Research On Flexural Performance Of Cast-in-place Joints Of UHPC Bridge Deck

Steel bridges are widely used worldwide because of their advantages of light weight,high strength,fast construction and recyclability.Steel brid ges in Japan and the United States account for 41% and 35% respectively,while in China,they are less than 1%.Considering that China has nearly half of the world's steel production every year,in July 2016,the Ministry of Transport promulgated the "Guid ing Opinions on Promoting the Construction of Highway Steel Structure Bridges",intending to promote the standardized design,industrial production and assembly construction of steel structure bridges,in order to improve the quality of the bridge structure.In September of the same year,the General Office of the State Council issued the "Guiding Opinions on Vigorously Developing Prefabricated Buildings",striving to make the proportion of prefabricated buildings occupying new buildings in more than 30% within 10 years.At present,there are three main types of prefabricated bridges: prefabricated concrete beams(hollow slabs,T-beams,small box girders,etc.),fabricated steel-concrete composite beams,and fabricated steel box girder.The prefabricated concrete beam is prone to cracks under the long-term load of the vehicle,which affects the structural safety and durability.The assembled steel-concrete composite beam will produce concrete tension and negative stress on the steel beam in the negative bending moment area;The box girder generally adopts the traditional orthotropic steel bridge deck system,and the problem of fatigue cracking of the steel bridge deck and frequent damage of the pavement la yer is difficult to solve.To this end,Professor Shao Xudong of Hunan University combined with the advantages of UHPC to propose a steel plate beam-UHPC fabricated "?" beam element with light weight,moderate span,no prestressing,good durability and low life expectancy.The assembled lightweight composite beam structure is formed by the beam unit,the UHPC diaphragm and the up-and-down longitudinal UHPC wet joint.In order to realize the smooth construction of the structure,it is necessary to solve the connection technology problem of each unit,and the connection betwee n the bridge panels is particularly important.In order to explore the reasonable form of longitudinal joints in the assembled lightweight composite beam structure,the test model of several sets of locally elevated joints and flat joints was made with the overpass bridge of Guangdong Mapu parking area as the engineering background,and the prefabricated whole was set.The plate member is compared with it.The structure performance of various joints was studied by four-point loading.details as follows:(1)Since the cast-in-place joints in the project cannot be steamed,the sides of the end of the test piece are restrained,and the influence of the shrinkage of the simulated UHPC on the localized height joint and the flat joint cracking load is affected.The results show that due to the shrinkage of UHPC,the flat joint cracking load is reduced by about 7%,and the local heightening joint is reduced by about 3.1%.(2)Compared with the whole plate test piece,the localized height joint cracking load is reduced by about 15%,and the flat joint structure cracking load is reduced by more than 56%.The localized height joint construction has better crack resistance than the flat joint construction.(3)Increasing the reinforcement ratio of the same size,the cra cking load of the locally elevated joint is increased by about 50.5%,which is more than three times that of the flat joint.In addition,after increasing the reinforcement ratio,the initial cracking position of the locally elevated joint can be transferr ed from the new and old concrete interface to the precast panel position.(4)The locally heightened joint structure can effectively reduce the performance degradation caused by the discontinuity of the steel fiber and the unfavorable influence of the UHPC constrained shrinkage tensile stress,so that the final failure position of the locally elevated joint plate test piece occurs in the change of the prefabricated plate.At the section,the joint strength is higher than that of the base metal.(5)The new and old concrete interface is chiseled to increase its roughness,which has a great influence on the cracking load.The flat joint cracking load is increased by 64.5%,and the local heightened joint is increased by 55%.The flat joints have a high sensitivity to roughness,which indirectly proves that the local heightening joints are relatively low in construction technology requirements.(6)Using ABAQUS to perform local finite element analysis on the background engineering bridge model,the peak stress of the key point of the bridge deck under the design load is obtained.Based on the cracking load of the static test,the overall bridge deck cracking safety factor is 3.50,and the local heightening joint is 5.53,which meets the design requirements.(7)The overall force analysis of the bridge was carried out by Midas,and the UHPC bridge deck stress meets the design requirements.