Experimental Investigation of Axial Pull-out Behavior of Glued-in Threaded Rods in Cross-Laminated Timber

Cross-laminated timber (CLT), known for its high performance, prefabrication, low carbon emission, and eco-friendliness, has gained widespread adoption in the construction industry. Glued-in rod (GiR) connections, which offer a concealed appearance, high strength, withdrawal stiffness, ease of construction, and fire resistance, have become a promising solution for CLT structures. This study experimentally investigated the axial pull-out behavior of GiR connections in CLT. Fortyfive CLT specimens with single GiR were designed and tested under pullout conditions. The experimental variables included embedment length, threaded rod diameter, and rod-to-grain angle (parallel and perpendicular). The results revealed that CLT connections with GiR parallel to the grain exhibited an ascending load-slip response until peak load, followed by a sudden failure, while those with GiR perpendicular to the grain showed a linear increase to peak load with a subsequent gradual load reduction. Increasing the embedment length from 5 d to 15 d enhanced the pull-out load but decreased the average bond stress. Additionally, larger rod diameters led to higher pull-out loads and withdrawal stiffness within a certain range but reduced the average bond stress. The study also evaluated the effectiveness of existing bond stress-slip models and pull-out load prediction models for GiR connections in CLT, providing a foundation for future standardization efforts.