This set of Design of Steel Structures Multiple Choice Questions & Answers (MCQs) focuses on “Stiffeners”.
1. The function of bearing stiffener is to
a) improve buckling strength of web
b) preclude any crushing of web
c) restrain against torsional effects
d) increase buckling resistance of web
Explanation: The function of bearing stiffener is to preclude any crushing of web at locations of heavy concentrated loads. Thus, they transfer heavy reactions or concentrated loads to the full depth of web. They are placed in pairs on the web of plate girders at unframed girder ends and where required for concentrated loads.
2. Match the following
Stiffeners Function A) Load carrying stiffener (i) increases buckling resistance of web B) Torsional stiffener (ii) local strengthening of web C) Diagonal stiffener (iii) prevent local buckling of web D) Tension stiffener (iv) restrain against torsional effects E) Longitudinal stiffener (v) transmit tensile forces
a) A-i, B-ii, C-iii, D-iv, E-v
b) A-v, B-iv, C-iii, D-ii, E-i
c) A-iv, B-v, C-i, D-ii, E-iii
d) A-iii, B-iv, C-ii, D-v, E-i
Explanation: Load carrying stiffener prevents local buckling of web due to any concentrated load. Torsional stiffener are provided at supports to restrain girders against torsional effects. Local strengthening of web under the combination of shear and bending is provided by diagonal stiffeners. The tensile forces from the flange are transmitted to the web through the tension stiffener. A longitudinal stiffener increases the buckling resistance of web.
3. The outstand of stiffener from face of web is restricted to
Explanation: Unless the outer edge is continuously stiffened, the outstand of stiffener from face of web should not exceed 20tqε,where tq is thickness of stiffener. When the outstands of web is between 14tqε and 20tqε, then the stiffener design should be on the basis of a core section with an outstand of 14tqε.
4. What is the stiff bearing length?
a) length which cannot deform appreciably in bending
b) length which deform appreciably in bending
c) length of outer end of flange
d) length of web
Explanation: The stiff bearing length of any element b1 is that length which cannot deform appreciably in bending. To determine b1, the dispersion of load through a steel bearing element should be taken as 45˚ through solid material, such as bearing plates, flange plates, etc.
5. The effective length of web on each side of centreline of stiffeners for interior stiffeners is limited to
a) 10 tw
b) 50 tw
c) 40 tw
d) 15 tw
Explanation: The effective length of web on each side of centreline of stiffeners is limited to 20 times the web thickness, i.e. 40tw for interior stiffeners and 20tw for end stiffeners . The effective section is the full area or core area of stiffener together with effective length of web on each side of centreline of stiffeners.
6. The effective length of intermediate transverse stiffener is taken as
a) 2 times the length of stiffener
b) 0.7 times the length of stiffener
c) 1.4 times the length of stiffener
d) 0.5 times the length of stiffener
Explanation: The effective length of intermediate transverse stiffener is taken as 0.7 times the length of stiffener. The intermediate transverse stiffener is provided mainly to improve shear buckling resistance of the web.
7. The second moment of area of transverse web stiffeners not subjected to external loads or moments is given by
a) Is ≤ 0.75dtw2
b) Is ≥ 0.75dtw2
c) Is ≤ 1.5dtw2
d) Is ≥ 12.5dtw
Explanation: Transverse stiffeners not subjected to external loads or moments should have second moment of area Is about centreline of the web, if stiffeners are on both sides of the web and about face of the web, if stiffener is on only one side of the web such that Is ≥ 0.75dtw2 for c/d ≥ √2 and Is ≥ 1.5dtw2/c2 for c/d < √2.
8. Which of the following buckling check is applied to stiffeners?
a) [(V+Vc)/γm0] ≤ Fqd
b) [(V+Vc)γm0] ≥ Fqd
c) [(V-Vc)/γm0] ≤ Fqd
d) [(V-Vc)γm0] ≥ Fqd
Explanation: Stiffeners not subjected to external loads or moments should be checked for buckling for a force Fd = [(V-Vc)/γm0] ≤ Fqd, where Fqd is design resistance of intermediate stiffeners, V is factored shear force adjacent to the stiffener, Vcr is shear buckling resistance of the web panel designed without using tension field action. This check is required for intermediate stiffeners only when tension field action is utilized in webs.
9. The interaction expression for stiffeners subjected to external loads or moments is given by
a) [(Fq-Fs)/Fqd]+(Fs/Fsd)+(Mq/Myq) < 1
b) [(Fq-Fs)/Fqd]+(Fs/Fsd)+(Mq/Myq) > 1
c) [(Fq-Fs)/Fqd]-(Fs/Fsd)-(Mq/Myq) < 1
d) [(Fq+Fs)/Fqd]-(Fs/Fsd)-(Mq/Myq) > 1
Explanation: Stiffeners subjected to external loads and moments should meet the conditions of load carrying stiffeners. In addition, they should satisfy the following interaction equation: [(Fq-Fs)/Fqd]+(Fs/Fsd)+(Mq/Myq) < 1, where Fq is stiffener force, Fqd is design resistance of intermediate stiffeners corresponding to buckling about axis parallel to the web, Fs is external load or reaction at stiffener, Fsd is design resistance of load carrying stiffener corresponding to buckling about axis parallel to the web, Md is moment on the stiffener due to eccentrically applied load and transverse load, Myq is yield moment capacity of stiffener based on its elastic modulus about its centroidal axis parallel to the web.
10. Which of the following is not true regarding longitudinal stiffeners?
a) longitudinal stiffeners increase buckling resistance considerably as compared to transverse stiffeners
b) they consist of plane section for welded plate girder
c) first horizontal stiffener is provide at one-fifth of distance from compression flange
d) first horizontal stiffener is provide at neutral axis
Explanation: Longitudinal stiffeners are also called horizontal stiffeners. They increase buckling resistance considerably as compared to transverse stiffeners when the web is subjected to buckling. They consist of angle section for riveted/bolted plate girder and plane section for welded plate girder and are provided in the compression zone of the web. The first horizontal stiffener is provide at one-fifth of distance from compression flange to tension flange. If required another stiffener is provided at the neutral axis.
11. The connection of intermediate transverse stiffeners are designed for shear of
Explanation: Intermediate transverse stiffeners not subjected to external loading should be connected to the web so as to withstand a shear between each component of the stiffener and the web not less than tw2/5bs, where tw is thickness of web, bs is outstand width of stiffener.
12. The second moment of area of torsional stiffeners about center line of the web is given as
a) Is ≤ αssD3
b) Is ≤ 0.34αsD3Tcf
c) Is ≥ 0.34αsD3Tcf
d) Is ≥ αsD3
Explanation: When bearing stiffeners are required to provide torsional restraint at the support of the beams, the second moment of area of the stiffener section about center line of the web should be such that Is ≥ 0.34αsD3Tcf , where αs = 0.006 for LLT/ry ≤50, 0.3/( LLT/ry) for 50< LLT/ry≤100, 30/( LLT/ry)2 for LLT/ry ≥100, D = overall depth of beam at the support, Tcf = maximum thickness of compression flange in the span under consideration, KL = laterally unsupported effective length of compression flange of beam, ry = radius of gyration of the beam about minor axis.
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