Contents PROBLEM PROBLEM ................................. .................................................. .................................. .................................. .................................. .................................. ...................... ..... 2 INTRODUCTI INTRODUCTION ON ................................. .................................................. .................................. .................................. ................................... ............................ .......... 3 SIGN BOARD BOARD IMAGE ...................... ....................................... .................................. ................................... ................................... ........................... .......... 8 OBJECTIVES OBJECTIVES................................... ................................................... .................................. ................................... .................................. ................................. ................ 9 THEORY AND ANALYSIS ............................................................................................... 10 LIST OF FORMULA FORMULA ............................. .............................................. .................................. .................................. ................................... .......................... ........ 14 MATERIAL MATERIALS S ................................... ................................................... .................................. ................................... .................................. ............................... .............. 15 ALUMINIUM ALUMINIUM ................................. .................................................. ................................... .................................. .................................. ............................. ........... 15 STEEL ................................. .................................................. .................................. .................................. ................................... .................................. ...................... ...... 17 SIGN BOARD DRAWING (SOLIDWORK) ...................................................................... 20 CALCULA CALCULATIONS TIONS ................................. .................................................. .................................. .................................. ................................... .......................... ........ 24 WIND LOAD LOAD .................................. ................................................... ................................... .................................. .................................. ............................. ........... 24 BOARD LOAD (Aluminium sheet metal) ....................................................................... 25 BRACKET BRACKET LOAD LOAD ............................... ................................................. ................................... .................................. ................................... ....................... ..... 25 FREE FREE BODY DIAGRAM DIAGRAM ................................. ................................................. .................................. ................................... ............................ ........... 26 STRESS ANALYSIS OF POINT A, E AND C ............................................................... 28 STRESS ANALYSIS OF POINT B AND D.................................................................... 29 DISCUSSION DISCUSSION................................... ................................................... .................................. ................................... .................................. ............................... .............. 30 SUGGESTION SUGGESTION ................................. ................................................. .................................. ................................... .................................. ............................... .............. 32 REFERENC REFERENCES ES ................................. ................................................. .................................. ................................... .................................. ............................... .............. 33
PROBLEM Choose any sign in the campus. Determine the state of stress at points A, B, C, D and E as shown in the figure. Sketch the stress element at each of these points. Loads to be considered are the weight of road sign and the wind load that acts normal to the surface of the road sign. The highest recorded wind speed in Malaysia is 150 km/h or 41.7 m/s (source: Malaysian Meteorological Department)
INTRODUCTION This report presents a design of road sign board and and how it can resist a force that pass through it. All of the information in this report we obtained through observation, calculation and analysis. Sign board plays a big role to us especially in finding a way. It makes our job easier. The purpose of a sign board is to communicate and to convey information such that its receiver can make cognitive decisions based on the information provided. There are many types of sign board that we can found. In general, signs can be classified into the following functions: a) Information
-
Signs giving information about services and facilities
-
E.g. maps, directories, instructions for use, etc
b) Direction
-
Signs leading to services, facilities, functional spaces and key areas
-
E.g. sign posts, directional arrows, etc
c) Identification
-
Signs indicating services and facilities
-
E.g. room names & numbers, toilet signs, number of floor, etc
d) Safety and Regulatory
-
Signs giving warning or safety instructions
-
E.g. warning signs, traffic signs, exit signs, rules & regulations, etc .
Traffic signs consist of three basic components:
A blank
Background sheeting
Sign copy
Blanks, usually constructed of plywood, aluminium, or steel, serve as the framework of the sign. Plywood is the least expensive blank material. It is fairly strong but is susceptible to weather damage since it is porous. Plywood blanks must be overlaid with a thin layer of plastic. Aluminium will not rust, but it is very lightweight and must be reinforced with metal braces along the back. It is the most expensive blank option. Steel is a more economical alternative to aluminium, it is also more sturdy and does not need reinforcement. Rusting can be prevented by applying a coat of zinc to the steel blank. Background sheeting and the letter and symbols for the sign copy are cut from retro-reflective sheeting. This sheeting consists of tiny glass beads or microprisms embedded in a flexible plastic surface, this construction allows light from car headlights to be reflected off the sign and back to the driver. Colored light is reflected from the sign if the sheeting is dyed with a pigment. For instance, to make “STOP” signs, red dye can be added to the sheeting mixture when it is in a liquid form.
