Leaderboard

Uplift will reverse moment diagram.

Top reinforcement is needed in isolated footing majorly for two reasons. 1) Due to negative pressure under some or whole part of footing. In part of footing where there is positive pressure, the footing is in complete contact with soil and tension is in bottom side of footing. But in part of footing where there is negative pressure the footing is no more in contact with ground. Either it is designed as it is (and reduced contact area is used for calculations) or it is made to become in contact with ground by help of over burden loads. In either case, the bending of footing is in such a way which causes tension of footing at top of foundation demanding top reinforcement in footing. Mostly top reinforcement is less than bottom reinforcement but for simplicity, if it is not affecting economy much same reinforcement can also be used for top and bottom. 2) Due to temperature and shrinkage control. Code says we can provide temperature based minimum steel either in one layer at center or at any face or we can divide total steel in two layers i.e. half at top face and half at bottom. According to Zahid Ahmad Siddique (Professor at UET Lahore) in his book concrete structures mentions it is better to provide temperature steel in two layers if thickness of footing increases 18 inch.

Top reinforcement might be required in isolated column footings in following circumstances: a. When the foundation is in tension b. To counter shrinkage cracks Regards.

Fatima, You can use a smaller slab thickness and do a deflection check to make sure stairs deflection it is below the maximum allowable. Service Live Load deflection based on Canadian Code should be less than L/360. I don't remember what ACI said, you can look it up. It should be similar. Other ways to reduce thickness would be to run a beam at the centre of stairs flight. For a stair run like shown above, such a beam would be hidden. Let us know how it goes. Thanks.