Load Duration and Probability Based Design of Wood Structural Members


  • Bruce R. Ellingwood
  • Erik M. Hendrickson
  • Joseph F. Murphy


Buildings, damage accumulation, design, duration of load, limit states, loads, probability, reliability, snow, statistics, structural engineering, wood


Methods are presented for calculating limit state probabilities of engineered wood structural members, considering load duration effects due to stochastic dead and snow load. These methods are used to conduct reliability studies of existing wood design criteria. When realistic load processes are considered, it is found that the importance of load duration and gradual damage accumulation has been somewhat overstated. One possible probability-based design method that should be useful in future code development work also is presented.


American Concrete Institute (ACI). 1983. Building code requirements for reinforced concrete (ACI Standard 318). Detroit, MI.nAmerican Institute of Steel Construction (AISC). 1986. Load and resistance factor design specification for structural steel buildings. Chicago, IL.nAmerican Institute of Timber Construction (AITC). 1980. Timber construction manual. Englewood, CO.nAmerican National Standards Institute (ANSI). 1982. Minimum design loads for buildings and other structures (ANSI Standard A58.1-1982). New York, NY.nBarrett, J. D., and R. O. Foschi. 1978. Duration of load and probability of failure in wood. Part I. Modeling creep rupture. Part II. Constant, ramp, and cyclic loadings. Canadian J. Civil Eng. 5(4):505-532.nBohannan, B. 1966. Effect of size on the bending strength of wood members. USDA Forest Service Research Paper 56. Madison, WI.nEllingwood, B. 1981. Reliability of wood structural elements. J. Struct. Div. ASCE. 107(1):73-87.nEllingwood, B. 1982a. Probability based load criteria: Load factors and load combinations. J. Struct. Div. ASCE. 108(5):978-997.nEllingwood, B. 1982b. Safety checking formats for limit states design. J. Struct. Div. ASCE. 108(7):1481-1493.nEllingwood, B. and R. K. Redfield. 1983. Ground snow loads for structural design. J. Struct. Eng. ASCE. 109(4):950-964.nFoschi, R. O., and J. D. Barrett. 1982. Load-duration effects in western hemlock lumber. J. Struct. Div. ASCE. 108(7):1494-1510.nFoschi, R. O., and R. K. Redfield. 1983. Ground snow loads for structural design. J. Struct. Eng. ASCE. 109(4):950-964.nGalambos, T. V. et al. 1982. Probability based load criteria: Assessment of current design practice. J. Struct. Div. ASCE. 108(5):959-977.nGerhards, C. C., and C. L. Link. 1983. Use of a cumulative damage model to predict load duration characteristics of lumber. IUFRO Division 5 Conference, Madison, WI.nGerhards, C. C., and C. L. Link. 1986. Effect of loading rate on bending strength of Douglas-fir 2 by 4's. Forest Prod. J. 36(2):63-66.nHendrickson, E. M., B. Ellingwood, and J. Murphy. 1987. Limit state probabilities for wood structural members. J. Struct. Eng. ASCE. 113(1):88-106.nItani, R., and K. Faherty, eds. 1984. Reliability-based design. Pages 169-171 in Structural wood research: State of the art and research needs. American Society of Civil Engineers. New York, NY.nMadsen, B. 1975. Strength values for wood and limit states design. Canadian J. Civil. Eng., 2(3):270-279.nMarx, C., and R. Moody. 1981. Strength and stiffness of small glued-laminated beams with different qualities of tension laminations. FPL Report 381, U.S. Forest Products Laboratory. Madison, WI.nMiner, M. A. 1945. Cumulative damage in fatigue. J. Appl. Mech. ASME. 12(3).nMoody, R. 1977. Improved utilization of lumber in glued-laminated beams. FPL Report 292, U.S. Forest Products Laboratory. Madison, WI.nMurphy, J. F. 1983. Discussion of load-duration effects in western hemlock lumber by R. O. Foschi and J. D. Barrett. J. Struct. Eng. ASCE. 109(12):2943-2946.nO'Rourke, M., et al. 1982. Uniform snow loads on structures. J Struct Div ASCE. 108(12):2781-2798.nSexsmith, R. G., and S. Fox. 1978. Limit states design concepts for timber engineering. Forest Prod J 28(5):49-54.nTurkstra, C. J., and B. Madsen. 1980. Load combinations in codified structural design. J. Struct. Div. ASCE. 106(12):2527-2543.nWood, L. W. 1951. Relation of strength of wood to duration of load. Report R1916, Forest Products Laboratory. Madison, WI.n






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