When selecting a material for a particular application, engineers must be confident that it will be suitable for the loading conditions and environmental challenges it will be subjected to while in service. The retro-reflective sheeting material is applied to the rigid sign backing, which can be aluminium, wood or a composite plastic.
Understanding and control of a
material’s properties is therefore essential. Thus, the materials with their properties that commonly used in making sign board is listed below.
Plywood
Plywood is used occasionally for temporary signs because it can be c heaper and is lighter than aluminium. Fibre glass reinforced plastic materials are used infrequently because of their handling and recycling issues.
Sheet metal
Sheet metal refers to metal that has a high surface area to volume ratio. Sheet metal is metal formed by an industrial process into thin, flat pieces. It is one of the fundamental forms used in metal working and it can be cut and bent into a variety of shapes. Countless everyday objects are constructed with sheet metal. Thicknesses can vary significantly; extremely thin thicknesses are considered foil or leaf, and pieces thicker than 6 mm (0.25 in) are considered plate. Sheet metal is used in the manufacture of cars, trains, aircraft, farm equipment, office equipment, furniture, house appliances, computers, machine components and beverage cans to name a few. Therefore, some of the sheet metal operations discussed may not be applicable to plate. Sheet metal manufacture is mostly performed on a press and parts are formed between two die. Sheet metal is usually formed cold, however warm or hot working of parts, (particularly plate), is possible. Generally for sheet metal applications there is essentially no change, or negligible change, in sheet thickness. Sheet metal manufacturing produces parts that typically have high strength, good surface and accurate tolerances.
Aluminium
Aluminium is by far the most commonly used material. The aluminium backing can be reused often, reducing the cost of signing and can be recycled easily to recoup a small portion of the cost. Aluminium has a unique and unbeatable combination of properties which means that it is an extremely versatile, highly usable and attractive construction material. Aluminium is light with a density one third of that of steel. Aluminium is strong with a tensile strength of 70 to 700MPa depending on the alloy and manufacturing process. Extrusions of the right alloy and design are as strong as structural steel. The Young's modulus for aluminium is a third that of steel (E=70,000 MPa). this means that the moment of inertia has to be three times as great for an aluminium extrusion to achieve the same deflection as a steel profile. A thin layer of oxide is formed in contact with air, which provides very good protection against corrosion, even in corrosive environments. This layer can be further strengthened by surface treatment such as anodising or powder coating. Aluminium is a good reflector of both light and heat.
Zinc
Zinc is a weak metal with a tensile strength less than half that of mild carbon steel. It is generally not used in load-bearing applications, although inexpensive mechanical parts can be die cast from zinc. Pure zinc has low toughness and is generally brittle, but zinc alloys generally have high impact strength compared to other die casting alloys. Between 212-312 o
F, zinc becomes ductile and malleable, but at elevated temperatures reverts to a brittle state.
Again, zinc alloys greatly improve on this property over the pure metal, allowing more complex fabrication methods to be used. Zinc’s conductivity is moderate for a metal. Its strong electrochemical properties, however, serve well in the galvanizing process and alkaline batteries.
Steel
The mechanical properties of steel can be carefully controlled through the selection of an appropriate chemical composition, processing and heat treatment, which lead to its final microstructure. The alloys and the heat treatment used in the production of steel result in different property values and strengths and testing must be performed to determine the final properties of steel and to ensure adherence to the respective standards. There are many measurement systems used to define the properties of a given steel. For example, yield strength, ductility and stiffness are determined using tensile testing. Toughness is measured by impact testing; and hardness is determined by measuring resistance to the penetration of the surface by a hard object. Tensile testing is a method of evaluating the structural response of steel to applied loads, with the results expressed as a relationship between stress and strain. The relationship between stress and strain is a measure of the elasticity of the material, and this ratio is referred to as Young's modulus. A high value of Young's modulus is one of steel’s most differentiating properties; it is in the range 190-210 GPa, which is approximately three times the value for aluminium.
