The behaviour of timber members subjected to axial compression or combined axial compression and bending is characterised by the non-linear increase of the deformation due to the increasing eccentricity of the axial load and due to the non-linear material behaviour. The paper presents a strain-based model taking into account these effects.
Design approaches given in timber structures design codes are compared and differences in the results obtained with the different approaches are identified. Furthermore, a strain-based model to analyse the load-bearing capacity of centrically and eccentrically loaded timber columns is described and its power is assessed. It is shown that in particular the non-linear behaviour of timber when subjected to compression parallel to the grain considerably influences the load-bearing capacity.
The model is validated on the basis of experimental investigations on solid Norway spruce beams loaded in combined axial compression and bending. A good agreement was found between the estimated values using the strain-based model and the experimentally derived values.
A comparison of the model with the design approaches given in the codes shows that the load-bearing capacity can be overestimated under certain conditions. Finally, it is illustrated how the design approaches can be modified in order to reach a more consistent design.