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This shear panel from Weyerhaeuser is designed to withstand seismic and wind damage.
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By Richard Wall
December 14, 2006/ — As the International Building Code marches into new areas of the country, forcing more residential builders to figure out proper bracing against earthquake and high-wind events, the International Codes Council has determined that its codes on bracing are a confusing mess based on questionable data and scant research. A complete overhaul is in the works, spearheaded by the ICC Ad Hoc Residential Committee on Bracing.
"A lot of external forces are converging on bracing as the single most important aspect of residential construction to keep houses from falling down and killing folks," says Ed Keith, PE, senior engineer at the APA Engineered Wood Association and one of 15 members on the ICC ad hoc bracing committee. "Residential bracing is growing like a good virus, spreading to more and more districts. And codes are the driving force."
New Concern: New Madrid
California and most other earthquake-prone areas of the West Coast require engineered seismic solutions and are generally in good shape on the bracing issue, according to Tim Reinhold, PhD, PE, director of engineering and a vice president of the Institute for Business and Home Safety. "The questionable parts of the country are high-wind areas and the New Madrid area," says Reinhold.
The New Madrid seismic fault is situated east of the Mississippi River near Memphis. A huge earthquake occurred along the fault in 1811-12, creating new lakes and forcing the Mississippi to flow backward. Insurers and building engineers are concerned that the area's housing is vulnerable to another quake.
That seismic danger and the regular tornado events in the region are reasons why Reinhold says IBHS, an insurance-industry organization dedicated to improving building practices, is focusing on the implementation of codes in the Midwest and fighting code exemptions. IBHS is working with the NAHB to help come up with cost-effective solutions for bracing codes.
"Some states are being more aggressive and active," says Reinhold. "Some states don't want to be involved. The question in the middle of the country is: What's the acceptable baseline? You're not using an engineering base, so as they go to these new systems, they're pegging performance to conventional construction techniques. And that's the area where the debate is going on."
Broken Bracing Code
There's debate — and there's confusion — even over the basic terms. Keith with APA explains that the term "shear wall" is commonly misused, because a shear wall is a designed component of commercial construction. "Bracing elements" is the preferred term for residential construction practices and products that act like shear walls in resisting earthquake and high-wind forces.
Whatever you call it, builders face the most confusion, says Ed. "As the bracing codes increase, builders are stopping at this section and saying, 'Look how complicated this is. I better pay attention to this.' It's raising a red flag for designers who use [the International Residential Code] that bracing's important, and they have to do it. This is such an enormous issue, and it's being recognized as a big roadblock in people's comprehension of how to build."
The IBC section on bracing, synthesized from 60 years of practice and preceding codes, is eight pages long and covers 11 bracing methods. ICC and APA are about to finalize a 120-page book explaining those eight pages. Keith says the ad hoc ICC bracing committee has already sorted the IBC material into a rational basis. But that's a very temporary solution, Keith says. "We know that the code is completely broken."
Devising Standardized Tests
Testing on a bracing method might have been done in 1948 — or in 2006. Much of it hasn't been tested at all, and there are glaring errors. "A good example is gypsum boards, which are recognized bracing for high seismic and wind," says Ed. "They don't perform the same in those events. We all know that, but it's [recognized] in the code."
Much standardized laboratory testing will be done to find out these basics. The result will be the development of a rational bracing table for wind and a separate one for seismic — both based on real science. "We're not sure how it's going to turn out," says Ed.
He does have an idea of when, though. By 2009, ICC should have the bracing issue clarified and should have it completely remodeled by 2012.
In the meantime, more and more builders will have to comply with bracing code as it stands. Reinhold with IBHS says most bracing solutions in conventional construction are fashioned on-site, using sheathing on the wood frame. Some builders are bringing in prefab panelized systems.
"There are nice products out there that can give you that shear resistance," says Reinhold. "That area will probably grow, because there is a lot more movement these days to do things in a controlled environment, where there is more potential for higher quality control."
Flexibility Required
Keith says companies such as Simpson Strong-Tie, James Hardie, Weyerhaeuser and others have panels that work well in residential bracing situations. However, as the bracing research eventually changes the code, manufacturers will probably have to make alterations concerning stiffness compatibility issues.
Jay Shansby, project manager for TJ-Shear Panels offered through Weyerhaeuser's iLevel integrated residential framing business, says they are moving beyond their traditional West-Coast market into the areas adopting prescriptive codes requiring stronger bracing for high winds, as well as seismic.
"We'll have the different seismic and wind ratings by prescribed market," says Shansby. "The builder doesn't have to calculate the loads and forces. A part of iLevel's focus is providing support out of our headquarters in Boise and out of the individual builder's market."
Shansby says the TJ-Shear Panels are particularly good solutions for challenges presented by large openings in short walls present shear challenges, such as a garage door taking up most of a wall. The panels are also good solutions in designs with high walls and lots of windows and doors. That should appeal to custom builders, says Shansby. And the simplicity should appeal to production builders.
"These things are simple and easy to install, and the builder doesn't have to worry about it passing inspection," says Shansby. "Since it's wood, the trades know how to work with it. It's designed to be a no-brainer to put it up, and you can attach things to it easily. We're always working with the product, especially as we roll into a new market."
Such flexibility will be needed as ICC pushes the bracing code forward from its current state. "Say you come up with a new kind of bracing wall," says Ed. "You prowl the building code and say, 'I'm going to prove that it's as good as wood structured panels.' Well, how do we know the wood structured panels are good themselves? To get to that point, you have to get everything tested out. Once we get the bracing sections adjusted to the realities of what technology will show us, then we can evaluate a new idea."
Richard Wall is a freelance writer and amateur historian in St. Augustine, Fla.
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