The physical properties of steel are related to the physics of the material, such as density, thermal conductivity, elastic modulus, Poison’s ratio etc. Some typical values for physical properties of steel are: 3
density ρ = 7.7 ÷ 8.1 [kg/dm ]
elastic modulus E=190÷210 [GPa]
Poisson’s ratio ν = 0.27 ÷ 0.30
Thermal conductivity κ = 11.2 ÷ 48.3 [W/mK]
Thermal expansion α = 9 ÷27 [10 -6 / K]
SIGN BOARD IMAGE
It is a road sign board
Located at the foot of the hill
FRONT VIEW
SIDE VIEW
BACK VIEW
OBJECTIVES
To determine the maximum load that can be applied to t he sign board.
To determine at which point the maximum stress will occur.
THEORY AND ANALYSIS Mechanical properties: Strength, hardness, toughness, elasticity, plasticity, brittleness, and ductility and malleability are mechanical properties used as measurements of how metals behave under a load. These properties are described in terms of the types of force or stress that the metal must withstand and how these are resisted. Common types of stress are compression, tension, shear, torsion, impact, 1-2 or a combination of these stresses, such as fatigue. Compression stresses develop within a material when forces compress or crush the material. A column that supports an overhead beam is in compression, and the internal stresses that develop within the column are compression. Tension (or tensile) stresses develop when a material is subject to a pulling load; for example, when using a wire rope to lift a load or when using it as a guy to anchor an antenna. "Tensile strength" is defined as resistance to longitudinal stress or pull and can be measured in pounds per square inch of cross section. Shearing stresses occur within a material when external forces are applied along parallel lines in opposite directions. Shearing forces can separate material by sliding part of it in one direction and the rest in the opposite direction. Some materials are equally strong in compression, tension, and shear. However, many materials show marked differences; for example, cured concrete has a maximum strength of 2,000 psi in compression, but only 400 psi in tension. Carbon steel has a maximum strength of 56,000 psi in tension and compression but a maximum shear strength of only 42,000 psi; therefore, when dealing with maximum strength, you should always state the type of loading. A material that is stressed repeatedly usually fails at a point considerably below its maximum strength in tension, compression, or shear. For example, a thin steel rod can be broken by hand by bending it back and forth several times in the same place; however, if the same force is applied in a steady motion (not bent back and forth), the rod cannot be broken. The tendency of a material to fail after repeated bending at the same point is known as fatigue.
Table - Mechanical Properties of Metals/Alloys
Strength
Strength is the property that enables a metal to resist deformation under load. The ultimate strength is the maximum strain a material can withstand. Tensile strength is a measure ment of the resistance to being pulled apart when placed in a tension load. Fatigue strength is the ability of material to resist various kinds of rapidly changing stresses and is expressed by the magnitude of alternating stress for a specified number of cycles. Impact strength is the ability of a metal to resist suddenly applied loads and is measured in foot-pounds of force.
Hardness
Hardness is the property of a material to resist permanent indentation. Because there are several methods of measuring hardness, the hardness of a material is always specified in terms of the particular test that was used to measure this property. Rockwell, Vickers, or Brinell are some of the methods of testing. Of these tests, Rockwell is the one most frequently used. The basic principle used in the Rockwell testis that a hard material can penetrate a softer one. We then measure the amount of penetration and compare it to a scale. For ferrous metals, which are usually harder than nonferrous metals, a diamond tip is used and the hardness is indicated by a Rockwell "C" number. On nonferrous metals, that are softer, a metal ball is used and the hardness is indicated by a Rockwell "B" number. To get an idea of the property of hardness, compare lead and steel. Lead can be scratched with a pointed wooden stick but steel cannot because it is harder than lead.
Toughness
Toughness is the property that enables a material to withstand shock and to be deformed without rupturing. Toughness may be considered as a combination of strength and plasticity. Table 1-2 shows the order of some of the more common materials for toughness as well as other properties.
