Track 1: Decline vs. Revival: Tempering the Impulse to Tear Down and Start Over
3 - Accommodating Seismic Code Requirements within Project Budgets
Monday, September 24
2:45 PM - 4:15 PM
Location: BNCC- 101AH
On August 23, 2011, a magnitude 5.8 earthquake hit Mineral, Virginia, about 90 miles southwest of Washington, DC. The resulting accelerations damaged many buildings, including the Washington Monument, the National Cathedral, and the Armed Forces Retirement Home. Estimates of the damage range up to $100 million, and concern for seismic risk grew in the DC Metro region as a direct result. Building owners began to ask the following questions: “Are we safe?” and “How much will seismic retrofits cost?” Engineers on renovation and preservation projects were confronted with a concerned and more-informed public, but still had to contend with tight budgets.
Seismic retrofit of historic structures is a costly enterprise, and therefore, limiting the scope of seismic retrofit to the essential elements is often crucial to keep a project within budget. Understanding upfront when these code provisions would be triggered is essential to informed early-stage decisions by the owner and project team in developing, from the outset, a scope and approach that best suit the project needs and provide some improvement in public safety. Late, unexpected triggering of code provisions that may lead to a project so over budget that an Owner may delay action on the project, resulting in no improvement to public safety or repairs to historic fabric. This presentation will walk through the latest codes for existing buildings and discuss specific provisions under what circumstances and to what extent seismic upgrades are required in various cases. The presentation will provide an overview of these codes and look at general concepts for seismic retrofit that owners should ask their engineers as projects begin. The presentation will then go through specific examples and highlight different approaches taken to provide high value (high benefit for relatively lower cost) seismic upgrades to existing buildings. For contrast, the presentation will also review a project where invasive and extensive seismic retrofits were required as a direct result of the 2011 earthquake. This contrast will highlight the importance and value of seismic evaluation and proactive retrofit of existing buildings.
The 2011 Mineral Virginia earthquake demonstrated that upgrading existing historic buildings to fully meet current codes can greatly improve public safety; however, this process can be so extensive that it is grossly destructive of historic fabric, and furthermore, it can be costly to the building owner and that can prevent any project (and hence any improvement to public safety) from proceeding. Understanding the building code and limiting the intervention to crucial elements is important to reducing project costs and enable/greenlight a project that includes some level of seismic retrofit, thereby improving public safety. After all, if no seismic retrofit because they are too expensive, then the built environment does not become any safer.
- Identify code provisions that require seismic analysis of existing structures.
- Identify architectural and structural elements vulnerable to earthquake damage in existing buildings.
- Determine when code proscribed thresholds are exceeded as part of the seismic analysis and structural alterations are then required to satisfy code provisions.
- Specify geotechnical investigations useful in developing seismic site class for a project site.