Chlorides (as cl)
200
1000
8
200
400
9
Sulphates(asSo4) ___ (mg/l) Fluorides (as F) (mg/l)
1.0
1.5
10
Nitrates (as No3)
45
45
11
Calcium (as Ca) (mg/l)
75
200
12
Magnesium(mg/l)
Not less than 30
150
13
Iron ( as Fe) (mg/l)
0.1
1.0
14
Mangsnese (mg/l)
0.05
0.5
15
Copper (as Cu) (mg/l)
0.05
1.5
16
Zinc (mg/l)
5.0
15.0
17
Phenolic compounds (mg/l)
0.001
0.002
18
Anionic detergents as MABS
0.2
1.0
19
Mineral oil (mg/l)
0.01
0.3
20 21
Toxic Materials Arsenic (as As) (mg/l) Cadmium (mg/l)
0.05 0.01
0.05 0.01
22
Chromium (mg/l)
0.05
0.05
23
Cynides (mg/l)
0.05
0.05
24
Lead (mg/l)
0.1
0.1
25
Selenium (mg/l)
0.01
0.01
26
Mercury (mg/l)
0.001
0.001
27
0.2
28
Polynuclear aromatic hydrocarbons PAH Gross alpha activity
3 pci/l
3 pci/l
29
Gross Beta activity
30 pci/l
30 pci/l
Physical Characteristics Turbidity: The presence of suspended material such as clay, silt, finely divided organic material, plankton, and other particulate material in water is known as turbidity. The unit of measure is a Turbidity unit (TU) or Nephlometric Turbidity unit (NTU). It is determined by reference to a chemical mixture that produces a reproducible refraction of light. Turbidities in excess of 5 TU are easily detectable in a glass of water and are usually objectionable for aesthetic reasons.
Clay or other inert suspended particles in drinking-g water may not adversely affect health, but water containing such particles may require treatment to make it suitable for its intended end
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use. Following a rainfall, variations in the groundwater turbidity may be considered as indication of surface or other introduced pollution. Color: Dissolved organic material from decaying vegetarian and certain inorganic matter cause color in water. Occasionally, excessive blooms of algae or the growth of aquatic microorganisms may be also imparting color. While color itself is not usually objectionable from the standpoint of health, its presence is aesthetically objectionable and suggests that the water needs appropriate treatment. Taste and odor: Taste and odor in water can be caused by foreign matter such as organic compounds, inorganic salts or dissolved gases. These materials may come from domestic, agricultural, or natural sources. Drinking water should be free from any objectionable taste to odor at point of use. Temperature: The most desirable drinking waters are consistently cool and do not have temperature fluctuations of more than a few degrees. Groundwater and surface water from mountains areas generally meet these crates. Most individuals find that water having a temperature between 10 -15 c is most palatable. Chemical Characteristics Chloride: Most waters contain some chloride. The amount present can be caused by the leaching of marine sedimentary deposits or by pollution from sea water, bring, or industrial or domestic wastes. Chloride concentrations in excess of about 250 mg/L usually produce a noticeable taste in drinking water. Domestic water should contain less than 100 mg/L of chloride. In some areas, it may be necessary to use water with chloride content in excess of 100 mg/L. in these cases, all of the other criteria for water purity must be met. Fluorides: In some areas, water sources contain natural fluorides. Where the concentrations approach optimum levels, beneficial health effects have been observed. In such areas the incidence of dental caries has been found to be below the levels observed in areas without natural fluorides. The optimum fluoride level for a given area depends upon the air temperature, since temperature greatly influences the amount of water people drink. Excessive fluorides in drinking water supplies may produce Florosis (mottling) of teeth, which increases as the optimum fluoride level is exceeded. State local health departments should be consulted for their recommendations. Iron: Small amounts of iron frequently are present in water because of the large amount of iron in the geologic materials. The presence of iron in water is considered objectionable because it imparts a brownish color to laundered goods and affects the taste of beverage such as tea and coffee. Lead: Exposure of body to lead, however brief, can be seriously damaging to health. Prolonged exposure to relatively small quantities may result in serious illness or death. Lead taken into the body in quantities in excess of certain relatively low and normal limits is a cumulative poison. Manganese: Manganese imparts a brownish color to water and to cloth that is washed in it .It flavors coffee and tea with a medicinal taste.
