# Design of Steel Structures Questions and Answers – Modes of Failure, Slenderness Ratio and displacement

This set of Design of Steel Structures Interview Questions and Answers for Experienced people focuses on “Modes of Failure, Slenderness Ratio and displacement”.

1. What is slenderness ratio of a tension member?
a) ratio of its least radius of gyration to its unsupported length
b) ratio of its unsupported length to its least radius of gyration
c) ratio of its maximum radius of gyration to its unsupported length
d) ratio of its unsupported length to its maximum radius of gyration

Explanation: Slenderness ratio of tension member is ratio of its unsupported length to its least radius of gyration. This limiting slenderness ratio is required in order to prevent undesirable lateral movement or excessive vibration.

2. What is the maximum effective slenderness ratio for a tension member in which stress reversal occurs?
a) 180
b) 200
c) 280
d) 300

Explanation: The maximum effective slenderness ratio for a tension member in which stress reversal occurs due to loads other than wind or seismic forces is 180.

3. What is the maximum effective slenderness ratio for a member subjected to compressive forces resulting only from combination of wind/earthquake actions?
a) 180
b) 200
c) 340
d) 250

Explanation: The maximum effective slenderness ratio for a member subjected to compressive forces resulting only from combination of wind or earthquake actions, such that the deformation of such member does not adversely affect stresses in any part of structure is 250.

4. What is the maximum effective slenderness ratio for a member normally acting as a tie in roof truss or a bracing member?
a) 180
b) 200
c) 350
d) 400

Explanation: The maximum effective slenderness ratio for a member normally acting as a tie in roof truss or a bracing member, which is not considered when subject to stress reversal resulting from action of wind or earthquake forces is 350.

5. What is the maximum effective slenderness ratio for members always in tension?
a) 400
b) 200
c) 350
d) 150

Explanation: The maximum effective slenderness ratio for members always in tension other than pre-tensioned members is 400.
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6. The limits specified for slenderness ratio are not
a) applicable to cables
b) applicable to angle sections
c) applicable to built-up sections
d) applicable to circular sections

Explanation: The limits specified for slenderness ratio in the IS code are not applicable to cables. They are applicable to angle sections, built-up sections, circular sections.

7. The displacement of tension member under service load is given by
a) PLEAg
b) PLE/Ag
c) PL/EAg
d) P/LEAg

Explanation: The displacement, that is increase in length of tension member, under service load is given by Δ = PL/EAg, where Δ = Elongation of member in mm, P= unfactored axial load in N, L = length of member in mm, E = elastic modulus = 2×105MPa, Ag = gross cross sectional area of member in mm2.

8. What is gross section yielding?
a) considerable deformation of the member in longitudinal direction may take place before it fractures, making the structure unserviceable
b) considerable deformation of the member in longitudinal direction may take place before it fractures, making the structure serviceable
c) considerable deformation of the member in lateral direction may take place before it fractures, making the structure unserviceable
d) considerable deformation of the member in lateral direction may take place before it fractures, making the structure serviceable

Explanation: Tension member without bolt holes can resist loads up to ultimate load without failure. But such a member will deform in longitudinal direction considerably(10-15% of its original length)before fracture and the structure becomes unserviceable.

9. What is net section rupture failure?
a) rupture of member when the cross section reaches yield stress
b) rupture of member when the cross section reaches ultimate stress
c) rupture of member when the cross section reaches less value than yield stress
d) rupture of member when the cross section is reaches very less value than ultimate stress

Explanation: The point adjacent to hole reaches yield stress first when tension member with hole is loaded statically. The stress at that point remains constant and each fibre away from hole progressively reaches yield stress on further loading. With increasing load, deformations continue until finally rupture of member occurs when entire net cross section of member reaches ultimate stress.

10. The tensile stress adjacent to hole will be ____________
a) about five times the average stress on the net area
b) about half the average stress on the net area
c) equal to average stress on the net area
d) about two to three times the average stress on the net area

Explanation: From the theory of elasticity, the tensile stress adjacent to hole will be about two to three times the average stress on the net area, depending upon the ratio of diameter of hole to the width of plate normal to direction of stress.

11. What is stress concentration factor?
a) ratio of average stress to maximum elastic stress
b) product of average stress and maximum elastic stress
c) ratio of maximum elastic stress to average stress
d) twice the average stress

Explanation: The ratio of maximum elastic stress to average stress (fmax/favg)is called as stress concentration factor. It becomes very significant when repeated applications of load may lead to fatigue failure or where there is possibility of brittle fracture of tension member under dynamic load. It may minimised by providing suitable joint and member details.

12. What is block shear failure?
a) failure of fasteners occurs along path involving tension on one plane and shear on perpendicular plane along fasteners
b) failure of member occurs along path involving tension on one plane and shear on perpendicular plane along fasteners
c) failure of member occurs along path involving tension on one plane and shear on parallel plane along fasteners
d) failure of fasteners occurs along path involving tension on one plane and shear on parallel plane along fasteners

Explanation: Failure of member occurs along path that involves (i) tension on one plane and (ii) shear on perpendicular plane along fasteners in block shear failure mode.

13. The possibility of block shear failure increases by
a) larger connection length
b) increasing the number of bolts per connection
c) with use of low strength bolts
d) with use of high bearing strength material

Explanation: The block shear failure becomes a possible mode of failure when material bearing strength and bolt shear strength are higher. When high bearing strength of material and high strength bolts are used, only few bolts are required in connection. Decreasing number of bolts per connection results in smaller connection length, but the possibility of block shear failure increases.

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