The Construct The Specimen Engineering Essay

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1.0 INTRODUCTION

As defined in ASTM D 3878-95c, composite material is a substance consisting of two or more materials, insoluble in one another, which are combined to form a useful engineering material possessing certain properties which not possessed by the constituents. According to Composites Worldwide, Inc. in 2001 composites are supposed to grow at a rate at minimum of 35% per year in infrastructure applications, primarily in bridges and the repair and strengthening of reinforced concrete structures.

Thin-walled composite-filled (TWCF) beams are made from two materials which are cold-formed steel element section and concrete infill. The steel element is formed into open box section so that the concrete can be casted in it easily. The steel is functioned as formwork and reinforcement. So, they do not require temporary formwork for the infill concrete and also do not need the reinforcement. Therefore, no skilled workers needed to do the formwork or to bend and cut the reinforcement. Compare with the conventional reinforced concrete, this type of beams are more easily to manufacture and build.

TWCF beams are less resistant to fire, even though reasonable protection to most fire loads is provided by the thermal mass of the concrete infill. Compare with the conventional concrete, the smooth metallic finish of TWCF beams is better and accepts more paint finish. These economical and aesthetical structural elements will captivate interest in the construction industry.

Problem Statement

Changes in technology have great impact on the development of the construction sector. Recently, many new technologies used in the construction industry throughout the world. The technologies used including structures, building materials and machineries. Increase in new technology causes the construction work more easily as well as reducing the cost. Thus, production of thin-walled composite-filled beams can also be a new design in structure.

According to research done by Hossain (2005) on the designing TWCF beams, he developed design guidelines for thin-walled composite-filled beams with various modes of strength-enhancement devices. His proposed design is acceptable to be used for the design of simple beam. However, his experiment is based on the test of beams subjected to positive moment. Therefore, this study is concern the negative moment capacity of TWCF beams. It is applicable for beams at internal support. The design steps and calculation are proposed in this study.

Objectives

Generally the study is to investigate the characteristic of TWCF beams at internal support where the beams are subjected to negative moment and the enhancement of moment capacity using welded plate. The objectives are:

To verify the load and displacement relationship at the mid span of TWCF beams subjected to negative moment

To establish load and strain relationship at mid span

To ascertain failure pattern of the beams

Scope of Work

This research involved theoretical and experimental study. Firstly, formulating the design equation will be done. The design includes the negative moment capacity for a continuous beam. The design criteria consist of yielding and buckling. Then, the laboratory investigation need to perform. Before doing the sample, the trial mix of the concrete must be done. It is to make sure the mixture of the concrete achieve the required strength.

The TWFC beams were classified into two types of specimen which are open section (OS) and welded plate (WP). For each type, two specimens will be used. The geometry of beam and welded plate are shown in Figure 1.2. The dimension of sample is listed in Table 1.1. Bending test and tensile test are used for determining the load, displacement of beam, yield stress and mode of failure.

Welded plate

Steel sheet

In-fill concrete

Figure 1.1: Thin-walled composite-filled beam

s

o

s

a

a

d

b

L

Figure 1.2 (a): Geometric of TWCF beam

Lp

t

w

Figure 1.2 (b): Geometric of welded steel plate

d

b

w

Figure 1.2 (c): Cross-section of beam a-a

Table 1.1: Dimension of specimen

Specimen

Dimension (mm)

Concrete

L

b

d

o

s

t

w

Lp

OS1

1100

125

125

45

40

0

0

0

C30

OS2

1100

125

125

45

40

0

0

0

C30

WP1

1100

125

125

45

40

1.5

65

700

C30

WP2

1100

125

125

45

40

1.5

65

700

C30

Significance of Study

The important of this study is to create a new innovation by technology in construction industry in order to improve the quality of the construction in buildings. With this new innovation, buildings can be constructed with economical value and in good quality. These beams not only reduce the cost but also reduce the time producing and the weight. By enhancing the TWCF beams with welded plate, the strength is increase and can be used safely in buildings. The TWCF beams have a potential to form as precast unit and also can fulfil the requirement of a great building. Therefore, it will help in the development of construction industry and also in economical sector.

