Larger imageTwo types of cracks found in steel frame buildings after earthquakes.

Source: Adapted from a photo provided by the Los Angeles Times

The Problem

In past earthquakes, fractures (cracks) occurred in steel frame buildings built before 1995 in two locations:

1. In welds and steel elements in or near steel beam-to-column connections (see drawing and photo A below); and
2. In column base plates (see photo B).

Such fractures are often small and hard to detect because they may be covered by fireproofing, interior walls and ceilings, and exterior facades. Slender or thin-walled steel braces can buckle prematurely in buildings built before 1982 (see photo C).

Larger imagePhoto A - This steel frame connection unexpectedly cracked in the 1994 Northridge earthquake.

Source: Earthquake Engineering Research Institute

The reasons for damage to steel members are not fully known but may include workmanship, design, welding procedures, and material characteristics.

Some buildings with subtle structural damage also will suffer movement-related damage such as cracked finishes around columns and beams, cracked or out-of-plumb partitions or door frames, damaged ceilings, and broken glass. In cases of extreme damage, partial collapse may be possible.

Larger imagePhoto C - A six-story steel braced frame building was damaged after the 1995 Kobe Earthquake in Japan. 4,000 to 8,000 small commercial buildings and 1,000 to 2,000 large commercial buildings were destroyed or severely damaged in that event.

Source: Earthquake Engineering Research Institute

Larger imagePhoto B - A 4-inch-thick steel plate supporting the base of a column at the Oviatt Library at CSU Northridge fractured in the 1994 earthquake.

Source: Earthquake Engineering Research Institute