Elasticity
When a material has a load applied to it, the load causes the material to deform. Elasticity is the ability of a material to return to its original shape after the load is removed. Theoretically, the elastic limit of a material is the limit to which a material can be loaded and still recover its original shape after the load is re moved.
Plasticity
Plasticity is the ability of a material to deform permanently without breaking or rupturing. This property is the opposite of strength. By careful alloying of metals, the combination of plasticity and strength is used to manufacture large structural members. For example, should a member of a bridge structure become overloaded, plasticity allows the overloaded member to flow allowing the distribution of the load to other parts of the bridge struct ure.
Brittleness
Brittleness is the opposite of the property of plasticity. A brittle metal is one that breaks or shatters before it deforms. White cast iron and glass are good examples of brittle material. Generally, brittle metals are high in compressive strength but low in tensile strength. As an example, you would not choose cast iron for fabricating support beams in a bridge.
Ductility and Malleability
Ductility is the property that enables a material to stretch, bend, or twist without cracking or breaking. This property makes it possible for a material to be drawn out into a thin wire. In comparison, malleability is the property that enables a material to deform by compressive forces without developing defects. A malleable material is one that can be stamped, hammered, forged, pressed, or rolled into thin sheets.
LIST OF FORMULA
i.
Flexure formula :
ii.
Shear stress :
iii.
Normal stress :
iv.
Wind force, FWIND : Wk x width x height (Based on BS code 6399)
MATERIALS
For this sign board chosen, materials used are aluminium and steel A-36. Aluminium is used in form of sheet metal while stee l A-36 is used for the sign board support. ALUMINIUM
Background
Aluminium is the world’s most abundant metal and the third most common element comprising 8% of the earth’s crust. The versatility of aluminium makes it the most widely used metal after steel.
Applications of Aluminium
Pure aluminium is soft, ductile, corrosion resistant, and has a high electrical conductivity. It is widely used for foil and conductor cables, but alloying with other elements is necessary to provide the higher strengths needed for other applications. Aluminium is one of the lightest engineering metals, having strength to weight ratio superior to st eel. By utilising various combinations of its advantageous properties such as strength, lightness, corrosion resistance, recyclability and formability, aluminium is being employed in an everincreasing number of applications. This array of products ranges from structural materials through to thin packaging foils.
Alloy Designations
Aluminium is most commonly alloyed with copper, zinc, magnesium, silicon, manganese and lithium. Small additions of chromium, titanium, zirconium, lead, bismuth and nickel are also made and iron is invariably present in small quantities. There are over 300 wrought alloys with 50 in common use. They are normally identified by a four figure system which originated in the USA and is now universally accepted. Table 1 describes the system for wrought alloys. Cast alloys have similar designations and use a five digit system.
Physical Properties of Aluminium
Density of Aluminium
Aluminium has a density around one third that of steel or copper making it one of the lightest commercially available metals. The resultant high strength to weight ratio makes it an important structural material allowing increased payloads or fuel savings for transport industries in particular.
Strength of Aluminium
Pure aluminium doesn’t have a high tensile strength. However, the addition of alloying elements like manganese, silicon, copper and magnesium can increase the strength properties of aluminium and produce an alloy with properties tailored to particular applications. Aluminium is well suited to cold environments. It has the advantage over steel in that its’ tensile strength increases with decreasing temperature while retaining its toughness. Steel on the other hand becomes brittle at low temperatures.
Corrosion Resistance of Aluminium
When exposed to air, a layer of aluminium oxide forms almost instantaneously on the surface of aluminium. This layer has excellent resistance to corrosion. It is fairly resistant to most acids but less resistant to alkalis.
Thermal Conductivity of Aluminium
The thermal conductivity of aluminium is about three times greater than that of steel. This makes aluminium an important material for both cooling and heating applications such as heat-exchangers. Combined with it being non-toxic this property means aluminium is used extensively in cooking utensils and kitchenware.
Electrical Conductivity of Aluminium
Along with copper, aluminium has an electrical conductivity high enough for use as an electrical conductor. Although the conductivity of the commonly used conducting alloy (1350) is only around 62% of annealed copper, it is only one third the weights and can therefore conduct twice as much as electricity when compared with copper of the same weight.
