| Steel Moment-Resisting Frame (MRF) has been widely adopted in seismicdesign of high-rise steel structures, and Welded-Flange-Bolted-Web (WFBW)connection is the most common type of beam-column connection in these structures.Many steel buildings failed from fracturing of beam-to-column connections in theNorthridge earthquake and Kobe earthquake. It was also found that most of theconnection failures were due to fracturing at the weld between the bottom flange ofthe beam and the column flange. The stiffness and strength contributed from concreteslabs may lead to the fracture on the bottom flanges of the connecting beams.Research on seismic behaviors of beam-column connections, considering thecomposite effect of concrete slab, became a hot spot in the following several years.This paper, by means of experimental study and finite element analysis,investigates the behavior of several types of beam-column connections withcomposite effect under cyclic loading. Strength, ductility and brittle behavior of theconnections are analyzed and design recommendations are given.Four specimens with different ratios of reinforcements in slabs and two types ofsteel joints, i.e. standard one and improved one, are tested. Their behaviors on theloading capacity, plastic deformation, distributing of stress and failure mode areinvestigated and compared between the four types of connections. Ductility parameterand seismic performance of composite connections are compared with steel ones.Finite element models are established based on the profiles of the tested specimens.Elasto-plastic analyses are conducted with the general-purpose finite elementprogram ANSYS. The analysis results are compared with the experimental data. Anda parametric study to examine the influencing factors has been carried out using theseismic model.According to the experimental and analysis results, the loading capacityincreases remarkably with the composite effect and it will help to realize the designidea of "strong connection, weak member" in the seismic design of the frame.Different ductile behaviors and failure modes of four connections are investigated,and the critical issues that affect the failure modes of the connections are tested.Mathematical models are derived to simulate the hysteretic behavior of theconnections under cyclic loading using the linear fit method. Connection stiffnessdegradation is discussed;energy dissipation capacity is also compared. At last basedon the proposal of the effective width of composite connections, the design methodsand the formulae calculating the elastic resistance and limit strength of the compositejoints are presented, which has been proved by the experimental results.All the results described above have brought valuable information to thedevelopment of the theory and method on the seismic design of composite joints. Itcan also promote the study on new type of joint that is more practical and moreefficient. |
PDF Full Text Request