Bond-Anchorage And Seismic Behaviors Of Glulam Joints With Glued-in Rods

There are several types of connections for timber structures, such as mortise-tendon connection, nail connection, bolted connection, metal plate connection and glued-in rod connection. With the development of modern timber structures, the structural joints with high performance for timber engineering are becoming urgently needed. It is difficult some times for the traditional timber connections to meet the requirements of the joint design for modern timber structures. Glued-in rod connection is a type of novel connector for timber engineering, characterized by high strength-to-weight ratio, high joint stiffness, good fire resistance and aesthetics appearance. This type of connection can meet the requirements of structural joints with high performance in modern timber structures. The bond behavior between glued-in rod and timber is one of the key influencial varibles on the structural performance of glued-in rod connections. Glued-in rod timber joints involve in three types of materials and two interfaces. The bonding between glued-in rod and timber could be considered as the bond issue among multi-mediums, which is still not fully understood until now. Given that, this paper carried out pull-pull tests on glued-in rod glulam joints to investigate the influence of different parameters on the bond and anchorage behavior between glued-in rod and glulam. The closed-form solutions of the interficial bond-anchorage variables were derivated theoretically aiming to evaluate the bond-slip mechanism between glued-in rod and glulam. As a result, the bond stress-slip relations considering location function were established. Finite element simulations were also conducted on the glulam joint with glued-in rod by ANSYS. The non-linear spring element (Combin39) was employed to simulate the bond behavior between glued-in rod and glulam. Reversed cyclic loading tests were exploratively conducted on the beam-to-column glulam joints with or without energy dissipaters to examine the joint seismic performance. Reliability analysis was carried out on the bond and anchorage behavior of the glulam joints with glued-in rod and the suggestions on seismic design were proposed for the glulam joints with glued-in rods. The main research works in this paper are summerized as follows:The influence of bar type, bar diameter, anchorage length and bond line thickness on the withdrawal strength and the bond-anchorage behavior of the glulam joints with glued-in rod was investigated by pull-pull tests. The test results indicated in a certain range, the increase of both the anchorage length and the bond line thickness resulted in the increasing of the withdrawal strength of the glulam joints with glued-in rod. It seemed that the glued-in rebar glulam joints were prone to fail at the rod/adhesive interface or in timber splitting. However, the glued-in threaded steel rod glulam joints mainly failed in timber shear failure. The bond-slip work mechanism between different types of glued-in rod and glulam differed from each other. The interfacial bond stress distribution was not uniform but concentrated near both the loaded end and the anchorage end and the maximum bond stress transferred gradually from the loaded end to the anchorage end as the external load increased. For the glued-in rebar glulam joints, when the anchorage length reached 12.5 times the rod diameter, the glued-in rod would fail in rod yielding. Appropriate increasing of the bond line thickness is beneficial to relieve the bond stress concentration.The bond-slip model for glued-in rod glulam joints was proposed based on the theoretical analysis on the bond-slip mechanism of the glulam joints with glued-in rod. Parametrical studies were also conducted based on the proposed bond-slip model. The results indicated that the bond-slip relations at different locations are different. The distribution of the bond-slip stiffness along the anchorage length is not uniform, but concentrates near both the loaded end and the anchorage end.The proposed bond-slip model for glued-in rod glulam joints was simplified as a tri-linear bond-slip model. The analytical solutions of the axial stress of the glued-in rod, the interfacial shear stress and the relative slip between the glulam and the glued-in rod were obtained by theoretical derivation and compared with the experimental results. The results indicated that the analytical solutions were in good agreement with the experimental results. Finally, the bond stress-slip relations considering location function were established based on the obtained distributions of the interfacial variables.Numerical simulations on glulam joints with glued-in rod were conducted by ANSYS based on the proposed bond-slip model. Timber was considered as orthotropic material. The non-linear spring element (Combin39) was adopted to simulate the bond-slip behavior between glulam and glued-in rod with the consideration of bond location function. The distributions of the glued-in rod axial stress, the interfacial shear stress and the relative slip between timber and glued-in rod were obtained by modelling and compared with the experimental results. The results indicated that the non-linear spring element can be adopted for the simulation of the bond behavior between the glued-in rod and timber effectively.Reversed cyclic loading tests were carried out on three types of beam-to-column glulam joints with glued-in rods and energy dissipaters aiming to evaluate the seismic performance of those type of composite glulam joints, including failure modes, hysteresis behavior, joint stiffness, energy dissipation and ductility. The test results indicated that the ductility and the hysteresis behavior of the beam-to-column glulam joints with glued-in rods and energy dissipaters were improved significantly compared with the beam-to-column glulam joints only with glued-in rods. The hysteresis loops of the beam-to-column glulam joints with glued-in rods and energy dissipaters were relatively plump. The energy dissipaters yielding were obseverd prior to the failure of glued-in rod or timber obviously during the testing. The difference on the load capacity between the beam-to-column glulam joints with glued-in rods and energy dissipaters and the beam-to-column glulam joints only with glued-in rods was insignificant. The beam-to-column glulam joints with glued-in rods and energy dissipaters exhibited slightly lower stiffness and less stiffness degeneration than the beam-to-column glulam joints only with glued-in rods.Reliability analysis on the bond-anchorage behavior of glued-in rod glulam joints was carried out based on the theory of reliability. The reliability solutions of the critical anchorage length for glued-in rod in glulam were obtained. The anti-seismic anchorage length was proposed as the product of the critical anchorage length and the amplification factor to ensure the rod yielding prior to the bond failure of the glued-in rod glulam joint.Finally, the hole diameter, rod spacing, edge distance, safety factor for fabrication and the choice of materials were discussed and summarized in detail, which provided the real applications of glued-in rod in timber engineering with theoretical references.