Performance of steel portal frame with RBS connection under cyclic load considering damage parameters

There are some Innovative methods to control the damage caused by seismic loads, and one of them is to concentrate the damages on the designated region or members. The reduced beam section connection, also known as the dogbone connection, is a promising option for improving the ductility of steel beam to column moment connections, especially in high-risk regions. By symmetrically trimming the width of the beam flanges over a discreet length in the vicinity of the beam ends, a ductile fuse can be created to accommodate the inelasticity that is required for seismic energy dissipation while is not only protecting the beam to column connection but also prevent causing the catastrophic and progressive collapse of the structure. This paperchr('39')s emphasis is the performance of the steel portal frame with RBS connections based on detail provided by AISC specification. The concentration of plastic deformations in the RBS region under cyclic load causes intensified stresses that accumulate damage. The prediction of ductile damage and fracture is one of the most important challenges in many engineering applications. Damages in a structure are caused by material degradation due to initiation, growth, and coalescence of microcracks/voids in a real-life material element from monotonic, cyclic/fatigue, or dynamic/explosive impact loading. The damage evolution law describes the rate of degradation of the material stiffness once the corresponding initiation criterion has been reached. In this study, the ductile damage model presented for steel is used. Damage Initiation parameters and damage evolution rules were obtained based on standard tensile test from literature and software procedure analysis. A coupon model has been established based on the standard tensile test to evaluate the ductile damage model. Also, to validate the steel portal frame with the RBS connection model two-step has been considered. In the first step, the global response of the steel moment frame was validated based on Wakabayashichr('39')s test. Also validation of the RBS connection model was checked based on Pachoumis experiments in the next step. Then, according to AISC 360 steel and AISC 341 steel, a steel moment frame design with RBS connection was designed. By selecting and extracting a single-span portal frame, the effect of considering damage was investigated by finite element analysis. Initial geometrical imperfections were determined using the AISC 360 Recommendation for out-of-plumbness, out-of-straightness, and localized geometrical defects. The cyclic displacement amplitude followed the loading protocol in the ATC-24. The study results show in the elastic region the behavior of the frame remains unchanged before the frame reaches the high amplitude cycle. But gradually, with increasing cycles, the size of the hysteresis loop and ultimate resistance became smaller. Thereby, if the aim is to focus on the load levels that lead to large localized plastic deformations, it is critical to consider the damage parameters to improve the reliability of the results. Measurement of the area below the graph in the last loading cycle shows that the dissipated energy in the two cases without vertical load and with a vertical load on the columns is decreased by 2.6% and 4.1%, respectively. The continued deterioration of the RBS region due to damage spreads leads to complete frame failure, which is not properly predicted when damage parameters are ignored.