Approximately 5,000 soft story structures in San Francisco require seismic strengthening. In 2013, the City of San Francisco passed the Mandatory Soft Story Retrofit Ordinance and received over a 99% response. At this late point in the program, remaining structures have limited time to comply with this important ordinance to protect their structures and their lives.
Approximately 13,500 soft story structures in the Los Angeles area require seismic strengthening. In May 2016, the City of Los Angeles started sending out orders to comply to building owners, based on their retrofit priority. Owners have two years from the date of receipt to submit proof of a completed retrofit, or plans to retrofit or demolish. Owners have 3.5 years from the date of receipt to obtain a permit to start construction or demolition. Construction of the retrofit must be completed within seven years of the date of receipt.
Many older structures have damaged foundations. By repairing these foundations, homeowners can add a great deal of earthquake resilience to their structure. After performing a large number of these foundation repairs, SFT Construction has become an expert and can evaluate foundations and suggest the most efficient repairs to the foundation.
Underpinning is when a structure's foundation is strengthened. This usually occurs by enlarging the structure's concrete foundation. The enlarged foundation not only provides more concrete to support the structure better, but it may also cover a more better suited soil. This is an area where SFT Construction has extensive experience and an area where experience really matters when creating solutions.
Brace + Bolt Retrofits are smaller retrofits performed on single-family residential homes. These retrofits often do not even require engineering. They consist of installing anchor bolts to anchor the wooden structure to its concrete foundation and bracing cripple walls to prevent the house from collapsing in the case of an earthquake. Most of these retrofits cost between $3,000 & $7,000, and government programs can often cover up to $3,000 of that amount.
Tilt up construction is a construction method that was used until approximately 1980. These concrete structures were built by first pouring concrete to make walls horizontally, and then lifting those horizontal panels to their vertical position. Although this construction method provided significant cost savings, it proved extremely unsafe in earthquakes. This was mainly due to the fact that lightweight plywood roofs were usually used in these structures. During earthquakes, these roofs became detached from the rest of the structure, and cause the walls to lose stability. SFT Construction is one of few contractors capable of retrofitting such structures.
Unreinforced Masonry (URM)
Unreinforced masonry structures are buildings built of bricks, without any additional support. These buildings are very rigid. Therefore, in case of an earthquake, they crack and easily topple. Much of the worst damage that is observed during earthquakes is that which has happened to unreinforced masonry structures. In order to strengthen these buildings, additional components, such as braces or anchoring, can be installed. SFT Construction has dealt with URM structures and always finds a solution to increase their earthquake resilience.
Non-ductile Concrete Building
Non-ductile reinforced concrete buildings are most concrete buildings constructed in California before 1980. They are "non-ductile," which means that they are not flexible, and they are constructed of reinforced concrete. These two-story to five-story structures, unlike modern buildings, lack the flexibility required to remain safe during an earthquake. The City of Los Angeles, alone, has over 1000 of these structures and has passed an ordinance with a 25 year time-frame requiring their retrofit. SFT Construction can perform these complex retrofits by taking the necessary actions such as installing steel shear walls or steel braced frames.
Retaining walls are walls that are used to separate two masses of soil, so that they can be at different levels. These walls are typically used at slopes, and serve to prevent soil from slipping and flowing down the slopes. Though not applicable to many properties, retaining walls can be of great necessity to many others, and SFT has constructed enough retaining walls to know when and where these can help in a retrofit.