| As one of the common bridge types for small and medium span bridges,assembled hollow slab bridges are widely used in engineering practice due to their high economy,mature technology and easy construction.The prefabricated hollow slab girders are connected by hinge joints,which are the key element in the transverse force transmission of hollow slab bridges.During operation,the hinge joints are generally damaged to a certain extent,which in turn affects the integrity and safety of the hollow-core slab bridge.Therefore,it is necessary to systematically study the mechanism of deep hinge joint transmission and the damage evolution process of hollow-core slab bridges.In this paper,the effects of paving layer thickness,interface treatment,hinge joint concrete strength and hinge joint form on the force transfer performance of deep hinge joints are systematically investigated through static load tests on deep hinge joint sections.The finite element model of a 10m span hollow slab bridge with deep hinge joints is then established.Through the non-linear finite element analysis of the whole bridge,the force transfer performance and damage evolution of the hinge joints of four types of hollow slab bridges,including traditional reinforced hollow slab bridges,traditional reinforced hollow slab bridges with notched joints,pin-connected reinforced hollow slab bridges with notched joints and pin-connected reinforced hollow slab bridges with straight hinge joints with notched joints,are revealed.The main findings are as follows:(1)Under flexure and shear loading,the deep joint specimens crack mainly at the interface between the joint and the loading segment.In the uncracked stage,the interface between the joint and the beam section played the main role in transmitting the load.In the cracking stage,as the load increases,the crack developed upwards to the lower edge of the pavement layer,and the bond between the joint and the beam section at the cracking location disappeared,with the tensile reinforcement playing the main role in transmitting the load together with the concrete column.(2)The thickness of the paving layer,the form of the straight hinge joint,the spraying of the interface with grooves,the pinned reinforcement and the width of the hinge joint all improve the hinge joint performance:the maximum increase in through-joint load from 0 to 100 mm increases by 114.30%;the through-joint load of the straight hinge joint specimen increases by71.00%compared to the pinned reinforcement specimen;the through-joint load of the sprayed interface with grooves increases by 19.51%compared to the manually chiselled specimen;the through-joint load of the pinned reinforcement specimen increases by 7.69%compared to the conventional specimen.The through-joint load of the pin-connected steel specimens increased by 14.29%compared to the conventional specimens;the through-joint load of the specimens increased by 7.69%when the hinge joint width was increased from 10 to 150 mm.Based on the analysis of the test results,AASHTO 5.7.4(2017)was revised to calculate the hinge joint load capacity with a correction factor of 0.54.The revised calculation results agreed well with the test values..(3)MIDAS FEA NX was used to establish a finite element model of the deep joint section,and sensitivity analysis was carried out on the material parameters of the hinge joint interface unit to investigate the relationship between the hinge joint bearing capacity,tensile reinforcement stress,relative deflection and crack width and the material parameters of the interface unit.The results showed that the tensile strength of the interface unit was positively proportional to the hinge cracking load and ultimate load,and inversely proportional to the reinforcement stress,relative deflection,and crack width;the normal and tangential stiffness moduli of the interface unit were positively proportional to the hinge cracking load and ultimate load in the range of 5000-15000N/mm~3 and 50-150N/mm~3 respectively,and after exceeding15000 and 150N/mm~3,the cracking load and ultimate load of the hinge joint no longer change;the fracture energy of the interface unit did not affect the cracking load and ultimate load of the joint.(4)Based on the sensitivity analysis,simulation analysis was carried out on the deep joint section specimens.Comparing the finite element analysis results with the test results,it can be seen that the maximum error of the crack penetration load was 12.20%,and the stress and relative deflection of the hinge joint tensile reinforcement were consistent with the test results,which verifies the accuracy of the finite element model and the material parameters of the interface unit.At the same time,both the hinge joint damage pattern and the hinge joint interface stress state indicate that the hinge joint damage was cracking at the joint surface of the hinge joint and the hollow slab,which is consistent with the experimental results.Before the formation of the through-joint load,the hinge joint interface showed a stress distribution with the lower part in tension and the upper part in compression,and the height of the tension zone gradually increased with the increase in load.(5)A finite element model of a 10m span assembled hollow-core slab bridge was established based on the hinge joint interface and concrete plastic damage unit characteristics parameters of the deep hinge joint section specimens,and the hinge joint damage evolution of the whole bridge was analysed.The results show that the damage evolution of the hollow-core slab bridge starts from the damage at the hinge joint interface where the load is applied,and the damage occurs successively in the concrete of the hinge joint and the concrete of the hollow-core slab beam under the continuous load,showing the characteristics of local force transmission.Cracks at the hinge interface develop symmetrically towards the ends along the span direction,with the length of longitudinal cracks reaching 4 and 2 m for conventional and pin-connected reinforced hollow-core slab bridges respectively under ultimate load.the hinge interface develops continuously along the height direction,eventually reaching 600 mm,and gradually decreases in height symmetrically towards the ends as the distance from the load location increases.The damage to the concrete at the hinge joints of conventional and pin-connected reinforced hollow slab bridges under ultimate load is 3-7 m and 4-6 m respectively.The stresses in the hinge joint tensioned reinforcement show a uniform growth-rapid growth-slow growth trend as the load increases.(6)The combined stresses,relative deflections,interface crack heights and widths of the hollow-core slab bridges with notches in the hinge joints,the hollow-core slab bridges with notches in the pin-connected steel hinge joints and the hollow-core slab bridges with notches in the pin-connected steel straight hinge joints,in that order,improved and outperformed the hollow-core slab bridges with notches in the conventional steel hinge joints.Compared to the conventional reinforced hollow slab bridge,the ultimate load of the pin-connected reinforced hollow slab bridge with straight hinge joints with grooves is increased by 62.80%,which is in line with the strengthening effect of the deep hinge joint section specimen(68.42%);the stresses and relative deflections of the hinge joints are lower for the same load,and the corresponding loads are higher for the same crack width and height.Therefore,the hinge joint form of straight hinge joint with recess for pin jointed reinforcement can improve the interface bond,delay the development of hinge joint interface cracks,enhance the transverse force transmission capacity of the hinge joint,improve the force performance of the hollow slab bridge,and thus improve the integrity of the hollow slab bridge. |
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