Seismic Design in San Francisco

Constructing buildings in areas affected by significant seismic activity, such as in the city of San Francisco, requires specific expertise from all the professionals involved. From the creation of the plans and designs by the architects and engineers, to the skilled placement of the foundational building components executed by San Francisco’s commercial concrete contractors each stage of the process must keep an eye toward earthquake, or seismic, design. With the myriad forms buildings take on and the variety of materials employed in their construction, there are several strategies to ensure every structure, whether it is a skyscraper or apartment building, can withstand the violent forces of an earthquake.

Seismic engineering and construction materials

Engineers looking to design a structure that is earthquake-resistant and performs up to the expectations of building codes can utilize several approaches. One such strategy is base isolation, which entails floating a building above its foundation on a system of bearings or springs, which allows the building to experience less horizontal acceleration, even as its foundation is impacted during an earthquake. The materials used to construct the building can also work to allow the building to absorb and dissipate the forces of an earthquake. While concrete on its own has relatively low ductility and could be a liability when subject to the forces of an earthquake, concrete that is properly reinforced with steel allows the slab to better absorb energy instead of being buffeted by it. These slabs can either be pre-cast with the steel matrix woven within the concrete, or they can be cast-in-place with the use of formwork, steel rebar or cable, and concrete pumping technology.

The trusses of the Transamerica Pyramid

Another strategy of seismic design is to use braced frames on the vertical structure, such as the system of cross-braced trusses used in the Transamerica Pyramid in San Francisco. In this building, a distinctive feature of the city’s skyline that reaches 853 feet into the air, the exterior surfaces are supported with cross-bracing after the first floor, and the interior surfaces are similarly braced up to the 45th floor. The seismic integrity of this design was tested in 1989 during the 7.1 magnitude Loma Pietra earthquake, and while the top floors of the pyramid swayed side to side a staggering 12 inches, it did not incur any damage.

 
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