non-engineered buildings

Design and Management of Structures in Earthquake Zones – CIVE 5913M Report on “Non-Engineered Buildings”

ABSTRACT:

Nature Nature calamities calamities are unavoidab unavoidable le and unpredictable unpredictable.. It may happen happen at any time anywhere anywhere in the world. world. They They claim claim million millionss of life and money money,, if suitab suitable le resista resistant nt measur measures es are not followed. Earthquake is one such calamity which costs unaccountable damage to men and man-ma man-made de struct structure ures. s. Develo Developed ped count countrie riess which which are prone prone to earthq earthquak uakee are very often often investing huge amount of money in building structures which are capable to resist earthquake effects. There by they reduce the amount of damage caused to public and to the structures built built by or built built for the public public.. Econom Economica ically lly undeve undevelop loped ed countr countries ies which which are prone prone to earthquake are still struggling and losing their wealth very often to the hands of earthquake. Due to lack in economy and engineering, most people of these countries are at risk from the collap collapse se of their their own homes homes.. These These are ‘non-e ‘non-eng ngine ineere ered’ d’ buildi building ngs. s. Hence Hence to protec protectt the population, there is an urgent need to increase the quality of the domestic construction to reduce their vulnerability to earthquake action. In terms of guiding those reports are prepared by many voluntary organisations on how to build low cost buildings in earthquake areas. This is one such report which discusses the ways to built buildings in an earthquake area and advant advantage agess and and disadv disadvant antag ages es of the materi materials als used used for const construc ruction tion.. Photog Photograp raphs hs and sket sketch ches es are are incl includ uded ed in this this repo report rt to prov provid idee clea clearr view view abou aboutt earth earthqu quak akee effe effect ctss on buildings and on improvement measures. A case study on reducing vulnerability on buildings in earthquake prone country (India) is done in order to provide clear understanding on this topic.

Course Work 2 – Student Student ID: 2004 40013

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1 INTRODUCTION:

Earthquake is a hazardous calamity which causes damage to life and money. Buildings which are engine engineere ered d to this this effect effect stands stands during during an earthq earthqua uake ke and those those not engine engineere ered d fails. fails. Existing buildings which are not engineered are to be improved in order to resist the earthquake effect effects. s. Streng Strength th of earthq earthqua uake ke depen depends ds on the intens intensity ity,, freque frequency ncy,, time durati duration on and and soil soil conditions. Damages on buildings also depend on these criteria along with the quality of construction, strength and durability. From the history of the earthquakes it can be understood that many people people were killed or badly injured injured because because of poorly poorly construct constructed ed buildings. buildings. In earthqua earthquake ke prone undeveloped undeveloped countries countries buildings buildings are erected erected without without proper proper engineer engineering ing advice advice with usag usagee of poor poor qual quality ity mate materi rial als, s, cons constru truct ctio ion n and and work workma mans nshi hip. p. More More ofte often n buil buildi ding ngss constructed with traditional materials like stones and bricks are suffered the most. In fact nonengine engineere ered d buildi building ngss are built built mostly mostly with load load bearin bearing g masonry masonry wall, stud stud wall, wall, piers piers in masonry and columns in RC, steel or wood

[3]

.

In view of the fact that in seismic zones of the world more than 90 percent of the population is still living and working in non-engineered buildings

[1]

. As earthquake forces are horizontal in

nature, vertical load carrying structural elements are forced to carry horizontal load and the shear associated with it. If the structural elements are not designed to carry this, the structure fails. Associated causes of earthquake like ground vibration and failure, tsunami and fire are also major disaster causing agents. From analysis of buildings in earthquake areas, it is clear that most of the building fail due to considering strong beams and weak columns, soft storeys and lack of transverse reinforcement

[4]

.

As per the 1991 census of India, the country has nearly 195.0 million non-engineered dwelling units

[3]

. On 26

th

January 2001, an earthquake rocked Gujarat, India and claimed millions of

lives. Most of the collapsed buildings are identified as non-engineered buildings. This is an exam exampl plee even eventt to poin pointt the the need need of earth earthqu quak akee resi resist stan antt cons constru truct ctio ion n of nonnon-en engi gine neer ered ed buildings. Recent earthquakes in Kobe-Japan and Anatolia-Turkey triggered the importance of skill skill in cons constru truct ctin ing g nonnon-en engi gine neer ered ed build buildin ings gs.. Coun Countr trie iess whic which h are are extre extreme mely ly pron pronee to earth earthqu quak akee damag damages es requ require ire a suita suitabl blee repo report rt whic which h will will be usef useful ul to peop people le invo involv lved ed in construction of new houses or repair and strengthening of existing buildings. In this report, the construction of earthquake safe non-engineered buildings plays a major role.


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2 BUILDING IN EARTHQUAKE ZONE:

Consider a typical two storey house in earthquake prone area which is subjected to seismic forces. The building is non-engineered one and constructed using locally available material. The building is designed designed and constructe constructed d by a local local artisan artisan over a soft soil stratum without any engineering knowledge. The materials used are locally available low quality fire burnt bricks, reinforced concrete for roof slab, graded cement, river sand, wooden joineries and wooden truss for sloped tile roof. Due to budget limitation form the owner, the builder decided to add slope sloped d woode wooden n roof roof with with burnt burnt roof roof tiles tiles as cover cover to secon second d storey storey instead instead of reinfo reinforce rced d concrete slab. As this building is constructed using traditional materials, its response to seismic forces will be large and may damage during an earthquake.

Figure 1: Typical two - storey house 2.1 Construction methods:

The walls were supported by masonry columns at the edges and at the centre. The RCC roof slab of first storey is made to rest on walls and partially on masonry columns. The masonry columns are continued from first storey to second storey to support wooden roof truss and roof tiles. Walls at first storey level are urged to carry the weight of first storey roof, walls at second storey level, partial weight from roof truss and tiles. Thus the walls act as a load-bearing one. Roof slab is placed above the wall and on column and it is not effectively tied to it. In both the storeys storeys floor to roof distance distance is uniform. uniform. The walls are unreinforc unreinforced ed with larger larger length-to-w length-to-width idth ratio on one side and other as simply supported supported masonry masonry wall. In considering considering foundation foundation for the house, columns are provided with isolated footings. Individual column footings are not tied to each other using plinth beam. Staircase to second storey is provided outside the building which Course Work 2 – Student Student ID: 2004 40013

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made of reinforced concrete and supported to lintel and column. Sufficient number of window openings is provided. Lintel beams are not continued through the building they are provided only above window and door openings.

