ANALYSIS OF HYGRO-MECHANICAL BEHAVIOR OF WOOD IN BENDING
Keywords:
Bending, solid wood, Norway spruce, creep, experimental methodology, mechano-sorption, viscoelasticityAbstract
The empirical test developed as validation for a new beam element model that can account for both mechanical and environmental load action in finite element analysis is presented. The testing protocol allows for the identification and analysis of contributing deflection components in bending under varying MC conditions, including mechano-sorption. The components of deflection in the shear-free span of a four-point bending test and their responses to varying moisture are evaluated with an analytical procedure. The experiment was conducted on clear-straight-grained sapwood and heartwood specimens of Norway spruce (Picea Abies)(30 x 15 x 640 mm3). The program consisted of three phases: (1.) long term (LT) experiments under constant temperature of 60oC and relative humidity (RH) cycles between 40% and 80%, (2.) a short term static experiment to determine the variation in the sample set and the load-level of the LT experiment on end-matched specimens, and (3) creep tests at 60o and constant humidity at either 40% or 80% to determine the effect of moisture on the viscoelastic creep. Mass changes and hygro-expansion measured on matched specimens were used in the analytical method. Constitutive models used for describing the material-level response to loads and moisture changes were applied to the shear-free segment of the specimens disregarding actual moisture gradients and fiber orientation inside the test specimens. A successful identification of each deflection component and isolation of mechano-sorption component was accomplished. In the 90 da of testing, the dominant component of the total deflection was the elastic component, followed by the mechano-sorptive component. Creep was found to be nonnegligible and important in the correct description of mechano-sorption. The effect of moisture on the viscoelastic behavior showed most important during loading and first stages of decreasing deflection rate phase.
References
Armstrong LD, Christensen GN (1961) Influence of moisture changes on deformation of wood under stress. Nature, 4791:869-870
Armstrong LD, Kingston RST (1962) The effect of moisture content changes on the deformation of wood under stress. Australian Journal of Applied Science, 13:257-276
Bengtsson C (1999) Mechano-sorptive creep in wood: experimental studies of the influence of material properties. PhD, Chalmers University of Technology
Bengtsson C (2001) Variation of moisture induced movements in Norway spruce (Picea abies). Annals of Forest Science, 58:569-581
Bodig J, Jayne BA (1982) Mechanics of wood and wood composites. Van Nostrand Reinhold company, New York
Brancheriau L, Bailleres H, Guitard D (2002) Comparison between modulus of elasticity values calculated using 3 and 4 point bending tests on wooden samples. Wood Sci Technol, 36:367-383 doi:DOI 10.1007/s00226-002-0147-3
Bratasz Ł, Kozłowska A, Kozłowski R (2012) Analysis of water adsorption by wood using the Guggenheim-Anderson-de Boer equation. Eur J Wood Prod, 70:445-451 doi:DOI 10.1007/s00107-011-0571-x
Carlsson H, Thunell B (1975) Shrinking behaviour of wood during drying effect of tensile stresses. Paperi ja Puu, 7
Castera P Tensile creep of small wood specimens across the grain under drying conditions. In: IUFRO International Wood Drying Symposium, Seattle, 1989.
Dinwoodie JM (1981) Timber: its nature and behaviour, Second Edition. E&FN Spon Taylor & Francis Group,
EN 13183-1 (2003) Moisture content of a piece of sawn timber - Part 1: Determination by oven dry method. European Committee for Standardization (CEN), Brussels
EN 408 (2012) Structural timber - structural timber and glued laminated timber - determination of some physcial and mechanical properties. European Committee for Standardization (CEN), Brussels
Engelund ET, Salmen L (2012) Tensile creep and recovery of Norway spruce influenced by temperature and moisture. Holzforschung, 66:959-965
Hanhijärvi A (2000) Advances in the knowledge of the influence of moisture changes on the long-term mechanical performance of timber structures. Materials and Structures, 33:43-49
Hearmon RFS, Paton JM (1964) Moisture content changes and creep of wood. Forest Products Journal, 8:357-359
Hering S, Niemz P (2012) Moisture-dependent, viscoelastic creep of European beech wood in longitudinal direction. Holz Roh-Werkst, 70:667-670
Holzer SM, Loferski JR, Dillard DA (1988) A review of creep in wood: concepts relevant to develop long-term behavior predictions for wood structures. Wood Fiber Sci, 21:376-392
Hunt DG (1989) Linearity and non-linearity in mechano-sorptive creep of softwood in compression and bending. Wood Sci Technol, 23:323-333
Hunt DG (1999) A unified approach to creep of wood. The Royal Society, 455:4077-4095
Keunecke D, Sonderegger W, Pereteanu K, Lüthi T, Niemz P (2007) Determination of Young's and shear moduli of common yew and Norway spruce by means of ultrasonic waves. Wood Sci Technol, 41:309-327
Lagaňa R, William GD, Muszyński L, Shaler SM (2011) Moment-curvature analysis of coupled bending and mechano sorptive response of red spruce beams. Wood Fiber Sci 43:280-292
Morlier P (1994) Creep in timber structures Rilem report 8. Rilem Technical Committee, London
Muszyński L, Lagaňa R, Shaler SM (2006) Hygro-mechanical behavior of Red spruce in tension parallel to the grain Wood Fiber Sci, 38:155-165
Muszyński L, Lagaňa R, Shaler SM, Davids W (2005) Comments on the experimental methodology for determination of the hygro-mechanical properties of wood. Holzforschung, 59
Ormarsson S, Dahlblom O (2013) Finite element modelling of moisture related and visco-elastic deformations in inhomogeneous timber beams. Engineering Structures, 49:182-189
Ormarsson S, Gíslason Ó, V. (2016) Moisture-induced stresses in glulam frames. Holz Roh-Werkst, 74:307-318 doi:DOI 10.1007/s00107-016-1006-5
Ormarsson S, Steinnes JR (2014) An enhanced beam model for glued laminated structures that takes moisture, mechano-sorption and time effects into account. Paper presented at the World Conference of Timber Engineering, Quebec, Canada, August 10-14
Ottosen N, Petersson H (1992) Introduction to the Finite Element Method. Prentice Hall,
Persson K (2000) Micromechanical modeling of wood and fibre properties. Doctoral thesis, Lund University, Lund, Sweden.
Perstorper M, Johansson M, Kliger R, Johansson G (2001) Distortion of Norway spruce timber: Part I Variation of relevant wood properties. Holz Roh-Werkst, 59:94-103
Ranta-Maunus A (1975) The viscoelasticity of wood at varying moisture content. Wood Sci Technol, 9:189-205
Risbrudt CD, Ritter MA, Wegner TH (2010) Wood handbook: wood as an engineering material. Forest Product Laboratory, Madison, Wisconsin
Rybarczyk W (1973) Study on the development of mathematical model of mechanical properties of some wood materials undergoing changes in their moisture content 66. Prace Institute of Technology Drewna,
Salin J-G (1992) Investigation of heartwood/sapwood and wood anisotropy influence on timber drying by a two-dimensional simulation model. Paper presented at the 8th International Drying Symposium, Montreal, Quebec, Canada, August 2-5
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