ASCE Structural Engineering and Materials 3 — Questions and Answers
Question 1: Per ACI 318, what is the minimum specified cover for cast-in-place concrete cast against and permanently exposed to earth?
- 1.5 in.
- 2 in.
- 3 in. (Correct answer)
- 0.75 in.
Correct answer: 3 in.
ACI 318 requires 3 in. of cover for concrete cast directly against earth.
Question 2: At what age is the specified compressive strength f'c of concrete normally determined?
- 7 days
- 14 days
- 28 days (Correct answer)
- 56 days
Correct answer: 28 days
f'c is based on cylinder tests at 28 days unless the contract specifies another age.
Question 3: The slump test (ASTM C143) is mainly used to measure which property of fresh concrete?
- Air content
- Workability/consistency (Correct answer)
- Compressive strength
- Setting time
Correct answer: Workability/consistency
Slump measures the consistency, or workability, of fresh concrete.
Question 4: In the ACI rectangular stress block, what is β1 for concrete with f'c ≤ 4,000 psi?
- 0.65
- 0.75
- 0.85 (Correct answer)
- 0.90
Correct answer: 0.85
β1 = 0.85 for f'c up to 4,000 psi and drops by 0.05 per 1,000 psi above that, down to a minimum of 0.65.
Question 5: All else equal, what is the main effect of raising the water-cement ratio of a concrete mix?
- Higher strength
- Lower permeability
- Lower strength and durability (Correct answer)
- Faster strength gain
Correct answer: Lower strength and durability
Per Abrams' law, a higher w/c ratio adds porosity, which lowers strength and durability.
Question 6: Which ASCE 7 LRFD load combination typically governs for gravity-only dead and live load?
- 1.4D + 1.6L
- 1.2D + 1.6L (Correct answer)
- 1.0D + 1.0L
- 0.9D + 1.6L
Correct answer: 1.2D + 1.6L
1.2D + 1.6L (+0.5 of roof load) is the usual governing gravity combination; 1.4D governs only when live load is very small.
Question 7: What is the degree of static indeterminacy of a propped cantilever (fixed at one end, roller at the other)?
- 0
- 1 (Correct answer)
- 2
- 3
Correct answer: 1
It has 4 reactions and 3 equilibrium equations, so it is indeterminate to the first degree.
ASCE Structural Engineering and Materials 3
Per ACI 318, what is the minimum specified cover for cast-in-place concrete cast against and permanently exposed to earth?