Solution:

• Structure may be subjected to the different combinations of loads.
• These loads in combinations do not act for long period.
• Most of the national codes allow some increase in permissible stresses.
• Increase in permissible stresses as per IS : 800 is taken as follows:

1. When the effect of wind or seismic load is taken in to account, the permissible stress in steel are increased by 33? percent.
2. For rivets, bolts and tension rods, the permissible stresses are increased by 25 per cent, when the effect of wind or seismic load is taken in to account.

The increased values of permissible stress must not exceed yield stress of the material.

• Hence option B is the correct answer.