Investigation of Reinforced Concrete Beams Serviceability Using Finite Element Analysis

Abstract

Building structures designed by limit state approach may have adequate strength but, they exhibit excessive deflection and excessive crack widths. This study focuses on serviceability of reinforced concrete beams using finite element approach. The effects of span to depth ratio, comparison of computed deflection with allowable limits, reinforcement ratio, steel grade and concrete grade computed based on various design standards is studied. The design standards include, EBCS-2 (1995), ACI 318 (2002), EC2 (2004) and BS 8110 (1997). The analytical computations were performed with the commercial general finite element method Abaqus software which incorporates linear and nonlinear behavior of reinforced concrete beams. Hand calculations are performed with regard to design codes. The accuracy of the model is verified with laboratory results which are taken as secondary data. In the finite element model three sample beams were modeled by using concrete damage plasticity at mesh sizes of 50mm to obtain load deflection curves. The results of mid span deflections of the three beams were calculated by the above code standards, and using finite element software Abaqus. The results of finite element method were more accurate than manual computation of the different codes. From three samples of beams in sample one the result of ACI code is closer to the finite element result for long term deflection and for short-term deflection. The result of EBCS codes, long term-deflection had larger values due to the deflection factor included in the formula. In the cases of sample two the concrete grade, the steel grades and young‟s modulus of the beam were changed, and the results of manual computation for long term deflection for EC-2 was obtained as near to that of the Finite element result. But for short-term deflection EBCS-21995 result was obtained to be better than the others. In sample three model, reinforced concrete grade as per Ethiopian most applicable material properties have been used and the results were compared with that of the finite element method, and the results were obtained with better values of deflection for the Finite element approach. service loads increase more than cracking loads, the crack width becomes wider and number of cracks becomes larger. The crack widths of RC beam are calculated by four codes. EBCS2,1995 and EC-2 code crack widths results are smaller than another two of codes.