A new beam-column model for seismic analysis of RC frames – Part I: Model derivation

In this study, a reliable and computationally efficient beam-column model is proposed for seismic analysis of Reinforced Concrete (RC) frames. The model is a simplified version of the Flexibility-Based Fiber Models (FBFMs), which rely on dividing the element length into small segments and dividing the cross section of each segment into concrete and steel fibers. In the proposed model, only the two end sections are subdivided into fibers and uniaxial material models that consider the various behavioral characteristics of steel and concrete under cyclic loading conditions are assigned for the cross section fibers. The proposed model is simpler than the FBFMs as it does not require monitoring the responses of many segments along the element length, which results in a significant reduction in computations. The inelastic lengths at the ends of the proposed model are divided into two inelastic zones; cracking and yielding. The inelastic lengths vary according to the loading history and are calculated in every load increment. The overall response of the RC member is estimated using preset flexibility distribution functions along the element length. A flexibility factor ŋ is utilized to facilitate selecting the proper flexibility distribution shape. The proposed model is implemented into the computer program DRAIN-2DX.