The Study On Shear Property Of Bolted Joint With Northeast Larix Glued Timber And Steel Plate

Traditional timber structure,as a kind of environmental protection,renewable and recyclable natural resources has been widely used in building structures since ancient times.Modern timber structure,As a new type of green building material not only overcomes the natural defects of small span of traditional wood structure,but also has many advantages.Such as high strength-to-mass ratio,good seismic resistance,heat insulation,green environmental protection,harmonious and beautiful,and suitable for rapid assembly construction,etc.It is developing towards large-span and high-rise structures.In order to popularize the application of domestic northeast Larch glued timber in modern engineering fields such as long-span bridges and high-rise buildings,it is urgent to solve the problem of long-span joints of glued timber components in long-span timber structures.In order to realize the spanning of the length of plywood members,this paper takes Bolted glued Larch in northen connections with steel plate by bolt as the research object.The shear behavior of bolted glued laminated timber connections with steel plate by bolt was studied by means of experimental study,theoretical analysis and numerical simulation.The main research work includes the following aspects.(1)In view of the structural characteristics of the bolted glued laminated timber connections with steel plate by bolt,the influences of the ratio of thickness to bolt diameter,bolt spacing,bolt parallelism and staggered arrangement are considered.Three types of 17 groups of 51 protrusive test-piece were designed,and the shear behavior of bolted glued laminated timber connections with steel plate by bolt under longitudinal load was tested by protrusive test method.Three shear failure modes,failure mechanism and influencing factors of shear resistance of bolted glued laminated timber connections with steel plate by bolt were discussed.(2)The shear performance test results of bolted glued laminated timber connections with steel plate show that with the increase of thickness-diameter ratio,the failure mode of bolted joints gradually changes from "bolt rigidity" to "single hinge" and then to "double hinge" in Single-bolted joints with plywood-steel splints.The optimum thickness-diameter ratio is 7.5.In multi-bolted joints,the bending degree of bolts decreases from top to bottom,and some glued timbers have pin groove failure.With the increase of bolt spacing,the shear capacity of the connection increases,while the initial stiffness decreases.With the increase of the number of bolts,the failure mode of the glued timber is changed from the splitting failure of single-row bolts along the middle to the splitting failure of two-row bolts,and the ductility of the two-row is the best.When the number of bolts is the same,the shear capacity of staggered arrangement is higher than that of parallel arrangement,but the ductility of staggered arrangement is better than that of staggered arrangement.(3)Based on Johansen's "yield theory" and pin-groove ideal elastic-plastic model,combined with existing research and standard of wood structure,the load bearing capacity of single-bolt connection is calculated according to three typical failure modes of bolted glued laminated timber connections with steel plate by bolt,and the shear capacity of bolted glued laminated timber connections with steel plate by bolt is deduced.Comparing with the calculation formulas of bolted connections in Chinese,American,European and Canadian formulas for wood structure design,find out the deviations and the reasons for the deviation of the formulae in various countries,which provides a way for the calculation of the shear capacity of the bolted glued laminated timber connections with steel plate by bolt to consider the factors of each factor and reference.(4)In order to verify the rationality of the test results,the finite element numerical simulation method was used to simulate the shear capacity of the bolted glued laminated timber connections with steel plate.The results show that not only the finite element calculation results of the shear capacity of the bolted joints are in good agreement with the experimental results,but also the stress and deformation calculation results of the bolts and gaskets in the limit state are basically consistent with the experimental results.At the same time,whether or not to install bolt gaskets has little influence on the shear bearing capacity of the connectors,so bolt gaskets can not be considered when calculating the shear bearing capacity of bolted glued laminated timber connections with steel plate,but bolt gaskets must also be used as structural requirements in the design of bolted glued laminated timber connections with steel plate.(5)The results of the finite element analysis on connections of parallel and staggered show that the stress and deformation of the bolt holes in the top row are the largest in both parallel and staggered ways,and the stress of the bolt holes decreases in turn as the bolt position is far away from the directly loaded end.The shear capacity of staggered bolts is higher than that of the parallel bolts,but the ductility of the arrangement is not the same.The performance is better than that of staggered arrangement and so on.Both the finite element results of single bolted connector and multi-bolted connector fully verify the rationality of the proposed test,and also verify the reliability of the finite element results.(6)Aiming at the problems of low efficiency and poor convergence of the existing three-dimensional finite element model of wood structure pin-bolt connection,a macroscopic finite element modeling method is proposed.The results show that the finite element macro-modeling method greatly reduces the cost of modeling and calculation,and improves the calculation efficiency.It provides a useful reference for the theoretical calculation of the bolted connection between plywood and steel splints.(7)In order to expand the application scope of the finite element macro-model,the macro-model is used to calculate and analyze the bolted connection of Wood-Concrete composite structure,and it is concluded that the finite element macro-model also greatly improves the calculation efficiency.The simplified finite element calculation of the performance of bolted joints in wood structures is realized,which facilitates the numerical calculation of bolted joints.At the same time,it provides a new method and idea for the calculation and analysis of multi bolts and group bolts connections in wood structure connections.