Seismic Damage


On an early January morning in 1994, the Northridge area of Southern California was shaken by an earthquake that measured 6.6 on the Richter scale and lasted approximately 30 seconds. The repercussions are still being felt throughout the engineering community

After billions of dollars in building and equipment damage, and an extensive investigation that measured the structural successes and failures of mounted
machinery and electrical equipment, the conclusions are quite clear. Cushioning and restraint are the key factors and lack of it can cause earthquake-generated accelerations to amplify 30 to 50 times. Codes simply don’t account for proper energy absorption when equipment is not hard mounted and braced, and the Northridge study bears this out.

The data for the study was accumulated by our structural and mechanical licensed engineers using professional photographers to document site damage.

The systems that were documented are specifically covered throughout these pages. We will examine nonisolated as well as isolated, mechanical and electrical, and floor mounted and suspended systems. The data offers excellent insights into which systems survived, which systems failed, and why.

In most cases, the seismic gV and gH next to the photos are ground level readings, depending on the locations of the seismic instrumentation. Since the damage is so extensive, the resonant amplification of these forces by the structural components is self-evident.

We have described the Mason mountings in the photographs wherever Mason was used. Out of courtesy to our competitors, we have not named the companies or products that did not do well. It would seem that we omitted the Mason failures, but that is not the case. If only one of our mountings had failed, we would have examined the failure in detail. Thankfully, we could not find one example.