The January 17, 1994 Northridge, CA Earthquake
An EQE Summary Report, March 1994

Industrial Facilities

Industries in the affected region are mostly light manufacturing and service-oriented industries such as high-technology, defense, and aerospace firms; small- and medium-size manufacturers that support high-technology industries; entertainment, health care, insurance, and financial services; warehousing and distribution; and other miscellaneous light industries typically found in modern industrial parks. With a few notable exceptions, heavy or very large manufacturing industries are generally located outside of the region that had the strongest ground accelerations.

Most facilities surveyed had nonstructural damage to buildings and equipment, resulting in inventory loss and business interruption. Many businesses had substantial structural damage and, often, were required to vacate their facilities. Concerted efforts by employees, suppliers, and contractors enabled many businesses to return to service quickly if they had no critical damage.

  • indu40.gif (32456 bytes)
    This concrete-frame building is a critical part of a large industrial complex near the epicenter, which has been evaluated and strengthened by EQE over the last five years. Shown on this page is the undamaged, strengthened building after the earthquake. A shear wall was added next to the tower, replacing one of three window areas, to provide resistance to lateral forces. None of the strengthened buildings at the site had significant damage. A collapse of this structure would have caused major business interruption, lasting up to 18 months.

Retrofitted Industrial Facilities

The performance of two industrial facilities that were extensively strengthened before the Northridge Earthquake is of particular interest.

The first, a company that manufactures products for the building and health care industries, has been in the process of seismically retrofitting its California facilities for the last seven years. EQE has been using its three-phase earthquake risk reduction program to evaluate and upgrade the facilities, and was about 75% complete when the Northridge Earthquake occurred. Before the earthquake, the seismic risk and operations vulnerability for every facility had been assessed, and detailed seismic analysis had been performed for most. The third phase of the program, risk reduction, had been implemented for a few facilities, including retrofit of some buildings in the company’s hard-hit Northridge facility. The retrofitted buildings were primarily of precast concrete construction. The retrofits entailed supplemental anchorage of floor and roof systems to perimeter shear walls. Those buildings that had been retrofitted performed well. Buildings slated for future retrofit that were heavily damaged were tilt-ups with precast concrete wall systems and gypsum roofs poured over a steel frame. At least one of the damaged buildings is now scheduled for demolition.

The second facility is one of the larger manufacturing plants in the San Fernando Valley. It is located within an 8-km radius of the epicentral region. The facility is surrounded on all sides by severely damaged structures. Nearby strong-motion records indicate that the site had peak horizontal accelerations of at least 0.5g.

The site contains several large industrial-type buildings, of vintages going back to the mid-1950s. Several are very large warehouse-type structures; others contain large equipment, including processing equipment. The structures include large steel-frame buildings and a variety of reinforced concrete buildings, most of which predate the 1971 earthquake. The structures critical to operations and life safety had been evaluated for earthquake risk during the past five years, and it was determined that several would require extensive strengthening to make them acceptable to the current corporate criteria for safety and business protection.

An aggressive program was initiated to strengthen the weaker structures. Several very large structures and numerous heavy process equipment items were strengthened. Numerous tanks were also braced and/or anchored. One of the main structures was an older, multi-story, reinforced concrete building of the type that was severely damaged elsewhere in the valley. Additional shear walls on three floors and other strengthening features were part of the retrofit program. In another building, exterior structural braced frames were added, because the interior of the structure was too congested to accommodate strengthening. A few weeks before the earthquake, a multi-story reinforced concrete process tower was removed because it was hazardous and was no longer needed for the modernized processes.

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    Shown here is the same building seen on page 40, but before strengthening. Numerous similar buildings in the immediate area that had not been retrofitted were extensively damaged.

The strengthened buildings and equipment had no significant structural damage. Other equipment, such as sprinkler piping that had not yet been braced or otherwise strengthened, were damaged. Some structural damage also occurred in the structures that had not yet been strengthened because of their lower priorities in the company’s overall retrofit program. Significant inventory losses also occurred when stored finished product fell off of pallets.

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    Left: About 280 cylindrical, horizontal tanks, measuring 4.25 m in diameter by 12 m long, were strengthened before the earthquake by adding diagonal bracing in both directions. Many other tanks that had been strengthened throughout the site also had no significant damage. Damage to these tanks would have caused serious and long-term business interruption. Other equipment that had not been anchored were damaged.
    Right: Steel buttresses were added to the exterior of this building (because of inadequate room inside) to provide necessary reinforcing. The owner of this facility estimated that the retrofit program may have prevented several hundred million dollars’ worth of direct damage and business interruption losses from the earthquake.


Larger vertical and horizontal tanks that are not specifically designed for earthquake resistance have proved to be highly damage-prone in strong earthquakes. Frequently, older bulk fluid storage tanks, such as those for storing fuel or fire-fighting water, have had severe damage and loss of contents in strong earthquakes throughout the world. Many such tanks were severely damaged or collapsed in the Northridge Earthquake. Severe tank damage was observed throughout the affected area, including extensive buckling near tank toes, called “elephant-foot” buckling.

For example, an unanchored 250,000-gallon fire-water tank just west of the Northridge Fashion Center, had a compression failure in its shell. The tank apparently uplifted about 30 cm during the earthquake and then dropped, severing the adjacent piping and losing its contents. The baseplate weld remained intact. The tank was designed in 1990 and was situated on a concrete pad foundation. It appears that the current American Water Works Association code is sufficiently conservative for the design of tank shells and baseplates, but flexibility in the adjacent piping must be emphasized. Numerous other tanks had damaged piping because of inadequate flexibility in the piping.

Numerous PVC piping breaks were observed in an adjacent chemical tank farm. A modern, 15,000-gallon, anchored steel tank emptied waste oil when its anchors stretched 8 cm and severed a PVC pipe. Adjacent 8,000-gallon tanks exhibited similar anchor stretching. Anchored fiberglass caustic soda tanks appeared to be intact, but PVC piping broke at unanchored pumps.

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    Left: This storage tank in San Fernando fell over after pulling its tie-down anchors out of its concrete base. It luckily did not rupture, and its contents are being transferred to a truck. Note the extensive roof collapse in the adjacent concrete tilt-up.
    Right: A completely ruptured fuel storage tank at a gas field in Aliso Canyon.

Numerous old horizontal tanks 4.25 m in diameter by 12 m long, which had been strengthened with horizontal diagonal pipe braces, were undamaged in a large industrial facility located centrally in the valley. Their loss in an earthquake could have caused extensive business interruption to processing activities.

Warehouse Racks

The collapse of industrial storage racks has proved costly in previous earthquakes, and the Northridge event was no exception. Many unanchored or poorly anchored racks collapsed, causing damage to both contents and buildings from impact.

A 5,115-square-m concrete tilt-up warehouse barely withstood the failure of the warehouse racks inside. The failure appeared to initiate in two multi-bay rows of racks that tipped over and progressively collapsed 40% of the racks. The racks were loaded at 60% of their design load. Many bracing members in the upright racks buckled. More redundant rack-member design and more stringent baseplate and anchorage guidelines appear warranted.

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    Heavy damage to storage racks in this warehouse nearly caused the entire building to collapse. These racks were loaded at 60% of their design load.

Return to Northridge Summary Report 1994 Contents page.