2.0 LITERATURE REVIEW

Composite beams

Refer to Gramoll (2010), composite beams are made from more than one material to increase stiffness or strength. In this study, the two materials used are steel and concrete. By combining these two materials, the structure will achieve better in quality based on its material properties. Both materials, steel and concrete have their own characteristics which will give benefits to composite beam.

According to a book edited by Nethercot (2003), composite beams have been the major structure for mid range steel bridges. Besides, composite beams ordinarily be as the composite element in steel frame building. He defined composite beams as elements restraining only flexure and shear that consist of two longitudinal components connected together either continuously or by a series of discrete connectors. In this study, the beams can be used in small to medium sized building. The type of beam being used is continuous beam.

From the condition when the connection between the two layers is non-present to the condition where the bond between the layers approaches infinite stiffness and strength, the composite beams differ in behaviour. There is little influence in the overall strength and stiffness of the beam in a weak and flexible component. Besides that, behaviour is also changed by the stress states in each component that exist prior to connection. (Nethercot, 2003).

Recently, continuous composite beams are commonly used. The advantages of continuity turn up with a design price in that composite beams behave very differently in this condition and can almost never provide the same strength or stiffness in the negative moment sections. (David A. Nethercot, 2003). Therefore, this study is concern the negative moment capacity of TWCF beams. It is applicable for beams at internal support.

According to research by Oduyemi et al (1989) and Wright et al (1991), their tested beams which are composite beams showed three kind of failure: flexural (steel yield prior to concrete crushing), horizontal slip (failure of shear connectors) and vertical shear (due to insufficient shear capacity of concrete and studs). However, local buckling of the steel may come before the three failure patterns. Therefore, in this study, the beam will be enhanced by welded plate in order to tackle the failure.

Thin-walled composite-filled beams

Thin-walled composite-filled (TWCF) beams are made from two materials which are cold-formed steel element section and concrete infill. To make it easier to cast the concrete, the steel element is formed into open box section. The steel have two important roles which are acting as formwork and as reinforcement. The formwork is permanent and therefore, no reinforcement needed.

Basically, the difference between hot formed and cold formed steel sections is that hot formed steel section is formed to its sizes while hot enough to scale (over 1700 degrees F) while cold formed steel section is formed to its sizes well below scaling temperatures. Most of structural elements are made from sheet steel. They are referred to as light gage steel products due to they are typically formed from very thin sheets. Figure 2.1 below shows some of the cross sections of these products. (Parker, 1990)

Figure 2.1: Cold-formed structural shapes

Thin-walled beam may and usually behave quite differently from thick walled beams under the same loading conditions. The term "thin-walled beam" does not only define the appearance of a beam but also its behaviour under load. (Zbirohowski-Koscia, 1967).

Thin-walled, cold-formed steel structural members have been broadly utilized in building construction and different types of structural systems since the early 1940s. Nevertheless, these members have been used limitedly in composite concrete beams even though the use of composite cold-formed steel-concrete slabs has been very extensive in building construction and other areas. (Nguyen 1991).

Research has been conducted by Richard P. Nguyen (1991) on thin-walled, cold formed steel composite beams whereby the results prove that by replacing the conventional steel reinforcing bars with thin-walled, cold-formed steel sections of equal cross-sectional areas, the ultimate strength of the composite beams in bending and shear can be achieved.

Hossain (2005) had proposed design guidelines for TWCF beams with various modes of strength-enhancement devices in his research on the designing TWCF beams. He done the experiment based on the test of beams subjected to positive moment. His proposed design is acceptable to be used for the design of simple beam. For this study, the test of beams is concern the negative moment capacity and it is applicable for beams at internal support. The design steps and calculation are proposed in this study.

Behaviour of TWCF beams

TWCF beams have better structural behaviour compared to ordinary beams. In terms of strength, TWCF beams have increase of flexural and shear strength. Besides that, it also has lower risk of deflections.

