Aseismic behaviors of steel moment resisting frames with opening in beam web

Abstract

Opening in beam web short away clear of beam-to-column connection is an effective method to improve the aseismic behaviors of steel moment resisting frames (MRFs). The pseudo-dynamic (PSD) test and the quasi-static test on the aseismic behaviors of full-size steel MRFs with opening in beam web are carried out. The PSD test shows that the tested frame can satisfy the design requirement and its stiffness isn’t weakened by the web opening. It can be judged from the strain distribution around the beam-to-column connection that the seismic energy is dissipated by local deformation in the weakened area of the beam due to the opening in the case of severe earthquake action, and the expected failure mode of a ductile frame (‘strong column but weak beam’ and ‘strong connection but weak component’) is reached. In the quasi-static test, the failure mode of the tested frame is in conformity with the judgement, i.e., Vierendeel mechanism is formed in weakened areas due to web opening and brittle weld fracture is avoided, which results in an improvement of the aseismic behaviors of steel MRF. Based on numerical analysis, the non-linear analysis model of steel MRF with opening in beam web is provided. Some experimental tests are numerically re-analyzed by applying the proposed model and the numerical results are in conformity with the test results, which verify the validity of the model. A 17-story steel MRF building, damaged during the Northridge earthquake and measured in detail after the earthquake, is selected as the studied case. Push-over analysis shows that the ultimate displacement of the modified building with web openings increases a lot due to the opening and the building’s ductility is improved greatly. Plastic hinge distribution in time-history analysis indicates that brittle weld fracture can be avoided in the frame including connection with opening and the maximum plastic zone moves to the weakened areas. It can be concluded that the aseismic behaviors of steel MRF are improved due to the opening in beam web.