| The steel-UHPC lightweight composite deck which composed of orthotropic steel deck(OSD)and a thin UHPC layer through shear bolts is an innovative solution for comprehensively improving the fatigue cracking problem of traditional OSD and easy breakage of the asphalt pavement layer.Due to the novel structure of steel-UHPC lightweight composite bridge deck,there are still few applications of this type of real bridges.At present,most of the research on steel-UHPC lightweight composite bridge deck system was carried out in laboratory tests and theoretical analysis.The fatigue research based on real bridge test data is still rare.In addition,the influence of the UHPC layer on the common fatigue details of the real bridge with OSD is still not clear.Moreover,the method for determining the thickness of the UHPC layer is also lacking.To this end,this paper mainly carried out the following research and got the corresponding conclusions:(1)Field measurement study.The stress response history of the common fatigue details of the OSD is obtained by the field test on the lightweight composite bridge deck with and without the UHPC layer.The characteristics of the stress response history are compared and analyzed with and without the UHPC layer,the stress response of each detail decreased significantly after the UHPC layer was laid.By comparing the stress reduction of the details at different locations,the law of the influence of the UHPC layer on the stress response of the lightweight composite bridge deck structure is revealed.(2)Finite element analysis simulation study.Based on the comparison between the static loading experimental data of the lightweight composite deck strip model and the analysis results of three finite element models(complete slip model,partial sl ip model and non-slip model),the suitable model for fatigue analysis is determined.Based on this,the finite element analysis model of Fengxi Bridge was established and compared with the measured results.The correctness of the finite element model was determined.The effects of different vehicle speeds and multi-vehicles on the dynamic response of the lightweight composite deck were also analyzed.It is determined that the factors such as vehicle speed and multi-vehicle have little effect on the fatigue assessment.(3)Fatigue assessment study.Based on the real bridge test data and sub-model analysis techniques,the nominal stress fatigue assessment method,the hot spot stress fatigue assessment method and the equivalent structural stress fatigue assessment method were used to evaluate the fatigue of the common fatigue details of the steel-UHPC lightweight composite deck structure.In addition,the fatigue assessment process of those methods and the corresponding assessment results of those details were given.Moreover,the applicability of those fatigue assessment methods is compared and analyzed.Furthermore,different fatigue assessment methods were recommended for different details.Moreover,a method for fatigue assessment of free edge on cutouts is also recommended.(4)Research on UHPC layer thickness design curve.It is determined that the thickness of UHPC layer has a great influence on the stiffness of the lightweight composite bridge deck via the parametric analysis tests which considered the parameters of shear studs spacing,protective layer thickness,steel bar spacing and UHPC layer thickness.The influence surfaces of various thicknesses of the UHPC layers and various thicknesses of steel deck were calculated.Based on the influence surface results,the UHPC layer thickness design curve was given.The use method is given by an example,and the UHPC layer thickness design curve has good practicability.(5)Optimization of cutouts.Four common type of cutouts,such as the highway bridge cutout Type1 recommended in Eurocode 3,the Normal cutout Type2,the Haibach cutout Type3,and the AASHTO-recommended cutout Type4,were respectively analysis by the sub-model analysis technique.The arc shape optimization is performed on the cutouts form with better relative performance.In the comparative analysis study,the arc shape optimization of the curved shape of the relat ively better performance was performed.Based on this research,a lightweight composite deck structure with no cutouts structure is proposed.It is found that the fatigue resistance of the non-cutout structure form is obviously better than those with cutouts structures,which can be used for the new bridge to obtain a lighter and thinner light weight composite bridge deck,and can also be the reinforcement of old bridges that have been cracked.Bridge reinforcement,this structural form has strong engineerin g application significance. |
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