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Sodium: The presence of sodium in water can affect persons suffering from heart, kidney, or circulatory ailments. When a strict sodium-free diet is recommended, any water should be regarded with suspicion. Home water softeners may be of particular concern because they add large quantities of sodium to the water Sulphate : Waters containing high concentrations of sulphate, caused by the leaching of natural deposits of magnesium sulphate (Epsom salts ) or sodium sulfate (Glauber’s salt), may be undesirable because of their laxative effects. Zinc: Zinc is found in some natural waters, particularly in areas where zinc ore deposits have been mined. Zinc is not considered detrimental to health, but it will impart an undesirable taste to drinking water. Toxic inorganic substances: Nitrates (NO3), Cyanides (CN), and heavy metals constitute the major classes of inorganic substances of health concern. Methemoglobinemia (infant cyanosis or blue baby syndrome) has occurred in infants who have been given water or fed formula prepared with water having high concentrations of nitrate. CN ties up with the hemoglobin sites that bind oxygen to red blood cells. This results in oxygen deprivation. A characteristic symptom is that the patient has a blue skin color. This condition is called cyanosis. CN causes chronic effect on the thyroid and central nervous system. The toxic heavy metals include arsenic (As), barium (Ba), Cadmium (Cd), Chromium (Cr), Lead (Pb), mercury(Hg), Selenium(Se), and Silver(Ag),. The heavy metals have a wide range of effects. They may be acute poisons (As and Cr for example), or they may produce chronic disease (Pb, Cd, and Hg for example). Microbiological Characteristics
Water for drinking and cooking purposes must be made free from disease-producing organisms (pathogens). These organisms include viruses, bacteria, protozoa, and helminthes (worms). Some organisms which cause disease in people originate with the fecal discharges of infected individuals. Others are from fecal discharge of animals. Unfortunately, the specific disease-producing organisms present in water are not identified. The techniques for comprehensive bacteriological examination are complex and time-consuming. It has been necessary to develop tests that indicate the relative degree of contamination in terms of microorganisms of the coli form group. This grouping includes two genera Escherichia coli and Aerobater aerogenes. The name of the group is derived from the world colcon. While E.Coli are common inhabitants of the intestinal tract, Aerobacter are common in the soil, on leaves, and on grain; on occasion they cause urinary tract infections. The test for these microorganisms, called the Total Coli form Test, was selected for the following recessions: The group of organisms normally inhabits the intestinal tracts of humans and other • mammals. Thus, the presence of coli forms is an indication of fecal contamination Even in acutely ill individuals, the number of coli form organisms excreted in the feces • outnumbers the disease-producing organisms by several orders of magnitude. The large numbers of coliform make them easier to calculate than disease producing organisms. The coliforms group of organisms survives in natural waters for relatively long periods • of time, but does not reproduce effectively in this environment. Thus, the presence of coli form in water implies fecal contamination rather than growth of the organisms
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because of favorable environmental pathogens. This means that the absence of coli forms is a reasonably safe indicator that pathogens are not present. The coli form group of organisms is relatively easy to culture. Thus, laboratory technicians can perform the test without expensive equipment.
Current research indicates that testing for Escherichia Coli specifically may be warranted. Some agencies prefer the examination for E.Coli as a better indicator of biological contamination than total coli forms. WASTE WATER MANAGEMENT SYSTEM
In general water which is consumed by the consumers, becomes a waste water. The consumption may either be domestic consumption or industrial consumption. The waste water coming out of industries are called industrial waste and that from residential localities as domestic waste or municipal waste. The engineering task involves collection of waste water, design of underground network of pipes (sewers), design of pumps and other accessories, treatment of waste and safe disposal into land and water bodies. This is given in Figure. 3.24
Fig.3.24 Waste water Management System Treatment Systems
Treatment plants can be classified as simple disinfection, filter plants, or softening plants. Plants employing simple chlorination have a high water quality source and chlorinate to ensure that the water reaching customers contains safe bacteria levels. Generally, a filtrations plant is used to treat surface water and a softening plant to treat groundwater. In a filtration plant, rapid mixing, flocculation, sedimentation, filtration, and disinfection are employed to remove color, turbidity, taste and odors, and bacteria. Additional operations may include bar racks or coarse screens if floating debris and fish are a problems. Figure.3.24 shows a typical flow diagram of a filtration plant. The raw (untreated) surface water enters the plant via low-lift pumps. Usually screening has taken place prior to pumping. During mixing, chemicals called coagulants are added and rapidly dispersed through the water. The chemical reacts with the desired impurities and forms precipitants (flocs) that are slowly brought into contact with one another during flocculation. The objective of the flocculation is to allow the flocs to collide and grow to a settable size. The particles are removed by gravity (sedimentation). This is done to minimize the amount of solids that are applied to the filters. For treatment works with high-quality raw water, it may be possible to omit sedimentation and perhaps flocculation. This modification is called direct filtration.
