Effective Length Factor Of Column In Eccentrically Braced Steel Frames With Semi-rigid Connections

There are two systems of conventional tall steel buildings:moment-resisting frames and concentrically braced frames.Moment-resisting frames have good inelastic behavior and are easy in interior planning thanks to being without obstacle between columns.Being with great flexibility,however,it is not economical to meet the inter story driftlimit when the building is high.Concentrically braced frames can provide high elastic stiffness and are widely used.But the buckling of the brace can make the capacity drop.Eccentrically braced frames have the advantages of both moment-resisting frames and concentrically braced frames.This system can provide high elastic stiffness and large inelastic energy dissipation capacity in resisting laterall oadsc ausedb ys eism ic a ctivity.They can reduce material consumption,and keep good ductility at extreme overloads.In high seismic regions,eccentrically braced frames are quite popular,they have good ductility and can sustain to severe cyclic loads, and they are used widely in seismic design.The trditional analysis and design of steel frame assume beam-column connections are fully rigid or ideal pin connections.In fact,all connections of the steel structures,in practice,are between to fully rigid and pin connections and belong to semi-rigid connections.The effect of connection behavior can be described by beam-to column connection moment-rotation curve.On base of concept effective length factor of columns in semi-rigid steel frames stability design,by considering semi-rigid moment-rotation nonlinear behavior of semi-rigid connection in whole loaded range,finite element models of eccentrically braced steel frames with semi-rigid and rigid connections were established using ANSYS program.Nonlinear finite element analysis of steel frames with four angle connections and top-seat angles connections and double web angle connections were conducted in literature.Through buckling analysis of eccentrically braced steel frames with semi-rigid connections,the effective length factor of eccentrically braced steel frames was derived.In conclusion,a simple formula of effective length of column was brought forward for engineering design.