Cyclic pull-out behavior of screwed-in threaded rods embedded in glulam elements: Experimental and numerical studies

In this study, to support the application of screwed-in threaded rods (STRs) in timber connections, STRs with varying anchorage lengths were tested under cyclic pull-out loading. A new type of hysteresis model was developed in OpenSees to describe the cyclic shear-slip behavior of the timber layer in STRs by modifying the classical SAWS hysteresis model, and the parameters of the model were identified through the genetic algorithm implemented in MATLAB. Based on the numerical model, a cohesive layer possessing the modified SAWS shearslip hysteresis rule was developed in an ABAQUS user subroutine and adopted into finite element (FE) models to simulate the pull-out behavior of STRs. The test results demonstrated that the withdrawal capacity of the STRs increases with increasing anchorage length, while the anchorage length has a limited influence on the withdrawal stiffness at the serviceability state. The hysteretic curves of the STRs with an anchorage length of 200 mm or 300 mm show a significant pinching effect due to the shear failure of the timber layer, while those of the STRs with an anchorage length of 400 mm exhibit plump hysteresis loops owing to the fully utilized plastic behavior of the steel rod. The numerical analyses indicated that the cyclic shear-slip behavior of the timber layer in the STRs can be well captured by the modified SAWS model. Benefiting from the specially developed cohesive layer and the elastic-plastic damage material constitutive model in the FE analysis, the FE numerical results show good agreement with the test results in terms of the failure mode, withdrawal properties, cumulative energy, and load-displacement curves.