Construction Materials $($CON$4121)$

Assignment $($AY$2024/25)$

Submission Deadline : $20/11/2024($Wed$)$

Please write all your answers on A$4$ size papers. Hand writing is required and computer typing is prohibited. Mark $(10\%$ per day$)$ will deducted for late submission.

Q$.1$ A student performed a tensile test on a Grade $250$ steel reinforcing bar to determine its tensile properties. The data of the steel reinforcing bar is:

Length: $1$ m

Diameter: $20$ mm

A tension of $62\mathrm{.}8kN$ was applied to the steel reinforcing bar and the extension was $1mm.$ The steel reinforcing bar returned to its original length and shape after the tension force was removed.

When the bar was subjected to the force of $62\mathrm{.}8$ kN $,$ calculate:

a$)$ the stress;

$(4$ marks$)$

b$)$ the strain; and

$(3$ marks$)$

c$)$ Young's Modulus of the bar.

$(3$ marks$)$

When the tension reached $79kN,$ the extension increased significantly without any change in stress. Necking of the bar began when the tension reached $92$ kN $.$

Calculate:

d$)$ the yield strength $($stress$)$; and

$(3$ marks$)$

e$)$ the allowable stress of the bar if the factor of safety is $2.$

$(3$ marks$)$

After the tensile test was completed, the student studied the elastic and plastic behavior of the bar.

f$)$ With the aid of diagrams and examples, briefly compare elastic and plastic behavior of a material.

$(9$ marks$)$

Q$.2$ A project manager of a local contractor conducted an inspection on a construction site where a reinforced concrete domestic building was being built. He observed the following two situations.