# Design of Steel Structures Questions and Answers – Proportioning of Web & Flanges

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This set of Design of Steel Structures Multiple Choice Questions & Answers (MCQs) focuses on “Proportioning of Web & Flanges”.

1. The depth-to-thickness ratio of web connected to flanges along one longitudinal edge only when transverse stiffeners are not provided is _____ to meet serviceability criteria.
a) >180ε
b) ≥90ε
c) ≤90ε
d) >90ε

Explanation: When transverse stiffeners are not provided, the depth-to-thickness ratio of web connected to flanges along one longitudinal edge only is ≤ 90ε and when web connected to flanges along both longitudinal edges is ≤ 200ε to meet the serviceability criteria.

2. The depth-to-thickness ratio of web when only transverse stiffeners are provided and 3d ≥ c ≥d, where c is clear distance between stiffeners and d is depth of web is_____ to meet serviceability criteria
a) ≤ 200εw
b) ≥ 200 εw
c) > 200 εw
d) ≤ 400 εw

Explanation: For serviceability criteria, when only transverse stiffeners are provided, the depth-to-thickness ratio of web should be ≤ 200 εw, when 3d ≥ c ≥d and for c > 3d, the web is considered as unstiffened, where c is clear distance between stiffeners and d is depth of web, εw = √(250/fyw), fyw is yield stress of web.

3. The depth-to-thickness ratio of web when only transverse stiffeners are provided and c < 0.74d, where c is clear distance between stiffeners and d is depth of web is_____ to meet serviceability criteria
a) ≤ 200 εw
b) ≥ 270 εw
c) > 200 εw
d) ≤ 270 εw

Explanation: For serviceability criteria, when only transverse stiffeners are provided, the depth-to-thickness ratio of web should be ≤ 270 εw when c < 0.74d and c/tw ≤ 200 εw, when 0.74d ≤ c ≤d, where c is clear distance between stiffeners and d is depth of web, εw = √(250/fyw), fyw is yield stress of web.
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4. What is the range of c to meet serviceability criteria when transverse and longitudinal stiffeners are provided at one level only, at 0.2d from compression flange and c/tw ≤ 250 εw ?
a) c < 0.74d
b) 0.74d ≤ c ≤ d
c) c ≥ d
d) c > 2d

Explanation: For serviceability criteria, when transverse and longitudinal stiffeners are provided at one level only, at 0.2d from compression flange d/tw ≤ 250 εw for 2.4d ≥c ≥ d, c/tw ≤ 250 εw for 0.74d ≤ c ≤ d and d/tw ≤ 340 εw for c < 0.74d, where c is clear distance between stiffeners and d is depth of web, εw = √(250/fyw), fyw is yield stress of web.

5. When second longitudinal stiffener is provided, d/tw to meet serviceability criteria is
a) ≤ 400 εw
b) ≥ 400 εw
c) > 800 εw
d) ≤ 800 εw

Explanation: When second longitudinal stiffener is provided at neutral axis, d/tw ≤ 400 εw to meet serviceability criteria, where d is depth of web, εw = √(250/fyw), fyw is yield stress of web.

6. When a plate girder bends, vertical compression in web is due to
a) downward vertical component of compression flange bending stress only
b) downward vertical component of tension flange bending stress only
c) downward vertical component of compression flange and upward vertical component of tension flange bending stress
d) upward vertical component of compression flange and downward vertical component of tension flange bending stress

Explanation: When a plate girder bends, its curvature creates vertical compression in web is due to downward vertical component of compression flange and upward vertical component of tension flange bending stress. The web must have sufficient vertical buckling strength to withstand this squeezing effect.

7. The d/tw should be ___ to avoid buckling of compression flange into web when transverse stiffeners are not provided
a) ≥ 500 εf2
b) ≤ 345 εf2
c) ≥ 345 εf2
d) ≤ 500 εf2

Explanation: To avoid buckling of compression flange into web when transverse stiffeners are not provided, d/tw ≤ 345 εf2, where d is depth of web, εf = √(250/fyf), fyf is yield stress of compression flange.

8. When only transverse stiffeners are provided and d/tw < 345 εf to meet compression flange buckling criteria, the range of c should be
a) c ≥ 4.5d
b) c > 3d
c) c > 1.5d
d) c < 1.5d

Explanation: To avoid buckling of compression flange into web, d/tw ≤ 345 εf2 for c ≥ 1.5d, d/tw < 345 εf for c < 1.5d when only transverse stiffeners are provided, where c is clear distance between stiffeners, d is depth of web, εf = √(250/fyf), fyf is yield stress of compression flange.

9. The optimum depth of web of plate girder is given by
a) (k/fy)0.33
b) (Mzk/fy)
c) (Mzk/fy)0.33
d) (Mzk/fy)2

Explanation: The depth of plate girder for which area of steel used is minimum and will have minimum weight is called optimum depth. It is given by (Mzk/fy)0.33, Mz is moment resisted entirely by flanges, k = d/tw, d is depth of web, tw is thickness of web, fy = design strength of flanges.

10. The minimum area of flange angles with cover plate for riveted/ bolted plate girder should be
a) 1/6th of calculated flange area
b) 1/3rd of calculated flange area
c) 1/8th of calculated flange area
d) 1/4th of calculated flange area

Explanation: Flanges of riveted/ bolted plate girder consists of pair of angles with or without cover plates. The flange angles should form as large part of the area of the flange as practicable and preferably not less than 1/3rd of the calculated flange area to keep the centre of gravity of flange within back of angles and not in the flange cover plate else stability is affected.

11. Which of the following angle should be ideally used in bolted plate girder flange?
a) bulb angle
b) equal angle
c) unequal angle with short leg horizontal
d) unequal angle with long leg horizontal

Explanation: Unequal angles with long leg horizontal are preferred. It is because the moment of inertia of the section will be more and a large length will be available for making the connection with the flange plate.

12. For which of the following cases are equal angles preferred in bolted plate girder flange?
a) when large number of connectors are required to connect flange angle to web
b) when very few number of connectors are required to connect flange angle to web
c) for reducing cost
d) for aesthetic appearance

Explanation: When shear is heavy, large number of connectors are required to connect flange angle to web. In such case, equal angles may be preferred, if unequal angles are used, the longer leg msy be placed parallel to the web.

13. Flange cover plates are used in plate girder when
a) flange cover plates are not used
b) for aesthetic appearance
c) when moment resisting capacity has to be increased
d) when moment resisting capacity has to be decreased

Explanation: When moment resisting capacity of the plate girder has to be increased, flange cover plates are provided over flange angles. The moment of inertia and consequently the moment resisting capacity of the girder is increased considerably as the flange cover plates are at the greatest distance from neutral axis.

14. The thickness of flange cover plate should be ______ flange angle in bolted connections
a) less
b) more
c) twice
d) can be more or less

Explanation: The flange cover plates should not be thicker than the flange angles in riveted/bolted connections. Hence, more than one plate may be required. It is preferred that all cover plates should have same thickness. If they are of different thickness, then outer plates should not be thicker thin the inner plates.

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