A new dual system for seismic design of steel buildings

摘要

Steel moment resisting frames often consist of a perimeter rigid frame (Fully-restrained frame, FR), mainly for lateral load resisting purpose, and interior columns simply connected to interior beams, mainly for gravity load. During a strong ground motion, the perimeter frame would attract large lateral load which could drive the frame to its limit state imposing excessive deformation demand on the beam-to-column connections, which was demonstrated by hundreds of steel buildings damaged in the 1994 Northridge Earthquake. It is a logic step forward to bring the interior columns into lateral-load resisting system by changing the simple connections to semi-rigid connections (Partially restrained frames, PR). Without increasing much cost of construction, introduction of the semi-rigidity to the interior columns increase significantly the lateral strength and defense lines. This paper proposes a new dual system in steel buildings consisting of FR and PR based on an analytical investigation of two steel buildings with interior semi-rigid steel frames with beam-to-column connections with different strength and stiffness ratios. The two buildings, with 5 stories and 10 stories, are designed in compliance with AISC and UBC design codes, assuming that the exterior frames of the buildings are rigidly connected and the interior frames are semi-rigid. The buildings were subjected to three representative earthquakes, namely, El Centro, Taft, and Northridge (Newhall Station). The results indicate that the interior semi-rigid frames can lead to less story shear and lower column and connection moments and increase the lateral load capacity of the buildings. The input energy is dissipated in the dual system by FR and PR frames, and the concentrated energy demand on the connections may be controlled to the acceptable level.