Research On The Fatigue Mechanism Of Bolted Connectors In Timber-Concrete Composite Structure

Timber-concrete composite(TCC)structures is a new type of composite structure developed on the basis of timber and concrete structure,and the shear connectors are the key components of TCC.Under the load,the concrete slab is in compression and the timber beam is in tension,which give full play to the excellent performance of both materials.Compared with concrete structure,TCC has the advantages of low energy consumption,low emission and renewability,which is consistent with the concept of modern ecological architecture.Fatigue damage mechanism of bolted TCC is influenced by many factors and its experimental results are discrete,its more complicated than static damage mechanism.Although the fatigue problem of connectors has been studied to some extent,the mechanism and degree of fatigue damage have not been fully studied.In this thesis,the mechanism and degree of fatigue damage of bolted connectors are studied based on experimental studies and theoretical derivation.The main research contents and findings are as follows:(1)9 connections(6 bolted and 3 timber-steel connections)were designed and subjected to static and fatigue experiments,and the bearing capacity of the bolt connector under different loading ratio were investigated.The law of ultimate bearing capacity,stiffness degradation and residual slippage were analyzed,and the fatigue damage modes of bolted connections were obtained.(2)Numerical models of the bolted connections under static loading were first established based on FEA software ANSYS and were validated by static results.Then the fatigue analysis was carried in software nCode,and the analytical results are consistent with fatigue experimental results.(3)The 3 stages of fatigue damage mechanism of bolted connections are obtained based on the failure modes and the law of residual slippage.Timber and concrete crushed in the first stage,and the damage develop rapidly;In the second stage,the stress state of the bolts shift from pure shear to bending shear and the bolts deform plasticly,the damage develop moderately;In the third stage,the local damages of timber and concrete continue,the effective area of the bolts cross-section decrease gradually and bolts stress increase,the bolts fracture brittlely in the end.(4)The residual slippage is selected as the damage variable,and the relationship between the variable and load cycles is provided,then the two stages fatigue damage model of the bolts was established.The mechanism and degree of fatigue damage of bolted connectors are studied in this thesis,and the fatigue damage mechanism of bolt connectors are revealed.Based on the residual slippage,two stages fatigue damage model are established.The works in this thesis provide a reference for the fatigue design of TCC structures,and are of great significance for the promotion and application of TCC structures.