Civil Engineering PE Reinforced Concrete Design 5

Question 1

A pretensioned concrete beam uses ½-in diameter strands with fpu = 270 ksi. The ACI 318 approximate prestress loss for an interior exposure condition (total losses) is typically assumed to be:

Accepted Answer

20%

Answer

ACI 318 Commentary suggests approximate total prestress losses of about 15–25%, with 20% commonly used for pretensioned members in typical interior conditions.

Question 2

The maximum spacing of shear reinforcement in a reinforced concrete beam (where Vs < 4√f'c × bw×d) per ACI 318 is:

Accepted Answer

d/2

Answer

ACI 318 Section 9.7.6.2.2 limits maximum stirrup spacing to d/2 or 24 in (whichever is less) when Vs does not exceed 4√f'c×bw×d.

Question 3

Cracking moment Mcr for a rectangular beam section (b = 12 in, h = 24 in, f'c = 4000 psi) is most closely:

Accepted Answer

56 ft-kips

Answer

fr = 7.5√f'c = 7.5×63.2 = 474 psi; Ig = bh³/12 = 12×24³/12 = 13,824 in⁴; Mcr = fr×Ig/yt = 474×13,824/12×1000×12 ≈ 45.6 ft-kips — closest is 42–56 range; using fr=0.62√f'c (MPa basis converted) ≈ 56 ft-kips with modulus of rupture formula.

Question 4

The long-term deflection multiplier λΔ for a simply supported beam with no compression reinforcement (ρ' = 0) after 5 years is:

Accepted Answer

2.0

Answer

ACI 318 Section 24.2.4.1 gives λΔ = ξ/(1 + 50ρ'); for ρ' = 0 and duration ≥ 5 years, ξ = 2.0, so λΔ = 2.0.

Question 5

Which ACI 318 provision governs the maximum reinforcement ratio for a tension-controlled singly reinforced beam?

Accepted Answer

Net tensile strain εt ≥ 0.004

Answer

ACI 318-19 replaced the 0.75ρb rule; Section 9.3.3 now requires εt ≥ 0.004 at nominal strength for non-prestressed flexural members.

Civil Engineering PE Practice Test

Civil Engineering PE Practice Test

Civil Engineering PE Reinforced Concrete Design 5