250+ TOP MCQs on Design Strength of Laterally Supported Beams – III and Answers

Basic Design of Steel Structures Questions and Answers on “Design Strength of Laterally Supported Beams – III”.

1. What is shear lag effect?
a) the phenomenon of non uniform bending stress not due to influence of shear strain induced on bending stresses in flanges
b) the phenomenon of uniform bending stress not due to influence of shear strain induced on bending stresses in flanges
c) the phenomenon of uniform bending stress due to influence of shear strain induced on bending stresses in flanges
d) the phenomenon of non uniform bending stress due to influence of shear strain induced on bending stresses in flanges
Answer: d
Clarification: The shear strain induced influences bending stresses in flanges and causes sections to warp. This consequently modifies the bending stresses determined by simple bending theory and results in higher stresses near junction of web to flange elements with stress dropping as distance from beam web increases. The resultant stress distribution across flange is therefore non uniform and this phenomenon is known as shear lag.

2. As per IS 800:2007, shear lag effects in flanges may be disregarded for outstand elements if
a) b_o ≥ L₀ / 20
b) b_o ≤ L₀ / 20
c) b_o > L₀ / 20
d) b_o = L₀ / 10
Answer: b
Clarification: As per IS 800:2007, shear lag effects in flanges may be disregarded for outstand elements if b_o ≤ L₀ / 20, where b_o = width of flange outstand, L₀ = length between points of zero moment in the span.

3. As per IS 800:2007, shear lag effects in flanges may be disregarded for internal elements if
a) b_i ≤ L₀ / 10
b) b_i ≤ L₀ / 20
c) b_i > L₀ / 10
d) b_i = L₀ / 20
Answer: a
Clarification: As per IS 800:2007, shear lag effects in flanges may be disregarded for internal elements if b_i ≤ L₀ / 10, where b_i = width of internal element, L₀ = length between points of zero moment in the span.

4. Shear lag effect depends on
a) material of beam
b) width of beam only
c) width-to-span ratio
d) cost
Answer: c
Clarification: Shear lag effect depends upon width-to-span ratio, beam end restraints, and type of load.

5. Which of the following is true?
a) point load causes less shear lag than uniform load
b) point load causes more shear lag than uniform load
c) point load causes half times the shear lag than uniform load
d) point load causes equal shear lag as uniform load
Answer: b
Clarification: The resultant stress distribution across flanges is non-uniform and is called shear lag. Point load causes more shear lag than uniform load.

6. The moment capacity of plastic section for V > 0.6V_d is given by
a) M_dv = M_d – β(M_d – M_fd)
b) M_dv = M_d + β(M_d – M_fd)
c) M_dv = M_d – β(M_d + M_fd)
d) M_dv = M_d + β(M_d + M_fd)
Answer: a
Clarification: The moment capacity of plastic or compact section for V > 0.6V_d is given by M_dv = M_d – β(M_d – M_fd), where M_d = plastic design moment of whole section disregarding high shear force effect but considering web buckling effect, M_fd = plastic design strength of area of cross section excluding shear area, considering partial safety factor γ_m0, β is constant.

7. The value of β in equation of moment capacity of plastic section for V > 0.6V_d is given by
a) ([V_d/V] -1)²
b) (2[V_d/V] +1)²
c) (2[V_d/V] -1)²
d) (2[V_d/V] -1)
Answer: c
Clarification: The value of β in equation of moment capacity of plastic section for V > 0.6V_d is given by β = (2[V_d/V] -1)², where V_d = design shear strength as governed by web yielding or web buckling, V = factored applied shear force.

8. The check for moment capacity of plastic section for V > 0.6V_d is given by
a) M_dv ≥ 1.2Zef_y/γ_m0
b) M_dv ≤ 1.2Zef_y/γ_m0
c) M_dv > 1.2Zef_y/γ_m0
d) M_dv = 2.2Zef_y/γ_m0
Answer: b
Clarification: The check for moment capacity of plastic section for V > 0.6V_d is given by M_dv ≤ 1.2Zef_y/γ_m0, where Z_e = elastic section modulus of whole section, f_y = yield stress of material, γ_m0 = partial safety factor.

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