Prediction of Bow and Crook in Timber Studs Based on Variation in Longitudinal Shrinkage
Keywords:
Compression wood, warp, model, moisture contentAbstract
This paper presents a model that describes the change in magnitude of bow and crook between two moisture contents below the fiber saturation point. The model shows that the variation in the longitudinal shrinkage coefficient over the cross section and along the stud could explain most of the change in bow and crook in the studs. It was possible to identify evenly curved bow and crook, as well as S-shaped bow and crook. The results show that the model predicts changes in bow better than changes in crook.
The results of measurements of distorted geometry along the length of 12 studs are presented. The equipment for measuring distorted geometry is described. The distorted geometry was measured at two moisture contents. The studs were then sawn into sticks (10 X 10 X 200 mm), a total of 3,600. The longitudinal shrinkage coefficient in these sticks was obtained for a change in moisture content from 18% to 8%. The sticks were also classified visually into three groups depending on their compression wood content: no compression wood, mild compression wood, mild compression wood, or severe compression wood.
The variation in the longitudinal shrinkage coefficient was large in the studied sticks (x 0.0111, SD 0.0111). The sticks classified as containing severe compression wood had a significantly larger longitudinal shrinkage coefficient than the sticks classified as no or mild compression wood. Moreover, sticks classified as mild compression wood had a significantly larger shrinkage coefficient than the sticks classified as no compression wood.
References
Archer, R. R. 1987. Growth stresses and strains in trees. Springer-Verlag, Berlin, Germany. 240 pp.nBeard, J. S., F. G. Wagner, F. W. Taylor, and R. D. Seale. 1993. The influence of growth characteristics on warp in two structural grades of southern pine lumber. Forest Prod. J.43(6):51-56.nBengtsson, C. 2001. Variation of moisture-induced movements in Norway spruce. Ann. Forest Sci.58(5):569-581.nBjörklund, L., L. Moberg, and H. Lindström. 1998. Stand and tree selection—Field measurements of stand, trees, and log properties. Final Report sub-task AB1.1. FAIR CT 96-1915. Report STUD.SIMS.FR:AB1.01. Swedish University of Agricultural Sciences, Dept. of Forest-Industry-Market studies, Uppsala, Sweden.nDu Toit, A. J. 1963. A study of the influence of compression wood on the warping of Pinus Radiata D. Don timber. South African Forestry J.44:11-15.nEastin, I. L., S. R. Shook, and S. J. Fleishman. 2001. Material susbstitution in the U.S. residential construction industry, 1994 versus 1998. Forest Prod. J.51(9): 30-37.nForsberg, D. 1999. Warp, in particular twist, of sawn wood of Norway spruce (Picea abies). Doctoral thesis, Swedish University of Agricultural Sciences, Dept. of Forest Management and Products, Silvestria 119, Uppsala, Sweden.nGaby, L. I. 1972. Warping in southern pine studs. USDA Forest Service, Southeastern Forest Experiment Station Research paper SE-96, Asheville, NC.nHallock, H. 1965. Sawing to reduce warp in plantation Loblolly pine studs. USDA Forest Service, Forest Products Laboratory. Research paper FPL-51, Madison, WI.nJohansson, G., I. R. Kliger, and M. Perstorper. 1994. Quality of structural timber—Product specification system required by end-users. Holz Roh- Werkst.52(1): 42-48.nJohansson, M. 2000. Moisture-related distortion in Norway spruce timber—Influence of material properties. Licentiate thesis, Publ S 00:4, Steel and Timber Structures, Chalmers University of Technology, Göteborg, Sweden.nJohansson, M., and R. Kliger. 2002. Influence of material characteristics on warp in Norway spruce timber. Wood Fiber Sci.34(2):325-336.nKliger, R., M. Johansson, and M. Perstorper. 