Creep Behavior of Structural Timber under Varying Humidity Conditions
Publication: Journal of Structural Engineering
Volume 120, Issue 9
Abstract
The effects on wood of simultaneous mechanical and moisture loading are studied. A constitutive model is given for the case of uniaxial stress in the longitudinal direction. The model has been quantified on the basis of test results found in literature. The validity of the model was checked independently against other tests and a number of practical load situations were studied. Finally the serviceablity requirements for design are discussed. The calculations show that the model is capable of describing the response of wood with reasonable accuracy. Some differences in behavior are found to depend on moisture cycling. The results of the simulations show that there is a significant influence of strain on the shrinkage and swelling response. An influence of beam dimensions has been found. The relative deflection for a small beam is larger than the deflection for a larger beam. Studies of the effect of varying load show that a temporarily applied load has little effect on the long‐term deflection of structural timber. A simulation of snow‐load variation shows that the long‐term deflections are small in comparison with the case when the characteristic load is assumed to be constant over time.
Get full access to this article
View all available purchase options and get full access to this article.
References
1.
“Actions on structures. Live loads in buildings. CIB W81. CIB.” (1989). Rep. Publ. 116, Int. Council for Building Res. Studies and Documentary, Rotterdam, the Netherlands.
2.
Åkerlund, S. (1988). Snow load in Umeå. Department of Structural Engineering, University of Lund, Lund, Sweden.
3.
Forsler, S., Jonasson, L., Landin, W., Schärnell, L., and Åkerlund, S. (1971). “Snow depth and water content.” Rep. 24, Building Technology, Lund, Sweden.
4.
Fridley, K. J. (1992). “Designing for creep in wood structures.” Forest Products J., 42(3), 23–28.
5.
Gril, J. (1988). “Modelling of the hygromechanical behavior of wood,” PhD thesis, University of Paris, Paris, France.
6.
Hearmon, R. F. S., and Paton, J. M. (1964). “Moisture content change and creep of wood.” Forest Products J., 8, 357–359.
7.
Hunt, D. G., and Shelton, C. F. (1988). “Longitudinal moisture‐shrinkage coefficients of softwood at the mechano‐sorptive creep limit.” Wood Sci. Technol., 22.
8.
Leicester, R. H. (1971). “A rheological model for mechano‐sorptive deflections of beams.” Wood Sci. Technol., 5, 211–220.
9.
Leivo, M. (1988). “Effect of moisture changes on the deformations of wooden beams and nail plate joints.” Proc. IUFRO Timber Engrg. Meeting, Finland, 286–293.
10.
Leivo, M. (1991). “On the stiffness changes in nail plate trusses.” Publication 80, Tech. Ctr. of Finland, Espoo, Finland.
11.
Mårtensson, A. (1992). “Mechanical behavior of wood exposed to humidity variations.” Report TVBK‐1006, Lund Institute of Technology, Lund, Sweden.
12.
Mårtensson, A., and Thelandersson, S. (1992). “Control of deflections in timber structures with reference to Eurocode 5.” CIB‐W18/25‐102‐2, Meeting 25, Int. Council for Building Res. Studies and Documentation, Ahus, Sweden.
13.
Mohager, S. (1987). Studies of creep in wood. Royal Inst. of Tech., TRITA‐BYMA, Stockholm, Sweden.
14.
Mukudai, J., and Yata, S. (1987). “Further modeling and simulation of viscoelastic behavior (bending deflection) of wood under moisture change.” Wood Sci. Technol. 21, 49–63.
15.
Ranta‐Maunus, A. (1976). “A study of the creep of plywood.” Report 5, Tech. Res. Ctr. of Finland, Espoo, Finland.
16.
Taylor, G. D., West, D. J., and Hilson, B. O. (1991). Creep of glued laminated timber under conditions of varying humidity. Proc., 1991 Int. Timber Engrg. Conf., London, 4:211–4:219.
17.
Toratti, T. (1992). “Creep of timber beams in a variable environment.” Report No. 31, Lab. of Struct. Engrg. and Build. Physics, Helsinki Univ. of Tech., Helsinki, Finland.
Information & Authors
Information
Published In
Journal of Structural Engineering
Volume 120 • Issue 9 • September 1994
Pages: 2565 - 2582
Copyright
Copyright © 1994 American Society of Civil Engineers.
History
Received: Mar 8, 1993
Published online: Sep 1, 1994
Published in print: Sep 1994
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.