Design of the new rigid joint model determining panel zone deformation by both bending and shear distortion

Beam-to-column connection in the Moment-resisting frame plays a significant role in the seismic responses of the structure, including its ductility. Panel zone is subjected to large asymmetric anchors under seismic loads, which causes shear ductility. Therefore, an accurate estimation of the panel zone behavior during the structure's design is essential. Existing relationships have problems in estimating the behavior of the panel zone. Some relationships, such as the Krawinkler model, have good accuracy but are highly complex in the modeling process, and some of the proposed models for estimating the behavior of the panel zone, such as the scissors model, are easy to use. However, they do not have good accuracy. For this reason, engineers typically abandon panel zone modeling when using software such as SAP and ETABS to design structures, and consider the panel zone to be rigid. This method of modeling the panel zone in short-rise buildings does not have much effect on the deformation of the frame. However, with increasing the height of the structure, the effect of accurate modeling of the behavior of the panel zone on the overall behavior of the structure will increase.Given this issue, it is necessary to provide an accurate and, simultaneously, simple numerical model to predict the behavior of the panel zone. For this purpose, in this research, first, the weaknesses and strengths of the existing models were carefully studied, and then by combining these models and performing various analyzes in OpenSees software, the final model was presented. In this numerical model, a torsional spring with trilinear behavior is used to simulate the behavior of the panel zone, considering both the bending and shear effects. The relationships used in the proposed model are derived from Krawinkler relationships that have been optimized for the conditions of the new model. Using this model, the independent degree of freedom of the panel zone has been reduced by 75% compared to the Krawinkler model, and the capacity of the panel zone in the nonlinear region has been increased 6.8 times and is almost identical to the experimental results.