Design of Steel Structures Multiple Choice Questions on “Factors affecting Lateral Stability”.
1. Which of the following does not affect lateral stability?
a) cross sectional shape
b) support conditions
c) type of loading
d) height of building
Answer: d
Clarification: The factors affecting lateral stability are cross sectional shape, support conditions, effective length, level of application of transverse loads.
2. Which of the following statement is correct?
a) I-section has high torsional stiffness
b) Closed section has high torsional stiffness
c) Closed section has less stiffness
d) Hollow circular tube has more efficiency as flexural member
Answer: b
Clarification: I-section with the larger in-plane bending stiffness does not have matching stability. in contrast, closed sections such as tubes, boxes and solid shafts have high torsional stiffness, often high as 100 times that of an open section.
3. Which of the following statement is not correct?
a) Hollow circular tube has more efficiency as flexural member
b) Hollow circular tube has lesser efficiency as flexural member
c) It is the most efficient shape for torsional resistance
d) It us rarely used as a beam element
Answer: a
Clarification: Hollow circular tube is the most efficient shape for torsional resistance, but is rarely employed as beam element because of difficulties encountered in connecting it to other members and lesser efficiency as a flexural member.
4. Open cross sections have major part of material distributed
a) is not distributed
b) on the centroid
c) towards centroid
d) away from centroid
Answer: d
Clarification: In open cross sections ( I and channel sections), major part of material is distributed at the flanges, i.e. away from their centroids, to improve their resistance to in-plane bending stresses.
5. The effective length factor is _____ for beams flanges fully restrained
a) 1
b) 0.5
c) 0.75
d) 1.5
Answer: b
Clarification: The effective length factor K is 0.5 theoretically for flanges fully restrained. But for design purpose, it may be taken as 0.7.
6. The effective length of compression flange of simply supported beam not restrained against torsion at ends is
a) 1.2 L
b) 1.0 L
c) 0.8 L
d) 0.5 L
Answer: a
Clarification: The effective length of compression flange of simply supported beam not restrained against torsion at ends is 1.2 L, where L is span length.
7. Effective length of compression flanges at the ends unrestrained against lateral buckling is
a) 1.5 L
b) 0.85 L
c) 0.5 L
d) L
Answer: d
Clarification: Effective length of compression flanges at the ends unrestrained against lateral buckling (i.e. free to rotate in plan) is L, where L is length of span.
8. Effective length of compression flanges at the ends partially restrained against lateral buckling is
a) 1.75 L
b) 1.0 L
c) 0.85 L
d) 0.5 L
Answer: c
Clarification: Effective length of compression flanges at the ends partially restrained against lateral buckling (i.e. free to rotate in plane in the bearings) is 0.85 L, where L is length of span.
9. Restraint against torsion can be provided by
(i) web cleats, (ii) bearing stiffeners acting together with bearing of beam, (iii)lateral end frames to ends of compression flanges
a) i only
b) i and ii
c) ii and iii
d) i, ii and iii
Answer: d
Clarification: Restraint against torsion can be provided by (i) web or flange cleats, (ii) bearing stiffeners acting together with the bearing of beam, (iii) lateral end frames or external supports to ends of compression flanges, (iv)the beam built into the supporting walls.
10. The most severe loading condition for cantilever is
a) point load acting at centre
b) point load acting at tip
c) point load acting between centre and fixed end
d) point load acting at L/4 distance
Answer: b
Clarification: For cantilevers, the most severe loading condition is point load acting at the tip because the tip is unsupported.
11. Provision of intermediate lateral supports ______ lateral stability of beam
a) increases
b) decreases
c) does not change
d) cannot say
Answer: a
Clarification: Provision of intermediate lateral supports increases the lateral stability of beam. For bracings to be effective, the braces should be prevented from moving in axial direction.
12. The requirement of effective bracing is
a) it should not have sufficient strength not to withstand forces transferred to it by beam
b) it should not have sufficient strength to withstand forces transferred to it by beam
c) it should have sufficient stiffness so that buckling of beam occurs in between braces
d) it should not have sufficient stiffness so that buckling of beam occurs in between braces
Answer: c
Clarification: The requirements of effective bracing are (i) it should have sufficient strength to withstand forces transferred to it by beam, (ii) it should have sufficient stiffness so that buckling of beam occurs in between braces.
13. Which of the following is correct?
a) torsional bracing attached near bottom flange should bend in single curvature
b) torsional bracing attached near bottom flange should not bend in single curvature
c) its flexural stiffness should be 4EIb/S
d) its flexural stiffness should be 6EIb/S
Answer: a
Clarification: Torsional bracing attached near bottom flange should bend in single curvature and its flexural stiffness should be 2EI/S, where Ib is moment of inertia of brace, S is spacing between girders.
14. The lateral stability of tranversely loaded beam is dependent on
a) arrangement of load only
b) level of application of load only
c) both arrangement and level of application of load
d) is not dependent on any of these
Answer: c
Clarification: The lateral stability of tranversely loaded beam is dependent on the arrangement of load as well as level of application of loads with respect to centroid of cross section.