Soft story retrofitting in Los Angeles, Santa Monica, and West Hollywood is not just recommended, the soft-story retrofit requirements are pointed by the Law! Los Angeles, Santa Monica, and West Hollywood presently have the nation's toughest seismic building codes in the nation. The Ordinance 183893 and 184081 of Los Angeles City Soft-Story retrofit, detail which structures are affected. The city of West Hollywood passed Ordinance 17-1004 and Ordinance 17-1011 bringing new seismic requirements for seismic retrofitting within their municipality. This year the city council of Santa Monica passed Ordinance 2537 to require seismic retrofitting of buildings that are at risk of collapsing during an earthquake.
Ordinances of Los Angeles City Soft-Story Retrofit
As it was mentioned above - the 183893 and 184081 Ordinances of Los Angeles City Soft-Story retrofit, detail which structures are affected. All the Soft-story structures which are designed and approved before 1978, are considered weak and vulnerable by current engineering standards. A considerable amount of soft-story buildings were constructed from 1960 to 1979 and those structures have the propensity of experiencing catastrophically damaged in the event of any major earthquake. Soft-story buildings have failed during significant seismic activity. They are considered vulnerable because they have un-reinforced openings on the ground floor which causes a way more movement than the structure would withstand without them. When this happens, resulting in the upper floors COLLAPSING on top of the lower levels.
Soft-Story Building Condition
So-called soft-story buildings conditions are the ones, having first stories much less rigid than the stories above, are particularly susceptible to earthquake damage because of large, unreinforced openings on their ground floors and in their typically wood-frame construction. These openings often accommodate parking spaces, large windows, and expansive lobbies in residential and retail buildings. Without proper design, such structures are much less able to withstand the lateral forces - forces that push a structure side to side -- that earthquakes generate. Once the first-floor folds, the upper floors pancake down on top of it, crushing anything underneath.
That's clearly a big problem in population-dense, earthquake-prone areas like Los Angeles and San Francisco (and, theoretically, any high-density city, earthquake-heavy area with similar construction), yet those cities still have thousands of soft-story buildings in need of improvements. A study conducted by the California Institute of Technology found that, of Los Angeles' estimated 20,000 soft-story buildings, only 800 had been improved and the San Francisco faces a similar situation with its roughly 10,800 soft-story buildings.
What can be done to prevent such a disaster? Learn more about soft-story seismic retrofitting.
Soft-Story Seismic Retrofitting
Soft-story seismic retrofitting addresses those oversights, adding the structural components needed for buildings to remain standing after an earthquake hits. Read on to find out how the process works and how cities are encouraging building owners to make these improvements.
It is believed lateral stiffness and strength are the key ingredients to make buildings 'earthquake safe.' In a soft-story building, the lateral components were either never considered or they are just not strong enough to resist the imposed earthquake forces.
Analyze the Soft-Story Structure
The first step in any soft-story seismic retrofitting is to analyze the soft-story structure and determine the best way to strengthen the property. Structural engineers and contractors have to weigh several factors when deciding the best way to approach such a project. Not only do they have to ensure the building will meet the structural standards required of retrofitted buildings, but they also have to minimize the impact on the building's functionality. As easy as it might be to reinforce buildings by filling their ground floor parking spaces with braces or walling over their picture windows, both city zoning laws and wary building owners ensure that's not an option. Instead, engineers and contractors typically use a few different approaches to complete a soft-story seismic retrofit.
Some structural engineers explain some of the approaches can strengthen the existing walls, add new shear walls or add a steel frame in the soft areas of the building. To strengthen existing walls, finishes like drywall or stucco are replaced with sturdier plywood. Anchoring walls to the foundation is also part of the process. A steel frame may pose the best option, though such frames may be more expensive and dangerous to install than other techniques.
Rather than making buildings earthquake-proof, retrofitting aims to make earthquake-safe buildings, which means that they will still be standing when the shaking stops. It is also pointed out that even with these improvements, retrofitted buildings still will not meet the structural standards of modern construction.
In most cases, the Guidelines for the Seismic Retrofit of Existing Buildings require that soft-story retrofits provide at least 80 percent strength of the level above which is considered to be the vulnerable story and that the retrofitted stiffness be approximately 60 percent of that required for new construction.
The Cost of Soft-Story Retrofit
The cost of a soft-story retrofit varies greatly depending on the scope of the project, but a large building can cost upward of $100,000 to retrofit in some cases.
Clearly, soft-story seismic retrofitting is not cheap, but it can be money well spent - for saving human lives and being safe. However, building owners often do not want to deal with the hassle and expense of the process, so cities are adopting a variety of approaches to encourage or, sometimes even require owners to retrofit their buildings.
In some cities, owners of soft-story buildings must have their buildings assessed for structural weaknesses. Whether they then choose to rectify those weaknesses is up to them, but if an owner decides to go without the expense, they must post a warning informing all residents and guests that the building is likely unsafe in the event of seismic activity. Other cities encourage retrofits by waiving zoning requirements for parking and other building codes, providing tax incentives, or preventing building owners from performing other renovations or improvements until they've first retrofitted their building. Going further, cities like Fremont simply call for owners of soft-story buildings built before 1978 to retrofit them or face heavy fines. Hopefully, policies like these, rather than another earthquake, will bring much-needed attention to the issue of soft-story retrofitting.