Preparing for Natural Disasters
International Code Council members stand as the first line of defense in applying building codes to the construction of safe, sustainable, and more affordable and resilient structures. The entire month of May pays tribute to that distinguished service with the 37th annual Building Safety Month.
This installment of Codes Counts concentrates on the theme of week three of Building Safety Month: Manage the Damage – Preparing for Natural Disasters.
The topic is a broad one. We’ll narrow the focus on a natural disaster that is on the rise across the U.S., with cities as diverse as Boston, New York City, Memphis, Charleston, S.C., Albuquerque, Newark, Atlanta, St. Louis, Tacoma, and Philadelphia vulnerable to its effects.
We’re talking about, of course, earthquakes. FEMA, the Federal Emergency Management Agency, reports average annual earthquake losses in the U.S. now add up to $4.4 billion, nearly equivalent to the losses from floods and hurricanes. Adding to the challenge is the spiking number of earthquakes in unexpected areas such as Oklahoma, Colorado, and Ohio. Last September, for example, the largest reported earthquake in Oklahoma state history rocked the region with a 5.6 magnitude quake. Fracking operations are believed to be the cause.
For code officials, enforcing codes that anticipate seismic activity has long been a way of life. This is especially true on the West Coast, with southern California leading the way with about 10,000 earthquakes each year (though only several hundred are actually felt).
Over the decades, the difficult lessons learned from Alaska, Washington, Oregon, and California earthquakes have helped shape national code development. In observance of Manage the Damage week, it’s appropriate to examine why a growing body of architects and owners are electing to manage the damage through mass timber construction.
There are approximately 400 million square feet of public school space in California. About 80 percent of this area is built with wood for good reason: “wood frame buildings are known to perform well in earthquakes,”(as the California Department of Government Services wrote in its 2002 report, Seismic Safety Inventory of California Public Schools) and were exempted in a legislated inventory and earthquake worthiness assessment of schools.
Today, owners and designers are applying the hard lessons learned at the 1971 San Leandro, 1989 Loma Prieta, and 1994 Northridge earthquakes — and many other worldwide — to apply code-compliant, mass timber construction techniques across nearly all property types, including office/mixed-use, public and institutional, multifamily, and even hospitality.
The 2015 International Building Code (IBC) and American Society of Civil Engineers/Structural Engineering Institute Minimum Design Loads for Buildings and Other Structures (ASCE 7-10) represent codes and standards for seismic-resistive, wood-frame buildings. The 2015 IBC recognizes how ductile detailing, redundancy, and regularity contribute to mass timber’s inherent seismic-resistance characteristics.
A useful adjunct to those standards is the National Design Specification (NDS) for Wood Construction, an IBC-referenced design standard for lumber, glulam, structural composite lumber, and cross-laminated timber (CLT), including fire design, fasteners, and connections (a U.S. mass timber building cannot be designed without the NDS).
Let’s briefly look at why it’s likely code officials will be asked to review more mass timber projects in their jurisdictions.
- Ductility. Ductility is the ability of a structure to sustain extreme outside forces, notably an earthquake, without collapse. Mass timber buildings rapidly dissipate seismic energy across numerous load paths when faced with an earthquake’s sudden lateral stress.
- Redundancy. Typical mass timber construction is comprised of hundreds of structural elements and thousands of nail connections. When one load path fails, another one compensates, helping restore building integrity.
- Weight. Mass timber is a comparatively lightweight building material. Because of that, the foundation is typically a fraction of the weight of steel or concrete construction. For example, the walls used in insulated concrete form wall construction are many times as heavy as mass timber. Inertial forces are greater when the building material is heavier, so earthquake forces are more extreme in heavier structures.
- Connectivity. The unitized connection of the walls, floors, and roof framing to a solid foundation helps resist the racking forces of an earthquake.
- Strength/Stiffness. Wall stiffness can be modulated through mass timber panel thickness and the size/number of nails that hold it all together. Heavy braced shear walls resist lateral distortion.
This combination of structural attributes presents architects and owners with a robust alternative to more traditional building methods. Today, a comprehensive array of testing is underway in university research centers to further improve mass timber seismic performance. For code officials seeking examples on how others are using mass timber construction to help mitigate seismic hazards and other natural perils, read “An Overview of CLT Research and Implementation in North America,” a comprehensive paper released last summer in conjunction with the 2016 World Congress on Timber Engineering. This and other research is available online at the reThinkWood Research Library.
Earthquakes remain an elusive mystery, defying prediction. Armed with evolving codes that continually seek to lift best building practice, code officials remain one of the best ways to help the building industry “manage the damage” of inevitable earth movement.
During Building Safety Month, take the time to inform yourself of the projects your peers have reviewed in seismically challenged areas such as the West Coast. Improved understanding of mass timber construction means and methods will help you better uphold the highest standards of public safety, sustainability, and building performance.
For More Information
- reThink Wood Research Library
- Designing for Earthquakes
- Mass Timber in North America
- Designing Modern Wood Schools
- National Design Specification (NDS) for Wood Construction
- Earthquakes: Risk and Insurance Issues
The views and opinions expressed in this article are those of the sponsor and do not necessarily reflect those of the International Code Council, or Hanley Wood.