Basic Performance Of Orthotropic Steel Plate-ECC Bridge Deck Pavement Composite Structure

Asphalt concrete pavement is often used in traditional orthotropic steel bridge decks.Due to the poor thermal stability and low elastic modulus of asphalt materials,two typical diseases such as pavement damage and fatigue cracking of steel structure are easy to occur.The emergence of high toughness and high durability concrete materials provides a new way to solve the above problems,among which the most representative are Ultra-High Performance Concrete(UHPC)and Engineering Cementitious Composites(ECC).There are a lot of researches on UHPC steel bridge deck pavement system in China,and it has been successfully practiced in the large-span Bridges such as Zhaoqing Mafang Bridge in Guangdong Province,Wuhan Junshan Yangtze River Bridge and Nanjing Yangtze River No.5 Bridge and achieved good application results.However,there are still few studies on ECC steel bridge deck pavement system,the strength of cross-sectional combination and mechanical behavior of the ECC pavement are not clear yet.Therefore,the following research works have been carried out in this paper:(1)Basic mechanical properties and constitutive model of ECC.The stress-strain characteristics of ECC were studied by basic mechanical experiments(axial compression,axial tension,four-point bending and triaxial compression tests).The experimental results show that the 28d compressive strength of ECC can reach 51.6MPa.When the confining pressure increases from 0 to 4.5MPa,the compressive strength increases by 59%.The 28d tensile strength of ECC is 4.6MPa,and the ultimate strain is more than 4%,which is more than 400 times that of ordinary concrete.The 28d flexural strength is 17.3MPa,more than 40 times that of ordinary concrete,and the ultimate mid-span deflection is 21.7mm.According to the experimental results,the constitutive model of ECC material was constructed.The stress-strain response of ECC under triaxial compression and stress-deflection response of ECC under four-point bending test were in good agreement between the experimental results and simulation,and the relative error was less than 15%,which indicated that the constitutive model could reflect the basic mechanical characteristics of ECC satisfactorily.(2)Interfacial shear behavior of steel-ECC composite structure.The shear performance of the studs in ECC was studied through four groups of static pull-out tests.The test results show that the bonding between steel plate and ECC layer is beneficial to the initial stiffness of specimen,but has little effect on the shear capacity.The influence of stud corrosion rate,height,diameter,strength and ECC compressive strength of the stud on the shear performance was studied by using 12 finite element pull-out models.The simulation results show that when the corrosion rate increases from 0%to 20%,the shear capacity of the composite structure decreases by 46.3%.When short studs are used(the ratio of length to diameter is less than 3),the shear capacity of the composite structure decreases by about 5%.The increase of diameter of the stud significantly increases the shear bearing capacity,yield load and shear stiffness.However,studs with different strength grades only affect the shear bearing capacity and yield load,and the initial shear stiffness does not change.With the increase of ECC strength,the shear capacity of the composite structure increases,but when the strength garde exceeds 80MPa,the increase is not significant.(3)Local bending performance of steel-ECC composite structure.The local bending behavior of steel-ECC composite plate was studied through four-point bending tests.The test results show that ECC layer can work together with steel plate effectively,the composite structure therefore has good bearing capacity and multi-crack characteristics.The maximum tensile strain of pure bending section is more than 3%,the maximum compressive strain is about 4.6%.The thickness of the protective layer has a significant effect on the bending capacity of the composite structure.When the thickness of the protective layer decreases from 35mm to 25mm,the bending capacity increases by 21%-25%.The influences of the number of studs,the arrangement of studs,the ratio of reinforcement,the strength of reinforcement,and the thickness of ECC layer on the local bending performance of composite structures were studied through 17 finite element models.The simulation results show that the positive bending capacity of the composite structure is significantly affected by the studs in the shear bending section.When the studs are removed,the bearing capacity decreases by about 11%,while when the number of studs increases from 1*4(pieces)to 2*15(pieces),the bearing capacity increases by 120%.With the increase of reinforcement ratio,reinforcement strength and ECC plate thickness,the bending capacity of the composite structure also increases significantly.It is recommended that the transverse reinforcement can be arranged on the longitudinal reinforcement in the design of composite structure,and the studs of the shear section can be increased while the studs of the pure bending section can be reduced to improve the bending capacity.(4)Overall mechanical performance of steel-ECC composite structure.Based on ABAQUS sub-model technology,the mechanical performance and influencing factors of bridge deck pavement materials under the coupling action of global deformation and local deformation are analyzed.The simulation results show that ECC bridge deck pavement has excellent fatigue life,which up to 3.4 x 10^8(times).In addition,the sensitivity analysis of ECC pavement shows that the thickness of bridge deck has the most significant effect on the maximum tensile stress of ECC,followed by the thickness of stiffeners and the thickness of ECC layer.When the thickness of bridge deck increases from 16mm to 20mm,the maximum tensile stress of ECC decreases by 39%.When the U-rib thickness increases from 6mm to 10mm,the maximum tensile stress of ECC decreases by 19%.When the thickness of ECC layer increases from 50mm to 60mm,the maximum tensile stress of ECC decreases by 4%.The research provides a basic design understanding and optimization basis for ECC to be used as a steel bridge deck pavement layer.