IRC Bracing Methods, Relevant Test Data, and Recommended Design Values for Wind Bracing Analysis of Conventional Wood-Frame Homes
September 23, 2006
Prepared by: Jay Crandell, P.E., Applied Residential Engineering Services
The following report, supplement, and appendix were prepared for the ICC / IRC Ad Hoc Committee on Wall Bracing. These documents are created to assist the Ad Hoc Committee members as they consider its recommendation on IRC code change proposal, RB 182. This proposal will be heard by the IRC Committee in Orlando, FL during its September 28-October 1, 2006 hearings. Final action will be taken in Rochester, NY in 2007.
(Note: The following report should be considered as a final “draft” as it awaits technical peer review by members of the IRC Ad Hoc Committee. It is being provided as it stands now to help educate all those interested in this issue, and who want to take a position on RB 182 during the 2006-07 code change cycle.)
- Review all available literature regarding in-plane (racking) shear capacity of wall constructions relevant to bracing methods found in the 2006 International Residential Code (IRC).
- Evaluate the data in regard to similarities and differences in test methods, results, and other factors to determine characteristic ultimate shear strength values as well as recommended allowable design shear values for each bracing method.
- Identify and recommend corrections or enhancements to the bracing methods as currently prescribed in the IRC.
There are three parts and an appendix to this report:
- Construction Requirements for IRC 2006 Bracing Methods (R602.10.3)
- Review and Evaluation of Relevant Wall Bracing Test Data
- Summary & Recommendations
APPENDIX A (pdf): Tabulated Test Data and Table References
While some of the findings in this report and the data included in Appendix A are relevant to design of seismic bracing, the focus of this report is on shear value design appropriate for proper wind bracing specifications used in conventional wood-frame homes within the scope of the IRC. Additional work, including consideration of seismic response modifiers for the various bracing methods in the IRC, is required for the purpose of re-evaluating the seismic bracing provisions in the IRC.
It should be recognized that the current bracing amounts in the IRC were based on an evaluation of seismic load only and are not necessarily adequate for wind loading in all conditions of use. Thus, this study is considered as a first step toward a thorough and practical re-evaluation of bracing amounts and bracing method requirements in the IRC for the purpose of ensuring adequate resistance to racking loads caused by wind.