While a building designed for resilience is always a safe building, a building designed for life safety is not always a resilient building. In the United States, building codes require the design of building structures to meet minimum standards for the life safety of their occupants. Code standards for the construction of new buildings are written to ensure that structural systems are designed to yield and fail in a controlled and ductile manner that prevents collapse, allowing occupants to safely evacuate the building following an earthquake.
A code designed building’s seismic performance is analogous to the way a car performs in a collision. The car crumples and absorbs the energy of an impact to protect the occupants but is often left unusable and/or a total financial loss. Repair costs and recovery time apply not just to repair of structural elements but often times more critical, the repair of mechanical, electrical, plumbing, and architectural elements that are damaged as a result of the substantial side-to-side movement (drift) that is permitted to occur in a code designed building.
Extensively tested and researched technologies, systems, and design strategies exist that can significantly improve the performance of a building under seismic forces1. It may be in the best interest of a building’s stakeholders to consider a structural design that goes beyond the minimum requirements of the code.
Initial Cost vs Opportunity Cost
An evaluation of the opportunity cost of not designing for resiliency is critical. What could a poorly performing structure mean to a building and its owner, occupants, commercial tenants, business operations and physical assets should a significant earthquake occur? The disruptive effects may significantly exceed the cost of repair for damages to the building. Can the financial impact on tenant businesses be absorbed during the months or even years following an earthquake while the building must remain unoccupied?
When considering the initial cost of improving the resiliency of a structural system, a wholistic approach should be taken. Often the cost premium of resiliency is presented as a percentage increase of the structural system costs. However, it is not appropriate to consider the structural system costs alone because resiliency protects, and is an investment in the entire building, all the assets contained within and a protection against future losses. Designing for resiliency can add as little as zero up to as much as 1.5% to total construction costs, depending on the systems that are considered and project specific requirements.
A High Probability of Risk
According to research published by the United States Geological Survey in March 20152, in the Los Angeles and San Francisco Bay Areas, there is a 60% and 72% (respectively) probability that a magnitude 6.7 or greater earthquake will occur by 2045. For scale, the Northridge earthquake that struck the Los Angeles area in 1994 was measured at magnitude 6.7 and the Loma Prieta earthquake that struck the San Francisco Bay area in 1989 was measured at magnitude 6.93,4. If subjected to an earthquake of this magnitude, most buildings constructed in these regions today would suffer significant damage to the structure, MEP systems and interiors.
The Power of a Rating System
The US Resiliency Council, a 501(c)3 non-profit organization, has developed a Verified Earthquake Rating system, for both new and existing buildings, that is technically sound, credible, transparent and easy to understand. Ratings inform stakeholders of the seismic resilience of a building in three key categories; safety, damage repair costs, and recovery time5. Verified ratings provide confidence that investments are protected and that the communities in which we live are prepared to recover from an impending earthquake in an efficient and timely manner.
- Clark Pacific Precast Hybrid Moment Frame https://www.clarkpacific.com/products/structural-solutions/precast-hybrid-moment-frame/
- Source: https://pubs.usgs.gov/fs/2015/3009/pdf/fs2015-3009.pdf
- Damage to building in Northridge following Northridge earthquake. Source: https://www.usgs.gov/media/images/northridge-ca-earthquake-damage
- Damage to buildings in Santa Cruz following Loma Prieta earthquake. Source: https://www.mercurynews.com/2018/10/17/photos-loma-prieta-earthquake-scarred-bay-area-29-years-ago/