The Experimental Study On Fatigue Performance Of Timber-Concrete Bolted Composite Beams

The timber-concrete composite beam is a new kind of composite structure.The upper concrete slab and the lower timber beam are connected as a whole through the shear connector,which can bear common forces.Under the external load,concrete compression,timber beam tension,give full play to the excellent performance of the two materials.As a renewable resource,wood has attracted increasing attention and application because of its high strength-weight ratio,good flexibility,impact resistance,low energy consumption and easy processing and decomposition.With social progress and economic development,on the one hand,traditional building materials-steel and concrete demand is growing,on the other hand,concrete and steel with the features of high energy consumption and high pollution,has been seriously affecting the sustainable development of the environment.Therefore,the development of new environment-friedly building materials to replace traditional building materials has become a new challenge in the field of civil engineering in the 21st century.In recent years,the static performance,long-term performance and fatigue performance of wooden bridge have been studied at home and abroad.The research on timber-concrete composite beams mainly focuses on the introduction of specimens and the static performance of composite beams.The fatigue life of timber-concrete composite structures is only based on experience and lacks theoretical and experimental research.Domestic research is still blan.Based on the full-length model of the wood-concrete composite beam bridge,three 1:4 timber-concrete bolted composite model test beams were made,corresponding nonlinear finite element analysis models were established,and static and fatigue tests were conducted.The fatigue behavior and failure mechanism of wood-concrete composite beams are obtained by analyzing test phenomena and comparing test and calculation results.The main results are as follows:(1)At the initial stage of static loading,the load and mid-span deflection show a linear relationship,as the load increases,the load and mid-span deflection show a nonlinear relationship.The ultimate failure load is 78KN.(2)After 2 million fatigue loads,the static failure load of composite beam fscb-2 is 76KN,indicating that composite beam has good fatigue performance under the action of low load amplitude.(3)With the increase of the fatigue load amplitude,the stiffness of composite beams degrades significantly.The stiffness of composite beams fscb-2 and fscb-3 decreases by 36.11%and 43.87%respectively after undergoing the fatigue load.(4)The results of finite element analysis are in good agreement with the experimental results.(5)With the increase of fatigue load,the fatigue life of composite beam decreases gradually.When the upper limit of fatigue load exceeds 50%of the static limit load,the fatigue life decreases rapidly.