Figure 2: Building plan of two-storey house 2.2 Forces acting on the building: 2.2.1 Inertia forces:

Basically seismic forces are movements which act randomly in all directions and unpredictable. Due to self weight of the building resists the seismic forces acting on it. This resistant of the building due to its self-weight is called as inertia force. Mostly buildings collapse due to inertia force forcess only. only. During During seismi seismicc load load the buildin building g moves moves abrupt abruptly ly and inertia inertia forces forces are create created d throughout the building and in its contents

[1]

. If the weight of the building is more the inertia

force will more and vice versa. As the building is constructed using traditional materials like bricks, RCC for roof slabs; the weight of the building is more. For an earthquake prone area, the buildings should be built less weight, such that the inertia forces will be less. 2.2.2 Seismic Seismic forces on whole structure: structure:

As seismic forces are abrupt, the vertical vibrations created by that will impose an additional vertical load effect to the walls and columns. As the walls and columns are not designed to it failure failure will occur. In addition to that they have to carry horizontal horizontal bending and and shearing stress. stress. From the construction methods of the building it is observed that the link between walls and columns columns is poor. No reinforceme reinforcement nt is provided provided in that link. Connectio Connection n between roof slab with wall and column is not well detailed.


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Figure 3: Behaviour of two-storey house to seismic force Seismic force acts horizontally to the building on a whole, due to inertia the building manages itself to be in position. As deflection increases with height, second storey responds more to seismic forces and will start to slide from its original position. Due to ineffective column this may happen. The columns are made from masonry work without reinforcement and in this case it had failed due to shearing. Due to improper linkage between the members of the building this type of failure occurred. The connection between the walls and columns are not well detailed to resist the seismic forces acting on it. 2.3 Response of first storey:

When considering first storey alone, the earthquake force is acting in plane of the wall B and opposite to wall A. As the adhesion between the slab and wall is poor, the inertia force of the slab will not be transferred to the walls A and B. Due to this the slab will tend to slide from its initial position.

Figure 4: Response of first storey Wall A is not designed to carry load in X-direction, this results in occurrence of crack near the connection between the columns and may fail due to bending action. At the same time wall B Course Work 2 – Student ID: 2004 40013

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will act as a shear wall withstanding the force from the roof and its own inertia force. The plate action of wall A has to be restrained by the roof at the top and by column supporting it. The seismic forces are amplified in this case due to ineffective joint connection between the members. In real conditions, the building on whole should act as a box; transferring forces effectively. The diaphragm action of the roof slab is not adequate to transfer its inertia force to the side walls

[1]

. If the roof slab is linked well to the walls, wall B will carry most of the inertia

force from the roof than wall A; as because wall B has more stiffness in that direction than wall A. The relative displacement of wall will bring down the roof slab. 2.4 Response of second storey:

The masonry columns are continued from first storey to second storey. As no reinforcements are provided in the columns, they will shear and fail. If reinforcement is provided, failure due to shear and bending can be prevented.

Figure 5: Response of second storey Same as first storey the seismic forces are acting in X-direction. As this storey deflect more than first storey, they develop more crack due to shaking effects. The inertia force created by the roof will only go to the vertical elements in which they are supported. On failure of columns the roof will collapse. The integrity of roof is more important for earthquake resistance. In this case the wooden truss is made to simply rest on the columns, walls and will offer resistance to motion through friction only

[1]

.

The walls B are gabled to receive the purlins of the end bays. During seismic force along Xaxis, the inertia force from the purlins will transmitted to trusses and from trusses to wall A. Wall A which is supported to columns will bend on deflection and may fail, which results in sliding of roof truss in one direction and fail. As the truss is made to support on wall A, on failure the truss will collapse. By adding suitable horizontal bracing in the truss, it can be made to transmit the force horizontally to wall B. Course Work 2 – Student ID: 2004 40013

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2.5 Seismic forces on individual parts:

The ability of the structure to withstand seismic force depends on the characteristics of individual members. 2.5.1 Column:

Columns in this structure are assumed to be made of masonry without any reinforcements in it. The main purpose of this column is to support the walls and to carry partial loads from first storey roof slab and roof truss. As there is no cross reinforcements in the column, it will fail easily due to bending and shear. These columns are the one which is intended to hold the building as a single element. To avoid failure columns are to be tied with each other particularly to the footing, through which the load is transmitted to the ground. The roof and wall connection to the columns are to be well detailed in order to perform like a box. 2.5.2 Roof slab and roof truss:

The roof slab is made of RCC and it is placed on the walls to transmit the inertia force created during an earthquake. For this transmission the slab has to be joined effectively to the walls and to columns. The diaphragm effect of the slab in essential for it to behave as an active resistant to seismic force. The roof truss has to efficiently fix at edges to the columns and supported to the wall. The wall supporting the truss has to be designed to carry the inertia forces from the truss created during earthquake. 2.5.3 Walls:

As walls are designed to act as load bearing one, they have to be effectively fixed to the supports mainly columns at sides. The earthquake is assumed to be in x-direction, in which wall A is weak to carry that seismic force than wall B which acts as shear wall. This is due that the seismic forces are acting in plane to wall B. From fig: 3, performance of the wall during an earthquake in x-direction can be analysed. The perpendicular seismic force acting on wall A makes it to bend and even to overturn, if the top of the wall is not fixed to the roof effectively. In this the joints at the edges of the wall with the column will fail. Apart from its own inertia force, the walls are subjected from vertical loads from the roof slab and weight of second storey.

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2.5.4 Footing:

Though the site is located on soft soil, plinth band is not used to tie all footings. This is because the column has no reinforcement in it and connection with plinth is not possible. The footing is assumed to be isolated, so occurrence of differential settlement may possible. Due to bending action of the column the footing may fail at the junction. The amount of lateral force acting during seismic force will be enormous. To avoid failure footings are advised to be continuous. 3 LOAD PATH TO THE GROUND:

Basically seismic load is a combination of both horizontal and vertical load. The loads acting on the structure has to be transferred to the ground for dissipation. Efficient load path depends on durable joints between the members. Flow chart below explains the load path of the building discussed earlier.

