Lincoln Electric D1.8 manual Background

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D1.8 Seismic Supplement Welding Manual

Background

In January 1994, the Northridge, California earthquake caused unexpected damage to a number of welded steel-framed buildings in the greater Los Angeles area. The Federal Emergency Management Agency (FEMA) funded a variety of investigations that sought to address both the immediate and long-term needs related to solving the performance problems associated with welded steel moment-frame connections. Several documents were published as a result of these investigations, including Recommended Specifications and Quality Assurance Guidelines for Steel Moment-Frame Construction for Seismic Applications (FEMA 353)1.

FEMA 353 discusses what has come to be known as the “Pre-Northridge Connection” and concluded that “…the typical moment-resisting connection detail employed in steel moment-frame construction prior to the 1994 Northridge earthquake… had a number of features that rendered it inherently susceptible to brittle fracture. These included the following:

The most severe stresses occurred in the connection “Wildcat” welding position

Connection detail makes it hard to inspect

Significant flexural stresses on the beam flange at the column face Weld access hole geometry

High restraint Weak panel zones

The report continued on to say “…additional conditions contributed significantly to the vulnerability of connections...” including:

Low toughness FCAW-S welding the consumables Low redundancy

Matching beam and column strength

FEMA 353 then proposed a variety of recommendations and quality assurance guidelines that addressed various topics, including:

Overall structural design Connection design Connection details

Materials, including both base metal and weld metal Workmanship

Inspection

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