Resilience

Modern wood construction meets resilience objectives to withstand and recover.

 

As natural disasters become more severe and costly, and the threats posed by climate change become more evident, the question being asked is how to make homes and buildings more resilient. Across the government and in architectural, engineering, and design firms, more attention is being paid to improving safety and to better protecting property. In multiple studies, wood consistently meets or exceeds these higher performance goals and resiliency objectives.

  • Seismic Events: Among wood’s strengths is the ability to carry substantially greater maximum loads for short durations, characteristics well-suited to withstand and absorb minimal damage during seismic activity and high winds.
  • High Wind and Tornados: Wood’s elastic nature allows it to resist higher stresses when the load is applied over short periods of time. Elasticity, coupled with wood’s strength, helps wood achieve high rates of performance in wind events. In tests by APA, walls fully sheathed with plywood or OSB were three times stronger than walls constructed with gypsum wall sheathing or let-in bracing.
  • Hurricanes: Using wood and complying with modern building codes improves resiliency during severe weather events. Research done on homes in Texas and Florida damaged by hurricanes showed that homes built in accordance with the modern International Residential Code had less damage by hurricane-force winds than homes not built to the current standards.
  • Safe Rooms: Wood was shown to be well-suited for FEMA-approved safe rooms at the International Builders Show. AWC demonstrated how wood can be used to build a “safe room” for refuge during natural disasters. FEMA safe-room requirements include passing a 250 mph wind test and a 100 mph “missile” test.
  • Fire: Wood products and buildings are designed to meet rigorous standards for fire performance. In the context of resiliency, passive fire protection systems play a key role in containing and slowing the spread of fire.
The Benefit of Designing to Code

A National Association of Home Builders study determined homes built before 2003 in Texas and Florida, in compliance building codes in place at the time, sustained more damage during hurricanes than homes built to modern codes. Very few homes built under modern codes suffered severe damage to roof systems, wall sheathing, and framing or total loss and collapse of those components.

  • The National Institute of Building Sciences (NIBS) found that for earthquakes, designing to exceed 2015 codes provides $4 in benefit for each $1 invested.
  • NIBS also found that for a hurricane surge, designing to exceed 2015 codes delivers $7 in benefit for every $1 invested.

Case Study: Shaking Things Up

Researchers at the University of California, San Diego built a two-story, mass timber building on a large, outdoor shake table to simulate an earthquake and analyze the overall performance of the structure. The test building incorporated a lateral force-resisting system of two post-tensioned rocking walls made of cross-laminated timber (CLT) panels. The structural system was designed to be resilient, and in testing was subjected to a series of 14 earthquake ground motions and pushed to a maximum of five percent roof drift.

The results underscore the resiliency of wood and mass timber products. After the hazardous testing, the building re-centered with no unintended structural damage, highlighting the ability of mass timber rocking wall systems to withstand and recover from seismic events.