Civil Engineering PE Steel Structure Design Methods 5 — Questions and Answers
Question 1: A composite steel beam uses shear studs to transfer horizontal shear between the steel section and concrete slab. The total horizontal shear force V' for full composite action between the point of maximum moment and zero moment is:
- The lesser of 0.85f'cAc and AsFy (Correct answer)
- The sum of 0.85f'cAc and AsFy
- AsFy only, regardless of concrete strength
- 0.85f'cAc only, regardless of steel yield
Correct answer: The lesser of 0.85f'cAc and AsFy
Full composite action requires the shear connection to transfer the lesser of concrete compression capacity (0.85f'cAc) and steel tension capacity (AsFy).
Question 2: In AISC LRFD, what is the design flexural strength φbMn for a compact W-shape beam with adequate bracing?
- φbMn = 0.90 × Mp = 0.90 × FyZx (Correct answer)
- φbMn = 0.90 × My = 0.90 × FySx
- φbMn = 0.75 × Mp = 0.75 × FyZx
- φbMn = 0.85 × Mp = 0.85 × FyZx
Correct answer: φbMn = 0.90 × Mp = 0.90 × FyZx
For a compact, adequately braced section, Mn = Mp = FyZx and φb = 0.90, so φbMn = 0.90FyZx.
Question 3: Serviceability deflection limits for steel floor beams under live load are typically:
- L/360 (Correct answer)
- L/240
- L/180
- L/480
Correct answer: L/360
IBC and AISC recommend a live-load deflection limit of L/360 for floor beams to prevent cracking of brittle finishes.
Question 4: Which steel property is used to calculate thermal expansion in steel structures, critical for bridge design?
- Coefficient of thermal expansion α = 6.5 × 10⁻⁶ /°F (Correct answer)
- Modulus of elasticity E = 29,000 ksi
- Shear modulus G = 11,200 ksi
- Poisson's ratio ν = 0.30
Correct answer: Coefficient of thermal expansion α = 6.5 × 10⁻⁶ /°F
Thermal deformation ΔL = αLΔT; for steel, α = 6.5 × 10⁻⁶ /°F is the standard value used in structural calculations.
Question 5: In the plastic design method for continuous steel beams, collapse occurs when enough plastic hinges form to create a:
- Mechanism (statically unstable structure) (Correct answer)
- Fully fixed condition at all supports
- Net section fracture at the weakest point
- Lateral-torsional buckling mode
Correct answer: Mechanism (statically unstable structure)
Plastic collapse occurs when sufficient plastic hinges form to convert the structure into a mechanism, preventing additional load resistance.
Question 6: A steel plate girder with a very slender web uses transverse stiffeners to develop post-buckling tension field action. This behavior is described by:
- Wagner's tension field theory, where diagonal tension carries shear after web buckling (Correct answer)
- Euler column theory applied to web panels
- St. Venant torsion resisting applied shear
- Reduced effective width method for web compression
Correct answer: Wagner's tension field theory, where diagonal tension carries shear after web buckling
Tension field action (Wagner theory) allows the web to carry shear through diagonal tensile stresses after the web has buckled, significantly increasing shear capacity.
Question 7: For seismic design of steel special moment frames (SMF), the connection must be capable of developing a minimum interstory drift angle of:
- 0.04 radians (Correct answer)
- 0.02 radians
- 0.01 radians
- 0.06 radians
Correct answer: 0.04 radians
AISC 341 requires SMF beam-column connections to demonstrate adequate performance at an interstory drift angle of at least 0.04 radians.
Civil Engineering PE Steel Structure Design Methods 5
A composite steel beam uses shear studs to transfer horizontal shear between the steel section and concrete slab.
The total horizontal shear force V' for full composite action between the point of maximum moment and zero moment is: