250+ TOP MCQs on Design Strength of Laterally Unsupported Beams – I and Answers

Design of Steel Structures Multiple Choice Questions on “Design Strength of Laterally Unsupported Beams – I”.

1. The design bending strength of laterally unsupported beams is governed by
a) torsion
b) bending
c) lateral torsional buckling
d) yield stress
Answer: c
Clarification: Beams with major axis bending and compression flange not restrained against lateral bending (or inadequate lateral support) fail by lateral torsional buckling before attaining their bending strength.

2. The effect of lateral-torsional buckling need not be considered when
a) λ_LT ≤ 0.4
b) λ_LT ≥0.4
c) λ_LT > 0.8
d) λ_LT = 0.8
Answer: a
Clarification: The effect of lateral-torsional buckling need not be considered when λ_LT ≤ 0.4, where λ_LT is the non dimensional slenderness ratio for lateral torsional buckling.

3. The bending strength of laterally unsupported beams is given by
a) M_d = β_bZ_p /f_bd
b) M_d = β_b /Z_pf_bd
c) M_d = β_bZ_p
d) M_d = β_bZ_pf_bd
Answer: d
Clarification: The bending strength of laterally unsupported beams is given by M_d = β_bZ_pf_bd, where β_b is a constant, Z_p is plastic section modulus, f_bd is design bending compressive stress.

4. The value of β_b in the equation of design bending strength of laterally unsupported beams for plastic sections is
a) 0.5
b) 2.5
c) 1.0
d) 1.5
Answer: c
Clarification: The value of β_b in the equation of design bending strength of laterally unsupported beams for plastic and compact sections is 1.0. This constant depends on elastic and plastic section modulus for semi-compact sections.

5. The value of β_b in the equation of design bending strength of laterally unsupported beams for semi-compact sections is
a) Z_e/Z_p
b) Z_eZ_p
c) Z_p/Z_e
d) Z_p
Answer: a
Clarification: The value of β_b in the equation of design bending strength of laterally unsupported beams for semi-compact sections is Z_e/Z_p, where Z_e is elastic section modulus, Z_p is plastic section modulus.

6. The value of design bending compressive stress f_bd is
a) X_LT f_y
b) X_LT f_y /f_y
c) X_LT f_y f_y
d) X_LT /f_y
Answer: b
Clarification: The value of design bending compressive stress f_bd is X_LT f_y /f_y, where X_LT is bending stress reduction factor to account for lateral torsional buckling, f_y is yield stress, f_y is partial safety factor for material (=1.10).

7. The bending stress reduction factor to account for lateral buckling is given by
a) X_LT = 1/{φ_LT + (φ²_LT – λ²_LT)}
b) X_LT = 1/{φ_LT – (φ²_LT + λ²_LT)}
c) X_LT = 1/{φ_LT – (φ²_LT + λ²_LT)0.5}
d) X_LT = 1/{φ_LT + (φ²_LT – λ²_LT)0.5}
Answer: d
Clarification: The bending stress reduction factor to account for lateral buckling is given by X_LT = 1/{φ_LT + (φ²_LT – λ²_LT)0.5}, where φ_LT depends upon imperfection factor and non dimensional slenderness ratio, λ_LT is non dimensional slenderness ratio.

8. The value of φ_LT in bending stress reduction factor is given by
a) φ_LT = [ 1 – α_LT (λ_LT + 0.2) + λ²_LT].
b) φ_LT = [ 1 + α_LT (λ_LT – 0.2) + λ²_LT].
c) φ_LT = 0.5 [ 1 – α_LT (λ_LT + 0.2) + λ²_LT].
d) φ_LT = 0.5 [ 1 + α_LT (λ_LT – 0.2) + λ²_LT].
Answer: d
Clarification: The value of φ_LT in bending stress reduction factor is given by φ_LT = 0.5 [ 1 + α_LT (λ_LT – 0.2) + λ²_LT], where α_LT is imperfection factor, λ_LT is non dimensional slenderness ratio.