For finite element analysis of reinforced concrete(RC) members a number of nonlinearities must be taken into account. Particularly, the tension stiffening effects become important in studying the load-deformation characteristics of RC shear walls and panels in the post-cracking range. Presented in this study is a new tension stiffening model, which is both capable of describing the actual behavior of tension stiffening with reasonable accuracy and simple enough to apply finite element analysis for planar RC members. In the proposed model average tensile stress of concrete in the post-cracking range is expressed by the tension stiffening factor. It is shown that the tension stiffening factor is a function of three parameters which are evaluated analytically based on the bond action between concrete and steel. Consideration of the tension stiffening effect in the direction of steel bar makes it possible to extend the proposed model to planar RC members. The proposed model is implemented in an orthotropic rotating-crack concrete model. The main feature of the material model includes the consideration of concrete expansion and confinement effect. The material model also combines features such as strength degradation due to transverse cracking, strength enhancement due to confinement, and pre- and post-ultimate stress-strain response in compression.
To establish the validity of finite element analysis program developed in this study, a numerical investigation is carried out, with reference to several RC shear walls and panels for which the experimental results are available. The comparison of calculated and experimental results shows that the program can predict the load-deformation responses, the ultimate strength, crack patterns, and failure modes with satisfactory accuracy.
On the other hand, in order to provide a practical method for predicting the distinctive points such as cracking point, crushing point, and steel yielding point for RC panels, the simplified methodology is also proposed in this study. Features of the proposed model, based on the governing equations derived in the secant form, include the consideration of the tension stiffening effect and multidirectional reinforcement. For the practical purpose, due to simplicity of the modeling and ability to obtain the response of RC panel with minimum amount of computation, the proposed method offers attractive alternatives to the use of available complicated models. The reliability of the proposed model is confirmed by comparison between predicted and test results.