250+ TOP MCQs on Proportioning of Web & Flanges and Answers

Answer: b
Clarification: 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/t_w ≤ 250 εw for 0.74d ≤ c ≤ d and d/t_w ≤ 340 ε_w for c < 0.74d, where c is clear distance between stiffeners and d is depth of web, εw = √(250/f_yw), f_yw is yield stress of web.

5. When second longitudinal stiffener is provided, d/tw to meet serviceability criteria is
a) ≤ 400 ε_w
b) ≥ 400 ε_w
c) > 800 ε_w
d) ≤ 800 ε_w
Answer: a
Clarification: When second longitudinal stiffener is provided at neutral axis, d/t_w ≤ 400 εw to meet serviceability criteria, where d is depth of web, ε_w = √(250/f_yw), f_yw 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
Answer: c
Clarification: 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/t_w should be ___ to avoid buckling of compression flange into web when transverse stiffeners are not provided
a) ≥ 500 ε_f²
b) ≤ 345 ε_f²
c) ≥ 345 ε_f²
d) ≤ 500 ε_f²
Answer: b
Clarification: To avoid buckling of compression flange into web when transverse stiffeners are not provided, d/tw ≤ 345 ε_f², where d is depth of web, εf = √(250/f_yf), f_yf is yield stress of compression flange.

8. When only transverse stiffeners are provided and d/t_w < 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
Answer: d
Clarification: To avoid buckling of compression flange into web, d/t_w ≤ 345 ε_f² for c ≥ 1.5d, d/t_w < 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/f_yf), f_yf is yield stress of compression flange.

9. The optimum depth of web of plate girder is given by
a) (k/f_y)^0.33
b) (M_zk/f_y)
c) (M_zk/f_y)^0.33
d) (M_zk/f_y)²
Answer: c
Clarification: 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 (M_zk/f_y)0.33, M_z is moment resisted entirely by flanges, k = d/t_w, d is depth of web, t_w is thickness of web, f_y = design strength of flanges.

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