Experimental Study On Fatigue Performance Of CFRP Reinforced Glulam Beams

In recent years,the application of modern wooden structures has been widely used,but the service life of wooden structures has been greatly reduced due to the wood material defects and environmental factors.Therefore,it is necessary to strengthen the wooden structure.At present,domestic and foreign researches on the reinforcement of glulam beams are mainly in terms of static performance,and research on dynamic performance is far from enough.Therefore,it is of theoretical significance and engineering practical value to carry out CFRP-reinforced glulam beam static performance test research and constant amplitude fatigue performance test research.The research work and results of this article are as follows:A static load test was performed on CFRP reinforced glulam beams.The static load test was used to determine the ultimate load of the three test beams,and the failure modes were analyzed.The results show that the CFRP cloth can increase the ultimate bearing capacity of glulam,which is 13.5%higher than the theoretical value of glulam 90.6kN when it is not strengthened.Most of the cracks that caused the failure of the test beam appeared in the positions with defects such as knots and twill.The failure of glued wood beams was greatly affected by defects such as knots and twill.During the test,the test beam has undergone the elastic and plastic stages.The main manifestations are elasticity and the plastic stage is extremely short.Therefore,several test beams show brittle failure.CFRP can increase the ultimate bearing capacity of glulam beams,but cannot change Its brittle form of destruction.The strain in the mid-span of the test beam is linearly distributed along the beam height,indicating that the test beam conforms to the flat section assumption.The CFRP reinforced glulam beams were subjected to equal amplitude fatigue tests.The fatigue failure patterns of the test beams,the static load-deflection curve after fatigue,the strain distribution along the cross-section height at various stages,and the fatigue degradation conditions were analyzed.The results show that:under fatigue loading,as the number of cycles increases,fatigue damage gradually accumulates,the wood in the compression zone yields first,and then the test beam undergoes fatigue damage.The load-deflection curve of each test beam is linear after a set number of fatigue cycle loads.As the number of cycles increases,the slope of the curve gradually decreases.The strain of the test beam is linearly distributed along the cross-section height,which meets the assumption of a flat cross-section.Under fatigue loading,as the load level increases,fatigue damage will increase rapidly.Curve fitting of the stiffness degradation curve of the test beam,the actual stiffness and the number of cycles are linearly higher.The slopes of the stiffness degradation curves of F-1,F-2,and F-3 are-1.84972,-1.990644,and-5.07686,respectively.The test beam under constant-amplitude fatigue load,the higher the fatigue load level,the faster the stiffness degradation,the shorter the fatigue life,the F-1 stiffness was degraded by 15.6%,and the F-2 and F-3 stiffness were degraded by 9.1.Failure occurs at%and 9.5%.Therefore,in actual engineering,if the rigidity of the component is degraded by about 9%,the component should be vigilant for fatigue failure.When the stress levels are 0.6σu,0.65σu,0.7σu,and the stress ratio is 0.2,the fatigue life of F-1,F-2,and F-3 is 1120985 times,617317 times,and 286484 times,respectively.The larger the value,the shorter the fatigue life.At the same fatigue load level,the stiffness degradation rate of CFRP-reinforced glulam beams is smaller than that of ordinary glulam beams,and the fatigue life of CFRP-reinforced glulam beams is longer.Through finite element numerical simulation analysis,the results show that the fatigue life of the test beam decreases as the fatigue load increases,the life change trend is consistent with the test results,and the actual life of the test beam is in good agreement with the numerical simulation results.At 0.6Pu fatigue load level,the numerical simulation results and test results have not reached 2 million times,and the fatigue limit strength of CFRP reinforced glulam beam is less than 0.6Pu.Finite element numerical simulation of F-4 and F-5,under 0.57Pu and 0.58Pu fatigue load grades,their life is 2107564 times and 1928563 times,with 2 million times as the fatigue limit life of the test beam,CFRP reinforced bonding The fatigue load limit of the wooden beam is between 0.57-0.58Pu.