Evaluation of an element removal algorithm for shear-critical reinforced concrete frames

Abstract eng:
Progressive collapse assessment using nonlinear time-history finite element (FE) simulation is gaining popularity over traditional methods such as alternate path analysis. In order to model progressive collapse, an element removal algorithm based on dynamic equilibrium and the resulting transient change in system kinematics was developed for reinforced concrete (RC) structures and implemented into an open source FE program. This paper is comprised of the application of the aforementioned algorithm on a RC frame, which was previously tested using shaking table. The tested frame is a three-bay, one-story structure which was intended to reflect the common construction practice for school buildings in Taiwan. For the purpose of progressive collapse simulation, the frame intentionally had two ductile and two non-ductile RC columns. Subsequently, a three-bay, three-story frame is studied using the column properties of the tested one-story frame. The effects of beam-column joint modeling and the element removal algorithm are observed from the nonlinear time history analyses ('THA) conducted on this frame. The interstory drift ratio and force-deformation histories obtained from the experimental results are compared with those obtained from 'THA with and without using the element removal algorithm. It is observed that 'THA for both cases can predict the response recorded in the test. However, the benefits of the element removal are clearly shown for the three-bay, three-story frame. For beam-column joints, it is observed that using available models for joint flexibility may lead over-estimate such flexibility leading to unrealistic response predictions. Therefore, it is concluded that it is necessary to produce a realistic beam-column joint model for collapse simulations. Finally, the ongoing test program on beam-column joints for the collapse simulation of RC buildings is briefly presented.

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