Effect of near-field earthquake excitation on seismic behavior of knee-braced moment frames

Abstract

Inelastic behavioral characteristics of knee-braced moment-resisting frames having 3, 8 or, 12 stories were investigated under near-source earthquake excitation using initially pinned frames that were subsequently substituted with rigid knee elements. These frames were designed so that the knee braces would yield and buckle under seismic loading. Inelastic time-history analysis was carried out to assess the structural performance of the buildings by evaluating the maximum axial forces of the columns, vertical displacement of internal beams, roof horizontal displacement, and maximum base shear of columns in the building members using PERFORM-3D software. The nonlinear behavior of the frames was investigated by comparing the results of pinned and rigid knee elements subjected to near-field earthquakes. The results indicate that rigid-to-pinned connections for knee elements can increase the axial forces of columns by nearly 15% for a 3-story building and about 7% for 8- and 12-story buildings. The vertical displacement of the beams was noticeable, especially for the three-story building. The horizontal displacement of the roof and base shear of columns using pinned connections for knee elements were generally greater than for the rigid connections.