Every year on October 17, we take a moment to reflect on the 1989 Loma Prieta earthquake. The 6.9-magnitude earthquake was one of the most powerful and costly quakes to shake the San Francisco Bay area since the 7.9-magnitude earthquake of 1906. The quake caused an estimated $6 billion in damage and, tragically, resulted in 63 deaths and 3,757 injuries.
Many of those casualties were due to failing infrastructure when sections of the Nimitz Freeway collapsed.
Simpson Strong-Tie was founded in Oakland, California — practically in the heart of the Bay Area. Earthquakes were never far from the minds of our founders. It’s why even before Loma Prieta our mission was to provide solutions that help people design and build safer, stronger structures. However, it’s safe to say the earthquake not only reinvigorated our mission but inspired countless structural engineers who would go on to define the next 30 years of Simpson Strong-Tie research and development into community resilience.
I have a special place in my heart for old buildings. Every college design course I took was related to new design. Concrete, steel, or wood design, the design problem was invariably part of a new building. I thought structural engineers designed new buildings. When I showed up for my first day of work wearing dress pants, a button-down shirt and a tie, I was handed a flashlight, tape measure, a clipboard and a Thomas Guide map (no Google maps back then) and sent to do as-built drawings for a concrete tilt-up that we were retrofitting.
In San Francisco, thousands of building owners are already required by law to seismically retrofit multi-unit (at least five) soft-story, wood-frame residential structures that have two or more stories over a “soft” or “weak” story. These buildings typically have parking or commercial space on the ground floor with two or more stories above. As a result, the first floor has far more open areas of the wall than it actually has sheathed areas, making it particularly vulnerable to collapse in an earthquake.
San Francisco’s ordinance affects buildings permitted for construction before Jan. 1, 1978. Mandatory seismic retrofit program notices requiring that buildings be screened were sent out in September, 2013, to more than 6,000 property owners. It is anticipated that approximately 4,000 of those buildings will be required to be retrofitted by 2020.
“When we look at the demographic of these buildings, they house approximately 110,000 San Franciscans. It’s paramount that we have housing for people after a disaster. We know we will see issues in all types of buildings, but this is an opportunity for us to be able to retrofit these buildings while keeping an estimated 1100,000 San Franciscans in their homes and, by the way of retrofit, allowing them to shelter in place after a disaster,” according to Patrick Otellini, San Francisco’s chief resilience officer and director of the city’s Earthquake Safety Implementation Program. “This exponentially kick starts the city’s recovery process.”
One solution to strengthen such buildings is the Simpson Strong-Tie® Strong Frame® special moment frame. Its patented Yield-Link™ structural fuses are designed to bear the brunt of lateral forces during an earthquake, isolating damage within the frame and keeping the structural integrity of the beams and columns intact.
“The structural fuses connect the beams to the columns. These fuses are designed to stretch and yield when the beam twists against the column, rather than the beam itself, and because of this the beams can be designed without bracing. This allows the Strong Frame to become a part of the wood building and perform in the way it’s supposed to,” said Steve Pryor, S.E., International Director of Building Systems at Simpson Strong-Tie. “It’s also the only commercially-available frame that bolts together and has the type of ductile capacity that can work inside of a wood-frame building.”
Another key advantage of the Simpson Strong-Tie special moment frame is no field welding is required, which eliminates the risk of fire in San Francisco’s older wood-framed buildings.
To learn more about San Francisco’s retrofit ordinance, watch a new video posted on strongtie.com/softstory. For more information about the Strong Frame special moment frame, visit strongtie.com/strongframe.
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