Moisture Induced Deformations in Glulam Members - Experiments and 3-D Finite Element Model

Abstract

Experiments were performed on scaled glue laminated bending specimens to observe
time dependent development of deformations during drying and wetting. Measurements
determined changes in the average moisture content and external shape and dimensions
between when specimens were placed into constant or variable climates. Alterations in
the external shape and dimensions reflected changes in the average value and
distribution of moisture and mechanosorptive creep in the glulam. The results are being
used to develop a sequentially-coupled three-dimensional hygrothermal Finite Element
(FE) model for predicting temporally varying internal strains and external deformations
of drying or wetting solid wood structural components. The model implies temporally
varying, and eventual steady, state internal stress distributions in members based on
elastic and creep compliances that represent wood within glulam as a continuous
orthotropic homogenised material. Thus, predictions are consistent with smeared
engineering stress analysis methods rather than being a physically correct analogue of
how solid wood behaves. This paper discusses limitations of and intended improvements
to the FE modelling. Complementary investigations are underway to address other
aspects of the hygrothermal behaviour of structural members of wood and other
materials (e.g. reinforced concrete) embedded within superstructure frameworks of
multi-storey hybrid buildings.