Seismic Consideration Analysis Of Strengthened Beam-to-column Connection With Cantilever Beam Splicing

Many conventional beam-to-column connections with welded-flange-bolted-web of steel moment-resisting frame (MRF) have suffered unexpected brittle weld failures under earthquakes. Based on the failure of fully welded connections simulated by low cyclic reversed loading tests, it is shown that the bearing capacity of structural components is affected by the brittle mode of fracture. In particular, welding defects can be most vulnerable. Improvement of the ductility of the beam-to-column connections to form strong column-weak beam is discussed in connection with the plastic hinge analysis. This includes the performance of strengthened rigid connections with cantilever beams. The results showed that the steel frame structure behaved nonlinearly under simulated earthquake loading.Three different steel beam-to-column moment connections are simulated to failure using the MRF. The specimens consisted of one no strengthened connection as the BASE specimen and two connections with top beam flange cover plates or bottom beam with haunches in Yu Haiqun's experimental study, used finite element analysis the hysteretic behavior under monotonous and cyclic loading. By means of reasonable designing, the beam ultimate plastic rotation of connection with top beam flange cover plates is larger than 0.03rad, which satisfies the ductility requirement in FEMA. The connection of the beam bottom flange with haunches is also possible to meet the requirements. This may be attributed to the degradation of the material properties that would affect both stiffness and strength. The measured stress profiles along the beam flange and the beam web depth show that the elevated triaxial stress state at the end portion of the flange of beam is one of the causes of brittle fracture. It was found that the main factor of brittle fracture of the connections is to form serious stress concentration and three dimensions high stress. It appears that reinforcement of the connections can enhance the performance of steel MRF from a brittle to ductile behavior. More specifically, the appearance of the plastic hinges on the flange section, far from the column-beam crossing zone, contributed to the difference.