Prequalified Connections for Special and Intermediate Steel Moment Frames for Seismic Applications, ANSI/AISC 358-05

Building code provisions for the seismic resistant design of structures incorporate two basic types of requirements. The first of these is very similar to the code requirements for most other types of loading and comprises specification of minimum permissible strength and structural stiffness. The second is unique to design for seismic resistance and consists of prescriptive criteria on the detailing practice for the structural elements. While strength and stiffness requirements have been part of building codes for nearly 100 years, these detailing practice requirements, which include such things as prescription of the volumetric ratio and spacing of reinforcing in concrete structures, and permissible width/thickness ratios for elements of members in steel structures are a recent addition to the code. They were first introduced into the codes in the late 1960s and primarily affected the design of reinforced concrete structures. However, as researchers have continued to understand the importance of detailing to seismic performance and actual earthquakes have made clear to the profession that poor detailing practice directly leads to adverse structural behavior, the volume and complexity of these detailing requirements has steadily increased. AISC established a new ANSI standards committee, known as the Connection Prequalification Review Panel, in 2002 specifically to develop a standard containing pre-qualified connections and corresponding design procedures for critical connections in moment-resisting frames and eccentric braced frames designed under the AISC Seismic Provisions. Meanwhile, the American Welding Society commissioned Subcommittee 12-Seismic of its D1.1 Standards Committee, specifically to develop a seismic supplement to the D1.1 Structural Welding Code. As a result of these efforts, two new standards, AISC 358 and AWS D1.8 have just been published. The new AISC 358 connection prequalification standard contains design and detailing requirements for three types of moment-resisting connections: reduced beam section connections (Figure 4); unstiffened extended end plate connections (Figure 5); and stiffened extended end plate connections (Figure 6). Although it does not presently include several of the other pre-qualified connections contained in FEMA-350, it does significantly expand the limits of application for the connections that are included.