Since the 80's, Johanssen's Yield Theory has been adapted to fit new design practices: fastening of timber elements with a layer of insulation (or gap) between the elements or fastening with inclined fasteners. However no rules exist for connections with large gaps (up to 500 mm) and inclined fasteners. The behaviour of screwed connections (timber/large gap/timber) is modelled using an orthotropic material, cohesive surface, Hill criterion and a fictitious material that wraps the screw and models a complex medium where steel and wood interact. The calibrated FE model is finally compared to experimental results.
In this study, static coefficients of friction for laminated veneer lumber on steel surfaces were determined experimentally. The focus was on the frictional behaviors at different pressure levels, which were studied in combination with other influencing parameters: fiber orientation, moisture content, and surface roughness. Coefficients of friction were obtained as 0.10–0.30 for a smooth steel surface and as high as 0.80 for a rough steel surface. Pressure influenced the measured coefficients of friction, and lower normal pressures yielded higher coefficients. The influence of fiber angle was observed to be moderate, although clearly detectable, thereby resulting in a higher coefficient of friction when sliding perpendicular rather than parallel to the grain. Moist specimens contained higher coefficients of friction than oven-dry specimens. The results provide realistic values for practical applications, particularly for use as input parameters of numerical simulations where the role of friction is often wrongfully considered.
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