Push-out performance of inclined screw shear connectors used in nail-laminated timber-concrete composite

Abstract

Self-tapping screws (STSs) have been used as shear connectors in various timber-concrete composites, while research focused on the push-out performance of STS connectors used in nail-laminated timber-concrete composite (NLTCC) is limited. This paper presents the experimental investigation and numerical parametric analysis on the push-out performance of inclined screw shear connectors used in NLTCC. There were 30 specimens with the same configuration tested in this project. The preliminary experimental investigation indicates that the STS shear connectors, with a nominal diameter of 11 mm and a penetration length of 260 mm, can achieve a shear capacity and slip modulus of 32.5 kN and 6.92 kN/mm, respectively. The main failure modes include concrete cracking, screw two-hinge yielding and localized nail-laminated timber (NLT) embedment failure. A numerical model was then developed and verified using the test results to predict the behavior of this STS connectors. A parametric analysis, using the verified model, was carried out to quantify the influence of screw diameter and penetration length on its push-out performance. Analysis results show the push-out performance is in positive and linear correlation with the screw nominal diameter. A positive but nonlinear correlation is noticed between the screw penetration length into NLT and its push-out performance. This is because the controlling failure mode was changed from two-hinge yielding of STS to localized NLT embedment when penetration length was overly increased.