Simplified calculation of short-term deflection in prestressed two-way flat slabs

While the deflection control of reinforced concrete two-way slabs is generally achieved by satisfying code-specified minimum thickness, the ACI Building Code requires the immediate short-term deflection of prestressed concrete slabs to be computed by usual methods or formulas for elastic deflections and compared with the allowable values given in the Code. The calculation of deflections for two-way slabs, however is complicated even if elastic behavior can be assumed. In this paper simplified expressions for computing the short term elastic deflection of prestressed two-way flat slabs are proposed, they are based on results from extensive finite element analyses and are applicable to the computation of live load deflections. The proposed equations account for two-way action, support conditions, panel aspect ratio, and loading patterns. Predicted maximum deflections using the proposed equations are compared with results obtained from more exact but less analytically involved procedures proposed by other researchers and by ACI Committee 435. It is found that the proposed equations have the advantage of being relatively simple while significantly reducing computational effort in comparison with other procedures. Furthermore, the predicted results are sufficiently accurate and on the conservative side