A Technique for Seismic Rehabilitation of Damaged Steel Moment Resisting Frames

Abstract

Moment resisting frames (MRF) as one of the conventional lateral load resisting systems in buildings suffer from some limitations including code limitations on minimum span-to-depth ratio to warrant the formation of plastic hinges with adequate length at the ends of the beam. According to seismic codes, in ordinary steel MRFs the span-to-depth ratios should be larger than 5 and in special steel MRFs this ratio should not be less than 7, which is typically difficult to achieve in some cases. For instance, framed-tube structures typically have MRFs with span-to-depth ratios less than the above mentioned ranges. Therefore, existing buildings with small span-to-depth ratios may exhibit poor seismic performance when subjected to seismic excitation. In this paper, a method is presented to rehabilitate such MRFs. Although the idea of using shear link for design of new buildings has been investigated in recent years, this idea can also be used to rehabilitate existing MRFs. Moreover, the novelty of this proposed rehabilitation method in this paper is that it can be used for damaged MRFs after earthquakes to enhance their remaining strength and ductility capacity. While most of the available rehabilitation methods focus on improving the system strength and stiffness, the proposed rehabilitation in this paper is based on the weakening of the beam mid-span that causes the formation of the shear plastic hinge in middle of the beam instead of the two beam ends. Numerical evaluation is conducted to show the efficacy of this method, and the results show that the use of the proposed rehabilitation method considerably increases the ductility capacity of the system during subsequent earthquakes.