Earthquake Loss Estimates and Policy Implications for Nonductile Concrete Buildings in Los Angeles

Abstract

The collapse potential of nonductile concrete buildings represents a substantial life safety hazard globally that can be mitigated through carefully crafted policy. Mitigation policy should be approached incrementally by (1) understanding problem scale, (2) screening for low- and high-risk buildings, (3) performing engineering analysis for potentially vulnerable buildings, and (4) retrofit or replacement of high-risk structures. This research addresses initial stages of this sequence for Los Angeles, California. The intent was to investigate approaches for informing mitigation priorities by: characterizing the inventory of approximately 1,500 pre-1976 concrete buildings; estimating risk, including identification of building types that contribute most substantially to the risk; and investigating the impact of retrofit policy alternatives. Loss estimates for scenario events are based on the HAZUS™ Advanced Engineering Building Module. Depending on model assumptions, losses range from $1.8 to $28.5 billion and <50 to 8,300 fatalities. We investigate proposals targeting vulnerable buildings for retrofit as compared to retrofitting all buildings in the inventory. Awareness raised by this research contributed to the formation of the Los Angeles Mayoral Seismic Safety Task Force, which developed policy proposals.

A Detailed Inventory of Non-Ductile Concrete Shear Wall Buildings

“…Three of the groups identified by Anagnos et al (2016) with a total of 71 buildings have similar age, height, and occupancy as the 350 buildings in the current study. However, these buildings contributed a small percentage of the estimated fatalities and losses for the scenarios that were investigated (Anagnos et al 2016), thus the detailed inventory approach used in the current study would not be very useful for this group of buildings. On the other hand, the 49 pre-1930s, 8+ story commercial/office buildings do contribute significantly to the fatalities and losses so a more detailed inventory of these buildings could achieve further efficiencies in retrofit policy if the structural drawings were available.…”

“…Inventory approaches are still useful when structural drawings are not available. For example, Anagnos et al (2016) separated 1,500 pre-1976 concrete buildings in the city of Los Angeles into 12 groups based on the building age, height, and use, as a proxy for construction typology and expected structural performance, using this study to inform public policy development in Los Angeles to address the seismic risk from non-ductile concrete buildings. Three of the groups identified by Anagnos et al (2016) with a total of 71 buildings have similar age, height, and occupancy as the 350 buildings in the current study.…”

“…For example, Anagnos et al (2016) separated 1,500 pre-1976 concrete buildings in the city of Los Angeles into 12 groups based on the building age, height, and use, as a proxy for construction typology and expected structural performance, using this study to inform public policy development in Los Angeles to address the seismic risk from non-ductile concrete buildings. Three of the groups identified by Anagnos et al (2016) with a total of 71 buildings have similar age, height, and occupancy as the 350 buildings in the current study. However, these buildings contributed a small percentage of the estimated fatalities and losses for the scenarios that were investigated (Anagnos et al 2016), thus the detailed inventory approach used in the current study would not be very useful for this group of buildings.…”

“…Much of the opposition to these policies has come from building owners as a result of the costs of the programs, and the perceived inconsistencies and conservatism (Egbelakin et al 2011). Researchers (e.g., Anagnos et al 2016) have shown the efficacy and much lower cost of mitigation policies that target only those buildings that have the highest risk, which a detailed inventory can help to identify. Furthermore, models developed based on the more detailed inventory data would help in establishing consistent and rational performance targets for at-risk buildings.…”

Seismic Policy, Operations, and Research Uses for a Building Inventory in an Earthquake-Prone City

“…Other examples of such databases of buildings and prioritization of retrofits programs include: Comerio (2000) for building assets owned by the University of California, Berkeley; Walsh et al (2016Walsh et al ( , 2017 on an asset database of buildings owned by Auckland City Council (the largest city in New Zealand); Anagnos et al (2016) on an inventory of nonductile concrete buildings in the city of Los Angeles and Anagnos et al (2012) for other cities in California; Yathon et al (2017) for a detailed inventory of pre-1980 high-rise reinforced concrete buildings in Vancouver (Canada); Palermo et al (2018) for a survey on similar European efforts; Hancilar et al (2018) for a building inventory assessment in Muscat (Oman); Jaiswal and Wald (2008) Each one of these works takes a somewhat different approach, but ultimately they all conduct pre-earthquake seismic resilience needs assessments for various sets of assets. Many of the earlier efforts, as described in Jaiswal and Wald (2008), were aimed at developing the required inputs into seismic risk modeling.…”