# Design of Steel Structures Questions and Answers – Lacings

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

1. The radius of gyration of combined column about axis perpendicular to plane of lacing should be _____ than about axis parallel to plane of lacing.
a) cannot be compared
b) smaller
c) greater
d) equal to

Explanation: The radius of gyration of combined column about axis perpendicular to plane of lacing should be greater than about axis parallel to plane of lacing.

2. Which of the following is correct?
a) lacings and battens should not be provided on opposite sides of same member
b) lacing system should not be uniform throughout length of column
c) single and double laced systems should be provided on opposite sides of same member
d) single laced system on opposite of main component shall be in opposite direction view from either side

Explanation: Lacing system should be uniform throughout length of column. Single and double laced systems should not be provided on opposite sides of same member. Lacings and battens should not be provided on opposite sides of same member. Single laced system can be in same direction view from either side on opposite of main component so that one is shadow of other.

3. Lacing shall be designed to resist a total transverse shear equal to ____ of axial force in member
a) 5%
b) 1%
c) 4.3%
d) 2.5%

Explanation: Lacing can be designed to resist a total transverse shear at any point in the member equal to 2.5% of axial force in member. This shear shall be divided among lacing systems in parallel planes. Lacings should also be designed to resist any shear due to bending moment or lateral load on member.

4. Slenderness ratio of lacing is limited to
a) 200
b) 145
c) 500
d) 380

Explanation: Slenderness ratio is the ratio of effective length by radius of gyration. Slenderness ratio of lacing shall not exceed 145.

5. Which of the following is true about effective length?
a) effective length shall be taken as length between inner end bolts/rivets of bars for single lacings
b) effective length shall be taken as length between inner end bolts/rivets of bars for double lacings
c) for welded bars, effective length shall be taken as 0.9 times distance between inner end welds connecting single bars to members
d) effective length shall be taken as 1.5 times length between inner end bolts/rivets of bars for double lacings

Explanation: Effective length shall be taken as length between inner end bolts/rivets of bars for single lacings and 0.7 times length between inner end bolts/rivets of bars for double lacings. For welded bars, effective length shall be taken as 0.7 times distance between inner end welds connecting single bars to members.

6. Minimum width of lacing bars shall _______
a) be less than 3 times diameter of connecting bolt/rivet
b) be less than 5 times diameter of connecting bolt/rivet
c) not be less than 3 times diameter of connecting bolt/rivet
d) be less than 2 times diameter of connecting bolt/rivet

Explanation: Minimum width of lacing bars shall not be less than approximately 3 times the diameter of connecting bolt/rivet.

7. Thickness of lacing member should be
a) less than 1/40th of the effective length for single lacing
b) not less than 1/60th of the effective length for double lacing
c) less than 1/60thof the effective length for double lacing
d) less than 1/60th of the effective length for single lacing

Explanation: Thickness of lacing member should not be less than 1/40th of the effective length for single lacing and not less than 1/60th of the effective length for double lacing.

8. Which of the following condition should be satisfied for spacing of lacings?
a) maximum slenderness ratio of component of main members between two consecutive lacing connection should be greater than 50
b) maximum slenderness ratio of component of main members between two consecutive lacing connection should be not greater than 50
c) maximum slenderness ratio of component of main members between two consecutive lacing connection should be more than 0.7 x most unfavourable slenderness ratio of combined column
d) maximum slenderness ratio of component of main members between two consecutive lacing connection should not be more than 0.9 x most unfavourable slenderness ratio of combined column

Explanation: The spacing of lacing bars should be such that maximum slenderness ratio of component of main members between two consecutive lacing connection is not greater than 50. It should not be greater than 0.7 times most unfavourable slenderness ratio of combined column.

9. Which of the following is not true?
a) when welded lacing bars overlap main members, amount of lap should not be less than 4 times thickness of bar
b) welding is to be provided along each side of bar for full length of lap
c) lacing bars fitted between main members should be connected by fillet welds on each side
d) when lacing bars are not lapped to form connection to components of members, appreciable interruption in triangulated system is allowed

Explanation: When welded lacing bars overlap main members, amount of lap should not be less than 4 times thickness of bar. Welding is to be provided along each side of bar for full length of lap. Lacing bars fitted between main members should be connected by full penetration butt weld or fillet welds on each side. Lacing bars shall be connected such that there is no appreciable interruption in triangulated system when lacing bars are not lapped to form connection to components of members.

10. lacing bars shall be inclined at an angle of ___ to axis of built up member.
a) 20o
b) 35o
c) 50o
d) 90o

Explanation: Lacing bars shall be inclined at an angle of 40o to 70o to axis of built up member.

11. Effective slenderness ratio of laced column shall be _________
a) equal to the maximum slenderness ratio of column
b) 1.05 times the maximum slenderness ratio of column
c) 0.5 times the maximum slenderness ratio of column
d) 2 times the maximum slenderness ratio of column

Explanation: Effective slenderness ratio of laced column shall be taken as 5% more than the maximum slenderness ratio of column i.e. 1.05 times the maximum slenderness ratio of column, to account for shear deformation effects.

12. Compressive strength in lacing bars in single lacing system is equal to
a) Vt /(N secΘ)
b) Vt /(N cosecΘ)
c) Vt N cosecΘ
d) (Vt /N) cosecΘ

Explanation: Compressive strength in lacing bars is equal to (Vt /N) cosecΘ for single lacing system and (Vt/2N) cosecΘ for double lacing system, where N = number of shear resisting elements.

13. Minimum radius of gyration for lacing flats is
a) t/√12
b) t/12
c) t/√24
d) t/24

Explanation: Minimum radius of gyration for lacing flats is t/√12 , where t is thickness of flat.

14. The load on rivet/bolt when two lacing flats are connected at same point is
a) (Vt / N) cotΘ
b) 2(Vt / N) cotΘ
c) 2Vt N cotΘ
d) Vt NcotΘ

Explanation: Strength of bolt /rivet should be greater than load coming over rivet/bolt. The load on rivet/bolt when two lacing flats are connected at same point is 2(Vt/N)cotΘ.

15. The load on rivet/bolt when two lacing flats are connected at different point is
a) (Vt / N) cotΘ
b) 2(Vt / N) cotΘ
c) 2Vt N cotΘ
d) Vt NcotΘ

Explanation: Strength of bolt /rivet should be greater than load coming over rivet/bolt. The load on rivet/bolt when two lacing flats are connected at different point is (Vt/ N) cotΘ.

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