The behavior of concrete and reinforced concrete beams is very difficult to simulate in analytical models and one of the famous analytical tools to study the behaviour of reinforced beams is the finite element method. But there are various beams related to modeling the properties of concrete, like stress-strain behavior, anisotropy, heterogeneity, cracking etc., which make it a challenging task. In recent times size effects which reflect differences in response even if the systems are designed with geometric similarity are assuming greater importance. This paper presents the results of numerical study to simulate the linear and nonlinear behavior of reinforced concrete beam using finite elements. A series of linear and non-linear finite element analyses were carried out to predict the modeling effect for three different models and three different sizes of reinforced concrete simply supported beams. The response effects for flexure and shear on reinforced concrete beams under the uniformly distributed loading case is studied. Both load-deflection and moment-rotation curves are plotted for different stages to enhance the ductility at system level and flexibility at cross-section levels. Using this, the effects of models and size on bending stiffness and rotational flexibility are brought out. From the study it was found that the effects of size on finite element models of reinforced concrete structures brings out the different responses. It is observed that each of the three different types of elements used to model the beam needs a certain correction factor to reflect size, and linear/nonlinear response so that consistent results are obtained. © 2006 by School of Engineering and Technology, Asian Institute of Technology.