Figure 6: Load path of the building Abrupt forces acting on the structure is transferred from all parts of the members to the nearest load path and reaches the ground. Load from roof truss reaches the ground by the help of columns and walls at second floor level supporting that. Similarly load from first storey roof reaches the ground by columns and walls at first storey level. In this same fashion, load acting at different elements of the structure will take their nearest load path and reach the ground to nullify the damage effect to be caused to


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them. For efficient transmission of loads the members and the joints should be durable and strong enough to carry them without any damage to the structure. 4 FORMS OF CONSTRUCTION AND MATERIALS:

Materials, methods and shapes used for construction will vary from place to place. These many times represent culture and tradition of individuals. In certain places economy places a major role in selection of these. Countries prone to earthquake effects often have dwelling spaces built using traditional construction materials, methods and shapes. For discussion, buildings are categorised as per their materials, methods of construction and shapes used. 4.1 Materials used for construction:

Normally non-engineered buildings are constructed using Fire burnt masonry bricks, stone, wood and earth. These are easily available material and cost less for constructing a building. Depending on availability of material construction of buildings will vary. 4.1.1 Fire burnt masonry bricks:

Bricks are one of the material which as acceptable compressive strength and unacceptable tensile strength. Its strength can be upgraded when combined with reinforcement steel. Load carrying capacity of bricks in building is increased if bond with mortar is good. Normally bricks are used to built buildings, where the load to be carried is more. Bricks are used at places where clay fields are more. As a material it resists seismic load applied on it, if proper construction method is used. 4.1.2 Rubble stone:

Buildings built of rubble stone are more in rural areas. As this is easily available material, many are intended to use to this material. Same as brick it has very good compressive strength. With introduction of mortar and reinforcement, the strength and load carrying capacity can be increased. Exhibits poor strength when used with mud mortar

[1]

. When considering the height of the building, it is advisable to use

reinforcement with rubble stone. Well dressed polished and unpolished stones are available in the market. Buildings destroyed at Gujarat, India during earthquake in the year 2001 are more of Rubble stone or cut stone type


[2]

. This material suffered

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extensive damage and complete collapse during earthquakes. As these types of buildings weigh more, the inertia forces created during seismic reaction will be more and easily prone to damage. 4.1.3 Wood:

Good damping material. Buildings built with wood experienced less damage when comparing to buildings built with other materials. Depending upon quality price of material varies. More often used in hilly areas. In order to protect environment, cutting of trees is banned in many countries. Decrease in forest area due to population increase reduced wood usage in construction. Wooden buildings are constructed in areas where availability of the material is more or in unavoidable situations only

[1]

.

Wooden frames used in buildings may fail due to impose of high lateral load to the frame from heavy cladding. Easily catches fire and may cause mass damage. 4.1.4 Earth:

Buildings using earth are informally constructed in many parts of the earthquake prone countries. They often use wooden sticks as reinforcement. Due to minimal costs, good acoustics and thermal insulation effects it is widely used in rural parts. The performance of this material under earthquake and water is very poor

[1]

.

Currently in India there are about 74.7 million earthen dwelling units which constitute 38% of total dwelling units

[3]

. These are the ones which causes the greatest loss of

life and damage during seismic events. 4.2 Methods used for construction:

Though the material is tough against seismic load, the method followed in constructing that may lead to failure of material. Many time materials will not fail by crushing, it will fail due to improper bonding and connection details. Majority of non – engineered buildings are constructed under two main categories

[5]

.

a) Load bearing masonry b) Reinforced concrete frames


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4.2.1 Load bearing masonry:

In this type of construction the entire load of the slab is concentrated on supporting walls, which are reinforced or many times unreinforced. The supporting walls are to carry the inertia forces from the slab. On absence on this, the structure collapses. Most of these buildings use masonry units like burnt bricks, concrete blocks, rubble stone and rough dressed stones. Even sun dried clay bricks are used in this type of construction. The units are bonded with each other using available mortar variety. Roof structure often consists of tiles laid on timber planks supported by wooden purlins and rafter. If the number of storey exceeds normally reinforced concrete slabs are used

[5]

.

This type of construction is very economical and suitable for single storey buildings with low load carrying capacity. For efficient performance, the roof has to tie to the walls supporting it. Do well, if the sides of the walls are short. Non reinforcement usage, usage of heavy stone blocks and roofs will make the building to vulnerable to earthquake. Masonry units with mud mortar perform worst in this type of construction. This type highly depends on tie between roof and walls, size and spacing of openings. 4.2.2 Reinforced concrete frames:

In this type of construction the loads are designed to carry by members assigned in the structure, preferably for buildings taller than three storeys. Usually the masonry infill is built using stone block or clay brick. Frames are designed such that the inertia forces created by the roof are carried through a load path and get dissipated at ground level. This method is efficient for earthquake construction, if properly designed. Poor detailing of open first storey combined with poor quality of construction will make the frame to fail. Beam-column connections are to be designed to carry torsion and lateral forces acting on them. Continuity of columns and beams are a major issue in this type of construction. 4.3 Shapes of construction:

Shape and geometry of structure decides the structural response during an earthquake. Structures with simple shape and geometry perform well during an earthquake. It is always preferred to have simple shapes during construction such that all the members


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and joints associated can be well designed. Symmetrical plans with suitable size openings make the structure to behave as whole; where as unsymmetrical plans leads to torsion and extreme corners are subjected to very large earthquake forces

[6]

.

Structure should avoid projections in it. “For long narrow rectangular blocks, the length of a block is restricted to three times its width”

[1]

. Structure should be a simple

one with out ornamental effects on it. On requirement it should be effectively tied to the structure. Separate enclosed rooms perform well than the rooms without intermediate wall.

Though symmetrical plans are suitable for earthquake construction, due to their simple appearance they are often neglected. On using unsymmetrical plan, separation joints have to be provided such that the torsion and corners effects are neglected.

From figure: 9, it is clear that due to inertia force, the failures at the junction; mostly with rotation type of failure. The same plan when built with few separation joints make the structure to work against seismic force and inertia force in it.


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Symmetrical buildings are more advantageous than an unsymmetrical building. They can easily dissipate the energy created on them, if properly designed to seismic force. Buildings with ornamental effects are to be designed with at most care. Few projections and unrelated members can create more effects and may lead to failure. Cantilever projections in buildings are provide in order to accommodate more space. But this enhances occurrence of rotation and causes failure (Figure: 8). Probable mode of failure will be crushing failure of columns. Pendulum effects in building plan should be avoided. As inertia increases with height, pendulum effects will easily cause failure to the building. Many buildings which failed during 2001 earthquake in Gujarat, India are buildings with cantilever projections, unsymmetrical plans and uneven openings

[2]

. Even symmetrical sections with unequal openings will cause

failure. Effects of openings in buildings will be discussed in modes of failure. Thus for better performance during an earthquake, buildings are to be designed for symmetry, regularity and simplicity. 5 POTENTIAL MODES OF FAILURE:

Structural members under designed to carry seismic forces fail easily than any other members. Though nature of seismic forces are not predictable, the modes are failure shown by members due to seismic forces are predictable. Each and every member exhibits their own modes of failure. Modes of failure depend on shape, material and method of construction. For discussion purposes, modes of failure are described as per the materials used in construction of buildings.


