Effects of edge restraint on slab behavior

Abstract

This study was performed in conjunction with a Federal Emergency Management Agency program to plan, design, and construct keyworker blast shelters. The keyworker shelters are box-type structures in which damage is much more likely to occur in the roof slab than in the walls or floor. In this part of the program, the effect of edge restraint on slab behavior was investigated. The primary objective was to determine the effects of partial edge restraint on the strength, ductility, and failure mechanism of the slab. Sixteen one-way, reinforced concrete plate elements were tested in a specially designed reaction structure under uniform static water pressure. Facilities were designed and constructed to measure the slab end actions, including thrusts, moments, and rotations. The primary parameters which were investigated included the span-thickness ratio, reinforcement ratio, and degree of edge restraint. Most of the slabs were loaded until significant tensile membrane forces had been developed. Rotational restraint was found to have a significant influence on the overall behavior of the slabs. If a slab is to develop significant compressive membrane forces, both lateral and rotational restraint must be provided. Small rotational freedoms were found to have a relatively small effect on the compressive membrane response of the slabs. However, when large rotational freedoms were permitted, the slabs generally snapped through to the tensile membrane stage before significant thrusts were developed. Comparisons between the slabs with different thicknesses revealed that the thin slabs generally exhibited a much better tensile membrane response and were able to undergo larger deflections before collapse. Based on the results of this study, design recommendations were made for implementation in the keyworker blast shelter program. Also, an analytical procedure which considers nonlinear geometric behavior was proposed for investigating the total response of slabs.