Nonlinear numerical model for analyzing reinforced concrete structures

Abstract

Reinforced concrete (RC) structures are commonly used and are designed to satisfy criteria of serviceability and safety. To ensure the serviceability it is necessary to predict the cracking and the deflections of RC members under loads and accurate estimation of the collapse load is essential to provide margin of safety. The behavior of RC members is complex due to its constituent materials which led engineers in the past to rely heavily on empirical formulas, for the design of concrete structures, derived from numerous experiments: The advent of digital computers and powerful methods of analysis obviate the need for experiments recognizing that tests are time consuming and costly. Hence, the development of a nonlinear numerical model is necessary for the analysis ofRC beams, columns, and frames up to collapse load. The objective of this study was to develop reliable and computationally efficient finite element model for the analysis of RC members. The stress-strain behavior of the reinforcing steel is assumed bilinear which can model elastic perfectly plastic and elastic with strain hardening. The stress-strain behavior of concrete is considered to be parabolic. The constituents of a RC section such as concrete and reinforcing steel are represented by separate material models, which are combined together with the model of the interaction between concrete and reinforcing steel considering perfect bond to describe the behavior ofthe section. A number of correlation studies have been conducted to evaluate the ability of the numerical model in predicting the response of load-deflection and moment-curvature behavior of RC members. Comparisons are made on available experimental data and also on the analytical results. These comparisons consist of 6 experimental results for RC beams, 2 for RC columns and 3 for RC frames. Analytical investigation has been made on the RC beams and columns. From analyses using the model it has been found that the present model captures the load-deflection and moment-curvature behavior quite well. The material nonlinearity of the RC section has been effectively used to present the complex behavior of RC members. Effect of tensile strength of concrete on the ultimate load carrying capacity is insignificant but the strain hardening of reinforcing steel plays a vital role for the collapse mechanism. The ductility of a singly reinforced RC section decreases as the tension reinforcement increases. The presence of compression steel increases the ductility of a RC section significantly. The flexural response ofHSC beams has also been analyzed considering the material stress-strain relationship used in the model. Increase of axial load in a RC column increases the moment carrying capacity up to a certain limit and then the effect reverses and decreases the ductility of the section. Increase in steel content increases the load carrying capacity of RC columns but decreases the ductility for the same concrete strength. The ductility of RC columns increases as the concrete compressive strength is increased.