| The steel-UHPC composite orthotropic bridge deck is an innovative structure,in which the shear studs are employed to connect deck plate and reinforced UHPC layer.This composite structure can improve the fatigue performance of structural details in traditional orthotropic steel deck(OSD)and durability of pavement.However,to achieve an infinite fatigue life for steel-UHPC composite orthotropic bridge deck,it is essential to retrofit the design of traditional OSD with epoxy pavement.Based on practical bridge engineerings,the rational detailings for three types of steel-UHPC composite bridge panels were investigated in this paper.The main contents and conclusions are stated as follows:The multi-scale finite element(FE)models were established for steel-UHPC composite bridge panel with closed ribs in an in-situ continuous girder bridge.The mechanical behaviors of structural details in OSD under fatigue truck were analyzed,and the stress responses were validated by comparing with the data from field measurement.The studies show that an application of 45 mm thick UHPC layer can reduce the stress responses of fatigue details with various levels.The reduction rate of stress range at deck side of rib-to-deck(RD)joint is up to 50%,followed by rib side of RD joint and fatigue details at rib-to-floorbeam(RF)joint.The fatigue assessment implies that all the three details(i.e.,the rib side of RD joint,the wrap-around weld and floorbeam side of RF joint)are finite fatigue life.To obtain an infinite-life design for fatigue details in steel-UHPC composite bridge panel with closed ribs,a multi-objective optimization approach with discrete variables was proposed based on conditional constrains and a large number of neutral network(NN)training data set derived from FE analysis.The structural optimization of composite bridge deck was carried out,and the stress ranges and bridge deck weight were selected as optimization objectives.The statistical analysis of orthogonal test was employed to obtain the influence of design parameters on the stress ranges of structural details.Combining with the NN algorithm,the mapping relation model between the stress ranges of structural details and the design parameters was derived.By using the ideal point method,the multi-objective optimization model was transformed into the single-objective optimization model,and the structural design schemes satisfying the infinite fatigue life were achieved by genetic algorithm.The thicknesses of rib and floorbeam shall be 10 mm and 16 mm,respectively,when the UHPC layer is 45 mm,while the thicknesses of the rib and floorbeam can be 8mm and 12 mm,respectively,when the UHPC layer is thickened to 60 mm,and the clearances of floorbeam cutout related to both of the schemes are 30 mm.A steel-UHPC composite bridge deck with no extra cutout at the closed rib-tofloorbeam intersection was proposed,which can simplify the manufacture of OSD and significantly improve the economic benefit.The refined FE method was employed to analyze the stress response of fatigue details under wheel loads,and the idea of using the rib with variable thickness at the bottom to realize the infinite-life design was presented.The effects of structural parameters on the fatigue performance of RF joint were investigated,and the parameter combinations with infinite fatigue life were provided.The results show that the RD joints indicate infinite fatigue life,and the stiffness of panel meets the requirements of specification.There is a significant stress concentration at RF joint,and the effects of the thicknesses of UHPC layer and deck plate on the stress are not significant.Increasing the thickness of the rib bottom as well as decreasing the floorbeam thickness and spacing can reduce the stress range of rib side at RF joint,and the 10 mm thick floorbeam is preferable.The UHPC layer can be50 mm if the rib with variable thickness are used,while the UHPC is required to 60 mm and the floorbeam spacing is 2.5m if the rib with uniform thickness is adopted.To investigate the fatigue performance of steel-UHPC composite bridge panel with open ribs,combining with the structural design of steel-UHPC composite bridge panel with open ribs in an in-situ bridge,the multi-scale FE models were built for the structure,and the mechanical behaviors of fatigue details under wheel loads were analyzed.The results show that the stress responses of all fatigue details are small,indicating an infinite fatigue life for all fatigue details except for the floorbeam detail of RF joint.Approximate models of stress ranges of fatigue details versus design parameters were obtained via both the experimental design method and response surface(RS)method,and the stress ranges of structural details under various design parameter combinations can be rapidly obtained without FE calculation.The RS models have good correlation and high significance,which can replace the real points of the test to analyze the results and facilitate engineering design.To achieve an infinite-life design for steel-UHPC composite bridge panel with open ribs,a multi-objective optimization method with discrete variables based on NSGA-II algorithm was proposed.The optimal Pareto fronts suggest that the lower the stress ranges of fatigue-prone detail are,the greater the bridge deck weight will be.When the structural parameter varies,the Pareto sets moving along the coordinate axis of stress range indicate that the structural parameter has a significant effect on the stress range of detail but a little effect on bridge deck weight.Under the principle of relatively low bridge deck weight,the obtained structural parameters satisfying infinite fatigue life imply that the deck plate thickness is 10 mm,and the floorbeam spacing is2.4m as well as the floorbeam thickness is not less than 12 mm. |
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