Local contact behaviour of Norway spruce under compression parallel to fibres

Abstract

Timber joints designed to transfer forces directly through timber-timber contact represent one possible approach to reducing the use of metal components in timber buildings. However, in tall timber buildings, joints are subjected to large loads that may lead to fibre crushing when wood fibres are compressed against other fibres parallel to the fibres. This phenomenon reduces the global stiffness and strength of such joints, and the details of this interaction are investigated in this study. Experimental tests were performed using compression tests to locally examine and characterize the mechanical properties of two types of contacts: (i) wood fibres loaded in the longitudinal direction against steel and (ii) wood fibres interacting with other wood fibres. The stiffness of the damaged regions was approximately 1% of the stiffness of the non-contact regions. Postmortem micrographs showed fibre crushing primarily in the earlywood regions, while, when wood fibres were in contact with steel, all fibres are susceptible to simultaneous buckling. In addition, the proposed numerical micromechanical models successfully reproduced earlywood fibre buckling, and the predicted global stress-strain responses showed good agreement with the trends observed in the compression tests.