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5.1 Masonry buildings:

Usually masonry buildings are built using fire burnt bricks, solid concrete blocks and with hollow concrete blocks. They are built together using mortar for providing good bond. On a whole masonry building has wall, column, beam and other essential structural members. For load bearing constructions masonry walls are important. Consider a masonry wall which is supported only at the base. If a seismic force acts perpendicular to the wall, it collapses by overturning. As the load is applied opposite to the plane direction, the wall failed. If the load is applied to the plane the wall might not be collapsed but slightly move from its initial position. Diagonal tension cracks can be seen on the surface of the walls if the seismic load is acting on the plane. Occurrence of cracks on walls depends on length to width ratio.

Figure 10: Modes of Failure Walls A and B in above figure clearly explains the modes of failure that could happen on occurrence of seismic force. For wall B the seismic load is in plane, as the wall is unreinforced shear cracks may develop. This is due to “to and fro motion” of seismic forces. Occurrence of diagonal cracks indicates the effect of length and width ratio. Possibly the ratio is moderate for wall B. Horizontal cracks in gable ends may occur if the roof truss is not fixed properly to the supports. This is due to transmission of truss loads directly from the end purlins to the gable ends. Bending cracks in wall B is due to compressive action from the supports provided by masonry columns. On seismic force, wall A shows majority of bending cracks only. As wall A is not designed to carry loads in perpendicular directions, this would have occurred.


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If the walls are not supported properly to the columns, formation of cracks at the joint connection may occur and the wall will fail by overturning effect. Due to non-proper fixity, during earthquake force the roof truss may move from its original position and fail. For flat roof cases, the inertia developed by roof will be transmitted to the walls beneath it. Majority of inertia force will be transmitted to wall B. This happened due to larger stiffness of wall B in x-direction. This action reduces the bending and overturning effect of wall A, if wall A is fixed clearly to its supports

[1]

. More often

damages start from openings provided in wall panels. They also decide the strength of walls. For increased strength the openings provided in wall panels should be small in size and centrally located. Diagonal cracks usually start from corner of openings and centre of wall segments. This type of cracks even causes complete collapse of the building

[1]

.

Columns and beams in frame construction carry heavy loads during an earthquake. Mostly these members fail at their junctions due to hinge formations. A framed structure is to be designed with “weak beams and strong columns”. If this is followed collapse of entire structure can be prevented. Hinge formation at the junction creates easy collapse of the structure. Columns and beams are to be designed by sufficient reinforcement with proper spacing of shear connectors. Stirrups with proper spacing protect these members from failing from shear.

Connection between roofs with

beams and columns has to be perfect such that they behave as one. If not sliding of roof will occur and may cause severe damage. Lack of transverse reinforcement in beam – column connections, column splice regions and inadequate splice length combined with short column effects could cause complete collapse of the structure


[4]

. In adequate load path formation may also

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collapse the structure. On a whole earthquake effects occur in both the directions of the building and creates bending and shearing effects together, such that these possible failure modes often occur in combination. Building with unsymmetrical plans often fails by torsion and wrapping. This mode of failure creates cracks in shear walls. Due to failure of ground during an earthquake, foundations may fail by differential settlement

[1]

.

5.2 Stone buildings:

Stone buildings often use round stone boulders. Some times cut or chiselled, polished or unpolished stones are used. They are joined together using mortar either of cement or mud. This type of buildings is more built in rural areas than urban. Majority of stone buildings are constructed as load bearing ones. During an earthquake stone buildings easily fail at corners and at T-junctions. This results to wall overturning and roof collapsing. Due to uneven stone shapes and poor mortar usage in developing a bond this would have happened. During shaking the tensile strength of mortar and stone exceeds the limit and make the walls (Wythes) to bulge and collapse

[7]

.

Few stone buildings will fail if their roof slabs are not properly tied to the walls. During seismic load the roof will be displaced and stone associated with it will cave in. Provision of heavy slabs as roof should be avoided in this type of buildings. This type of buildings is not recommended in the areas of high seismic influence. This type of buildings is often provided with stone footings. Stone footings on soft soil perform very poor during an earthquake. The 26

th

January 2006 earthquake in Gujarat, India

caused major damage to this type of buildings and claimed thousands of lives


[2]

.

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5.3 Wooden buildings:

As a structural material, wood offers a good amount of resistance towards seismic load. With more absorbing capacity wood can easily dissipate the energy produce on it. Though wood as many qualities to survive seismic load, it fails on certain aspects. Regarding roof tiles, it had to be fixed properly to the frame. If not falling of roof tiles during an earthquake may hurt people. Wooden buildings mostly damaged by fire due to earthquake. Prevention of fire is most important in case of wooden buildings. Joints connecting columns and girders frequently fail during lateral loading. Due to structural deterioration and roof weight the restoring forces at the joints are impede to movement. This leads to sliding after joint fracture. Even buildings with horizontal bracings will not survive this

[3]

.

Figure 13: Possible wooden failures Usually in storeys more than two, lower storey suffers more damage than any other storey. On failure lower storey falls first and other storeys remain undamaged. If anchor bolts are not fixed properly to the foundation, sliding of entire structure may happen

[1]

. If wooden buildings are built over soft soil, chance of getting damaged

during an earthquake is more. This may be due to soil settlement or soil liquefaction. 5.4 Earthen Buildings:

Earthen buildings are highly vulnerable to seismic effects and easily fail during an earthquake. Damage is always much more severe in two storeyed when compared to single storeyed. Mostly crushing failure occurs in this type of construction. Corner failures and out of plane collapse of walls are common mode of failures. Failure of


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roofs is common in single storeyed and complete disaster may happen in two storeyed. Certain factors influence the damage in this type of buildings namely heavy tile roof, lack of horizontal reinforcement, poor adobe quality, walls too high and too long and many more

[1]

.

