Aspect ratio consideration in flat plate concrete slab deflection

Abstract EN

This paper addresses the effect of the aspect ratio (long span/short span), concrete strength grade and live load on the long-term deflection of uniformly loaded corner flat plate floor panels without edge beams.

It outlines in particular the effects of not considering the aspect ratio parameter in five national codes of practice provisions for the minimum slab thickness and tries to search for the “slab reference span” along which the calculated actual relative deflection and the maximum permissible deflection are determined.

The calculations of deflections have been done by the finite element SAFE software through a parametric study with variable long span length, aspect ratio, thickness as recommended by ACI 318-14, concrete grade and live load.

The results showed that, for the range of concrete grade and live load studied, the slab panel aspect ratio parameter has the largest effect on the long-term deflection; the parameter which is overlooked by all the five codes of practice.

In spite of this effect, the applicability of the ACI 318-14 provisions for thickness of flat plat floors without beams seemed to be adequate for the L/360 limit, L/240 limit for typical spans and concrete strength grade but showed to be inadequate in many cases to satisfy the L/480 limit.

Further, the results showed that the relative deflection along the long span could be recommended for deflection control in flat plate floors without edge beams.