Research has showed that by providing profiled steel sheets to the sides of reinforced concrete beams, their flexural and shear strengths can increase without loss of ductility and that the profiled-sheet/concrete-beam interface is not prone to shear bond failure. Besides, from the theoretical studies, it is recommend that by providing side profiled sheets will reduce long-term deflections due to creep and shrinkage of the concrete. The span/depth ratio also will be allowed to increase about 20%. (Oehlers, 1993).

Advantages of using TWCF beams

Basically, for every new technology must have the advantages of producing it. The most important benefits of the TWCF beams are can reduce cost of construction and more easily to manufacture and build. These beams do not require temporary formwork and also do not need the reinforcement bar. Therefore, no skilled workers needed to do the formwork or to bend and cut the reinforcement.

The advantages of a composite cold-formed steel-concrete beam are savings in cost and time of construction without increasing the area of steel required for reinforcement. (Nguyen 1991).

Research done by Oehlers (1993), showed that the composite profiled beams gave two major advantages which are reducing the cost and can act compositely with the reinforced concrete slab. The profiled sheet is cheap and act as formwork that substantially make the site labour costs become lower. By being compositely with the reinforced concrete slab, it will make the strength and the stiffness more high and substantially reduce the thickness of the slab.

Concrete mix design

Concrete is a compound of cement, sand, course aggregate, concrete binder and water. Before this material is combined, a comprehensive test on materials must be done such as moisture content, bulk density, sieve analysis and other parameters. The water cement ratio (w:c) is used for measure the consistency of concrete. The water cement ratio also will influence the compressive strength, tensile strength, durability and permeability of concrete. Thus, the design mixing should be calculated appropriately before mixing them together. (Siti Hawa et al, 2008)

Concrete mix design can be defined as the procedure to determine the proportions of the constituent materials to produce a concrete that fulfil all the required properties at the minimum cost in any given set of condition. The basic requirements of concrete are considered in two stages which are hardened state and plastic state. When it is in hardened state, it should have the required durability, desired strength and adequate surface finish. While it is in plastic state, it should have workability. It is mean by:

The concrete should be able to flow into and fill in the formwork

There should not be segregation during placing

The concrete must be fully compact when placing it

The concrete should get the required surface finish

To produce the hardened concrete with required properties, make sure the workability of the concrete at plastic state is achieved. (Jackson, 1996)

Good durability of hardened concrete can be achieved by ensuring full compaction, an adequate cement content and a lower water-cement ratio. (Jackson, 1996)

There are many approaches of concrete mix design have been proposed. The most recent and broadly used is Design of Normal Mixes from DOE 1988. Besides, Hughes (1971) approach considers the optimum content of coarse aggregate. (Jackson, 1996)

The process of concrete mix design can be divided into five stages and is explained in British Standard (BS1881). The stages are: (Siti Hawa et al, 2008)

Selection of target water/cement ratio

Selection of free-water content

Determine cement content against maximum or minimum value which has been specified

Determine total aggregate requires for fully compact concrete

Selection of fine and coarse aggregate

Design moment capacity

Analytical models for the flexural strength are done by considering the buckling and yielding of steel and failure patterns of the experimental beams. The design point is referred to the maximum moment that reacts at the beams. In reality, usually the beams will exhibit partial connection which means the position of the neutral axis for concrete Nc is different with that for the steel sheeting Ns. (Hossain, 2005)

bs

Nc

Ns

d

y-(d-Ns)

εsl

d-Ns

y

Strain

v

w

s

s

(b)

Partial shear connection

(a)

Cross section

Figure 2.2: Strain distribution in thin-walled composite-filled beams

Concrete section

0.85fc'

