| Ultar High Performance Concret(UHPC)is a kind of cement-based composite material with ultra high strength and durability.It is used for ?-shaped prefabricated beams and cast-in-situ wet joints to form UHPC ?-shaped beam bridge.It has small weight,no need for deck construction,few cast-in-situ wet joints and high durability of wet joints.It can effectively solve the problems existing in traditional concrete beam bridges.Therefore,the basic mechanical properties of UHPC ?-shaped beam bridge are studied by finite element simulation and theoretical analysis.The main work and conclusions are as follows:(1)Referring to the existing engineering examples of UHPC ?-shaped beams at home and abroad,the cross-sectional dimensions of UHPC ?-shaped beams with span of 30 meters are preliminarily drawn up,and then the performance and economy of UHPC ?-shaped beams and normal concrete T-beams with the same span and ultimate bearing capacity are compared.The results show that although the section is much smaller than that of concrete T-beams,the ultimate elastic bearing capacity and cracking strain of UHPC ?-beams under bending and shearing are significantly higher than that of concrete T-beams,and the self-weight of UHPC ?-beams is 30%less than normal concrete T-beams,and the life cycle cost of bridges is much lower than that of concrete T-beams.(2)The effects of the thickness of deck,transverse reinforcement and diaphragm on ths transverse mechanical properties of UHPC ?-shaped beam are studied by finite element model analysis.The results show that the transverse performance of UHPC ?-shaped beam can be improved by increasing the thickness of deck and the total area of transverse reinforcement and strengthening the restraint of diaphragm.The ratio of width to thickness of bridge deck should not be greater than 25 or less than 13.3,and the recommended interval is 16.67-20.It is suggested that the ratio of deck width to transverse reinforcement spacing is 10-20,and the reduction of reinforcement diameter can effectively reduce the crack development speed and width.It is suggested that the spacing between diaphragms be 15 meters.Based on the Specification for Highway Bridges and theoretical derivation,the transverse checking method of UHPC ?-shaped beam is given.(3)Suggested the UHPC wet joint,established the simulation model of bridge deck jointed by UHPC wet joint,obtained the transmission mechanism of UHPC wet joint,and studied the influence of joint depth and cantilever length on the performance of deck.The results show that UHPC wet joints transmit force by extruding UHPC at the bottom of U-shaped end hook of transverse reinforcement;the depth of joints and cantilever length have great influence on the stress and deformation of bridge deck and joints,and the recommended depth of joints is 180 mm;the ratio of cantilever plate length to thickness is suggested to be 4.9-6.6.(4)Based on the energy variational principle,the analytical solution of shear lag effect of UHPC ?-shaped beam is deduced and the effective distribution width is calculated.The results show that the shear lag effect of UHPC ?-shaped beam is mitigated.The calculation method of effective width of Specification for Highway Bridges in China is too conservative to apply to UHPC ?-shaped beam.Based on the energy variational principle,a proposed method for calculating the effective width of UHPC ?-shaped beams is presented.An example shows that the proposed method is accurate and safe,and is suitable for engineering design.(5)The whole finite element model of UHPC ?-shaped beam is established,and the overall mechanical properties of UHPC ?-shaped beam bridge are studied.The results show that there is no risk of cracking in the deck of UHPC ?-shaped beam bridge under vehicle loads,and the load of bridge can be well transmitted between multiple girders of UHPC ?-shaped beam bridge connected by UHPC wet joints and diaphragms. |
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