Study On The Mechanical Behavior Of Timber-concrete Joints With Glued-in Bolts

Timber-concrete structure is a new type of construction that combines the two materials of timber and concrete by various shear connectors.Concrete bears the pressure while wood bears the tension.The best properties of both dissimilar materials can be exploited due to the timber in the tensile zone to resist tensile forces and the concrete in the compression zone to resist compressive forces.It has the advantages of light weight,convenient installation and better insulation,etc,and has been widely used in European and American countries.As an important part of timber-concrete joint,shear connectors not only transmits the longitudinal shear force between concrete and wood,but also resists the lift between concrete and wood.Bolts,dowels,and screws are the most widely used shear connectors,but they need to be pre-drilled when inserted into the wood,so that there is a gap between the connector and the wood,which reduces the shear stiffness and bearing capacity of the joint.The adhesive in the glued-in bolt connection can not only fill the gap between fastener and wood,but also improve the stiffness of the connection.The shear strength of the structure can be enhanced by the connection with glued-in bolt.However,due to the lack of relevant studies on wood-concrete joint with glued-in bolt and its calculation theory of bearing capacity,this paper studies the mechanical properties of wood-concrete composite structure with glued-in bolt.In this paper,the effect of diameter,insertion depth and inclination angle of single glued-in bolt on the shear strength and stiffness of the joint was studied through the test of of wood-concrete joint with glued-in bolt.In addition,the effect of the distance and arrangement of the connectors on the mechanical properties of the joints was also studied.The embedding strength is the key parameter in the calculation of shear bearing capacity of timber-conctere joint.In the existing codes in the world,the theoretical calculation formula of embedding strength of dowel and bolt connectors is the same,and there is no calculation formula of embedding strength of glued-in bolt connectors.In fact,the surface condition of the connector has a great influence on the embedding strength of connector,while the surface condition of the bolt and the glued-in bolt connector is quite different from that of the dowel.In this study,embedding tests using dowels,bolts and glued-in bolts are carried out.The test results of embedding strength are compared with theoretical results,founding that the existing specification underestimates the bearing strength of the wood pin groove for bolted fittings On the basis of the theoretical formula of embedding strength for dowel,an empirical expression of embedding strength in timber for bolt and glued-in bolt is proposed.At present,the calculation of the shear capacity of the wood-concrete joint with dowel type of connectors is mainly based on the three stress analysis models of steel-wood,wood-wood and steel-fixed clearance-wood.Concrete exhibits brittleness under compression,and the material model cannot be simply regarded as steel or wood,so the first two models are not correct.The gap in the steel-fixed-clearance-wood model is formed after the concrete is crushed.The value of the gap in the current model is the fixed value 5mm given by experience,without considering the influence of concrete on the bearing capacity of the connection.In this paper,considering the influence of concrete strength on clearance,clearance(concrete crush depth)was deduced theory formula,and then the steel-clearance-wood model was improved,and gives the the experience formula of rope effect which can contribute shear bearing capacity of the connection.In addition,based on the improved steel-clearance-wood model,the formula for calculating the bearing capacity of the joint with inclined glued-in bolt was derived,and the theoretical results were compared with test results.Finally,by comparing the shear stiffness of the test and the test data in the literature with the results of the two existing theoretical calculation methods of shear stiffness,it is found that the existing theoretical calculation formula of shear stiffness cannot accurately predict the shear stiffness of wood-concrete joints with bolt type of connectors.