California is no stranger to the shakes and tremors of seismic activity. However familiar, this particular force of nature can pose a huge risk to property owners, especially if they are concerned their building cannot withstand the major earthquake scientists predict will occur in California in the coming decades. Though it may not seem pressing today, many business owners are considering the benefits of a seismic retrofit of their buildings and working with a local
general contractor to complete the retrofit that is right for them.
Retrofit Triggers
A seismic retrofit involves new construction in an existing building that increases or enhances a building’s capacity to withstand earthquakes. There are several instances when businesses undertake a seismic retrofit, outside of voluntarily initiating the new construction in order to decrease the risk to people and property in the event of an earthquake. Many cities update or change their building code ordinances over time, and the ordinances that govern the seismic integrity of buildings are no exception. For the cities along the west coast of the US in particular, it is common for the city to enact
mandatory retrofit programs via building code ordinances. These programs typically allow businesses several years to come into compliance before they are subject to the hefty penalties for code violations. Businesses may also require a seismic retrofit of their building if there is a change in the type of occupancy or use. For example, if the building increases its use of space for storage, building codes would require a certain percentage of the total storage weight be calculated into the seismic mass of the building, which could necessitate a retrofit. Lastly, in the aftermath of an earthquake, most buildings are not only subject to repairs, but also to seismic retrofits in many cases.
Retrofitting Strategies
The steps necessary to perform a seismic retrofit on vulnerable buildings depends on the materials used in its construction, the design of the building, and the weaknesses revealed in previous earthquakes. In general, a seismic retrofit often focuses its construction on the specific elements or areas of the building that would provide the greatest impact on the overall integrity and resiliency of the structure. For buildings with unreinforced masonry, like brick or cinder blocks, a retrofit may involve securing the structure to its foundation, joining building elements to avoid independent movement of various parts of the structure, and introducing steel bracing systems. For buildings with non-ductile concrete, which typically means concrete that is not adequately reinforced with rebar or tensioning cables, a seismic retrofit would likely entail adding braces, shear walls, and base isolators, in addition to
stiffening prevailing building elements, such as with seismic
foundation repair.