As earth is weak in tension, vertical and horizontal reinforcements are needed to overcome failure. Though reinforcement is provided earthen buildings fail due to their nature of brittleness. Ductility of material earth is very low when compared to any other material. Provision of openings close to corners and large door and window openings can stimulate the failure pattern.

Figure 14: Possible earthen failures 6 IMPROVEMENT OF STRUCTURES:

Structure prone to earthquake can be improved by following certain construction practices. Few methods should be adopted before constructing a new building and retrofitting methods should be followed on existing building. This is to reduce the vulnerability of the building to earthquake. Risks of failure can be overcome by implementing simple guidelines such as: a) Following simple geometry for the building. If not, separation joints should be used. Course Work 2 – Student ID: 2004 40013

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b) Openings should be provided as per the guidelines. c) Control on thickness, length and height of walls in a room. d) Proper use of reinforcement when using traditional materials. e) Good quality of materials and workmanship. f) Supervision from experienced personals. g) Retrofitting existing buildings. h) Overall reference of guidelines specified for non-engineering constructions. 6.1 Masonry buildings: 6.1.1 Mortar:

The cement mortar should be used in the ratio of 1 parts of cement with 4 parts of sand for category I and 1:6 for category II,III,IV

[1]

(Ref table:1 ) or even richer mix

can be used. Table 1: Categories of buildings for strengthening purposes


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6.1.2 Seismic bands:

A reinforced concrete flat runner through both external and internal masonry walls at plinth level, levels of lintels of doors and windows and at the ceiling level of roofs

[8]

.

These seismic bands are a very important feature in masonry buildings towards earth quake resistant. These bands hold the building together and makes it to move as a single unit during shaking

[9]

. The size of the band and reinforcement used depends on

length of the walls between the perpendicular cross walls. Reinforcing bars will be Fe 415 type (TOR or HYSD bars)

[8]

.

Horizontal reinforcement helps walls to gain strength towards horizontal bending against plate-action due to inertia load. It also helps in preventing shrinkage and temperature cracks. The amount of reinforcing and minimum size of the band depends upon importance of buildings, seismic coefficient, type of soil and number of storeys [1]

.


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6.1.3 Openings in bearing walls:

As doors and windows reduce the lateral loads resistance of the walls, they should be located centrally and preferably small in size. The requirements of openings with respect to good seismic performance are shown in fig: 17.


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6.1.4 Vertical reinforcement:

Vertical reinforcements are to be provided at corners of walls from the foundation concrete and should be covered with rich mortar mix. Window openings larger than 60 cm in width will also need such reinforcement

[8]

. The diameter of the reinforcing

bars depends on number of storeys. These vertical bars start from foundation pass thro all seismic bands effectively tied to horizontal and lateral ties using binding wires. On lapping of vertical reinforcement, a minimum of 50 times diameter of the bar has to be provided

[8]

.


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Eave and gable band:

6.1.5 Dowel at corners and junctions:

As a supplement to seismic bands dowels are inserted at regular intervals of 50 cm and taken into walls to entire length. This is to provide full bond strength. Wooden dowels are also used successfully instead of steel dowels


[3]

.

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6.1.6 Reinforcement in Hollow and solid concrete block masonry:

All specifications for this type of construction are same as brick masonry. Hole formation for vertical reinforcement in solid block walls is not feasible. Special concrete blocks with one hollow are cast and used at the bar-points. In hollow blocks holes are available and this eases the provision of vertical reinforcement.

6.2 Stone buildings: Mortar:

Mortar can be of same type that had used for masonry construction. Clay mortar should be avoided because of its low bonding capacity and less strength towards earthquake. 6.2.1 Dimension control for stone masonry using cement mortar [8]:

a) Heights of buildings are restricted to one storey for category I and II and can be two storeys for III and IV category. b) Thickness of wall is limited to 350 mm and stones of inner and outer walls are interlocked with each other. c) Maximum storey height should be 3.2 m and span of walls between cross walls has to be limited to 7 m. d) For rooms larger than 7m, buttress wall should be provided at intervals not more than 5m. e) Buttress should have a top width equal to wall thickness and base thickness equal to one sixth of the wall height. Course Work 2 – Student ID: 2004 40013

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f) Stone masonry buildings should not be taller than 2 storeys when built with cement mortar and 1 storey when built with mud mortar

[7]

.

6.2.2 Control of openings in bearing walls:

For perfect provision of openings, the ratio of total length of opening in wall to length of wall in a room should not exceed 0.5 in single storeyed and 0.42 in two storeyed. Distance of opening from inside cover should be greater than or equal to 450 mm. And width of pier between two consecutive openings should be greater than or equal to 600 mm

[8]

.


25


6.2.3 Masonry work:

Construction lifts in stone buildings is restricted to 600 mm. Through stones or bond stones should be used at every 600 mm height and at a maximum spacing of 1.2 m along the length. Wooden planks, Hooked steel links and S-shaped steel ties can be used as alternatives to through stones. This is vital in preventing the wall from separation as Wythes

[7]

.

Bonding elements of concrete bars 50mm x 50 mm section with 8mm dia bars placed centrally or solid concrete blocks of 150mm x 150mm x wall thickness, can be used in place of through stones. At wall corners and at T-junctions, long stones of 500mm600mm in length can be used

[8]


.

26



Seismic bands are same as masonry buildings provided continuously in all internal and external walls without any break. Requirement of reinforcing bars is RC bands is given in table: 2. For sloping roofs, triangular gable walls are enclosed in eave level band and a band at the top of the gable wall. The bands are to be cast directly on the masonry and its top surface is made rough to achieve good bond with masonry. In lintel and plinth bands, stones are projected out of the concrete by 50mm to 75 mm. this is to done to continue that into stone walls

[8]

. It is important to provide at least

one band either roof or lintel band in stone construction. This provides integrity to the building and holds the walls together to resist horizontal effects

[7]

.

6.2.5 Vertical reinforcements:

Vertical reinforcements are provided at corners and at T-junctions at window sill level and at jambs of doors and large windows. Vertical reinforcement is made to continue from foundation level to roof band at the top. If the opening provided in the building does not comply with standards they are reinforced or boxed in reinforced concrete all – round or reinforcement bars provided in jambs through the masonry

[3]

.

During installation of the vertical reinforcements, PVC casing pipe of 100mm external dia of 600-750mm long is used. Around which the masonry is built and the pipe is removed once the masonry hardens. In that place, a rod 12 mm dia of 600mm ling is inserted and well compacted using M 20 concrete


[8]

.