1997. Influence of three-dimensional variation in shrinkage on distortion. Pages 153-164 in Proc. COST Action E8, Int. Conference on Wood-Water Relations, June 16-17, Copenhagen, Denmark.nKliger, R. 1997. Field measurements in forests and at sawmills. Project Report sub-task AB1.1. FAIR CT 96-1915. Report STUD.CTH.PR:AB1.01. Chalmers University of Technology, Steel and Timber Structures, Göteborg, Sweden.nKliger, R., 1999. Quantification of distortion in sawn timber—Measured after sawing, after drying and during different moisture loads. Final Report sub-task B6.1. FAIR CT 96-1915. Report STUD.CTH.FSR:B6.1. Chalmers University of Technology, Steel and Timber Structures, Göteborg, Sweden.nKloot, N. H., and M. W. Page. 1959. A study of distortion in Radiata pine scantlings. Division of Forest Products, CSIRO, Australia, Technical Paper No. 7.nMeylan, B. A. 1972. The influence of microfibril angle on the longitudinal shrinkage—Moisture content relationship. Wood Sci. Technol.6:293-301.nMishiro, A., and R. E. Booker. 1988. Warping in new crop Radiata pine 100 x 50 mm boards. Bull Tokyo University Forests80:37-68.nOkuyama, T., and Y. Sasaki. 1979. Crooking during lumbering due to residual stresses in the tree. Mokuzai Gakkaishi15(11):681-687.nOrmarsson, S. 1999. Numerical analysis of moisture related distortion in sawn timber. Doctoral thesis, Department of Structural Engineering, Chalmers University of Technology, Göteborg, Sweden.nPerstorper, M., P. J. Pellicane, I. R. Kliger, and G. Johansson. 1995. Quality of timber products from Norway spruce. Part 2: Influence of spatial position and growth characteristics on warp. Wood Sci. Technol.29:339-352.nPerstorper, M., M. Johansson, R. Kliger, and G. Johansson. 2001. Distortion of Norway spruce timber—Part 1. Variation of relevant wood properties. Holz Roh- Werkst.59(1-2):94-103.nSaaranpää, P. 1994. Basic density, longitudinal shrinkage, and tracheid length of juvenile wood of Picea abies (L.) Karst. Scan. J. Forest Res., 9:68-74.nShelly, J. R., D. G. Arganbright, and M. Birnbach. 1979. Severe warp development in young-growth Ponderosa pine studs. Wood Fiber11(1):50-56.nSimpson, W. T., and T. D. Gerhardt. 1984. Mechanism of crook development in lumber during drying. Wood Fiber Sci.16(4):523-536.nSkaar, C. 1988. Wood—Water relations. Springer-Verlag, Berlin, Germany. 283 pp.nStanish, M. A. 2000. Predicting the crook stability of lumber within the hygroscopic range. Drying Technol.18(8):1879-1895.nTimell, T. E. 1986. Compression wood in gymnosperms. Springer-Verlag, Berlin, Germany. 2190 pp.nVoorhies, G., and B. R. Blake. 1981. Properties affecting drying characteristics of young-growth Ponderosa pine. Arizona Forestry Notes, No. 14, School of Forestry, Northern Arizona University.nVoorhies, G., and W. A. Groman. 1982. Longitudinal shrinkage and occurrence of various fibril angles in juvenile wood of young-growth Ponderosa pine. Arizona Forestry Notes No. 16. School of Forestry, Northern Arizona University.nWarensjö, M., and C. Lundgren. 1998. Samband mellan tjurved och formfel hos gran—en studie vid limmareds sågverk, (Impact of compression wood on deformations of sawn spruce (Picea abies (L.) Karst.), in Swedish). Swedish Univ. of Agricultural Sciences, Dept. of Forest Products, Report No. 255, Uppsala, Sweden.nWoxblom, L. 1999. Warp of sawn timber of Norway spruce in relation to end-user requirements—Quality, sawing pattern and economic aspects. Doctoral thesis, Swedish University of Agricultural Sciences, Dept. of Forest Management and Products, Silvestria 126, Uppsala, Sweden.nZobel, B. J., and J. R. Sprague. 1998. Juvenile wood in forest trees. Springer-Verlag, Berlin, Germany. 300 pp.n
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