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Strength model and design methods for bending and axial load interaction in timber members Buchanan, Andrew Hamilton


This thesis describes a model for predicting the strength of timber members in bending, and in combined bending and axial loading, on the basis of axial tension and compression behaviour of similar members. Both instability and material strength failures are included. The model is based on a stress-strain relationship which incorporates ductile non-linear behaviour in compression, and linear elastic behaviour associated with brittle fracture in tension. The model includes the effects of variability in timber strength, both within a member and between members. Size effects which predict decreasing strength with increasing member size are quantified using separate parameters for member length and member depth. An extensive experimental program on a large number of timber members in structural sizes has been used to calibrate and verify the model. Test procedures and results are described for members of different lengths tested to failure in bending and in axial loading. The axial testing included both tension and compression loading using several end eccentricities. Several alternative design methods based on the strength model are investigated and compared with existing methods. Recommendations are made for design methods for timber members subjected to combined bending and axial loading.

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