Influence Of Shrinkange Crack On The Mechanical Performance Of Timber Structure Joints

Shrinkage crack is one of the most important factors that affect the safety and durability of wood structures.With the advantages of direct force transmission and convenient installation,the bolt-type joint with slotted-in steel plate is becoming widely-used in modern wood structures.However,the occurrence of shrinkage cracks could weaken the mechanical properties of the joints,and related research is rare.Based on existing study,how initial artificial cracks affect the mechanical properties of the joints was studied by experimental study,numerical simulation and theoretical analysis in this paper.According to the undamaged joints and its environmental test results,12 damaged glued joints were designed.These damaged glued joints were manufactured by initial artificial cracks with different lengths,different positions,different sides,and different depths.These test joints were carried out by monotonic load.The test results show that the joints are split along the transverse beam of the bolt line on the tension side.Besides,there is unobvious deformation in the steel plates and bolts.From the load displacement curve and the final failure mode,it can be seen that the cracks on the compression side and the neutral axis of the beams affect the bearing capacity of the joints slightly.But the bearing capacity decreases with different lengths on the tension side.For the same depth of cracks on the tension side,the bearing capacity of crack joints on the one side decreases more obviously than that of the double sides.In addition,for the same length of cracks on the tension side,the bearing capacity decreases with different depths.Based on the finite element analysis software ABAQUS,the analysis model of the joint is established.C3D8 I solid elements are applied to simulate the wood columns,wood beams,bolts and steel plates and other components.The weak elements are defined by the wood damage constitutive law to simulate the initial artificial cracks.The simulation results prove that the pre-defined weak element can simulate the initial artificial crack very well.The failure mode,displacement load curve and bearing capacity of the joint are similar in both experimental and numerical results,which verifies the correctness of the finite element model.Based on this model,the mechanical properties of the joint with different lengths,different positions,different sides and different depths cracks are analyzed.The different bolt diameters and crack lengths are parametric analysis as well.The results show that the longer the bearing capacity decreases with increasing crack length.The failure mode would change from transverse split failure to bolt yield failure with decreasing bolt diameter,and the shrinkage cracks also have a certain effect on the failure mode.Based on the experiments and numerical simulation,the calculation model of joint was established.Moreover,the calculation formula of bearing capacity was deduced.The influence of crack on the joint was analyzed by mechanism analysis and simplified assumptions.The calculation results are corresponding to the test results and numerical simulation calculation results.It can provide theory for the safety appraisal of modern glued structure.