Reinforced Concrete Design Flashcards
7 cards from real Civil Engineering PE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Reinforced Concrete Design flashcards as text
A rectangular beam has b = 14 in, d = 22 in, f'c = 4000 psi, fy = 60,000 psi, and As = 3.0 in². What is the approximate nominal moment capacity Mn?
Answer: 248 ft-kips
With a = Asfy/(0.85f'cb) = 3.0×60/(0.85×4×14) ≈ 3.78 in, Mn = Asfy(d - a/2) = 3.0×60×(22 - 1.89)/12 ≈ 248 ft-kips.
According to ACI 318, the minimum clear cover for reinforcement in a concrete beam exposed to weather (deicing salts) is:
Answer: 2.5 in
ACI 318 Table 20.6.1.3 requires 2.5 in clear cover for #6 through #11 bars exposed to weather (deicing salts).
For a doubly reinforced concrete beam, the compression steel stress f's is typically determined by:
Answer: Using strain compatibility with εs' = (c - d')/c × 0.003
Strain compatibility requires εs' = 0.003(c − d')/c, then f's = Es×εs' ≤ fy to verify whether compression steel yields.
A T-beam floor system has a 5-in slab, beam web width bw = 12 in, center-to-center spacing of beams = 72 in, and span = 20 ft. The effective flange width per ACI 318 is:
Answer: 60 in
Effective flange width = min(span/4, bw + 8hf each side, center-to-center) = min(60 in, 12+80=92 in, 72 in) = 60 in.
The ACI 318 minimum shear reinforcement for a beam is not required when:
Answer: Vu ≤ φVc/2
ACI 318 Section 9.6.3.1 allows omission of minimum shear reinforcement when Vu ≤ φVc/2 for most beams.
The development length for a #8 top bar (f'c = 4000 psi, fy = 60,000 psi, normal weight concrete, cover = 1.5 in, no transverse reinforcement) is approximately:
Answer: 60 in
Using ld = (3fy/(40λ√f'c)) × (ψt ψe ψs / ((cb+Ktr)/db)) × db with ψt=1.3 (top bar), (cb+Ktr)/db limited to 2.5, gives approximately 60 in.
Which failure mode must be prevented to ensure ductile behavior in a flexural member per ACI 318?
Answer: Concrete crushing before tension steel yields
ACI 318 limits reinforcement ratio to ensure the tension steel yields before concrete reaches εu = 0.003, guaranteeing ductile behavior.