| The steel-concrete hybrid continuous rigid frame bridge can avoid the problems of long-term downward deflection and web cracking in the long-span continuous rigid frame bridge by setting the steel structure section in the middle of the main span,and the reasonable span range of the continuous rigid frame bridge can be increased,which has broad it’s application prospect.The steel-concrete joint is the core component of this type of bridge,and its connection performance is related to the overall mechanical behavior and long-term performance of the structure.In the super-large-span steel-concrete hybrid track continuous rigid-frame bridge,the steel-concrete joint has the characteristics of various material combinations,sudden stiffness change,and complex structure.In addition,the track bridge bears a large proportion of dynamic loads.Therefore,more urgent requirements are put forward for the static and fatigue performance of the joint.In order to explore the fatigue damage behavior,static force transfer mechanism,and bearing capacity safety reserve of the steel-concrete joint of the continuous rigid frame bridge on the super-long-span track,this thesis conducts experiments and theoretical experiments on the static and fatigue performance of the steel-concrete joint section of the continuous rigid-frame bridge on the long-span track.The performance evolution of the joint under the action of design fatigue load and overload fatigue load is explored.The mechanical behavior and failure mechanism of the joint in the limit state are clarified.The force transmission mechanism,stress distribution law,and calculation method of shear connectors,the end-face bearing of steel beams,and bearing plates are studied.The bearing capacity safety reserve of the joint under various damage conditions was quantitatively assessed.This thesis relies on the National Science Fund for Distinguished Young Scholars: Bridge Monitoring and Reinforcement(51425801)to carry out the above research.The main research work and results are as follows:(1)The multi-scale analysis of the numerical model of the steel-concrete joint was carried out,the most unfavorable stress state of the joint was clarified,and the high fatigue damage risk area was determined based on the stress concentration state.The research shows that most of the steel structure stress in the joint area is at a low level,and there is a significant stress concentration at the abrupt change of the section of the stiffener in the transition section of the steel beam and the contact position between the steel plate and the bearing plate,and there is a relatively high risk of fatigue damage.On this basis,through numerical simulation,the interface force distribution state of each member in the joint with different stiffness is analyzed.The results show that the increase of the interface stiffness of the joint can reduce the maximum slip value,and the increase of the length of the joint segment has little effect on the maximum slip value.In addition,the existence of end-face steel beams and bearing plates further limits the relative slip between the steel structure and the concrete.(2)The fatigue model test of the steel-concrete joint section of the Jiahua Jialing River track bridge was carried out.The verification test under the design fatigue load of2 million times was carried out.Overload tests were also conducted under 1.5 times(500,000 times)and 2.0 times(500,000 times)design fatigue loads.The test results show that the structure’s mechanical properties are attenuated less after fatigue loading,the joint is in an elastic working state during the entire loading process,and no fatigue cracks are found,indicating that the joint section has a high anti-fatigue safety reserve.The hot spot stress analysis was carried out for each key position.The hot spot stress at the sudden change of the stiffener section and the upper weld toe of the top plate opening steel plate was higher,which was the focus area of the initial design and later monitoring.(3)Model tests and numerical analyses are carried out for the mechanical behavior of the steel-concrete joint under different static cyclic load conditions.The results show that: under the action of the design load cycle,the stress-load curve of each loading has a linear relationship and basically coincides,the maximum stress change of each measuring point does not exceed 4.8%,and the static performance of the joint section is almost not attenuated during the cycle;Under the action of the ultimate load cycle,the interfacial adhesion properties are all degraded to a certain extent,and there is a significant decrease in the sixth cycle,and the joint section shows strong failure toughness as a whole.(4)To clarify the force transmission mechanism of the shear connectors in the joint,the end-face bearing of the steel beam,and the bearing plate,4 groups of 12 model tests were carried out.The test results show that the maximum slip of the steel beam end-face compression specimens is more than 10 mm,exhibiting ductile failure,and the ultimate average compressive stress of the steel beam end-face can reach 52.9MPa,and the force transmission effect is remarkable;The average ultimate bearing capacity of a single PBL connector is 87.5k N,and all of them show ductile failure,which has a good force transmission effect;The push-out test results of the bearing plate show that the average ultimate bearing capacity of the bearing plate exceeds 3500 k N,and the failure mode exhibits certain ductility characteristics.The effect of the bearing plate on the load transfer of the joint is the most significant.(5)The calculation method of bearing capacity of three types of force transmission methods of the shear connector,end-face bearing of steel beam,and the bearing plate is proposed.A simplified calculation model of the joint section is established,and a calculation method for the bearing capacity of the joint is proposed.Furthermore,based on the redundancy theory of structural bearing capacity,the safety reserve analysis of the joint section considering the phenomenon of slip hysteresis is carried out.The results show that the current design of the joint section has high bearing capacity redundancy and can still ensure the reliable connection of steel-concrete even when some components are significantly damaged. |