27


6.2.6 Dimension control for stone masonry using mud mortar

[8]

:

g) Heights of buildings are restricted to one storey for category I and can be two storeys for II, III and IV category. h) Thickness of wall is limited to 450 mm and stones of inner and outer walls are interlocked with each other. i) Maximum storey height should be 2.7 m and span of walls between cross walls has to be limited to 5 m. j) For rooms larger than 5m, buttress wall should be provided at intervals not more than 3.5m. k) Buttress should have a top width equal to wall thickness and base thickness equal to one sixth of the wall height. Masonry work is same as stone work in cement mortar. In few cases seasoned wooden battens of size 50mm x50 mm can be used as bonding element. Seasoned wooden battens of size 60mm x 60mm can be used as an alternative to long stones at wall corners and T-junction. 6.2.7 Control of openings in bearing walls:

Total length of openings in a wall should be equal to 0.33 of wall length in all categories of constructions. Distance of openings from inside corner should be greater than or equal to 600 mm. Pier widths between consecutive openings should be greater than or equal to 600 mm

[8]

.


Horizontal bands made of wood are used in this type of construction. Wooden planks of rectangular sections, effectively spliced and held by lateral members in lattice form are used in timber available regions as horizontal bands. This is a perfect alternative to steel reinforcing. Same as cement mortar construction the wooden bands are provided continuously through the building


[1]

.

28


6.2.9 Vertical reinforcement at corners:

Two wooden planks of size 50mm x 30mm is nailed together to form an L-section. And this vertical member is nailed to wooden seismic bands at plinth, sill, and lintel and eaves level. This vertical reinforcement is to be placed at all corners of the room.


29


6.3 Wooden buildings: 6.3.1 Building plan:

The entire plan of the building is to be divided by bearing wall lines. The maximum spacing of the bearing wall is limited to 8m. The maximum width of openings is limited to 4m and should be at least 50 cm away from the corner. Bearing walls of lower storey are to be supported by continuous foundations, through sills or by column pedestal.

Bearing lines of upper storey are made to be supported over bearing lines of lower storey. Bearing wall types depends on type of construction. The height of building is always limited to two storeys 6.3.2 Foundations

[1]

.

[8]

:

Frame construction often starts above plinth level over masonry or concrete. The super structure should be connected to the foundation in one of the two ways. a) Small buildings of one storey with area less than 50 sq.m will made to rest on a firm plane ground such that the building is free to slide laterally during ground motion.


30


b) The superstructure will be fixed rigidly to the plinth masonry or concrete foundation.

6.3.3 Joints:

Joints are high prone areas of damage during an earthquake. The joints are to be effectively nailed or bolted together. Usage of metal straps in important joints is highly recommended. Joints like, columns with sill and wall plates with horizontal members are areas of most interest. 6.3.4 Frames:

In general two types of frame construction methods are followed: Stud wall construction and Brick nogged timber frame. General

[1, 8]

:

a) Sheathing boards are to be properly nailed to the timber frame, if not bracings should be used. b) The diagonal bracings are to be framed to the verticals or should be nailed to the surface. c) The sill in stud wall construction has to be connected to the foundation using anchor bolts. Anchor bolts are provided on both sides of joints of sills.


31


d) The size of studs used should not be less than 40mm x 90 mm. Storey height should not be more than 2.70m e) All studs will be connected to the adjacent studs using horizontal blockings at every 1.5m in height. f) The minimum dimension of braces is 20mm x 60mm. It should be effectively tied to the main member. g) The vertical framing members in brick nogged should have minimum finished size of 40mm x 100mm spaced not more than 1.5m apart. h) Horizontal framing members in brick nogged construction shall not be spaced more than 1m apart. i) The corner post should consist of three timbers, two of equal in size to studs and the third being a size to fit and as to make a rectangular section. j) Horizontal bracing should be provided at wall corners and at T-junctions of walls at sill, first floor and eave level. k) The top of studs should be connected to top plates, whose dimension should not be less than the dimension of the stud.


32


6.4 Earthen Buildings

[1]

:

This type of buildings is more prone to earthquake effects. As clay is the prime material in this type of construction, selection of clay should be done with utmost care. Certain tests are available to select the type of clay which is suitable for construction. 6.4.1 Walls:

a) Height of the building should be restricted to one storey in zone I and two storeys in Zone II,III and IV b) Vertical buttress should be provided for walls of longer lengths. c) The height and width of an opening of the wall is controlled. Height should not be greater than 8 times of its thickness and width of opening should not be more than 1.20m d) A minimum of 1.20m distance should be maintained between the corner and opening. e) To increase the seismic stability of the walls, pilasters should be provided at equal intervals at all corners and at junctions. f) A minimum of 50cm should be maintained as bearing length of lintels on each side of the opening. 6.4.2 Foundations:

a) In zones I and II, construction of earthen buildings in soils of type firm subsoil, sandy loose soils, poorly compacted clays and fill materials should be avoided. b) Constructing over water table is not encouraged. c) Sufficient amount of foundation depth should be maintained as per the guidelines available. d) Footing should be constructed using stones or bricks with rich cement mortar. Usage of mud mortar in construction of footing should be avoided.


33


e) A minimum height of 300mm from water table should be maintained while constructing plinth level. 6.4.3 Roofs:

a) Light material should be used as roof covering. Heavy covering such as RCC should not be used. b) Roof should not be made to rest over the walls directly. Preferably wooden or brick restings should be provided over the walls for this purpose. c) Roofs should be made waterproof such that the penetration of water is avoided. 6.4.4 Horizontal bands:

a) Two continuous bands made of wood should be used for this purpose. One at lintel level and other at roof level. Unfinished rough cut wood should be used. b) Horizontal bands should be effectively tied at corners and at wall junctions.

6.4.5 Vertical reinforcement:

a) Vertical reinforcements are provided in a mesh form of bamboo made or cane or with collar beams and bands. b) Mesh form of reinforcement is highly recommended in seismic areas. The vertical mash should be tied effectively to horizontal bands at all level.


34


c) These meshes are to be started from the foundation and should be tied with lintel and roof bands. d) Diagonal bracings can be provided using cane members. These have to be effectively nailed to the framing members.

6.5 Reinforced concrete buildings

[1]

:

6.5.1 Concrete mix:

Proportion of 1:2:4 is to be maintained while preparing the mix. The amount of water in the concrete should be enough to make a ball out of the mix by hand. Compaction should be achieved using vibrators or manually. After concrete cast, it has to be cured for at least 14 days. 6.5.2 Reinforcement:

a) Minimum clear cover should be maintained in slabs, beams and column. b) Longitudinal bars should be tied to transverse bars and stirrups. c) Beams should be reinforced both on top and at bottom. Minimum of two bars of 12 mm dia is used. d) Splices should be placed within two at least two stirrups. Vertical shear stirrups should be closely spaced. Course Work 2 – Student ID: 2004 40013

35


e) In column vertical reinforcements should be provided at all faces. Its strength can be increased by using ties with adequate anchorage and end hooks. f) Corner columns should be effectively provided with steel and minimum spaced lateral ties. g) Connection between column and beam should be well anchored to obtain full strength.


36



37


7 REAL PICTURES OF FAILURES: th

a) Location: Bhuj, Gujarat, India - 26 January 2001 Type of failure: Column failure in open first storey due

to hinge failure, Cantilever projection. Improvement measures: Sufficient hoop reinforcement

should be provided in order to eliminate failure in hinge region. Increase in size of column and reinforcement, avoiding cantilever projection in open first storey. th

b) Location: Bhuj, Gujarat, India - 26 January 2001 Type of failure: Failure of load bearing masonry walls

and lintel level crack. Improvement measures: Providing horizontal seismic

bands at all levels of the buildings and vertical reinforcement at corners. Provision of reinforcements in walls could even make the structure to perform well. Effective tying of walls to floor and roof should be done. th

c) Location: Bantul, Yogya, Indonesia – 27 May 2006 Type of failure: Failure due to racking shear could be

due to diagonal compression or tension. Improvement measures: Control of opening sizes,

strengthening of masonry around openings, provision of lintel and sill band. d) Location: Banda Aceh, Indonesia – 26 th December 2004 Type

of

failure:

Improvement

Beam-column

measures:

connection

Provision

of

failure.

transverse

reinforcement in beam-column connection, column splice regions and provision of adequate splice length in column.


38

Design and Management of Structures in Earthquake Zones – CIVE 5913M Report on “Non-Engineered Buildings” th

e) Location: Banda Aceh, Indonesia – 26 December 2004 Type of Failure: Column shear failure. Improvement

measures:

Provision

of

shear

reinforcements in columns. Effective connection between beam and column has to be done.

th

f) Location: Bantul, Yogya, Indonesia – 27 May 2006 Type of failure: Brick out of wall collapse combined

with roof collapse. Improvement measures: Provision of reinforcement in

between walls, effective reinforcement at corners. Introducing horizontal bands in each level. th

g) Location: Kachchh, Gujarat, India - 26 January 2001 Type of failure: Complete collapse of masonry buildings Improvement measures: providing good bond between

masonry, reinforcement, seismic bands, light roof, control on openings. In overall an efficient construction practice has to be followed.

h) Location: Maninagar, Gujarat, India - 26 thJanuary 2001 Type of failure: Plastic hinging and buckling failure Improvement measures: Provision of efficient concrete cover

and hoop reinforcement. Thickness of the column could have been improved in order to carry the load applied.


39


i) Location: Jabalpur, India – 1997 earthquake Type of failure: Typical joint failure in mud house,

shear cracks Improvement measures: Provision of vertical cane

reinforcement and wooden horizontal bands. Control on height of wall and opening in wall should be followed. ) Location: Kobe, Japan -1995 earthquake Type of failure: Typical first storey failure usually seen

in wooden buildings, crushing of column and separation of joint members. Improvement measures:

All bearing wall line of

upper storey should be supported by bearing wall lines of lower storey. Frame members should be effectively nailed to each other. Bearing lines of lower storey should be supported by continous foundation. k)

Location:

Killari,

Maharashtra,

India-1993

Earthquake Type of failure: Delamination of Wythes followed by

inner and outer stone wall collapse. Improvement measures: Provision of through stones,

horizontal bands and vertical ties. th

l) Location: Bantul, Yogya, Indonesia – 27 May 2006 Type of failure: Collapse of one side wall due to poor

reinforcement. Improvement measures: reinforcement at T-junctions

and corners. Horizontal bands at all levels of the building.


40


8 DOMESTIC CONSTRUCTION IN INDIA:

India though being an earthquake prone country it has nearly 195.0 million nonengineered dwelling units. This is as per 1992 survey of India on non-engineered buildings

[3]

.

As a native of southern part of India-Chennai, Tamilnadu; I have personally experienced few tremors of earthquake in the past and Tsunami on 26

th

December

2004. Any how we have not faced any damage by these disasters. Though my home town is in seismic zone IV (moderate exposure to earthquakes) there are many nonengineered dwelling units. Even my own house is a non-engineered single storey load-bearing masonry wall type, which was constructed a decade ago with minimal cost by locally employed persons. Fire burnt bricks, graded cement, river sand, FE 415 steel bars are used for the construction. Building is symmetrical and square in shape. Masonry columns are used to support the walls over which RCC roof slab is place. Such that the inertia transmitted by the roof will be carried by the adjoin walls. Roof to wall and column connection is good. Horizontal seismic bands are provided through the building. But provision of vertical reinforcements at corners and at T-junctions is absent. Openings of windows are not controlled and distance from corner of walls is less than 100mm. Footing is at the depth of 1.5 m from the ground level. Footings are connected to each other using plinth beam. Horizontal reinforcements are provided in between the bricks during wall construction. Parapet wall is provided over the roof. As parapet wall is not connected to any member of building, it may collapse during an earthquake. Vulnerability of my house to earthquake action is moderate. During an earthquake failure may occur near the corners and at near the openings. Diagonal shear cracks can be seen. Joint failure may occur near wall and masonry column junction. In plane failure may occur at some places. Procedures on how to built seismic resistant masonry brick units are discussed in previous chapters. As my house is an existing one, few retrofitting methods will help the structure to with stand an earthquake. Retrofitting involves repair, strengthen and modification of certain structural elements to with stand effects caused by earthquake.


41


8.1 Local modifications:

Local modification involves works such as closing the opening or providing reinforcement around it. As in my house the openings do not comply with the requirements, the openings are reinforced or boxed in reinforced concrete all – round or reinforcement bars in jambs through the masonry

[3]

.

8.2 FRP retrofit:

FRP composites are flexible and easy to apply. By following surface mounted techniques the FRP strips are applied to the walls vertically and diagonally to improve out of plane capacity in both way bending. Diagonal strip increases the in-plane shear capacity

[3]

.


