USC University Hospital, California: The Tested U.S. Base Isolated Building

The University of Southern California Teaching Hospital in east Los Angeles (1991) had a severe test in 1994, when the Northridge earthquake hit.

Though it was only 23 miles from the epicenter, the horizontal acceleration in the building was three or four times less than the peak acceleration outside: the building was effectively isolated from the motions that caused significant damage to buildings nearby.

During the 1994 Northridge earthquake, the isolators reduced the accelerations by 66% at the base and 40% at the roof.

BUILDING PROFILE
1.	LENGTH	92.35-m (303-ft)
2.	WIDTH	77.11-m (253-ft)
3.	BAY
	EAST-WEST(EW)	10
	NORTH-SOUTH (NS)	12
4.	IRREGULARITIES
	PLAN	Asymmetric with two wings, which are connected by a necked down region of the floor/base
	VERTICAL	The building has setbacks after the fifth floor
5.	STORY	Seven stories above the ground and a basement
6.	SUPERSTRUCTURE	Steel-braced framed building
7.	SUBSTRUCTURE	Reinforced concrete base slab

 

Fig. 1(a)

Fig. 1(b)

Fig. 1 shows the plan and elevation of the building. Metal decking and a grid of steel beams support all concrete floors. The superstructure bracing is located at the building perimeter. The steel superstructure is supported on a reinforced concrete base slab, which is integral with the reinforced concrete beams below, and drop panels below each column location.


 The isolators are connected between these drop panels and the footings below [Fig. 1(b)]. The footings also support a reinforced concrete pedestal provided for backup safety. The seismic isolation system consists of 68 lead-rubber isolators and 81 elastomeric isolators, as shown in Fig. 1. The building is located near the intersection of Highways 5 and 10.

The closest active faults to the site are the Raymond Fault and the Newport-Ingelwood Fault. The building was designed using spectrum compatible earthquakes—with the spectrum defined as 1.2 times the 0.4g ATC-3-06 or UBC spectrum.