Civil Engineering PE Steel Structure Design Methods 3

Question 1

A steel column with KL/r = 80 and Fy = 50 ksi falls into which AISC buckling category?

Accepted Answer

Inelastic buckling (KL/r < 4.71√(E/Fy) ≈ 113)

Answer

For Fy = 50 ksi, the transition slenderness is 4.71√(E/Fy) = 4.71√(29000/50) ≈ 113; KL/r = 80 is in the inelastic buckling range.

Question 2

Which effective length factor K applies to a column with both ends pinned (no rotational fixity)?

Accepted Answer

K = 1.0

Answer

A pin-pin column has no end restraint against rotation, giving K = 1.0 and an effective length equal to the actual length.

Question 3

What is the purpose of the Cb factor in AISC beam design?

Accepted Answer

It accounts for non-uniform moment along the unbraced length, allowing higher capacity

Answer

Cb is the lateral-torsional buckling modification factor; moments varying along the unbraced length are less severe than uniform moment, so Cb ≥ 1.0 increases the allowable strength.

Question 4

In AISC Chapter F, which condition defines a compact section regarding the compression flange?

Accepted Answer

λ ≤ λp where λ = bf/2tf ≤ 0.38√(E/Fy)

Answer

A compact flange requires bf/(2tf) ≤ 0.38√(E/Fy), allowing the section to reach the plastic moment before local buckling.

Question 5

For a steel beam experiencing lateral-torsional buckling in the elastic range, nominal moment Mn is proportional to:

Accepted Answer

1/Lb² (inversely proportional to unbraced length squared)

Answer

In the elastic LTB range, Mn decreases with 1/Lb via the elastic buckling moment Mcr ∝ (1/Lb)√(EIyGJ + (πE/Lb)²IyCw).

Civil Engineering PE Practice Test

Civil Engineering PE Practice Test

Civil Engineering PE Steel Structure Design Methods 3