42


Using near surface mounting technique, FRP rods can be placed in to the masonry walls. For this the masonry walls are to cuttted horizontally and vertically and FRP rods are placed in to the gaps followed by covering it a layer of specified adhesive

[3]

.

8.3 Strengthening of existing walls:

Method of confining by more ductile material i.e. wire mesh can be used. Two steel meshes of size 50mm x 50mm is attached to both sides of the wall and connected by steel at 500-700mm interval. A micro concrete layer is applied on both sides and the connected links are grouted. The brickwork in between the Ferro cement layer will behave efficiently when subjected to lateral load

[3]

.

8.4 Pre-stressing for wall strengthening:

Pre-stressing bars can be introduced in pairs in opposite sides of wall so that the out of plane bending of walls can be eliminated. In single storey building the vertical steel is anchored to the foundation

[3]

.

8.5 Strengthening the corners:

As corners in my house are weak, they are more prone to earthquake effects. In order to eliminate the failure the corners have to be strengthened. Plaster is removed for a height of 400mm above 80mm of the plinth level with a length of 300mm. the exposed joints are raked to a depth of 20mm and cleaned using wire brush. A welded mesh of 25mm x 50mm with 8mm gauge length is taken with a width of 350mm and


43


placed on the wall using long nails. Then with the help of plaster 1:4 ratio the mesh is covered up to 15mm thick and cured for 14 days

[3]

.

8.6 Strengthening wall to wall connection:

As T and L-junctions in my house are not reinforced, they can be integrated and anchored by effective sewing of perpendicular walls. Holes are drilled in an inclined manner and polymer grout is injected after inserting steel reinforcement


[3]

.

44


CONCLUSION:

In countries at risk from earthquake action, most people are living in non-engineered buildings. They are at risk from collapse of their own homes. To avoid this quality domestic construction has to be improved. It doesn’t mean that more amount of money has to be spent for earthquake resistant construction. Even with locally available material it can be achieved. Methods discussed in this report are more economical and attained using local materials. Method and measures suggested may vary from place to place. The methods can be improved better on basis of previous earthquake intensity reports. Due to constraint only few methods are discussed here. While building a dwelling unit, the owner or the builder may refer any other guidelines other than this. The final motto has to be construction of earthquake resistant buildings.


45


REFERENCES:

1. The Associated cement companies Limited, Mumbai, India, 2001 - “ Guidelines for earthquake resistant non-engineered construction”.

2. Gujarat Relief Engineering Advice Team (GREAT) publication, 2001 -“Repair and strengthening guide for earthquake damaged low-rise domestic buildings in Gujarat, India”. (www.arup.com/_assets/_download/download197.pdf -Accessed on 27/03/09 )

3. Government of Tamilnadu, UNDP, India, July 2006 – “ Guidelines for retrofitting of buildings”. (www.un.org.in/untrs/reports/Retrofitting_Guidelien_16th_%20Nov_2006.pdf Accessed on 27/03/09 )

4. Murat Saatcioglu, Ahmed Ghobarah, Ioan Nistor – ISET Journal of earthquake Technology, Paper No.457, Vol.42, No.4, December 2005, pp.79-94 – “ Effects of the December 26,2004 Sumatra Earthquake and Tsunami on Physical Infrastructure”.

(home.iitk.ac.in/~vinaykg/Iset457.pdf- Accessed on 27/03/09 ) 5. Jag Mohan Humar, David Lau, and Jean-Robert Pierre November

23, 2001 -“

Performance

of

buildings

–

NRC Reasearch press web, during

the

2001

Bhuj

earthquake”. (www.caee.uottawa.ca/Publications/Lessonf%20grom%20previous%20 EQs/PDF%20Files/India.pdf- Accessed on 27/03/09 )

6.

Dr D.K.Paul, Professor and Head – Department of Earthquake Engineering, IIT

Rourkee,India- Lecture PPT - “Buildings Vulnerability, building types and common problems, typical earthquake damage pattern”. ( www.quakesafedelhi.net/rollout/Paul.pdf Accessed on 27/03/09 )

7. IIT Kanpur,India-Buildings Materials and Technology Promotion Council,New Delhi,India - IITK-BMPTC Earthquake Tips, July 2003 -“ How to make Stone Masonry Buildings Earthquake Resistant?”. (www.iitk.ac.in/nicee/EQTips/EQTip16.pdf-Accessed on 9/04/09)

8. Prof.Anand S.Arya, National Seismic Advisor, GOI-UNDP DRM Programme, Ministry of Home Affairs, Government of India, October 2005 – “Guidelines for earthquake resistant reconstruction and New construction of Masonry buildings in Jammu & Kashmir state”.( www.ndmindia.nic.in/EQProjects/Kashmir%20Final.pdf-Accessed on 9/04/09 )


46


9. IIT Kanpur,India-Buildings Materials and Technology Promotion Council,New Delhi,India - IITK-BMPTC Earthquake Tips, July 2003 – “ Why are horizontal bands necessary

in

masonry

buildings?”.

(www.iitk.ac.in/nicee/EQTips/EQTip14.pdf-

Accessed on 9/04/09 ) FIGURES AND TABLES:

1. Figures: 11-12-13-14-24-27-19-32-33-34-35-36-37-38 Table: 1 The Associated cement companies Limited, Mumbai, India, 2001 - “ Guidelines for earthquake resistant non-engineered construction”.

2. Figure: 7 Dr D.K.Paul, Professor and Head – Department of Earthquake Engineering, IIT Rourkee,India- Lecture PPT - “Buildings Vulnerability, building types and common problems, typical earthquake damage pattern”. ( www.quakesafedelhi.net/rollout/Paul.pdf

-

Accessed on 27/03/09 )

3. Figures: 15-16-18-19-20-22-23-25-26-28-30-31 Tables: 2-3 Prof.Anand S.Arya, National Seismic Advisor, GOI-UNDP DRM Programme, Ministry of Home Affairs, Government of India, October 2005 – “Guidelines for earthquake resistant reconstruction and New construction of Masonry buildings in Jammu & Kashmir state”.( www.ndmindia.nic.in/EQProjects/Kashmir%20Final.pdf-Accessed on 9/04/09 )

4. Figures: 17-21-39-40-41-42 Government of Tamilnadu, UNDP, India, July 2006 – “ Guidelines for retrofitting of buildings”. (www.un.org.in/untrs/reports/Retrofitting_Guidelien_16th_%20Nov_2006.pdf Accessed on 27/03/09 )


47

non-engineered buildings

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