FLEXURAL STRENGTH OF FLAT PLATE WITH OPENING UNDER COMBINED LINEAR AND UNIFORMLY DISTRIBUTED LOADS

Abstract

This paper presents an analytical study to predict the flexural strength of reinforced concrete flat plate with opening of any size. The study includes both plastic and elastic analysis of flat plate with opening. The plastic analysis is based on yield line theory using modified collapse mechanism as found experimentally by others ,whereas, the elastic analysis is carried out by finite element technique using computer program. The slab is considered to be under linear load around the opening edge besides the design loads ( uniformly distributed load). Comparisons between theoretical results obtained from the proposed equations derived in this study and those obtained from test results published by others is shown. The ratio of ultimate design load of flat slab with opening to its resisting moment along yield line is inversely proportional to the ratio of opening size to span length. The proposed equation shows that the theoretical collapse load is drastically reduced as the opening size increases. The reduction in flexural strength reaches to about 70% when the opening size increased to about 25% of slab area. A good agreement is found between the theoretical flexural strength proposed here and those observed by test results. The average ratio of theoretical strength to the test result was about 0.82. On the other hand, finite element results of cracking loads and elastic deflections have shown good agreement with those obtained from test results. The average ratio between them was about 0.8.