db

Pcc

0.5 Nc

Nc

Nc

Pb

fb

Force

Stress

Strain

fsy

Steel section

Psc1

Psc2

Pst3

Psc

Ns

Pb

Pst1

d-Ns

Pst2

fsy

Force

Stress

Strain

Figure 2.3: Distribution of forces

Table 2.1: Notation for design moment

Pcc ,Pb

= compressive force due to concrete and force due to shear bond

Psc1 ,Psc2

= compressive forces in the steel plates at top and at welded extension

Nc ,Ns

= neutral axis position for concrete and steel section

Psc

= compressive forces in the steel plates at web

Pexp ,Mexp

= experimental ultimate load and moment capacity

Pst3

= tensile forces in the steel plate at welded extension

Pu ,Mu

= theoretical ultimate load and moment capacity

Pst1

= tensile forces in the steel plate at web

bc, y

= width of net concrete section and depth of WE respectively

Pst2

= tensile forces in the steel plate at bottom

= cross sectional perimeter of steel sheeting in contact with concrete

fb

= shear bond stress at the interface

x

= the distance from the support to the maximum moment

fsy, fy

= yield stress of steel plate and steel rod respectively

f'c

= Cylinder strength

o, s

= width of opening and top-stripped steel skin respectively

bs, d, L

= width, depth and span of TWCF beam respectively

ts ,v, w

=thickness of steel skin, welded extension and width of plate

* for convert cube strength, f'c into cylinder strength, used f'c = 0.8fcu

Partial shear connection

Nc Ns

Equilibrium of forces in concrete

Pcc = Pb .....(1)

0.85f'cNcbc = Pb .....(2)

Nc = .....(3)

Pb = fb .....(4)

For case 1: y>(d-Ns)

[Refer to figure 2.2(a)]

Equilibrium of forces in steel

Pb + Psc1 + Psc2 + Psc = Pst3 + Pst1 + Pst2 .....(5)

Pb + bstsfsy + 2(y-d+Ns)tsfsy + 2Nstsfsy = 2(d-Ns)tsfsy + 2(d-Ns)tsfsy + (2s+w+2v)tsfsy ...(6)

8Nstsfsy = - Pb- bstsfsy - 2(y-d)tsfsy + 2dtsfsy + 2dtsfsy + (2s+w+2v)tsfsy

Ns = .....(7)

Ultimate moment:

Mu = Pbdb - 0.85f'cNcbc(0.5Nc) - Pbdb - 2(y-d+Ns)(tsfsy)(Ns -) - 2Nstsfsy(

+ 2(d-Ns)tsfsy() + 2(d-Ns)tsfsy() + (2s+w+2v) tsfsy(d) …..(8)

= - 0.425f'c2Nc2bc - tsfsy(y-d+Ns)(Ns-y+d) - Ns2tsfsy + tsfsy(d-Ns)(Ns+d) + tsfsy(d-Ns)(Ns+d) + tsfsy(2sd+wd+2vd)

= - 0.425f'c2Nc2bc - tsfsy(yNs-y2+yd-dNs+dy-d2+Ns2-Nsy+dNs) - Ns2tsfsy + 2tsfsy(dNs+d2-Ns2-Nsd) + tsfsy(2sd+wd+2vd)

= - 0.425f'c2Nc2bc - tsfsy(-y2+2yd-d2+Ns2+Ns2-2d2+2Ns2-2sd- wd -2vd)

= - 0.425f'c2Nc2bc - tsfsy(-y2+2yd-3d2+4Ns2-2sd-wd-2vd) …..(9)

For case 2: y<(d-Ns)

d

bs

Ns

y

v

w

s

s

Cross section

Equilibrium of forces in steel

Pb + Psc1 + Psc = Pst3 + Pst1 + Pst2 …..(10)

Pb + bstsfsy + 2Nstsfsy = 2ytsfsy + 2(d-Ns)tsfsy + (2s+w+2v)tsfsy …..(11)

4Nstsfsy = - Pb- bstsfsy + 2ytsfsy + 2dtsfsy + (2s+w+2v)tsfsy

Ns = …..(12)

Ultimate moment:

Mu = Pbdb - 0.85f'cNcbc(0.5Nc) - Pbdb - 2Nstsfsy( + 2ytsfsy( + 2(d-

Ns)tsfsy() + (2s+w+2v) tsfsy(d) …..(13)

= - 0.425f'c2Nc2bc - tsfsy(Ns2-2yd+y2) + tsfsy(d-Ns)(Ns+d) + tsfsy(2sd+wd+2vd)

= - 0.425f'c2Nc2bc - tsfsy(Ns2-2yd+y2-d2+Ns2-2sd-wd-2vd)

