Another Look at Load Duration Effects in Wood
Publication: Journal of Structural Engineering
Volume 128, Issue 6
Abstract
Load duration behavior, arising from creep rupture, is one of the most significant effects distinguishing wood materials from other structural materials. The phenomenon of creep rupture has been widely studied over the past 2 decades. Recent experimental programs have focused on duration-of-load (DOL) effects in full-size lumber and a number of different cumulative damage models have been proposed. These models have been used in reliability analyses that take into account the stochastic nature of the loading process to evaluate appropriate load duration adjustment factors for use in design. More recently, the stochastic damage accumulation process itself has been investigated. This has resulted in proposals for simplified cumulative damage analyses and the re-emergence of the “killer pulse” concept for load duration effects in wood. The evolution of the new LRFD standard for wood provides a good opportunity to revisit this important issue. This paper will briefly review DOL research, with particular emphasis on the work used as the basis for the time effects factors in the LRFD standard, and describe a simplified approach to cumulative damage analysis using order statistics. It is shown that reliability analyses including DOL behavior can be performed more simply (efficiently) using an order statistics approach or even a simple first order reliability method analysis. Thus, it may be possible to evaluate load duration factors for design without having to perform complex stochastic cumulative damage analyses.
Get full access to this article
View all available purchase options and get full access to this article.
References
AFPA. (1995). “Standard for load and resistance design for engineered wood structures.” AFPA, Washington, D.C.
AFPA. (1997). “National design specification for wood construction.” AFPA, Washington, D.C.
Balakrishnan, N., and Cohen, A. C. (1991). Order statistics and inference: estimation methods, Academic, New York.
Barrett, J. D., and Foschi, R. O.(1978a). “Duration of load and probability of failure in wood. Part I: Modelling creep rupture.” Can. J. Civ. Eng., 5(4), 505–514.
Barrett, J. D., and Foschi, R. O.(1978b). “Duration of load and probability of failure in wood. Part II: Constant, ramp, and cyclic loadings.” Can. J. Civ. Eng., 5(4), 515–532.
Bulleit, W. M., and Liu, W.-F.(1995). “First-order reliability analysis of wood structural systems.” J. Struct. Eng., 121(3), 517–529.
Bulleit, W. M., and Schoch, C. G. III, (1986). “Simulation of load-duration effects in wood.” Wood Sci. Technol., 20, 157–167.
Cai, Z., Rosowsky, D. V., Hunt, M. O., and Fridley, K. J.(2000). “Comparison of actual vs. simulated failure distributions of flexural wood specimens subject to 5-day load sequences.” Forest Products. J., 50(1), 74–80.
Chalk, P., and Corotis, R. B.(1980). “A probability model for design live loads.” J. Struct. Div., ASCE, 106(ST10), 2017–2033.
Ellingwood, B. R., Hendrickson, E. M., and Murphy, J. F.(1988). “Load duration and probability based design of wood structural members.” Wood Fiber Sci., 20(2), 250–265.
Ellingwood, B., and Rosowsky, D. V.(1991). “Duration of load effects in LRFD for wood construction.” J. Struct. Eng., 117(2), 584–599.
Foschi, R. O., and Barrett, J. D.(1982). “Load-duration effects in western hemlock lumber.” J. Struct. Div., ASCE, 108(ST7), 1494–1510.
Foschi, R. O., Folz, B. R., and Yao, F. Z. (1989). “Reliability-based design of wood structures.” Rep. No. 34, Dept. of Civil Engineering, Univ. of British Columbia, Vancouver, Canada.
Foschi, R. O., and Yao, Z. C. (1986). “Another look at three duration of load models.” Proc., XVII IUFRO Congress, Paper No. 19, Florence, Italy.
Fridley, K. J., Tang, R. C., Soltis, L. A., and Yoo, C. H.(1992). “Hygrothermal effects on load-duration behavior of structural lumber.” J. Struct. Eng., 118(4), 1023–1038.
Galambos, T. V., Ellingwood, B., MacGregor, J. G., and Cornell, C. A.(1982). “Probability based load criteria: Assessment of current design practice.” J. Struct. Div., ASCE, 108(ST5), 959–977.
Gerhards, C. C.(1979). “Time-related effects on wood strength: A linear cumulative damage theory.” Wood Sci., 11(3), 139–144.
Gerhards, C. C.(1988). “Effect of grade on load-duration of Douglas-fir in bending.” Wood Fiber Sci., 20(1), 146–161.
Gerhards, C. C., and Link, C. L. (1983). “Use of a cumulative damage model to predict load-duration characteristics of lumber.” Proc., IUFRO Division 5 Conf., 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.
Haupt, H. (1867). General theory of bridge construction, Appleton, New York, 60–62.
Johns, K., and Madsen, B.(1982). “Duration of load in lumber. Part I: A fracture mechanics approach.” Can. J. Civ. Eng., 9(4), 502–514.
Karacabeyli, E. (1988). “Duration of load research in North America.” Proc., Int. Conf. on Timber Engineering, Madison, Wis., 380–389.
Liu, W.-F., and Bulleit, W. M.(1995). “Approximate reliability analysis of wood structural systems.” Struct. Safety, 17, 59–78.
Madsen, B.(1973). “Duration of load tests for dry lumber in bending.” Forest Products. J., 23(2), 33–40.
Madsen, B., and Johns, K.(1982). “Duration of load effects in lumber. Part II: Experimental data.” Can. J. Civ. Eng., 9, 515–525.
Murphy, J. F., Ellingwood, B. R., and Hendrikson, E. M.(1987). “Damage accumulation in wood structural members under stochastic live loads.” Wood Fiber Sci., 19(4), 453–463.
Philpot, T. A. (1992). “The effect of creep on the performance and reliability of wood structures.” PhD dissertation, Purdue Univ., West Lafayette, Ind.
Philpot, T. A., and Rosowsky, D. V. (1992). “Statistics for light-occupancy live load modeling.” Rep. CE-STR-92-3, Purdue Univ., West Lafayette, Ind.
Rosowsky, D., and Ellingwood, B. (1990). “Stochastic damage accumulation and probabilistic codified design for wood.” Rep. No. 1990-02-02, Johns Hopkins Univ., Baltimore.
Rosowsky, D., and Fridley, K.(1992). “Stochastic damage accumulation and reliability of wood members.” Wood Fiber Sci., 24(4), 401–412.
Rosowsky, D. V., and Fridley, K. J.(1995). “Directions for duration-of-load research.” Forest Products. J., 45(3), 85–88.
Turkstra, C. J., and Madsen, H. O.(1980). “Load combinations in codified structural design.” J. Struct. Div., ASCE, 106(ST12), 2527–2543.
Wood, L. W. (1951). “Relation of strength of wood to duration of load.” Rep. No. 1916, USDA, Forest Service, Forest Products Laboratory, Madison, Wis.
Information & Authors
Information
Published In
Journal of Structural Engineering
Volume 128 • Issue 6 • June 2002
Pages: 824 - 828
Copyright
Copyright © 2002 American Society of Civil Engineers.
History
Received: Jul 11, 2000
Accepted: Mar 27, 2001
Published online: May 15, 2002
Published in print: Jun 2002
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.