| In fully integral composite bridges,the steel girder–concrete abutment connection is subjected to complex loads,such as the shear force and the hogging moment from traffic loads,and the axial force due to the thermal expansion of the girder under seasonal temperature changes,and the structural behavior of the girder–abutment connection directly impacts the moment distribution between the girder and the concrete abutment,therefore becomes the key problem when designing this type of bridges.Furthermore,with the increasing span of fully integral composite bridges in these years,the previously applied structural detail,in which the steel girder is simply embedded in the concrete abutment,may not meet the design requirements any more,and perfobond connectors are often set inside the connection to increase the stiffness and the strength.However,current specifications and design manuals do not provide any related calculation equation,and studies on this type of girder-abutment connections are rather limited,and the strength and deformation properties remain unclear.To solve the above-mentioned issues,by means of model tests,numerical simulation and theoretical analyses,the load-bearing mechanism of girder-abutment connections with perfobond connectors was revealed,the effects of the shear-span ratio,the girder embedded length,the abutment width,the quantity and the arrangement of shear connectors on the structural behavior of the connection were clarified,an equation for the flexural strength of girder-abutment connections that incoporates the effects of perfobond connectors was proposed,and a method for the moment-rotation angle relationship of girder-abutment connections was established.(1)Based on the design example of British integral abutment composite bridges,1/3 scaled model tests were conducted on three structural details of I-shaped steel girder-concrete abutment connections with perfobond connectors under the most unfavorable condition in shear and moment.The three structural details were the better-performance detail,in which the connectors were set on the web and both flanges,the easier-placement detail,in which the connectors were only set on the web and the top flange of the embedded girder was removed,and the faster-construction detail,in which the connectors were set on the insert plate and the embedded plate.Results show that all the three structural details meet the design requirements,and the better-performance detail has the highest initial stiffness and strength,but the ductility is relatively low,whereas the other two details have similar load-bearing behavior;the relative rotation center between steel girder and concrete abutment shifts when the load is varied;in all three details,about half of the perfobond connectors have not reached their shear capacities when the connection is destroyed.(2)Based on 3D finite element method,a numerical study was carried out on the three tested models and a parametric study was conducted on the effect of connector quantities set on the critical plates.Results show that in all three details,perfobond connectors have a significant contribution in the moment bearing;the perfobond connectors can greatly increase the initial stiffness,the strength and the ductility of the connection,but may also have a negative effect when the shear connectors are set in the weak place;the moment in the embedded girder reaches the maximum near the first row of web connectors in the better-performance and easier-placement details,and reaches the maximum near the front bearing plate in the faster-construction detail,then decreases almost linearly with the embedded length.(3)Based on the parametric study of 90 finite element models,the effects of shear-span ratio,connector quantity,connector arrangement,the embedded length of steel girder and abutment width on the flexural strength of the better-performance detail were studied;according to the common shear-span ratios of fully integral composite bridges,the current equation for the flexural strength of simply-embedded girder connections was modified;based on the rigid body assumption and the constitutive equation of shear connectors,the relationship between any shear connector inside the connection and the relative rotation angle between the girder and the abutment,were established,and the relative rotation angle at the ultimate state was fitted;an equation for the flexural strength of girder-abutment connection that can incorporate the contribution of shear connectors and consider the uneven distribution of the shear forces among connectors was proposed.(4)Based on the proposed orthogonal component method,a calculation method was established to predict the moment-rotation angle curve of the girder-abutment connection.The components in the connection were identified and categorized,and the simplified spring model of the connection was established;by means of analytical analyses and parametric analyses,the equations for the mechanical parameters,such as the initial stiffness,the yield load,the yield displacement and the resistance,of the perforated plate component with an imposed displacement at one or both ends and the compressive concrete component near the bearing plate and the flanges,were determined;the proposed method was verified with parametric finite element analyses and experimental data,then the undetermined coefficient in the moment-rotation angle model was fitted,and the mathematical formula for the moment-rotation angle relationship of the connection was determined. |
