Creep Of Laminated Veneer Lumber-Experiment And Numerical Modelling

As a wood-based composite,Laminated Veneer Lumber (LVL) is a high performance,environment-friendly building material, which achieves greater strength, stiffness, and more stable material properties than solid lumber. LVL has been widely used in buildings and bridges worldwide.In this dissertation, tension and compression tests were conducted to obtain the basic mechanical properties of LVL, including the tension and compression strengths, and the moduli of elasticity. The tests show that the stress-strain relationships of LVL is elastic-plastic in compression and linear elastic in tension.Creep is one of the characteristics that make timber and wood-based composites distinguished from other structural materials. In using a wood-based composite like LVL, creep is, therefore, of the primary concern. In this study, both experimental work and numerical modeling were undertaken to investigate the creep of LVL and its effect on such structural members like beams, columns and trusses.Six sets of test apparatus with sufficient accuracy were designed and manufactured successfully, of which, three sets were for the tension tests, and the other three were for the compression tests, accommodating three stress levels.The creep tests for LVL, in both tension and compression, were conducted under three different stress levels. The creep strain-time curves of 9 tension and 9 compression specimens were obtained. On the basis of the test results, the constitutive model of LVL was established. The model can be used to simulate creep behaviour of LVL specimens and LVL structural members.The constitutive model so established was incorporated into the commercial finite element analysis software ABAQUS, by developing a user defined subroutine-UMAT. Numerical modelling of creep of the LVL specimens was conducted. The analytical results correlate the test results quite well. The finite element model was then extended to simulate, successfully, long-term behaviour of structural LVL members, covering beams, columns and trusses.This study provides a basic understanding of creep behaviours of LVL and a way to simulate and predict the creep behaviour of LVL and the structural members numerically. The finite element model developed can also be used to model the long-term behaviour of wood, wood composites and the more complex structures, in a broader sense.