The influence of moisture content variation on the withdrawal capacity of self-tapping screws

Due to high axial load-bearing capacity and economical application without pre-drilling, self-tapping screws are widely used in modern timber constructions nowadays. Their withdrawal behaviour, as one mechanism to be verified according to EN 1995-1-1 (2004), is discernibly influenced by the timber member and its moisture content. In case of increase of moisture content above 12 %, test results indicate a significant decrease in withdrawal capacity, which is actually not considered in design procedure. In our paper, we thus concentrate on these experimental studies, carried out in the frame of two research projects. Furthermore, we discuss two models developed for design procedure as well as for data assessment covering a large bandwidth of moisture content and compare them with results from previous investigations