Retrofit of Multi-Unit Wood-Frame Buildings with Weak First Stories
Retrofit of Multi-Unit Wood-Frame Buildings with Weak First Stories

Credit: 

  • Justin Moresco, PE, Director of Projects, Applied Technology Council
  • David Mar, SE, Partner, Mar Structural Design

Published: Structure Magazine, July, 2024

This article discusses recommendations from the FEMA P-807-1 report, which addresses retrofit strategies for improving the seismic performance of vulnerable soft, weak, or open-front (SWOF) wood-frame apartment buildings. These buildings, constructed from the 1950s to 1970s, are especially vulnerable to collapse during earthquakes due to weak lateral load-resisting systems. FEMA P-807 and its updated FEMA P-807-1 guidelines offer retrofit methodologies that strengthen the first story to reduce collapse risk while maintaining cost efficiency. Analytical studies show that ground floor retrofits, like those outlined in FEMA P-807, significantly lower collapse probabilities compared to simpler Line retrofits, which yield inconsistent results. The findings of FEMA-P-807-1 are timely because municipalities, particularly in California, have adopted retrofit ordinances targeting this typology in high-risk areas. These efforts aim to reduce the seismic risk posed by SWOF buildings, protecting public safety and minimizing post-disaster recovery costs. The guidelines balance the need for seismic resilience with practical considerations like cost, performance, and structural feasibility.

 

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