= - 0.425f'c2Nc2bc - tsfsy(2Ns2-2yd+y2-d2-2sd-wd-2vd) …..(14)

When y=0, w=0 and v=0 (For OS beam):

Mu = - 0.425f'c2Nc2bc - tsfsy(2Ns2-d2-2sd) …..(15)

When y=0, v=0 (for WP beams)

Mu = - 0.425f'c2Nc2bc - tsfsy(2Ns2-d2-2sd-wd-2vd) .....(16)

3.0 METHODOLOGY

3.1 Introduction

In order to verify the theoretical values obtained and to achieve the objectives, the experimental study need to be done. This experimental study is involved in determining the negative moment capacity of TWCF beams with welded plate. The laboratory experiments will be performed to determine the load, displacement of beam, yield stress and mode of failure by using tensile and bending test. Before that, the sampling must be carried out first. The TWCF beams were classified into two types of specimen which are open section (OS) and welded plate (WP). Two specimens will be used for each type.

Flow Chart of Experimental Work

Preparing steel section Preparing concrete infill

Construct the specimen

Laboratory work

Preparation of steel section

In order to obtain the accurate result from the laboratory work, there are a few important factors that must be taken in to consideration in the process preparation of steel section such as the geometry, labelling, shape and size. Before process of cutting and folding the thin sheet into the dimension of specimen needed, the thin sheet must be subjected to tensile test first. After that, the thin sheet will be measure, cut and fold into box shape. Besides, the procedure is also same for preparing the welded plate section.

Table 3.1: Dimension of steel section

Specimen

Dimension (mm)

L

b

d

o

s

t

w

Lp

OS1

1100

125

125

45

40

1.5

0

0

OS2

1100

125

125

45

40

1.5

0

0

WP1

1100

125

125

45

40

1.5

65

700

WP2

1100

125

125

45

40

1.5

65

700

d

b

w

Figure 3.1: The thin sheet is folded into box shape

Preparation of concrete infill

Concrete is a mixture of sand, cement, coarse aggregate and water. A comprehensive test on materials must be conducted before mixing them. The consistency, compressive strength, tensile strength, durability and permeability of concrete are depended on water cement ratio (w:c). Therefore, the concrete mix design process need to be done properly. The trial mix should be done first and followed by cube test. There are five stages of concrete mix design process which is explained in British Standard (BS 1881). The stages are:

a) Selection of target water cement/ratio

b) Selection of free-water content

c) Determine cement content against maximum or minimum value which has been specified

d) Determine total aggregate requires for fully compact concrete

e) Selection of fine and coarse aggregate

After mix design process, the trial mix is done. The mixture is put in six moulds and then it is stored in curing tank in room temperature. After 7 days, the three cubes of concrete is tested for their compressive strength and followed by another three cubes when achieved 28 days aging. If the trial mix achieves the target strength, the mix design can be used for the specimen.

Process flow for preparation of concrete infill

Figure 3.3: The wet concrete is put in cube mould

Figure 3.2: Concrete is mix in concrete mixture machine

Figure 3.4: Vibrator is used for releasing air-entrapped in concrete

Figure 3.5: Curing process

Figure 3.6: Compression Test Machine used to test the concrete cube

Laboratory testing

Compression Test

The compression test is referred to cube test. The compressive strength means that the maximum compressive load it can carry per unit area. The 150 mm 150 mm 150 mm concrete cubes will be tested using compression machine in determining the compressive strength which is accordance to BS8110-4:1997. The concrete cube should be stored in a curing tank at about 22°C-25°C to make sure the concrete cube that will be tested is under standard conditions. Usually, the cube test will be done at 7 days, 14 days and 28 days. However, in this study, three specimens will be tested at 7 days and three specimens at 28 days. Cube test results should be examined in relation to the average cube strength that expected from the mix proportions, water cement ratio and workability required consideration. The trial mix that give expected strength will be used for the specimens.