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Filtration is the final polishing (removal) of particles. During filtration the water is passes through sand or similar media to screen out the fine particles that will not settle. Disinfection is the addition of chemicals (usually chlorine) to kill or reduce the number of pathogenic organisms. Disinfection of the raw water is neither economical nor efficient. The color and turbidity consume the disinfectant thus requiring the use of the excessive amounts of chemical. Softening plants utilize the same unit operations as filtration plants, but use different chemicals. Thus primary function of a softening plant is to remove hardness (calcium and magnesium). In a softening plant (a typical flow diagram is shown in Fig. the design considerations of the various facilities are different than those in filtrations. Also the chemicals doses are much higher in softening, and the corresponding sludge production is greater. During rapid mix, chemicals are added to react with and precipitate the hardness. Precipitation occurs in the reaction basin. The other unit operations are the same as in a filtrations plant except for the additional re carbonation step employed in softening to adjust the final pH. MUNICIPAL WASTE WATER TREATMENT
The alternative for municipal waste water treatment fall in to three categories Primary treatment Secondary treatment, advanced treatment. It is commonly assumed that each of the degrees of treatment noted in the (Figure3.25) includes the previous steps .For example, primary treatment is assumed to include the pretreatment process: back rack, grit chamber and equalization process. Likewise, secondary treatment is assumed to include all the processes of primary treatment: rack, grit chamber, and equalization basin and primary settling tank. The purpose of treatment is to provide protection to the waste water treatment plant (WWTP) equipment that follows. In some older municipal plants the equalization step may not be included. The major goal of treatment is to remove from wastewater those wastewater those pollutants that will either settle or float. Primary treatment will typically remove about 60% percent of the suspended solids in raw sewage and 35 percent of the BOD5. Then soluble pollutants are not removed at one time, this was the only treatment used by many cities now federal law requires that municipalities provide secondary treatment. Although, primary treatment alone is no longer acceptable, it is still frequently used as the first treatment step in a secondary treatment system. The major goal of secondary treatment is to remove the soluble BOD5 that escapes the primary process and to provide added removal of suspended solids .Secondary treatment is typically achieved by using biological processes. These provide the same biological reaction that would occur in the receiving water if it had adequate capacity to assimilate the waste water. The secondary treatment processes are designed to speed up the natural water so that the breakdown of the degradable organic pollutants can be achieved in relatively short time periods. Although secondary treatment may remove more than 85 percent of the BOD5 and suspended solids, does not remove significant amount of nitrogen, phosphorus are heavy metals, nor it does it completely remove pathogenic bacteria and viruses.
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Fig. 3.25 Degrees of treatment
In case where secondary level of treatment is not adequate, additional treatment process are applied to the secondary effluent to provide advanced waste water treatment (AWT). These processes may involve chemical treatment and filtration of the waste water – much like adding a typical water treatment to the tail end of a secondary plant – or they may involve applying the secondary effluent to the land in carefully designed irrigation system where the pollutants are removed by a soil crop system. Some of these processes can remove as much as 99 percent of the BOD5, phosphorus, suspended solids and bacteria, and 95 percent of the nitrogen. They can produce a sparkling clean, colourless, odourless effluent indistinguishable in appearance form a high quality drinking water. Although these process and land treatment systems are often applied to secondary effluent for advanced treatment, they have also been used in place of conventional secondary treatment processes. Most of the impurities removed from waste water do not simply vanish. Some organics are broken down into harmless Co2 and water. Most of the impurities removed from waste water as a solid, i.e. sludge. Because most of the impurities removed from the waste water are present in the sludge, sludge handling and disposal must be carried out carefully to achieve satisfactory pollution control.
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