1. As per IS 456:2000, Minimum grade of concrete for plain concrete exposed to seacoast is _____.
[A] M20
[B] M30
[D] M25
[C] M40
Answer: Option A
2. Flexural strength (in N/mm²) of concrete is computed by ______.
[A] 5000√fck
[B] 7000√fck
[C] 0.7√fck
[D] 0.5√fck
Answer: Option A
3. If creep coefficient for concrete at 7 days is K1 and 28 days is K2 then ______.
[A] K1 > K2
[B] K1 < K2
[D] K1 <= K2
[C] K1 = K2
Answer: Option A
4. An ordinary mild steel bar has been prestressed to a working stress of 200 MPa. If the Young’s modules of steel is 200 GPa and permanent negative strain due to shrinkage and creep is 0.0008, what is the effective stress left in the steel?
[A] 190 MPa
[C] 85 MPa
[B] 170 MPa
[D] 40 MPa
Answer: Option D
Solution:
Initial prestress = 200MPa
Shrinkage Strain (ϵs) = 8 * 10^-4
Modulus elasticity of steel (Es) = 200GPa = 200 * 10^3 MPa
Now, loss of prestress = ϵs * Es = 8 * 10^-4 * 200 * 10 ^ 3 = 160MPa
Stress left in steel = 200 – 160 = 40MPa
5. The modulus of elasticity E = 5000 where fck is the characteristic compressive strength of concrete specified in IS:456-2000 is based on ______.
[A] Tangent modulus
[B] Initial tangent modulus
[C] Secant modulus
[D] Chord modulus
Answer: Option B