Tensile Test

The tensile test is a test that is used to test the ductility of a material, and can be used on both metal and rubber samples. In tensile test, a steel coupon is held hardly between a fixed grip and a moving grip (the crosshead) of Universal Testing Machine (UTM). A load cell is used for measuring the stress that builds up in the material as its length is being pulled by the moving crosshead. The change in the length of the sample as pulling proceeds is measured from either the change in crosshead position (extension), or a sensor attached to the sample called an extensometer. The data from the data logger is measuring the applied load and elongation of gauge length, Lo. From the data gained, the graph of stress versus strain is plotted to get the relationship.

Before the thin sheets being cutting and folding, it is need to do tensile test. Firstly, samples of the material are placed in a Universal Testing Machine, gripped by the ends, and a vertical force is applied until they break; they are pulled apart. During the stretching process, the machine measures the load or the force applied to the sample, and the displacement of the sample; along with the original cross sectional area of the sample and the original length, an engineering stress-strain curve can be created. Stress (δ), computed by dividing the load by the cross sectional area, is plotted against strain (ε), derived by dividing the displacement (s) by the length:

δ = ρ/Ao, ε = s/Lo

Figure 3.7: Example of coupon sheet

Figure 3.8: Tensile test machine

Sampling, concreting and casting

In this study, four samples will be used. Two samples are open section type and another two are welded plate type. In concreting, there are three processes involve which are mixing concrete, pouring the concrete and curing concrete.

Before mixing the concrete, it is needed to make sure the weight of sand, water, coarse aggregate and cement are exactly as in the design mix sheet which is already decided while doing the trial mix. Mix the coarse aggregate and sand together in the drum mixer and then, pour the cement and followed by water. The mixture of concrete is made sure to be well mix before pouring.

During casting, air-entrapped must be considered and partial segregation may possible occurred. Due to that, it will reduce the compressive strength in concrete. Therefore, the concrete should be compacted using vibrator to remove the air-entrapped. Last step is levelling the top surface of the concrete and allowing the concrete to cure for three days. The concrete cube should be stored in a curing tank at about 22°C-25°C to make sure the concrete cube that will be tested is under standard conditions.

Curing process is the chemical reaction occurring between cement, water and sand for over duration of time. The tricalcium silicate (C3S) in the cement reacts with silicon dioxide (SiO2) in sand and releases heat within one hour after mixing through the process of hydration. To obtain a good quality concrete, the curing process is suitable to be conducted in room temperature over duration of three days.

For welded plate sample, the plate can be welded at the open section at the top of the beam after the concreting process finished.

Instrumentation and Experimental Set-up

Instrumentations

After 28 days, the concrete will achieve the required strength. So, it is ready for instrumentation and experimental set up. These specimens are tested under four-point loading condition. The specimens were tested by a machine which will provide controlled uniformly increasing force, applied to the specimen.

The measuring devices used in testing the concrete are strain gauge, displacement transducer, load cell and data logger. From this test, the relationship between a load applied to a material and the deformation of the material can be determined. The test will produce the load-strain diagram.

P

P/2

P/2

Figure 3.9: Four-point load condition test

Strain Gauge

Strain (ε) is the quantity of deformation of a body cause by an applied load. Strain can be tensile (positive) or compressive (negative). A device used to measure deformation of an object is called a strain gauge. Strain gauge is attached to the surface of beam to measure its strain. The strain gauge will be installed at the mid-span of the beams. The strain gauge 1 will be placed at top while the strain gauge 2 will be at bottom of the beam.

Figure 3.10: Strain gauge

Linear Variable Differential Transducer (LVDT)

The LVDT is used to measure the displacement of specimen during testing. It provides an AC output voltage proportional to the displacement of its core passing through its windings.

Figure 3.11: LVDT

Load cell

A load cell is a kind of transducer which can converts force into a measureable electrical output. There are many types of load cells such as hydraulic load cells, pneumatic load cells and electric load cells. It is different in the way they detect weight and according to the type of output signal generated.

Figure 3.12: Load cells

Data Logger

Data logger can convert the electrical signals from instruments to strain (µε) and deflection (mm). It also can read many types of electrical signals and store data in its internal memory to be downloaded into a computer. There are many sizes and shapes of the data logger.

