Collapse Mechanism And Design Criterion Of Steel Beam-To-Column Four-Angles Connections Under Cyclic Load

Steel moment-resisting frames with welded beam-to-column connections were traditionally regarded as having excellent performance,and widely adopted in steel constructions,but this opinion changed after the 1994 Northridge earthquake and the 1995 Hyogoken-Nanbu earthquake.These earthquakes also arouse engineers to resurvey the behavior of semi-rigid connections.It is well known that foue-angles connections of top-and-seat with web angles have definite flexibility,which can Increase damp,prolong period.So It can reduce the damage.The structure system of semi-rigid connections with steel frames-wall of shearing is one of the best choices for resisting earthquake.However,because studies on four-angles connections were very limited,cognition on the damage mechanism of this type of joints was rather inadequate.To avoid casualties and decrease the loss in the future,analyses and response the damage mechanism of four-angles connections under seismic load is significant far theory and practice.In order to study the hysteretic behavior of four-angles connections and verify the rellabfllty of theoretical method,15 four-angles species were tested under cyclic load. Tests consist of three parts;material property test of panel,slippage coefficient test of bolt connection and cyclic load test of four-angles.Effects of column axial force and rib stiffener on hysteretic behavior of connections were synthetically considered for the first time during cyclic-loading.Results of the experiment shows that four-angles connections have excellent hysteretic behaviors,and the determination factors,which have crucial influence on the behavior,are angle thickness,column web thickness,and the rib stiffeners.This paper applies nonlinear(material,geometry and contact) finite element method to analyze the behaviors of four-angles connections under cyclic load at fist time.Contact elements are set between angle and neighborhood plane,screw cap and neighborhood plane,bolt bar and hole.After verification of FEM,more than 50 species of 15 series are computed.The major factors Include dimensions of angles,column axial force,arrangement of bolts,and so on.Advices for seismic design based on tests and calculation are presented at last.The problem of connection seismic behaviors is of great importance for structure field,and the foreground of study and application is very wide.Experiments and theoredcal analyses presented in this paper may well fit the realistic behavior of four-angles connections under seismic load.The conclusion can be useful for revising code,guiding design of engineering,and making a favorable base for analyzing the seismic behavior of whole structure.