Correct Answer - Option 4 : 40°
For the design of laced columns:
I) The sections to be laced are so spaced that the radius of gyration of the section about the axis perpendicular to the plane of lacing is not less than the radius of gyration about the axis in the plane of lacing.
II) The effective slenderness ratio should be taken as 1.05 times the actual maximum slenderness ratio, in order to account for shear deformation effect.
III) Angle of inclination of lacing bar should be kept between 40° - 70°. Lacing is most efficient between 35° to 45°, but angle less than 40° would result in a higher length of lacing bar which may then to buckle individually.
IV) The maximum spacing of the lacing bar should be such that the minimum slenderness ratio of the component member should not be greater than 50 or 0.7 times the slenderness ratio of the member.
V) The lacing for compression members should be proportioned to resist transverse shear equal to 2.5% of the axial force in the column.
VI) The minimum flat width should not be less than three times the nominal diameter of the end connector.
VII) The thickness of the lacing flat for single lacing system should be less than 1/40 of its effective length and for double lacing system it should be less than 1/60 of its effective length.
VIII) The slenderness ratio of the lacing bar should be less than 145.
X) The effective length of lacing bar is the length between the inner end rivets/bolts for a single lacing system and 0.7 times this distance for a double lacing system.