Figure 3.13: Data logger

Test Procedure

Firstly, the strain gauges are mounted on cleaned and smooth surface at the support of the beam. The loading device is assembled and then the testing apparatus is operated until the loading blocks are brought into contact with the upper surface of the beam. LVDT is positioned as required for measuring necessary displacement. Make sure all necessary measuring devices is connected to the data logger for data recording. After that, the load is applied at a specified rate of loading. The initiation and development of cracks is observed. After the sample has broken, all dimensions of crack widths, crack length and other data from data logger are obtained.

Figure 3.14: Experimental set-up for TWCF beam

3.7 Testing on specimen

By conducting experiment testing, the structural behaviour of TWCF beams element can be observed under static loading. All testing procedures must be followed closely as stated in the British Standard or Malaysian Standard. When the load is applied, some failures observation can be seen on the specimen such as structural failures, mode failures and damage. The observation made during testing need to be recorded, measured, wrote and took the photo. All the information and results gathered then will be discussed and interpreted.

Figure 3.15: Experimental set-up

4.0 EXPECTED RESULTS

Based on the experiment testing, there are some expected results that will be gained. These results will be then discussed and interpreted to get the conclusion and for proposing recommendations.

4.1 Tensile Test results

When the applied load reaches yield strength, the coupon starts to form a neck and lastly fractures. The applied force and change in length relationship can be obtained by plotting graph. Besides, the stress versus strain is plotted directly to gain their relationship. Stress can be calculated by dividing the applied load with cross-section area. Strain can be obtained by dividing the change in length over initial length (Lo).

Table 3.1: Tensile test result

Applied force (kN)

Displacement (mm)

Stress, σ (kN/mm2)

Principle strain, ε (mm/mm)

Area = mm2

Figure 3.1: Graph of stress versus strain

From the stress and strain graph, the Young's Modulus, yield stress, tensile strength, fracture stress and ductility can be determined. When the graph is analyzed, it can be found that the strain hardening of the material increases up to a certain maximum point, after which the strain begins to deform the material, softening it until it breaks. Graphically, it is the highest point on the engineering stress-strain curve. The maximum point is known as the Ultimate Tensile Strength, or UTS, and is used in measuring the ductility of metals.

Figure 3.2: Example of stress-strain curve

Figure 3.3: The elongation of steel coupon when subjected to tensile test.

4.2 Compression Test results

Three concrete cubes will be tested for seven days and another three will be tested for 28 days. The result will be recorded in the form as below.

Table 3.2: Cube test result form

Characteristic Strength = 30 N/mm2

Description

7 days

28 days

Remarks

(N/mm2)

(N/mm2)

Test no:

Cube 1 wt = kg

2 wt = kg

3 wt = kg

-

Test no:

Cube 1 wt = kg

2 wt = kg

3 wt = kg

-

4.3 Flexural test

The beam will be subjected under four point load. The result will be recorded in table such as table 3.3. After gain the result, the load value is converted into moment and then, the theoretical ultimate moment will be compared with the experimental ultimate moment. Besides, from this test, graph of load versus deflection and load versus strain can be gained.

Table 3.3: Result for flexural test on beam

Load (kN)

Deflection (mm)

Strain,ε (mm/mm)

a

b

Table 3.4: Comparison of ultimate moment between theoretical and experimental

Specimen

Theoretical ultimate moment, MTheo (kNm)

Experimental ultimate moment, MExp (kNm)

Ratio

MExp/MTheo

OS1

Mu = - 0.425f'c2Nc2bc - tsfsy(2Ns2-d2-2sd)

OS2

Mu = - 0.425f'c2Nc2bc - tsfsy(2Ns2-d2-2sd)

WP1

Mu = - 0.425f'c2Nc2bc - tsfsy(2Ns2-d2-2sd-wd-2vd)

WP2

Mu = - 0.425f'c2Nc2bc - tsfsy(2Ns2-d2-2sd-wd-2vd)

Figure 3.4: Relationship between applied load and deflection in beam

Figure 3.5: Relationship between applied load and strain in beam

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