The adoption of Soft-Story Retrofit Ordinance recognizes a vulnerable building type and mandates corrective measures.
It is common knowledge that California geology is vulnerable to earthquakes. Geological records show a pattern of seismic events that can be used to determine the locations most susceptible to an earthquake. The experience of seismic events within our lifetime has demonstrated the vulnerability in some building types that are described as “weak” or “soft-story” buildings. Having identified the more vulnerable building type what corrective measures can be taken to avoid a housing catastrophe on the scale of Hurricane Katrina?
Soft-Story buildings are common in many California metropolitan areas. They are typically constructed with tenant parking on the ground level and apartment living areas above. The parking level is referred to as a soft story because it supports the weight of the upper levels on very narrow walls or often times on posts to provide the opening required for parking cars. But in the event of an earthquake, these same narrow walls will be subjected to horizontal forces that can bring the building down as witnessed in the 1989 San Francisco earthquake and at the Northridge Meadows Apartments in 1994.
To demonstrate the structural shortcomings of soft story buildings, visualize a table with wobbly legs that are supporting a lot of weight. Shaking that table from side to side will cause the legs to buckle in the same way a soft story building will in a catastrophic collapse.
Who is Affected by the Ordinances?
Code officials in the San Francisco Bay Area and in the City of Los Angeles have recently adopted ordinances that require soft story seismic retrofits. The numbers are staggering, as will be the cost. There are currently 18,000+ wood frame buildings already identified that will require retrofitting under their local ordinance, and as an apartment owner, you may have already been notified of retrofit requirements.
The L.A. Times has reported in the City of Los Angeles alone there are an estimated 13,500 buildings identified, each of these must be retrofit with code-approve seismic structural solutions.
When Does the Work Have to be Done?
The amount of time building owners have to complete the fixes varies depending on the location of your buildings. In L.A., you have up to seven years to complete retrofit requirements. In San Francisco the due dates depend on the type of building you own. Type I buildings (“any building containing educational, assembly, or residential care facility uses”) must be retrofit by 9/17/2017. Type IV buildings (“any building containing ground floor commercial use”) has until 9/15/2018 to submit permit applications, and until 9/15/2020 for the work to be completed. (See City and County of San Francisco Department of Building Inspections – Mandatory Soft Story Program.)
Although the Los Angeles and San Francisco Building Departments were first to adopt the ordinances, they are often leaders in the adoption of new policies making it likely to spread to other counties and cities. (So, look for these ordinances to appear in other States with high Seismic Design Categories such as Oregon and Washington.)
Installing a Solution
Estimates as to the collective retrofit business range from $150 million to as much as $200 million meaning contractors who are qualified and capable of this type work are going to be in great demand. The industry is aware of the need to provide retrofit services and is responding. If you Google “soft story retrofit” you will get results of resources available including engineers, contractors, materials and descriptions of the work.
There is not a single structural solution for all buildings, nor a single solution within a particular building. For some buildings, conventional plywood “shear walls” are appropriate to offer resistance to seismic loads. In others, pre-fabricated structural shear wall systems or “Moment Frames” will be necessary. (“Moment Frames” are sturdy welded column-and-beam steel assemblies, specially designed for seismic events.) Given that many structures are two or more stories above ground level parking, with narrow vertical supports (and the need to protect parking spaces) Moment Frames are frequently the most appropriate solution. The types of Moment Frames used most often in soft story retrofits are Special Moment Frame, also called SMF, and they are designed to resist the “significant inelastic deformation” caused by earthquakes. Installation of a Moment Frame requires that column “base plates” be anchored to the foundation, which requires some excavation and disruption.
Moment Frame Types
There are primarily two manufacturers offering standardized, pre-fabricated Special Moment Frames: Hardy Frames, a MiTek Builder Product and Simpson Strong Tie. The pre-fabricated SMF’s currently offered primarily differ in two ways: the member sizes required and whether on-site assembly is required.
The Hardy Frame Special Moment Frame provides an advantage over Simpson because it is pre-assembled and welded at the factory, then delivered to the jobsite complete and ready to install. The first step in installation is excavating for concrete pads. When the foundation is prepared the frame is tilted at an angle then raised up snug to the building where it is attached through steel connectors. Once the SMF is in place concrete is poured to secure the frames anchorage to the foundation.
Property owners will be responsible for arranging and funding in areas where ordinances have been adopted. In these areas, there are guidelines permitting some of the expense to be shared with tenants through rent. Additionally, there will be owner benefits for having their building retrofit. Renters will prefer living in buildings that are safer and that they will not be displaced in the event there is a major seismic event. And the cost to retrofit is a fraction of the cost to repair or to replace a soft-story building with the type of damage it may experience. When viewed as investment, owners should consider a “performance based design” that goes beyond life safety design to dramatically reduce the sustainable damage.
- Hardy Frame: www.HardyFrame.com/softstory
- Simpson Strong Tie: www.StrongTie.com
- City of L.A. Dept. of Building Safety: http://ladbs.org/services/core-services/plan-check-permit/plan-check-permit-special-assistance/mandatory-retrofit-programs/soft-story-retrofit-program
- The City and County of San Francisco: http://sfdbi.org/property-owners
- Quake Map: http://www.nbclosangeles.com/news/local/Map-Largest-Magnitude-Earthquakes-California-Since-1900-296075431.html