Reflectivity of Aluminium
From UV to infra-red, aluminium is an excellent reflector of radiant energy. Visible light reflectivity of around 80% means it is widely used in light fixtures. The same properties of reflectivity makes aluminium ideal as an insulating material to protect against the sun’s rays in summer, while insulating against heat loss in winter. STEEL
Background
Steel is an alloy of iron and a small amount of carbon. Carbon is the primary alloying element, and its content in the steel is between 0.002% and 2.1% by weight. Too little carbon content leaves (pure) iron quite soft, ductile, and weak. Carbon contents higher than those of steel make an alloy commonly called pig iron that is brittle and not malleable. Additional elements may be present in steel: manganese, phosphorus, sulphur, silicon, and traces of oxygen, nitrogen and aluminium. Alloy steel is steel to which additional alloying elements have been intentionally added to modify the characteristics of steel. Common alloying elements include: manganese, nickel, chromium, molybdenum, boron, titanium, vanadium and niobium.
Classification of Steel
There are five major classifications of steels: carbon steel, alloy steel, high-strength low-alloy steel, stainless steel and tool steel. Carbon steels are the most common, containing various amounts of carbon; produce everything from machines to bedsprings to bobby pins. Alloy steels have definite amounts of vanadium, molybdenum, manganese, silicon and cooper. Alloy steels produce gears, carving knives and even roller skates. Stainless steels have chromium, nickel amongst other alloy elements which sustains their colour and reaction to rust. Stainless steel products include pipes, space capsules, surgical equipment to kitchen equipment. Last but not least, tool steels have tungsten, molybdenum amongst other alloy elements. These elements create the strength and ability of the tool steel products, which include parts for manufacturing operations as well as machinery. The varying amounts of carbon, amongst other elements in each of the types of steel create a variety in densities or specific gravities. (Specific gravity or relative density is the ratio of a material's density to that of water.)
Stainless steels are the densest, coming in at 8000 kg/m3. Though the densities vary, the density
of
steel
is
about
7700 kg/m3.
The
density
of
steel
are
measured
in g/cm3, kg/m3, kg/L and lb. /f3, with kg/m3 being the more commonly used measurement. A good way to remember the density of steel is to remember that titanium has about half the density of steel and aluminium is about one-third.
Applications of Steel
Iron and steel are used widely in the construction of roads, railways, other infrastructure, appliances, and buildings. Most large modern structures, such as stadiums and skyscrapers, bridges, and airports, are supported by a steel skeleton. Even those with a concrete structure employ steel for reinforcing. In addition, it sees widespread use in major appliances and cars. Despite growth in usage of aluminium, it is still the main material for car bodies. Steel is used in a variety of other construction materials, such as bolts, nails, and screws. Other common applications include shipbuilding, pipelines, mining, offshore construction, aerospace, white goods (e.g. washing machines), heavy equipment such as bulldozers, office furniture, steel wool, tools, and armour in the form of personal vests or vehicle armour (better known as rolled homogeneous armour in this role). Steel was the metal of choice for sculptor Jim Gary and a frequent choice for sculpture by many other modern sculptors.
Physical Properties of Steel The physical properties of an alloy depend on the percentage composition of the
constituent elements and the manufacturing process. The properties of steel are totally different from its component elements - iron and carbon. One of its major properties is the ability to cool down rapidly from an extremely hot temperature after being subjected to water or oil. And a particular amount of carbon can be dissolved in iro n at a specific temperature. The physical properties of steel include high strength, low weight, durability, ductility and resistance to corrosion. Steel, as we all know, offers great strength though it is light in weight. In fact, the ratio of strength to weight for steel is the lowest than any other building material available to us. The term ductility means steel can be molded easily to form any desired shape.
