Residential construction can be particularly vulnerable to natural disasters. A team of researchers, led by Colorado State University engineering professor John van de Lindt, have put forth significant effort into learning how to make structures with first-floor garages better withstand seismic shocks, spending a month shaking a four-story building on the shake table at the University of California San Diego.
Van de Lindt studies how to improve structures, particularly residential dwellings, so they can survive natural disasters. Along with Simpson Strong-Tie and other partners, he successfully led the world’s largest earthquake shake table test in Japan in 2009 – a test that proved midrise wood-frame buildings can be built to withstand major earthquakes.
"Earthquakes are particularly damaging to buildings with open spaces at street level because they collapse – the first-floor parking makes the building structurally weak and soft," van de Lindt said in a release. "There are tens of thousands of these multi-family buildings throughout California and much of the U.S., making this a serious safety issue."
Since July 2013, the team has tested a variety of earthquake retrofits on a full-scale, 4,000-square-foot building comprised of three stories atop an open first floor. The building was built specifically for this purpose and designed to contain features common to California’s architectural style. Many buildings were constructed with wood-frame structure during the 1920s and ’30s. Such buildings typically had a weak and soft first story and large openings for shop windows or parking on the first floor. They have horizontal wood siding, hardwood floors, and gypsum wallboard in place of plaster on the upper three floors. The test building mimicked these characteristics.
Some of the retrofits being tested were designed in accordance with FEMA P-807 guidelines – a standard that was selected because it is approximately equal to the requirements of San Francisco’s mandatory retrofit ordinance, signed into law in April 2013, on the 107th anniversary of the devastating 1906 earthquake.
The law requires buildings with "soft-story" conditions to complete retrofits over the next several years. This includes approximately 2,800 buildings in the city of San Francisco, many built before 1978. However, many more exist throughout Los Angeles and all of California.
The first test used cross-laminated timber, a relatively new wood-based product. The retrofit consisted of eight 2-foot-wide rocking walls with plywood on the underside of the second floor diaphragm attached with a number of Simpson Strong-Tie straps and clips. The cross-laminated timber was provided by Innovative Timber Solutions-Smartwoods from Whitefish, Mont. The first test series was successful, and simulated tremors up to 50 percent MCE – maximum credible earthquake.
With various other retrofits, the building has survived three of four simulated seismic events of increasing strength on the shake table at the University of California San Diego.
"The larger shakes have damaged the building, but with the retrofits in place, it is still structurally safe enough for occupancy," van de Lindt said in the release.
Van de Lindt, the George T. Abell Professor in Infrastructure in the CSU College of Engineering in Fort Collins, Col., obtained a $1.24 million grant from the National Science Foundation for the research. His team is working in conjunction with Rensselaer Polytechnic Institute, Cal-Poly Pomona, Western Michigan University, and Clemson University. Numerous industry partners, including Simpson Strong-Tie and the Forest Products Laboratory, and several other government entities are also collaborating on the tests.
The research is being done as part of the Network for Earthquake Engineering Simulation in the NSF’s shared facility at UCSD.
Other wood products for harsh enviroments
Builders face some significant construction challenges from Mother Nature. Chance Miller, a builder in New Orleans, faces near 100 percent humidity in the spring and summer, omnipresent threats of rain, and frequent weather-related construction delays. Protecting framing materials, which are often made from wood in residential construction, from the elements is a significant concern. Miller has turned to Huber Engineered Woods LLC’s ZIP System as a way to get walls erected and protected, while effectively guarding against moisture and water intrusion.
The product is also the first insulated structural panel to achieve code approval under the International Code Council Evaluation Service’s (ICC-ES) updated acceptance criteria for proprietary sheathing panels.
The ZIP System R-Sheathing is currently the only insulated structural panel to have achieved recognition under the new guidelines and to have 2009 and 2012 code-recognized shear wall design values.
"The quality of building products has become increasingly important to builders as energy and building codes become more difficult to meet. The stricter requirements set forth by the ICC-ES is reflective of that need," Matt O’Brien, vice president of commercial operations, said in a release. "We’re pleased that ZIP System R-Sheathing is the first product of its kind to have passed the more rigorous testing required by the new Acceptance Criteria. This accomplishment sets us apart from our competitors in terms of structural integrity and overall product quality."
ZIP System R-Sheathing is a five-in-one insulated panel designed to provide bulk water, thermal, air, and moisture resistance while delivering strength and durability. Installed with ZIP System tape to create a seamless airtight seal, ZIP System R-Sheathing’s insulated panel provides greater energy efficiency and reduced heating and cooling costs.
The ZIP long length panels comply with IBC 2009 without the need for over bracing.
"I use ZIP’s 10- to 12-foot structural sheet and those seams are anchored into the slab at the bottom plate and extend to the second floor," Miller says. "It is one continuous panel, which alleviates the need to have anchoring systems. It’s structurally engineered to avoid the necessity of strapping and bolting."
The product is reported to have advantages over regular plywood or OSB panels that need to be followed with housewrap or felt. Miller says the ZIP System roof sheathing provides an additional layer of protection, which is crucial in an area prone to storms.
"I use 5/8-in. ZIP System panels to achieve the same water protection on the roof. If some shingles happen to fly off during high winds, the home is still protected because of the ZIP System sheathing’s water resistant properties," Miller says.
Because he is not using plywood, Miller no longer has a need for hurricane clips. "Once the panels are laid on top of the rafters, we use a taping system similar to that used on the vertical walls to provide the same level of protection," he says.
Christina M. Zweig is a contributing editor. She can be contacted at firstname.lastname@example.org.