Load distribution between precast hollow core concrete slabs : an analytical approach

Abstract

The precast prestressed hollow core concrete slab system is a fairly recent construction member. The 7-wire strand, precasting, long-line beds and other innovations related to the production of hollow core concrete slabs were brought into focus in the U.S.A. only in the post-war period. Hollow-core slabs are most widely known for providing economical, efficient floor and roof systems. Structurally, a hollow core slab provides the efficiency of a prestressed member for load capacity, span range, and deflection control. The loads which can be supported by such members are thus much higher than those carried by normal in-situ concrete slabs. In local construction, one comes across a number of cases where the lower floor slab supports load bearing walls. Using in-situ concrete, the loads were usually supported by a network of beams placed beneath the load bearing walls. With the advent of the higher load support offered by prestressed hollow core slabs, the load bearing walls are usually directly supported by the hollow core slabs. As can be expected such recently used members bring with them the problem of relative lack of information. Precast prestressed hollow core floor units are designed and manufactured to carry uniformly distributed loads. This type of uniform load distribution is seldom encountered in practice. The problem of non-uniformly distributed loads has already been identified, and research and recommendations into the support of concentrated loads on hollow core slabs are being developed. With masonry load bearing walls, load transmission is not clearly identifiable. What may start as a concentrated load on top of a masonry block wall may be spread into a more dispersed line load. The inverse may also happen. Thus when considering the local context, it is not necessarily sufficient to treat the loads imposed by the walls as a series of line loads. Thus prior to analysing the load distribution pattern, it is first necessary to establish the load patterns actually being applied onto the slabs. It is possible to analyse the loads thus applied by using the more rigorous analytical methods. However such methods are complex and time consuming and thus impractical for normal design work. The aim of this dissertation is to use one such analytical method in order to move towards establishing a simpler method of analysis which can be applied to this increasingly common problem.