Important Question And Answer: Civil - Limit State Design For Flexure

1. Explain the check for deflection control in the design of slabs?

The deflection of a structure or part thereof shall not adversely affect the appearance or efficiency of the structure or finishes or partitions. The deflection shall generally be limited to the following:

a)     The final deflection due to all loads including the effects of temperature, creep and shrinkage and measured from the as-cast level of the , supports of floors, roofs and all other horizontal members, should not normally exceed span/250.

b)    The deflection including the effects of temperature, creep and shrinkage occurring after erection of partitions and the application of finishes should not normally exceed span/350 or 20 mm whichever is less.

2.     When do you do for doubly reinforced beams?

The section reinforced in both tension and compression zone is known as doubly reinforced section. The doubly reinforced beams are adopt when the balanced moment is smaller than the Actual moment.

3.     What type of slabs are usually used in practice, under reinforced or over reinforced?

The depth of slab chosen from deflection requirements will be usually greater than the depth required for balanced design. Hence the area of steel required will be less than the balanced amount. So, the slab is designed as under reinforced section.

4.     Why is necessary to provide transverse reinforcement in one way slab?

Since the one way slab bends in one direction and also in shorter direction, so it is necessary to provide transvers reinforcement in one way slabs. These slabs

adopted when availability of two supports in one direction.

5.     Distinguish between under reinforced and over reinforced sections.

A beam reaches its permissible stress in steel under the working moment before concrete reaches its stress is called as Under reinforced section.

A beam reaches its permissible stress in concrete under the working moment before steel reaches its stress is called as Over reinforced section.

6.Sketch the edge and middle strips of a two way slab.