Unlike the constituent element iron, steel does not corrode easily, on being exposed to moisture and water. The dimensional stability of steel is a desired property; it is found that the dimension of steel remains unchanged even after many years, or after being subjected to extreme environmental conditions. Steel is a good conductor of electricity, i.e., electricity can pass through steel. Steel grades are classified by many standard organizations, based on the composition and the physical properties of the metal. The deciding factor for the grade of steel is basically its chemical composition and the supplied condition. The higher the carbon content, the harder and stronger is the steel metal. On the contrary, high quality steel containing less carbon is more ductile. Earlier forms of steel consisted of more carbon, as compared to the present day steel. Today, the steel manufacturing process is such that less carbon is added and the metal is cooled down immediately, so as to retain the desirable physical properties. Rapid cooling (or quenching) of steel also alters the grain structure. There are other types of steel such as galvanized steel and stainless steel (corrosionresistant steel). Galvanized steel is coated with zinc to protect it from corrosion, whereas stainless steel contains about 10 percent chromium in its composition. The major advantage of steel is the ability to recycle it effectively, without destroying or losing any of its physical properties in the recycling process. Steel is very important in our day-to-day life; starting from cookware to scientific instruments like scalpel, steel is used in making several items. Steel is one of the most versatile and sustainable construction materials. Due to its cost-effectiveness and strength, it is used in engineering works and infrastructure developments such as roads, railways, bridges, buildings and stadiums. Indeed, the technological and economic progress gained momentum with the growth and development of steel industries, further promoting the industrial growth.
SIGN BOARD DRAWING (SOLIDWORK)
TOP VIEW
FRONT VIEW
BACK VIEW
ISOMETRIC VIEW
CALCULATIONS
WIND LOAD
Given from question, wind speed = 150 km/h. To calculate wind load from given speed, BS code 6399 is referred. Basic speed, V = 250 km/h = 41.67 m/s Topological factor, s1 = 1.10 Height above ground factor, s 2 = 1.01 Life of a structure factor, s3 = 1.00 Design wind speed, V s
= V x s1 x s2 x s3 = 41.67 x 1.10 x 1.01 x 1.00 = 46.30 kN/m2
Q
2
= 0.613 V s
= 0.613 (46.30) 2 = 1.314 kN/m
2
Take C p1 = 0.7 and C p2 = -0.25 Wind pressure, Wk
= Q (C p1 – C p2) = (1.314)(0.7 – (-0.25)) = 1.2483 kN/m2
Wind force, FWIND
= Wk x width x height = (1.2483)(0.905)(0.465) FWIND = 0.525 N
BOARD LOAD (Aluminium sheet metal)
ρ
al
V al
3
= 2800 kg/m
= 0.905 x 0.465 x 0.0005 = 2.104 x 10 -4
mal
= 2800kg/m3 x 2.104x10 -4 0.465 m
= 0.589 kg Find FPLATE
0.905 m
= 0.589kg x 9.81m/s 2 FPLATE = 5.77 N
BRACKET LOAD
To find FBRACKET ; ρSTEEL
= 7850 kg/m3
VSTEEL
= V1 + V2 + V3
V1 = V3
= 0.14 x 0.055 x 0.005
0.05cm
5.5cm
1
3
= 3.85x10-5 V2
= 0.14 x 0.005 x 0.025 = 1.75x10-5
VTOTAL
= 2(3.85x10 -5) + 1.75x10 -5 = 9.48 x 10 -5
mSTEEL
= 7850 kg/m3 x 9.48x10 -5 = 0.7442 kg
Find FBRACKET = 0.742kg x 9.81 m/s 2 FBRACKET
= 7.30 N
14cm 0.05cm
FREE BODY DIAGRAM
x-axis
-axis
X c m
7.30 N
7.30 N 5.77 N
N V
Mo
From the free body diagram; + ↑∑ FY
= 0; = FWIND + V = -0.525 (0.465) - V
V
+ →∑ FX
= 244 N ↑
= 0; = FPLATE + (2 x FBRACKET ) + N = 5.77 + (2 x 7.3) - N
N
= 20.37 N ←
= 0;
∑ MO
(counter-clockwise positive)
= FWIND + FBRACKET1 + FBRACKET2 + FPLATE + MO = (525)(0.465)(χ– 0.2325) – (7.3)(0.0275) – (7.3)(0.0275) – (5.77)(0.028) + M O MO
= 396.75 N.m (clockwise)
STRESS ANALYSIS OF POINT A, E AND C
A
E
C
NA
Since point A, E and C lies on Neutral Axis (NA), t here are no bending moment occurred on the points. And σA = σC = σE ;
=
[ ][ ]
= 11 919.25 Pa » 11.92 kPa
4 4 ′ ′ − ∑ȳ
) ( =
3
=
= 0.273MPa
14 − 0038 −003
= 1.00x10 -6 m4
τA = 0.273
A, E & C STRESS ELEMENT Y-AXIS VIEW
=
σA = 11.92 kPa
2 3 2 −
= 1.7906x10 -5 m3
= 273 066.5 Pa
STRESS ANALYSIS OF POINT B AND D
B At point B and point D, the shear stress is zero. And since both point located at the farthest location, The normal stress and bending moment are maximum.
