Parametric Tests on Unreinforced Steel Moment Connections

Abstract

Fully restrained steel moment connections have been designed following a codified design procedure. This design was invalidated by brittle connection fractures discovered after the 1994 Northridge earthquake. A new, widely accepted earthquake-resistant design has not been developed to date. This paper presents a summary of the test results on a post-Northridge steel moment connection design proposed by the SAC Joint Venture. The SAC post-Northridge connection design is a conventional unreinforced welded flange/bolted web connection made using notch-tough weld metal and improved welding practices. This connection achieves a mean plastic rotation of 1.5% radian, averaged over a wide range of connection parameters. The results of these tests show that weld fracture mitigation measures are beneficial, but are not sufficient to produce a connection design that satisfies the plastic rotation requirements for steel moment-resisting frames in regions of high seismicity. A new, earthquake-resistant connection design should be based on a combination of weld fracture mitigation measures and changes of connection configuration aimed at reducing the stress levels or redirecting the stress flow in the connection.