Experimental Study On Fatigue Performance Of Glulam Beams With Steel Plywood And Bolt Connection

Modern wood structure is usually connected by bolts,which has the advantages of simple processing,convenient assembly,good economic performance and reliable force transmission;When there is a need for extension,it is usually combined in the form of externally clamped steel plates.However,in practical engineering,the glulam beams connected with steel splints and bolts are not only subjected to static loads,but also to dynamic loads such as crowds,vehicles and wind loads,which may cause looseness among steel plates,bolts and glulam and reduce the synergy,thus bringing risks to the reliability of connectors.With the increase of service time,the fatigue problem should be paid attention to.Therefore,it is urgent to carry out an experimental study on fatigue performance of glulam beams connected with steel splints and bolts.In this paper,12 test beams with span-height ratio of 18 were designed by using domestic larch glulam,among which 9 beams were used in static load test,namely pure glulam beams group,glulam beams connected with steel splints and two rows of bolts group,and glulam beams connected with steel splints and three rows of bolts group,with three beams in each group.Then,the remaining three test beams were used for fatigue tests of glulam beams connected with steel splints and bolts at low,medium and high stress levels,and the corresponding fatigue life,residual strength,stiffness degradation law and cross-section stress distribution were studied.Finally,the test process of the test beam is simulated by ANSYS Workbench software,and then compared with the test results.The research results are as follows:(1)Compared with pure glulam beams,the early bending stiffness of glulam beams connected with steel splints and bolts group is higher,but as the load continues to increase,the rigidity is inferior to that of glulam beams,and the ultimate bearing capacity is slightly lower than that of pure glulam beams.The final failure forms are as follows:Brittle tensile failure of pure glulam beams in mid-span;glulam beams connected with steel splints and bolts yield in tension and compression and fail plastically,and their ductility is better than that of pure glulam beams.glulam beams connected with steel splints and two rows of bolts are penetrated by cracks in the upper and lower rows of bolt holes;Cracks in the upper and lower rows of bolt holes run through the glulam beams connected with steel splints and three rows of bolts,but no obvious cracks are found in the middle row.(2)After 2 million cyclic loads,the ultimate load of glulam beams connected with steel splints and bolts is degraded by 11.3%,which indicates that this connection mode can cooperate with each other and has good fatigue performance.All the test beams show that,in the process of cyclic loading,the stiffness degradation is not obvious at first,th en suddenly decreases sharply,and finally tends to be stable until failure.According to the observation results,combined with fatigue damage principle and fracture mechanics,a calculation model for fatigue life and damage process of glulam beams connected with steel splints and bolts is proposed.(3)ANSYS finite element software is used to simulate th e test process of pure glulam beams and glulam beams connected with steel splints and bolts,and the obtained load-displacement curves and fatigue life predictions are in good agreement with the test results.The fatigue damage analysis of glulam beams connected with steel splints and bolts shows that the connection mode of glulam beams connected with steel splints and bolts can effectively restrain the accumulation of fatigue damage in the scope of steel splints and bolts connection.