Prestress Design And Local Stability Analysis Of UHPC Continuous Bridge In Cantilever Construction

The ultra-high performance concrete(UHPC),compared with the traditional concrete,has the characteristics of ultra strength,high toughness and high durability,which can make the structural components of UHPC tend to be thinner,so that the size of the component is greatly reduced than that of the ordinary concrete.Currently,as the main structural material,UHPC is still mainly used to construct small and medium span simple supported beam and continuous beam,and the example of large span bridge is less.In order to promote its application in long-span bridges,it is necessary to research on the application of the long-span UHPC bridge.The main contents and conclusions of this paper are as follows:(1)Based on the RPC150,the UHPC material,a railway continuous bridge with a span combination of(60+100+60)m was taken as the prototype.Through using evaluation parameters and establishing the integrated finite element model of the structure,the slab thicknesses of the mid-span section and the pivot section were analyzed and compared,as well as the height of the mid-span section and the pivot secton.The results show that the dead weight(concrete weight)of the proposed UHPC scheme is 31.0% lower than that of the original bridge.In addition,when becoming flexible,the bridge needs to improve the stiffness of beams by increasing beam height.(2)By theoretical derivation,the formula and method of longitudinal prestress design based on the limit state of bending bearing capacity and the allowable stress on the upper and lower edge of the cross section are obtained.According to the two design formulas and methods of longitudinal prestress,the longitudinal prestress is designed separately for the UHPC continuous box girder bridge.At the same time,according to the results of structural stress after longitudinal prestressing,the necessity of transverse prestress and vertical prestress distribution is discussed.The results show that the quantity of longitudinal prestress of the UHPC continuous beam scheme is 14% less than that of the prototype by the estimation method of stress and 70% less than that of the prototype by the estimation method of flexural ultimate bearing capacity.Moreover,the scheme still needs Transverse Prestress to be designed in the top slab of box grider and vertical prestress to be designed at the area of zero block.(3)The overall stability and local stability of the UHPC continuous box girder bridge scheme after the longitudinal prestress are analyzed.Then the ultimate bearing capacity of the unidirectional uniform compression plate of RPC150 is analyzed and studied,and the reduction coefficient curve of the bearing capacity is obtained.By using this curve,the section of UHPC continuous box girder bridge is evaluated.Finally,the effect of two stiffening measures on the local stability of UHPC ultra-thin box girder,which are increasing plate thickness and adding stiffening rib,is compared.The results show that the scheme is not designed for compressive strength and stability,but for tensile stress strength.Furthermore,when the effective position of stiffener is clear and the relative width ratio of the plate is equal to about 1.4,adding the stiffener is more effective to improve the stability of the web than increasing the thickness of the web.