Reliability-Based Code Calibration for Design of Wood Members Using Load and Resistance Factor Design1
Publication: Journal of Structural Engineering
Volume 131, Issue 2
Abstract
The procedures underlying the load and resistance factor design (LRFD) format for engineered wood construction combine elements of reliability analysis with the experience gained from decades of successful use of allowable stress design procedures. However, the judgments applied in much of the early development or LRFD hinged directly on the load factors and underlying load distribution assumptions in the 1993 version of the ASCE 7 load standard. Since that time, load factors in ASCE 7 have changed several times and additional information is available regarding load distributions. Assumptions regarding resistance statistics also have evolved during the past decade. For example, early reliability analyses were based on resistance distributions derived from individual data sets. Unfortunately, this approach is confounded by often significant differences that occur between data sets. This approach also neglects the self-calibrating nature of engineered wood product specifications. This paper examines the range of computed reliability indices that result from updating the assumed load statistics and assumed resistance statistics. Several load cases involving dead, live, snow, and wind load are examined. The reference structural configuration is a simple flexural member. The results show that the range of computed reliability indices is most significantly influenced by regional variations in load statistics. While these results also show slight differences in computed reliability indices from one engineered wood product to another, these differences are not judged to be significant. The results of this study will not only assist the Structural Engineering Institute Design of Engineered Wood Construction Standards Committee in their upcoming revision of ASCE 16, but can also serve as a template for other material standards committees (steel, concrete) as they update their LRFD specifications to reflect evolutionary changes in ASCE 7.
Get full access to this article
View all available purchase options and get full access to this article.
Acknowledgments
This study was part of and SEI Special Project entitled “Re-evaluation of LRFD for Engineered Wood Products: Keeping Pace with Changes in ASCE 7.” Partial funding provided by the ASCE Structural Engineering Institute (SEI) is gratefully acknowledged. The writers also would like to thank the members of the SEI Committee on Reliability-Based Design of Wood who participated in this project, members of the AF&PA Subcommittee on Structural Design for their review of the resistance distribution information, and Mr. Kyung Ho Lee for his assistance in running the analyses and preparing selected figures.
References
American Forest and Paper Association (AF&PA). (1991). National design specification (NDS) for wood construction. Washington, D.C.
American Forest and Paper Association (AF&PA). (1997). Load and resistance factor design (LRFD) manual for engineered wood construction. Washington, D.C.
American Society of Civil Engineers (ASCE). (2002). “Minimum design loads for buildings and other structures.” SEI/ASCE 7-02, Reston, Va.
Ang, A. H-S., and Tang, W. H. (1984). Probabilistic concepts in engineering planning and design, decision, risk, and reliability, Vol. II, Wiley, New York.
Ellingwood, B., Galambos, T. V., MacGregor, J. G., and Cornell, C. A. (1980). “Development of a probability based load criterion for American National Standard A58.” Special Publication SP577, U.S. Dept. of Commerce, National Bureau of Standards, Washington, D.C.
Ellingwood, B., and Rosowsky, D. V. (1991). “Duration of load effects in LRFD for wood construction.” J. Struct. Eng., 117(2), 584–599.
Forest Products Research Society (FPRS). (1989). In-grade testing of structural lumber: Workshop summary, Madison, Wis.
Gerhards, C. C., and Link, C. L. (1987). “A cumulative damage model to predict load duration characteristics of lumber.” Wood Fiber Sci., 19(2), 147–164.
Gromala, D. S., and Line, P. (2004). “Wood product distribution parameters for use in reliability analysis.” Proc., 2004 ASCE/SEI Structures Congress (CD-ROM), Reston, Va.
Melchers, R. E. (1999). Structural reliability: Analysis and prediction, 2nd Ed., Wiley, New York.
Rosowsky, D. V., and Bulleit, W. M. (2002). “Another look at load duration effects in wood.” J. Struct. Eng., 128(6), 824–828.
Wallace, D. E., and Cheung, K. C. K. (1989). “U.S. in-grade testing program: Summary of piece properties and status of use.” Proc., In-Grade Testing of Structural Lumber Workshop, Forest Products Society, Madison, Wis., 87–92.
Information & Authors
Information
Published In
Journal of Structural Engineering
Volume 131 • Issue 2 • February 2005
Pages: 338 - 344
Copyright
© 2005 ASCE.
History
Received: Nov 21, 2003
Accepted: Jun 9, 2004
Published online: Feb 1, 2005
Published in print: Feb 2005
Notes
Authors are members of the ASCE/SEI Committee on Wood, Subcommittee on Reliability-Based Design
Note. Associate Editor: Daniel Dolan
Authors
Metrics & Citations
Metrics
Citations
Download citation
If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download.