Seismic performance of low and medium-rise steel frames

The expected performance of low and medium-rise steel frames designed according to the common force/strength approach of the UBC or NEHRP is evaluated. Several combinations of soil profile type, lateral-force-resisting system, and frame-member proportioning are included in the designs. Nonlinear frame models of the designed buildings are set up for dynamic time history analysis. Nonlinear material behavior, large displacements, interaction of axial force and bending moment regarding both strength and stiffness, and spread of plasticity within each frame-member are considered in the nonlinear frame models. A total of 18 ground motion time histories are selected from the recorded events and scaled to a spectrum-related "intensity" representative of each site. To evaluate the expected damage, appropriate structural response parameters such as, interstory drift, ductility demand, dissipated hysteretic energy are obtained. A modified form of Park-Ang damage index is alsocalculated for moment-resisting frames. The significance of each damage measure in predicting the performance and correlation between the different measures is investigated. The performance of the steel frames is also assessed according to the acceptance criteria of the NEHRP Seismic Rehabilitation Guidelines (FEMA 273) which sets forth plastic rotation and deformation limits to define the performance levels for various structural and nonstructural components.