In the early hours of January 4, 2018, a 4.4 magnitude earthquake hit the Bay Area – more precisely, a 5 mile distance along Hayward fault. As an area that is no stranger to earthquakes, we find this a perfect opportunity to discuss structural safety in regards to seismic activity.
USGS Geologist David Schwartz points out that the Hayward fault has experienced close to 30 earthquakes in the last 10 years, making this area of San Francisco an at-risk location for more frequent seismic activity. Even more worrisome than the Bay Area being at risk for more earthquakes, is the fact that about “5 percent of earthquakes are followed by larger earthquakes,” Schwartz goes on to explain.
Another interesting factor to this incident is how Hayward fault often undergoes high magnitude (damage prone) earthquakes every 150-years, which Schwartz points out, we are almost at the 150-year mark.
A 4.4 earthquake might not necessarily sound the alarms of many, but it can easily cause damage to homes and buildings which are not sound. This is increasingly true for soft story homes, a popular style for residences in the Bay Area.
Fortunately, there is a relatively easy solution to homes located in earthquake prone areas — seismic retrofits.
Seismic Retrofits, which are structurally engineered and secured to the foundation of homes and buildings, keep structures sound, and those in and around them safer. As high magnitude earthquakes not only cause structural damage and injuries, but also cause communities to be isolated from police, firefighters, and other rescue teams — basically, the more prepared you are, the better. Below are a few key reasons we suggest Bay Area and other California coast homes invest in seismic retrofits.
Image Source: USGS
According to California’s Department of Conservation, their 2016 geological report indicates that “over two-thirds of our nation’s earthquake losses will be in California.” From an economical and humanitarian standpoint, this is huge. As our two largest metropolitan areas (San Francisco and Los Angeles) are located on dangerously high hazard zones, the time to prepare for “the next big one” is now.
While death tolls have greatly subsided, when comparing San Francisco’s 7.9 magnitude earthquake in 1906 (killing 3,000) to Northridge’s 6.7 magnitude in 1994 (killing 61) – the overall monetary damage has not, with an average of about $15 billion of damage caused by these mega-quakes.
So, for those working and living on the California coast, it’s important to consider these structural reinforcements, which are engineered to lessen the impact of seismic activity and protect your home from collapsing and hurting loved ones – as structural safety is often a common misconception Bay Area residents have. In fact, although it’s common for today’s newer constructions to be built up to current city codes, that doesn’t necessarily mean a building has had seismic retrofits integrated. In fact, a 2016 report by The California Seismic Safety Commission states that “most Californians falsely believe that new buildings are earthquake proof.” For this reason alone, we urge property owners and property managers to have their residential buildings evaluated by a structural engineer and accommodated in any way necessary.
The reality for older residential buildings is a bit more grim. Homes built between the 1950’s – 1970’s usually weren’t designed to withstand seismic hazards. We often find these structures lack adequate foundation anchorage. In San Francisco, a good deal of these are what we call soft-story buildings; homes or apartment buildings where the bottom floor is open, often used as a garage or carport. These soft story buildings have difficulty safely supporting the upper levels of the building during an earthquake, making them dangerous places to be during a high magnitude earthquake.
Unfortunately, we can’t predict or stop seismic activity, but we can proactively take safety measures to protect ourselves, our family, and employees.
Top 5 Benefits of Seismic Retrofits
- Avoid loss of life
- Avoid large medical costs
- Avoid litigation from employees and/or tenants
- Avoid cost of temporary relocation
- Avoid loss of assets within the building
Residential Seismic Retrofitting – What’s The Process?
In general, seismically retrofitting a home consists of designing and building a shear wall. Sheer walls are made up of three parts: bolts, plywood, and sheer transfer tiles. With these elements, a structural engineer is able to draft plans for the contractor who will then:
- Anchor bolts to mudsill, which prevents homes and residential buildings from slipping off their foundations.
- Construct the home’s cripple wall, or the CLT panels used in crawl space or soft story garage. These are designed to soften any lateral shift from an earthquake. Cross Laminated Timber (CLT) CLT consists of layered timber where each layer is placed perpendicular to the adjacent layer. This creates a sturdy base for soft-story homes that are found to protect them from irreparable damage.
- Secure framing clips to the cripple wall which reinforces new structural integrity.
How Design Everest Can Help
Not all engineers are trained and experienced in seismic retrofit design. The retrofitting needs of homes and residential buildings vary; the enhancements might be as simple as straps to secure equipment or as complex as structural anchors or roofing modifications.
Design Everest structural engineers are trained in knowing which seismic retrofits a building will benefit most from. Our strong ethics in safety and our budget-conscious design plans will ensure that your property is secured and ready to mitigate high-impact seismic activity. When hiring Design Everest, you can expect our engineers to evaluate the current conditions of the home or commercial structure, including quality of construction, state of repairs, location, and year built.
During an on-site evaluation, one of Design Everest’s engineers will assess the existing structure, talk through any of your concerns, and propose recommended structural improvements to enhance safety or achieve your objective. Design Everest will then prepare a proposal for structural engineering drawings and calculations necessary for you to obtain a permit for the project.