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Strength model and finite element analysis of wood beam-columns in truss applications Lau, Wilson Wai Shing

Abstract

A. comprehensive stochastic finite element model for analyzing and predicting the load carrying capacity of beams and beam-columns is developed and presented. By incorporating the stochastic lumber properties, the model characterizes the within-member and betweenmember variability of the lumber properties to predict the response variability in the load carrying capacity. Applications of the model require the determination of model parameters by calibrating the model with experimental data. An extensive experimental program on a large number of members in both compact and structural sizes was conducted. In order to confirm the validity of the model, the model has been verified by comparing results obtained from additional full-size testing. The finite element model utilizes one-dimensional beam elements incorporating large displacement but small strains. Due to the large inherent displacements and yielding of the members before reaching the ultimate load, non-linearities in both geometry and material are assumed. In addition, a new stress-strain equation is proposed. The Newton-Raphson Method was also used to iterate to the true solution at each load step. Specific material properties of the member are modeled as one-dimensional stochastic field variables in the finite element program. As these properties may not be ergodic stationary processes, trend removal and normalization procedures were used to transform these material property processes into ergodic stationary processes. Fast Fourier transform was utilized to obtain the spectrum, transfer functions and coherence functions of these properties. Both auto- and cross-spectra were studied so that correlations between these processes were maintained during the simulations. Realizations of the material properties were simulated by a single input - multiple output random field model. Trends were then added to these ergodic stationary processes to generate the lumber properties. The interaction relation between applied axial load and moment was also studied. Using the finite element program and the random field model, the interaction behaviour of axial load and moment was simulated and percentile statistics were determined accordingly. Several other applications of the model and the finite element program are discussed, including the evaluation of the existing codes, axial load-slenderness curves, size, and load configuration effects.

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