Seismic capacity of retrofitted beam-column connections in high-rise steel frames when subjected to long-period ground motions

Abstract

The seismic capacity of beam-to-column connections in steel high-rise frames is a matter of concern, particularly when they are subjected to long-period ground motions. A previous full-scale shaking table test conducted at the E-Defense National Research Institute for Earth Science and Disaster Prevention in Japan disclosed cracks and fractures in such beam-to-column connections. This paper examines the effects of three types of beam-to-column connection retrofit: supplemental welds, wing plates, and a haunch. Quasi-static member tests and a series of shaking table tests applied to a full-scale specimen are conducted to quantify the respective performances of the retrofit schemes. The performance of a total of 28 connections tested by the member and shaking table tests is evaluated together with that of an additional 12 unretrofitted connections tested in the previous test. When the supplemental welds are applied only to the shear tab to the web, the connection fractures at the same instant as the connection without retrofit. The corresponding cumulative plastic rotation is not improved. When the supplement welds are further applied to the web-to-column connection, strain concentration at the bottom flange, primarily promoted by the presence of the RC floor slab, is significantly reduced, and the cumulative plastic rotation capacity is increased to eight times that of the connection without retrofit. For the wing plate connection and haunch connection, the critical section is moved from the beam end to the beam cross-section corresponding to the tip of the wing plates or haunch, resulting in an improvement of ductility by eight times that of the unretrofitted connection. © 2011 John Wiley & Sons, Ltd.