Damage Accumulation in Wood Structural Members Under Stochastic Live Loads

Authors

  • J. Murphy
  • B. Ellingwood
  • E. Hendrickson

Keywords:

Stochastic live loads, load modeling, floor loads, load history, damage accumulation, duration of load, creep rupture, structural engineering, wood

Abstract

Damage accumulation in wood structural members was assessed using realistic stochastic modeling of live load. The model indicates that practically all damage occurs when the live load intensity is equal or nearly equal to the nominal live load, Ln, a quantity required by codes for design. Currently, basic allowable stresses for wood are calculated assuming a period of 10 years spent at the nominal live load. The model indicates that the time the live load is at or above the nominal is not 10 years but about 40 days in a reference period of 50 years, strongly suggesting that the 10-year period generally assumed for setting allowable stresses is much too long.

References

American National Standards Institute. 1982. American National Standard minimum design loads for buildings and other structures. ANSI A58.1-1982. New York, NY.nBarrett, J. D., and R. Foschi. 1978. Duration of load and probability of failure in wood—Parts I and II. Canadian J. Civil Eng. 5(4):505-532.nChalk, P., and R. B. Corotis. 1980. A probability model for design live loads. J. Structural Div. ASCE 106(ST 10):2017-2030.nCorotis, R. B., and W.-Y. Tsay. 1983. Probabilistic load duration model for live loads. J. Structural Eng. ASCE 109(4):859-874.nEllingwood, B., and C. Culver. 1977. Analysis of live loads in office buildings. J. Structural Div. ASCE 103(ST8):1551-1560.nEllingwood, B., J. G. MacGregor, T. V. Galambos, and C. A. Cornell. 1982. Probability based load criteria: Load factors and load combinations. J. Structural Div. ASCE 108(ST5):978-997.nGalambos, T. V., B. Ellingwood, J. G. MacGregor, and C. A. Cornell. 1982. Probability based load criteria: Assessment of current design practice. J. Structural Div. ASCE 108(ST5):959-977.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., B. Ellingwood, and J. Murphy. 1987. Damage limit state probabilities for wood structural members. J. Structural Eng. ASCE 113(1):88-106.nMadsen, B. 1975. Strength values for wood and limit states design. Canadian J. of Civil Eng. 2(3):270-279.nMiner, M. A. 1945. Cumulative damage in fatigue. J. Appl. Mec. ASME 12(3):532-543.nPeir, J. C., and C. A. Cornell. 1973. Spatial and temporal variability of live loads. J. Structural Div. ASCE 99(ST5):903-922.nTurkstra, C. J., and H. Madsen. 1980. Load combinations in codified structural design. J. Structural Div. ASCE 106(ST12):2527-2543.nWood, L. 1951. Relation of strength of wood to duration of load. Report R1916, Forest Products Laboratory, Madison, WI.n

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Published

2007-06-22

Issue

Number 4 / October 1987

Section

Research Contributions

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