Civil Engineering PE Reinforced Concrete Design 4 — Questions and Answers
Question 1: A two-way flat plate has columns on a 20-ft × 20-ft grid. For punching shear, the critical perimeter bo around an interior column (18×18 in, d = 7 in) is:
- 100 in
- 116 in (Correct answer)
- 72 in
- 140 in
Correct answer: 116 in
Critical section is at d/2 from column face: each side = 18+7 = 25 in, bo = 4×25 = 100 in.
Question 2: The ACI 318 standard hook development length ldh for a #6 bar (fy = 60 ksi, f'c = 4000 psi, normal weight concrete, no confinement) is approximately:
- 8 in
- 11 in
- 14 in (Correct answer)
- 18 in
Correct answer: 14 in
ldh = (0.02ψe fy/(λ√f'c)) × db = (0.02×1.0×60,000/(1.0×√4000)) × 0.75 ≈ 14.2 in.
Question 3: For a spirally reinforced column, the minimum spiral reinforcement ratio ρs per ACI 318 is:
- 0.45(Ag/Ac - 1)(f'c/fyt) (Correct answer)
- 0.25(Ag/Ac)(f'c/fyt)
- 0.12f'c/fyt
- 0.01(Ag/Ac)(fy/f'c)
Correct answer: 0.45(Ag/Ac - 1)(f'c/fyt)
ACI 318 Section 25.7.3.3 requires ρs ≥ 0.45(Ag/Ac − 1)(f'c/fyt), ensuring the spiral replaces the lost capacity of the shell.
Question 4: A simply supported beam (span = 24 ft) carries a uniform service dead load of 1.5 k/ft and live load of 2.0 k/ft. The maximum factored moment Mu using ACI load combinations is:
- 360 ft-kips
- 414 ft-kips
- 468 ft-kips (Correct answer)
- 540 ft-kips
Correct answer: 468 ft-kips
wu = 1.2(1.5)+1.6(2.0) = 5.0 k/ft; Mu = 5.0×576/8 = 360 ft-kips — select 360.
Question 5: The slenderness ratio klu/r below which slenderness effects may be neglected for a braced (non-sway) reinforced concrete column is:
- 22
- 34 − 12(M1/M2) (Correct answer)
- 40
- 50
Correct answer: 34 − 12(M1/M2)
ACI 318 Section 6.2.5 allows slenderness to be neglected for braced columns when klu/r < 34 − 12(M1/M2), where M1/M2 is the end moment ratio.
Question 6: In a beam-column joint, horizontal joint shear Vjh is resisted primarily by:
- Stirrups within the joint
- A diagonal concrete compression strut (Correct answer)
- Longitudinal reinforcement in the beam
- The column spiral reinforcement
Correct answer: A diagonal concrete compression strut
The primary mechanism for joint shear transfer is a diagonal concrete compression strut forming across the joint panel.
Question 7: For a reinforced concrete wall with hw/lw > 2.0, the critical section for flexural design is located at:
- Mid-height of the wall
- The base of the wall (Correct answer)
- lw/4 from the base
- lw/2 from the base
Correct answer: The base of the wall
For slender walls (hw/lw > 2.0), the critical section for flexure and axial load is at the base where moments are maximum.
Civil Engineering PE Reinforced Concrete Design 4
A two-way flat plate has columns on a 20-ft × 20-ft grid.
For punching shear, the critical perimeter bo around an interior column (18×18 in, d = 7 in) is: