The Impact Effect Of Partial Fracture In Steel Frame Connections And The Dynamic Behavior Of The Whole Structure After Fracture

In Northridge and Hyogo-ken Nanbu earthquakes a number of beam-to-column connections were damaged because of fracture. It is found that the seismic behavior of steel moment frame is not as excellent as expected. The research on the fracture of beam-to-column connections is aimed at discovering the reasons and related factors of the damage and providing theoretical basis for the seismic design of beam-to-column connections.The impact induced by the fracture of connections in steel moment frame and the influence of the fracture on the dynamic behavior of the whole structure are two main subjects in the dissertation. On the basis of the investigation of the related research literatures abroad and at home, these two subjects are theoretically analyzed and experimental sudied.First of all, the property of the impact by connection fracture is sudied. In the case of earthquake, cracks in the flange of beams increase steadily until the critical size is reached. Then the cracks lose their stability and fracture occurs. During this moment, the ruptured flange loses its tensile strength in no time and the beam loses most of its bending capacity near the connection. While at the same time, the structure is still subject external loads. In other words, this sudden unbalance will induce an instantaneous impact on the structure and will affect the seismic behavior. By the above recognization , the author wants to evaluate the impact quantificationally and to find the upper limit on the dynamic effect of the impact.The effect of impact is investigated by experiments. By measurement of the change of external load, inner forces, strains during the fracture process, as well as by FEM analysis, the impulse due to the fracture and its effect are evaluated.It is understood that the fracture of beam-column connection did not lead the complete collapse of frame structure in the earthquakes mentioned above. However the dynamic behavior of a structure will change due to fracture of connections, so the analysis of damaged structure is an important research subject. It is necessary to make...