Experimental Investigation On Key Static Mechanical Performances Of Segmental Cast-in-Place UHPC Girder Bridge

Ultra-high performance concrete(UHPC)has been widely used in bridge engineering owing to its ultra-high mechanical properties,durability and excellent workability.At present,UHPC bridges are mainly prefabricated structures.However,due to the limitations of the construction site and the transportation,prefabricated bridges are difficult to be used in underdeveloped areas,such as in mountainous areas.Moreover,the bond strength of the dry-joint interface in the prefabricated UHPC bridge is low because of the discontinuity of steel fibers.However,the cast-in-place UHPC wet-joints can make the steel fibers at the interface continuous through the high-pressure water-jet roughening technology,and thus the UHPC wet-joints have stronger bond strength and crack resistance.In addition,the segmental cast-in-place construction method is a mature and economical technology and has been widely adopted in the construction of the long-span concrete girder bridges.Therefore,the segmental cast-in-place UHPC girder bridge should have a broad application prospect in the future.In this paper,the key static mechanical performances of the segmental cast-in-place UHPC girder bridges were studied by means of experimental,theoretical and numerical studies,mainly including the following contents:(1)The tensile properties of the UHPC monolithic interface and the UHPC wet-joint interface were studied.The effects of steel fiber characteristic parameter,reinforcement anchorage length and interfacial reinforcement ratio on the cracking mode and the interfacial tensile strength of UHPC wet joints were experimentally studied.Compared with the monolithic specimen,the tensile strength ratio(the ratio of interfacial tensile strength of the wet-joint specimen to that of the monolithic specimen)and the failure characteristics of the UHPC wet-joint interfaces were obtained.(2)The direct shear properties of the UHPC monolithic interface and the UHPC wet-joint interface were studied.The effects of steel fiber parameter on the cracking and failure modes,direct shear strength,direct shear strength ratio(the ratio of the direct shear peak strength of the flat wet-joint interface to that of the monolithic interface)and shear capacity of the UHPC monolithic specimens and the UHPC flat-wet-joint specimens were studied.A formula for calculating the direct shear capacity of UHPC monolithic interface and wet-joint interface was established,which was in good agreement with the test results.(3)The direct shear properties of the UHPC keyed-wet-joint interface were studied.The effects of keyed-joint shape and lateral stress on the cracking and failure modes,crack propagation,direct shear strength and shear-slip performance of UHPC wet-joint specimens were studied.A unified formula with clear-physical meaning,simple form and high precision for calculating the direct shear capacities of the UHPC monolithic interface,flat-wet-joint interface and key-wet-joint interface was established.(4)The flexural behavior of the monolithic interface of the reinforced UHPC beams was studied.The effects of reinforcement ratio and fiber volume fraction on the cracking and failure modes,crack propagation,deflection development and flexural capacity of the reinforced UHPC beams were experimentally studied.The calculation model of the flexural capacity of UHPC beams was constructed,and the moment-deflection curve and flexural capacity of UHPC beams were predicted.The calculation formula of the average crack spacing of UHPC beam was established,and the applicability of the specification formula for calculating the maximum crack width of UHPC beam was verified.(5)The flexural behavior of the reinforced UHPC beams with wet joints was studied.The effects of reinforcement ratio and keyed-wet-joint size on the cracking and failure modes,crack propagation,deflection development,flexural strength ratio(the ratio of flexural strength of the reinforced UHPC beam with wet-joints to that of the monolithic beam)and flexural capacity of the UHPC wet-joint beams were experimentally studied.Combined with the bond-slip constitutive model of the UHPC wet-joint interface,the parametric numerical analysis on the UHPC wet-joint beams was carried out.(6)The local compression performance of the anchorage zone of the segmental cast-in-place prestressed UHPC beam was studied.The local bearing effect of the UHPC box girder anchorage zone was analyzed by finite element method,and the stress characteristic of the anchorage zone in the diaphragm-anchor block integrated anchorage system was obtained.The large-tonnage full-scale tension test of the UHPC thin-walled box girder anchorage zone was carried out to verify the local compression bearing performance of the UHPC anchorage zone.According to the experiment results and the nonlinear numerical analysis results,the calculation formula of the local compression bearing capacity of the UHPC anchorage zone was checked and corrected.Finally,the parametric numerical analysis for UHPC anchorage zone was carried out.