CESMD
Information for Strong-Motion Station
Los Angeles - 32-story City Hall
CGS - CSMIP Station 24222
Earthquakes recorded by this station
 
(Station Photograph - click to enlarge)(Sensor Layout - click to see PDF File)
   
Latitude 34.0537 N
Longitude 118.2426 W
Elevation (m) 92
Site Geology Alluvium over rock (sedimentary)
Vs30 (m/sec) 393 (inferred)
Site Class C
Remarks/Notes Site information sources
 
No. of Stories above/below ground32/1
Plan ShapeRectangular
Base Dimensions469 x 272 ft
Typical Floor Dimensions5th - 11th Floors: 325 x 148 ft; 12th - 25th Floors: 98 x 98 ft
Design Date1926, 1997 (retrofit)
Instrumentation2004, 27 accelerometers and 3 relative displacement sensors, on 7 levels.
 
Vertical Load Carrying SystemConcrete slab supported on a pan-joist floor system and concrete encased steel frame with riveted connections. After seismic retrofit, the building is supported on isolation bearings.
Lateral Force Resisting SystemOriginal system consists of perforated unreinforced masony (URM) infill walls, lightly reinforced concrete walls, and steel frames with wind bracing. The building was retrofitted by using a hybrid system consisting of 526 base isolators and sliders at the base and supplemental dampers at the base (52 viscous dampers) and top of the building (12 dampers), and new concrete shear walls in the superstructure.
Foundation TypeSteel columns of the tower are supported by concrete mat foundation; other columns are supported by isolated spread footings. The spread footings were enlarged and tied by new grade beams during the retrofit.
RemarksThe building was seismically strengthened in 1997.