Investigation of tensile performance at the joint of different types of dowel reinforced glulam bolt holes
Bolted connections in timber structures are prone to stress concentration around the bolt holes,leading to wood cracking and a decrease in load-carrying capacity of the joints.Currently,most researchers have focused on studying reinforcement and strengthening methods for joints using traditional metal connectors such as self-tapping screws,steel sections,and steel plates.However,using metal connectors for reinforcement presents challenges in terms of maintenance and processing of timber components.Additionally,the insertion of metal elements in the struc-ture creates thermal bridges,which hinders energy efficiency and thermal insulation performance for buildings.There-fore,utilizing non-metallic dowel-type connectors perpendicular to the wood grain for reinforcement is expected to im-prove the aforementioned failure phenomenon.In order to investigate the enhancement effect of reinforcement by di-fferent types of vertical dowel on the joints at glued laminated bolt holes and provide experimental basis and theoretical foundation for the engineering application of wooden nail reinforcement at glued laminated bolt hole joints,in accor-dance with the American Standard(ASTM D1761-20),a series of monotonic tension tests with the material type and diameter of the dowel as variables was conducted on 26 glulam specimens,which was divided into four groups aligned parallel to the grain.The failure modes,load-displacement curves,maximum load-carrying capacity,stiffness,and energy dissipation of the joints at each hole positions were recorded and analyzed.The findings indicated that the per-pendicular nail insertion relative to the specimen's texture had minimal impact on the failure mode of the joints at each hole,but it can enhance the load-carrying capacity of the specimen's joints to a certain degree.Additionally,wooden nails exhibited significantly superior performance compared to steel nails in reinforcing the joints at the holes of the specimens.When compared to the unreinforced group SS1 specimens,the maximum load-carrying capacity of the wooden nail-enhanced groups SS2 and SS3,as well as the steel nail-enhanced group SS4,experienced respective in-crease of 19.75％,19.18％and 10.83％,while the energy dissipation was increased by 87.48％,82.59％and 28.33％,respectively.A slight change in the diameter of wooden nails had little effect on the enhancement effect of the joints.Therefore,when wooden nails were driven perpendicular to the wood grain,a shear structure was formed at the bolt hole joints,where the shear plane shared part of the shear load,thereby improving the load-carrying capacity and energy dissipation capability of the specimen,while avoiding the disadvantages of the aforementioned metal con-nectors.
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