Withdrawal capacity of screws in plywood and manufacturer dependencies

Within civil engineering and design of load-bearing timber structures, the use of self-tapping screws for connections is common practice. In certain situations, the axial withdrawal capacity of screws in a wooden panel may be required, for instance when utilizing the rope-effect contribution to the lateral resistance. This experimental study investigates the withdrawal capacity of self-tapping screws in plywood panels made of spruce. It specifically explores differences attributed to various manufacturers of essentially identical products. A data set of 504 individual tests is examined, based on 126 unique combinations of screw and panel, conditioned to an average moisture content of 8 %. The findings indicate that the coefficient of variation of the proposed model for the withdrawal capacity can be optimized to a level below 10 %. Furthermore, the use of a panel and screw factor effectively allows for revealing manufacturer-specific differences. Additionally, the study investigates the impact of simplifying the mechanical model to rely solely on screw diameter and panel thickness. This simplification leads to an overall increase in the coefficient of variation of about 3 %, but does not undermine the model significantly, rendering it a viable option for practical design. Lastly the conversion of a simplified mean value model to a characteristic model is illustrated.