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Constitutive and analytical models for structural composite lumber with applications to bolted connections Moses, David Michael

Abstract

Models for the behaviour of structural composite lumber and solid wood are presented and verified for a variety of configurations. In particular, laminated strand lumber (LSL) is investigated for the influence of strand orientation and stacking sequence on its material properties. LSL panels are modelled using laminate theory and the First Order Reliability Method to determine the probability distributions of elastic properties and ultimate strengths. The results are verified against properties determined from an extensive series of experiments on custom-manufactured LSL panels. The laminate theory is capable of predicting panel properties and indicates that the properties are related to the degree of strand alignment. This modelling technique allows material designers to set target levels on panel properties and on variability by using the properties of the constituent layers. The behaviour of single-dowel mild steel connections in the five LSL panel types are determined experimentally for three end distances, three slenderness ratios and two edge distances. (The connection specimens are cut parallel, perpendicular and at 45° to the main strand axis.) Three-dimensional finite element models of each tested connection are used to predict load-displacement behaviour, ultimate strength and mode of failure. The anisotropic plasticity constitutive model is used together with the Weibull weakest link strength criterion for brittle materials to simulate the material behaviour of the LSL panels in the connection. The three-dimensional models and the single-dowel connection experiments indicate that panels with some strands oriented at ± 45° fail at higher loads than fully oriented panels. A parametric study of the model is used to indicate the critical variables in connection modelling and to isolate the most significant material tests required for modelling. Applications of the three-dimensional model are illustrated for a number of cases, including: a) dowel embedment tests, b) shear block tests, and c) a simplified one-dimensional spring model for the single-dowel connection. The shear block model illustrates the effect of the non-uniform shear stresses on the failure plane and the effects of the specimen notch. The one-dimensional spring model is shown to be useful for predicting the load-displacement behaviour and ultimate strength of multiple-bolt connections. These applications indicate the adaptability of the model to changes in material properties and connection geometry, and its ability to predict load-displacement, ultimate strength and mode of failure.

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