WallBracing.org

APA Full-Scale House Test Project

Many researchers have conducted tests to study the effects of high wind or seismic events in wood frame construction systems. Much of this testing has been conducted on individual wall elements in a planar, two-dimensional configuration. Very little testing, however, has been conducted on full-scale, three-dimensional structures. Thus, load transfer among the various wall and floor diaphragm assemblies and interaction among these components is not well understood.

Beginning in early 2006, APA – The Engineered Wood Association expanded its laboratory capabilities to include three-dimensional, full-scale house structural tests. Using a new, state-of-the-art device, a lateral load was applied to a full-scale house to investigate the response of braced walls. This extensive study evaluates how various structural components work as a whole and provide us with a better understanding of a house’s true three-dimensional system performance, as well as specific measurements and data for wall bracing methods.

Preliminary Progress Reports

APA’s Technical Services Division is preparing a series of progress reports to keep you informed on the latest findings. The following preliminary progress reports have been completed:

• Overview of Test Project, Form 3D-001
• Effect of Return Corners and Hold Downs, Form 3D-002
• 3D Testing with 4:1 Aspect Ratio Wall Bracing, Form 3D-003
• 3D Testing with 6:1 Aspect Ratio Portal Frame Wall Bracing, Form 3D-004
• Effect of Bracing Configurations on Isolated Bracing (Method 3), Form 3D-005
• Wall Bracing with a 4:1 Aspect Ratio Using Sheathing Cut Around Openings, Form 3D-007

Download progress reports. Additional data will become available as more testing and analysis is conducted.

Phase 1 Testing of Whole House Wall Bracing Complete

APA has released a report that summarizes Phase I test results for a variety of wall bracing configurations using APA’s 3-dimensional full-scale house and a state-of-the-art loading apparatus. The report, Full-Scale 3D Wall Bracing Tests, APA Report T2007-73, is available as a downloadable PDF from the Publications Library.

This extensive study evaluates how various structural components work as a whole and provides the industry with a better understanding of a house’s true three-dimensional system performance, as well as specific measurements and data for wall bracing methods.

While the focus of these tests were mainly on the 2006 International Residential Code (IRC) wood structural panel wall bracing, a number of variables were studied, including:

• Hold down devices in building corners
• Return corners, both 2 feet and 4 feet
• Panel placement at corners or away from corners
• Single diagonal 1x4 bracing
• Isolated wood structural panel bracing
• Continuous wood structural panel bracing
• Continuous wood structural panel bracing cut around openings
• Wall braced only by 6:1 aspect ratio portal frames
• Wall braced with 50 percent 6:1 aspect ratio portal frames mixed with other continuous wood structural panel bracing.

Overview of APA Testing and Research

Over the years, builders and code officials have asked APA to help develop simple and economical bracing solutions for narrow walls—such as those next to garage, entry door and window openings—without the use of hold-down devices.

APA's solution, known as the Narrow Wall Bracing Method, permits walls as narrow as 16 inches without requiring hold down devices, provided the entire house is sheathed with structural wood panels. The method is based on an extensive series of full-scale cyclic wall tests using one of the strongest currently prescribed wall bracing methods as the benchmark—the continuously sheathed method as defined in the International Residential Code (IRC) R602.10.5.

APA's solution was subsequently accepted by IRC for garage openings and published in the 2004 IRC Supplement. (It will appear in the 2006 IRC). The acceptance is limited to single-story, or the first story of two-story applications, on rigid foundations, and in Seismic Design Categories A-C.

This prescriptive solution has proven very popular across the country because it is easy to build on-site using common materials and techniques, and because of the myriad other performance benefits that accrue from continuously sheathing a house with structural wood panels.

In addition to the current APA garage wall solution, the IRC also allows bracing as narrow as 24 inches wide on any story of a three-story home in all Seismic Design Categories in accordance with IRC provisions. Again, this narrow bracing is limited to houses with continuous structural wood panel wall sheathing (IRC R602.10.5).

Following the success of these narrow wall bracing methods, APA proposed an additional narrow wall bracing design for use with raised wood floors. Again, that proposal was based on numerous full-scale cyclic wall tests conducted at APA's accredited research laboratory using the strongest prescribed bracing as the benchmark. In fact, test results surpassed the strength capacities for APA's bracing method over rigid foundations.

Based on a review of the test data, many jurisdictions around the country currently accept APA's narrow wall bracing method over raised wood floors as an alternate construction method.

In March 2005, APA's bracing solution over raised wood floors passed the IRC Building and Energy Committee. At the September 30, 2005 Final Action Hearings, however, opponents of the prescriptive bracing solution argued that since industrywide testing criteria for IRC bracing does not exist, all IRC bracing should be open to question.

That argument, although widely recognized as a thinly veiled effort by some to protect proprietary products and interests, prevailed. As a result, the Narrow Wall Bracing Method for use over raised wood floors will not be included in the 2006 IRC. However, the existing IRC Narrow Wall Bracing Method acceptances continue in force, and use of the design over raised wood floors continues to be endorsed by APA and accepted by numerous local code jurisdictions around the country.

The case for Narrow Wall Bracing Method designs is straightforward and compelling. They provide design and on-site construction options and flexibility. They are cost-effective. They are based on extensive laboratory testing by an internationally accredited research laboratory in accordance with long-established and accepted test methods. They are proven in the field. They have real-world support of on-the-ground code officials in countless jurisdictions around the country. And perhaps most importantly, by prescribing that houses be fully sheathed with structural wood panels, they are an integral part of a total structure design solution that provides unsurpassed shear strength and racking resistance.

A Note on Narrow Wall Bracing Test Methods and Results

During the September 30, 2005 ICC Hearings in Detroit, those opposing APA's proposed code change argued that their own test results did not reproduce those presented by APA. However, it is known that setup details for those tests were different than APA's. Another party presenting test results declined to disclose test setup information. Only APA has made all of its test setup details and test results available for public review. (See links below.) Unless test setup details are the same, and without the ability to verify they are the same, differences in results are both misleading and meaningless.

For more information on APA Narrow Wall Bracing test methods and results, or APA laboratory accreditations, design and engineering capabilities and services, etc., contact APA at (253) 620-7400.