This set of Basic Design of Steel Structures Questions and Answers focuses 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

View Answer

Explanation: 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} ≥ L_{0} / 20

b) b_{o} ≤ L_{0} / 20

c) b_{o} > L_{0} / 20

d) b_{o} = L_{0} / 10

View Answer

Explanation: As per IS 800:2007, shear lag effects in flanges may be disregarded for outstand elements if b

_{o}≤ L

_{0}/ 20, where b

_{o}= width of flange outstand, L

_{0}= 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} ≤ L_{0} / 10

b) b_{i} ≤ L_{0} / 20

c) b_{i} > L_{0} / 10

d) b_{i} = L_{0} / 20

View Answer

Explanation: As per IS 800:2007, shear lag effects in flanges may be disregarded for internal elements if b

_{i}≤ L

_{0}/ 10, where b

_{i}= width of internal element, L

_{0}= 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

View Answer

Explanation: 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

View Answer

Explanation: 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})

View Answer

Explanation: 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)

View Answer

Explanation: 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}

View Answer

Explanation: 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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