D
15.065 MPa
σB
[][] −
B STRESS ELEMENT Y-AXIS VIEW
= 11 919.25 - 15 076 500 = 15.065 MPa
15.065 MPa
[][] = 11 919.25 + 15 076 500 = 15.09 MPa
D STRESS ELEMENT Y-AXIS VIEW
DISCUSSION Shear failure of reinforced concrete beam, more properly called “diagonal tension failure”, is difficult to predict accurately. Although the experiment research has been carried out so many years with the help of sophisticated computational tool, shear failure is still not fully understood. If a beam without properly designed for shear reinforcement is overloaded to failure, shear collapse is likely to occur. All points along the length of the beam, where shear and bending moment are not zero, and at locations other than extreme fibre or neutral axis, are subject to both shearing stresses and bending stresses. The combination of these stresses produces maximum normal and shearing stresses in a specific plane inclined with respect to the axis of the beam. By assuming that the hollow cylinder uses steel A-36 because of the rusting happens on the pole and the physical properties that can be seen, in which its yield strength for both compression and tension is 250 MPa, it is shown that from the result, this design will not face any failure. From the calculation made, it shows that the structure will not face failure since the maximum stress applied on the structure is 15.09 MPa (at point B and point D) with normal stress acting on the hollow cylinder is only 11.92 kPa. These stresses did not exceed the yield strength of the steel A-36. However, in beam design, there is one term of failure called buckling. In science, buckling is a mathematical instability, leading to a failure mode. Theoretically, buckling is caused by a bifurcation in the solution to the equations of static equilibrium. At a certain stage under an increasing load, further load is able to be sustained in one of two stat es of equilibrium: an undeformed state or a laterally-deformed state. Since this pole is considered as free-standing, vertical column, self-buckling might happen if the height of the column exceeds critical height. For steel A-36 with outer radius and inner radius are 0.038m and 0.03m respectively, the critical height is 46m, while the height of the signboard pole is only 1.86m. Thus, self-buckling also will not occur.
)() ( =
= 46m
One thing that a design should have is a safety factor. Safety factor is a term describing the structural capacity of a system beyond the expected loads or actual loads. Essentially, how much stronger the system is than it usually needs t o be for an intended load. Safety factors are often calculated using detailed analysis because comprehensive testing is impractical on many projects, such as bridges and buildings, but the structure's ability to carry load must be determined to a reasonable accuracy. Many systems are purposefully built much stronger than needed for normal usage to allow for emergency situat ions, unexpected loads, misuse, or degradation.
=
= 16.6 It shows that this design is way too safe since it is bigger than 1 or 100%.
SUGGESTION This design is far too safe for the load applied and acting on it. Since we already know the normal stress, shear stress and bending moment of this particular design, we can reduce the cost to produce this design by reducing some components in this design. However, the reductions need to be calculated again to get a specific value. In order to save production cost, we can reduce the diameter of t he pole used for this particular design. Not only the diameter, but the thickness of the pole can also be reduced. By reducing the thickness and diameter of this design, the weight of the steel pole is reduced thus lower its production cost. We can also use another type of metal for the pole that its yield strength is more than 16MPa. Since the stress on the load is too small, we can use fibre-reinforced plastic (FRP) as a replacement of this steel pole. However, the outer and inner diameter of FRP pole must be more or equal to the previous diameter. The height also should not exceed the height recorded.
