DYNAMIC BEHAVIOR OF PORTAL FRAME STRUCTURES WITH TAPERED MEMBERS

Using ANSYS program and considering the materials nonlinearity, the dynamic numerical simulation models of tapered portal steel frames are set up. The shape and amplitude of hysteretic curve obtained by numerical simulation analysis of the models coincide well with the test results. Dynamic modes analysis of 11 tapered portal steel frames with different spans show that the natural vibration frequencies of these structures decrease with span increasing and span 42m is a borderline of dynamic characteristics of the frames. The natural vibration frequencies of these frames vary slightly with spans longer than 42m. The numerical results and simulation analysis of hysteretic curves with different slenderness ratios and spans indicate that these structures have good plastic deformation and hysteretic energy-dissipated capacity, but the structural stiffness and material strength degenerate quickly and the structural ductility decreases rapidly with spans bigger than 42m and slenderness ratio greater than 90.