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The USC Hospital withstood the Northridge earthquake using seismic isolation at the foundation, staying open while 11 other health units had to close.
When the Northridge earthquake struck Los Angeles on January 17, 1994, the city faced one of its darkest scenarios. The tremor not only shook the ground but destroyed overpasses, ruptured gas lines, and severely compromised the region’s hospital infrastructure.
The disaster left 57 dead and thousands injured who, in a moment of despair, sought medical help. In this chaotic scenario, the USC University Hospital (currently Keck Medicine of USC) stood out as an engineering miracle, according to the website EngSette.
The collapse of the healthcare network in 1994
While 11 hospitals in the region had to be partially or completely evacuated due to structural damage, the USC unit remained with the lights on, equipment calibrated, and teams ready for service.
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The secret of this resilience was not in the strength of the walls, but in a technology quietly installed beneath its foundation: base seismic isolation. The healthcare sector was one of the hardest hit by the tremors. The violence of the Northridge quake was such that it turned modern hospitals into danger zones.
Damage to pipelines, ceiling collapses, and cracks in columns forced the immediate transfer of hundreds of patients. The USC hospital was inaugurated in 1991, just three years before the quake.
How did the building “float”?
Traditional engineering seeks to make buildings rigid to withstand swaying. The problem is that in violent tremors, this rigidity causes the structure to absorb all the ground’s energy, resulting in breakages.
The building was constructed on devices called seismic isolators, which are essentially sandwiches of layers of steel and high-strength rubber.
These devices function as giant shock absorbers with two critical functions:
- Horizontal Flexibility: Allows the ground to move violently from side to side while the building slides smoothly over the isolators.
- Vertical Rigidity: Ensures that despite the lateral movement, the structure supports the massive weight of the concrete and equipment without yielding.
A crucial detail for this technology to work is the seismic moat. It is an empty space left around the entire perimeter of the hospital. Since the isolators allow the building to move laterally by several centimeters, the building needs “room to sway”.
A New Standard for Civil Engineering
During the 1994 earthquake, the reports from those inside the USC Hospital were surprising. While in other buildings people could barely stand and furniture was thrown around, in the USC hospital the movement was described as a gentle and controlled sway.
Today, major architectural and governmental landmarks, such as the San Francisco City Hall and new emergency command centers in risk zones, use variations of this same system. The case of the USC hospital in Los Angeles serves as an example that preventive engineering, although invisible beneath the ground, is the real foundation of public safety in times of crisis.
Source: EngSette
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