Los Angeles’ Mayor, Eric Garcetti, presents “Resilience by Design”Jan 27 2015 · 0 comments · Nishkian Chamberlain, Seismic ·0
The most obvious threat from earthquakes is physical damage to vulnerable buildings. Buildings can be built to withstand strong earthquake shaking, but because of the increased costs associated with such enhancements, most are not. Many people believe that modern Building Codes ensures that our buildings will not be severely damaged in earthquakes. Current Building Codes, however, are designed to maximize life-safety, and not to minimize building damage. These standards mean that while buildings are designed to remain standing and protect occupants from collapse, they are not designed to necessarily remain usable or prevent damage after strong earthquakes. A strong earthquake in Los Angeles could cause some older buildings to collapse, but would leave many more standing but unusable or in need of repairs, which would close businesses, deny residents access to goods and services, and devastate our economy.
“Resilience by Design” presents the recommendations of the Mayoral Seismic Safety Task Force (headed by Dr. Lucy Jones of the United States Geological Survey as his Science Advisor for Seismic Safety). These recommendations address the city’s greatest vulnerabilities from earthquakes with significant and attainable solutions to:
• Protect the lives of our residents;
• Improve the capacity of the City to respond to earthquakes;
• Prepare the City to recover quickly from earthquakes; and
• Protect the economy of the City and all of Southern California.
The report addresses the most obvious threat from earthquakes, physical damage to vulnerable buildings. Pre-1980 Soft Story and Non-ductile Reinforced Concrete buildings built before the implementation of Los Angeles’ 1976 revision of the building code pose a significant risk to life in strong earthquake shaking.
Soft story buildings are typically wood frame buildings where the first floor has large openings, for example tuck-under parking, garage doors, and retail display windows that create an unusually flexible or weak first story. They therefore, do not have the resistance to an earthquake’s shear (sideways) motions that is needed to hold up the upper floors. Because the damage to a soft-first-story building is concentrated in the lowest level, the first floor collapses and the rest of the building “pancakes” onto the first floor. This results in the complete destruction of the building and the potential for significant loss of life. Currently, there are more than 29,000 wood-frame apartment buildings with five or more units built prior to 1978 (the year that California adopted the 1976 Uniform Building Code) in the City of Los Angeles, and nearly 16,000 of these are estimated to be soft-first-story buildings. All of them are subject to the rent-stabilization ordinance. The loss of these rent-stabilized buildings in a big earthquake would eliminate a large amount of affordable housing in Los Angeles.
The report recommends that owners of residential buildings with four or more units, two or more stories, be required to, within one year of passage of the implementing legislation, submit to the City documentation establishing that an acceptable retrofit has already been conducted, or that a retrofit is not required. Owners must obtain all necessary permits within two (2) years after receipt of the order, for rehabilitation or demolition. It is further recommended that demolition or retrofitting be required so that first floors are strengthened to the same capacity as second floors within five years.
Fortunately, the engineering problem with soft-first-story buildings is readily understood. The remedy to the structural problem is straightforward and should be able to be performed without considerable disruption to a building’s residents.
“Non-ductile reinforced concrete” buildings, on the other hand are at higher risk of collapse, because some parts of the building such as columns and frame connectors are too brittle and break in strong shaking. The weight of the concrete makes them particularly deadly when they fail.
Older non-ductile reinforced concrete buildings are currently used as apartment complexes, schools, hospitals, office buildings, warehouses and more. Thousands of people in Los Angeles live and work within these structures every day. Significant damage to this type of building could not only present immediate safety concerns following a major earthquake, but could cause long-term or even permanent disruption to a community.
Network for Earthquake Engineering Simulation (NEES) data estimates that Los Angeles has over 1,400 non-ductile reinforced concrete buildings, many of which could be at risk for collapse in future earthquakes.
Unlike other types of buildings, identifying the concrete buildings that are at risk pose their own challenges since a simple visual inspection does not reveal which buildings may be at risk. The engineering community has developed an approach to identifying vulnerable concrete buildings. The American Society of Civil Engineers (ASCE) has developed ASCE 41, a document that describes the standards and process for assessing and retrofitting these types of buildings. A FEMA-funded research project currently underway by the Concrete Coalition, a collaboration of entities focused on assessing and mitigating the risk associated with dangerous non-ductile concrete buildings, is developing a more refined set of criteria to better identify the buildings that are the most likely to fail during an earthquake. The results of this study are expected by 2016.
The Report recommends a mandatory retrofit of pre-1980 Concrete buildings and buildings that are excessively damaged in a low level of earthquake shaking. Owners would have 5 years after the enactment of the ordinance to complete an evaluation with a structural engineer to determine what, if any, retrofitting will be needed to meet the standards. The owners would have 25 years to complete any required retrofit work.
The Seismic Safety Task Force discussed a number of programs that could be adopted during the course of implementing the ordinances in order to ensure the successful implementation of the recommendations. These programs can include:
• Providing access to private lending sources based on the PACE financing program for soft-first story retrofits.
• Waiving fees required by the Department of Building and Safety and the Department of City Planning for permits and variances associated with mandatory retrofit work.
• Allowing a reduction of up to 20% in required parking for the necessary loss of parking associated with soft-first-story retrofits.
• Establishing a 5-year exemption from Business Tax for businesses that move into newly retrofitted buildings.
• Establishing a policy by which, if in the rare instance that a building must be demolished, an owner demolishes and replaces a concrete building determined to require retrofit, the new building may be built with the same entitlements.
• Offering a business tax credit or exemption for those retrofitting and/or those who build a structure above the minimum code requirements.
• Working with the State to determine feasibility of easing CEQA requirements for projects associated with concrete building retrofit work.
• Reviewing provisions under the rent stabilization ordinance addressing cost sharing between landlords and tenants to determine if these provisions require adjustment to protect low-income tenants.
As the City of Los Angeles is on the forefront of establishing a Mandatory Seismic Retrofit Program in Southern California, many adjacent cities, such as, Santa Monica, Glendale and Burbank to name a few, are gearing up to implement their own programs. The adoption of Los Angeles’ program is expected to occur as early as late spring of 2015.
Nishkian engineers are update-to-date with the latest information regarding retrofitting and the new City legislation requirements. As each project has its own unique cost-effective solution, feel free to contact any of our offices to talk with our experts regarding the new seismic retrofitting recommendations that are coming to cities across our state.