This paper introduces, with the development of user-subroutines in the finite-element software Abaqus FEA®, a new practical analysis tool to simulate transient nonlinear moisture transport in wood. The tool is used to revisit the calibration of moisture simulations prior to the simulation of mechanical behaviour in bending subjected to climate change. Often, this calibration does not receive sufficient attention, since the properties and mechanical behaviour are strongly moisture dependent. The calibration of the moisture transport simulation is made with the average volumetric mass data experimentally obtained on a paired specimen of Norway spruce (Picea abies) with the dimensions $$30\times 15\times 640\, {\mathrm{mm}}^{3}$$ 30 × 15 × 640 mm 3 . The data, from a 90-day period, were measured under a constant temperature of 60 °C and systematic relative humidity cycles between 40 and 80%. A practical method based on analytical expressions was used to incorporate hysteresis and scanning behaviour at the boundary surface. The simulation tool makes the single-Fickian model and Neumann boundary condition readily available and the simulations more flexible to different uses. It also allows for a smoother description of inhomogeneity of material. The analysis from the calibration showed that scanning curves associated with hysteresis cannot be neglected in the simulation. The nonlinearity of the analysis indicated that a coherent set of moisture dependent diffusion and surface emission coefficient is necessary for the correct description of moisture gradients and mass transport.

The use of cross-laminated structural timber elements is becoming increasingly popular. The number of layers varies normally from three upwards. The structural performance of five-layer cross-laminated timber elements was investigated. The five layers consisted of 19 mm thick boards, laid successively at right angles to each other and glued together with PU-adhesive, layers 1, 3 and 5 lying in one direction and layers 2 and 4 in the other. The stiffness and strength of four cross-laminated timber elements (4955 mm long, 1250 mm wide and 96 mm thick) were studied during in-plane bending. Two of the elements were first partitioned into two parts that were reconnected in two different ways prior to testing. The influence of the way in which the crosslaminated timber elements were reconnected was studied, the behaviour observed being compared with the test results for the unpartitioned specimens with respect to both strength and stiffness. The experimental tests performed showed the cross-laminated timber elements to possess a high degree of stiffness and strength. There was also found to be a marked difference in behaviour between the two different ways in which the elements were connected to each other. One of the two connecting methods studied, being of less good design but earlier frequently used in Sweden, showed as expected poor structural performance, whereas the other one applied as a safer alternative performed well.

Timber boards manufactured with a traditional sawing pattern often contain both heartwood and sapwood. In such boards, internal constraints can occur during drying because of a radial variation in greenstate (GS) MC between the heartwood (30-60%) and sapwood region (120-200%). Despite such knowledge, the initial MC is seldom considered when evaluating kiln-drying schedules. The effect of GS MC on the development of tangential tensile stress during drying is studied for four types of timber boards. A numerical model was developed that can simulate transient nonlinear orthotropic moisture flow and moisture-induced stress and distortion in wood with the use of the finite element method. The stress analysis considers elastic, hygroscopic, and mechano-sorptive strain. The study shows that the GS MC does not significantly influence the maximum stress state, but that it does influence the time at which the maximum tangential tensile stress occurs at different exchange surfaces. This results in several periods in the drying schedule where unfavorable high stress situations in the tangential direction arise, which could lead to crack propagation.

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