Experimental investigation and analytical modeling on withdrawal performance of self-tapping screw in bamboo scrimber

The withdrawal performance of self-tapping screw (STS) connectors in bamboo scrimber remains insufficiently understood, and existing timber-based analytical models cannot accurately predict the withdrawal performance of STS connectors in the high-density engineered bamboo material. In this study, axial withdrawal tests were conducted to investigate the impacts of screw diameter, embedding depth, and edge distance on the failure modes, load-displacement responses, withdrawal performance of STS connectors in bamboo scrimber. Two typical failure modes were identified from the experimental observations, including screw withdrawal failure and screw tensile failure. Increasing the screw diameter from 7 mm to 11 mm enhanced the withdrawal capacity and stiffness by 56.7% and 45.5%, respectively. Increasing the embedding depth from 100 mm to 140 mm enhanced the withdrawal capacity and stiffness by 54.7% and 21.6%, respectively. Increasing the edge distance improved the withdrawal performance by enhancing the lateral restraint of surrounding bamboo material. However, its beneficial effect became limited beyond a certain value. Comparisons with existing timber-based analytical models indicated that these models exhibited deviations when applied to bamboo scrimber connectors. Accordingly, modified prediction models were developed for withdrawal capacity and stiffness, considering the impacts of material density, screw geometric characteristics, and screw-to-edge distance.