ABSTRACT
Fatigue has been known to be a cause of failure in steel structures for over 100 years. More recently, the possibility that low-cycle fatigue is a failure mechanism was discussed by Bertero & Popov (1965). Tests of Pre-Northridge-type steel sections subjected to cyclic loads suggested that factors such as member size, connection details, and the state of stress in a member affect the fatigue
1 INTRODUCTION
1.1 Background
Steel moment frame buildings suffered extensive damage during the 1994 Northridge earthquake. The damage was not limited to older buildings, but included frames designed using a connection specifically developed to resist seismic motions, now commonly called the Pre-Northridge connection. The failure of these connections was unexpected, and initial speculation centered on faulty welding and inadequate inspection. However, subsequent studies (Bertero & Popov, 1994; Engelhardt & Sabol, 1994; SAC, 1996) found fundamental flaws in the design that lead to premature failure of the connection. It is now generally accepted that a major cause of failure in the Pre-Northridge connection, and many other steel moment frame connections, is low-cycle fatigue (Hamburger, 2007).
