Shrinkage Creep Prediction Model And Long-term Deformation Effect Of UHPC Box Girder

China’s railway industry has developed rapidly in recent years,the main trunk line has been comprehensively accelerated for many times,UHPC box girder as a new type of structure with its excellent mechanical properties,has won extensive attention from the engineering community,for the solution to the existing technical bottleneck of large-span ordinary concrete girder bridge provides an important way.However,due to the ultra-thin wall of the structure,it will cause the dual effects of shear hysteresis and web shear deformation,which seriously affects the safety of the structure.At the same time,creep and shrinkage are inherent timevarying characteristics of concrete itself,which have a great impact on the bearing capacity,stress state,deformation performance and crack control of concrete structures.Compared with ordinary concrete,UHPC presents the characteristics of large shrinkage deformation and small creep deformation,and accurately estimates and predicts the effects of shrinkage creep on the anti-arch and deflection and long-term deformation of large prestressed concrete box girder,which is an urgent problem to be studied and solved in the current bridge engineering design and construction.Although domestic and foreign scholars have carried out a large number of studies on shrinkage and creep and shear lag effect and made some achievements,the comprehensive consideration of the two for coupling analysis is rarely reported in the literature.Based on the above situation,the main research contents of this paper are as follows:(1)Based on the collection of a large number of data related to concrete shrinkage creep,the mechanism,influencing factors and main analysis methods of concrete shrinkage creep of concrete structure were systematically sorted out and summarized.Several commonly used shrinkage creep prediction models at home and abroad are evaluated in detail,including the establishment mechanism of each prediction model and the main factors that need to be considered.(2)To carry out the shrinkage and creep test of UHPC materials,combined with the measured data of UHPC shrinkage and creep test,the domestic and foreign CEB1990,GL2000,ACI209R(1992),B3,JTG2004 and DBJ43/T235-2017 representative shrinkage and creep prediction models were compared.The error sizes of the predicted values of different models and the measured results are different.Among the above commonly used concrete shrinkage and creep prediction models,DBJ43/T235-2017 model is relatively in good agreement with the measured results of UHPC shrinkage.ACI209R(1992)model is consistent with UHPC creep measurements.(3)Through the comprehensive research and judgment of the generation mechanism and influencing factors of shrinkage and creep of UHPC,the particularity of shrinkage and creep of UHPC and prediction models at home and abroad,the proposed shrinkage and creep prediction model of ultra-high performance concrete containing coarse aggregate(CA-UHPC)is put forward.The proposed model and the experimental results show that the calculated results are in good agreement with the experimental results,and the error is within the controllable range.The proposed models are based on the actual situation of concrete materials in our country,the corresponding parameters are simplified,the calculation is relatively simple,strong practical.(4)Comprehensively considering the influence of shear hysteresis and shear deformation effects on the deflection deformation of UHPC box girder,the shear hysteresis warpage displacement mode is redefined,the additional deflection caused by shear hysteresis effect with more clear physical significance is selected as the generalized displacement of shear hysteresis,the influence of prestressed equivalent loads is considered when calculating external force potential energy,and the control differential equation reflecting the box girder shear hysteresis,shear deformation effect and UHPC shrinkage creep effect is established by using the principle of energy variational method.The theoretical expression of shear hysteresis and additional deflection of shear deformation of UHPC and other cross-sectional simple support beams considering cross-sectional reinforcement and shrinkage creep of UHPC materials under uniform distribution load is derived.(5)Based on the existing design data of UHPC box girder,a UHPC box girder with a span of 48 m is taken as the actual background.The section and reinforcement of the box girder are simplified,and then the theoretical formula derived in this paper is used to calculate and analyze the short-term and long-term deformation performance of the UHPC box girder considering the shear lag and shear deformation effect,and the theoretical calculation results are compared with the numerical solution of ANSYS finite element to verify the relevant theoretical system.The influence of shear lag effect and shear deformation effect on the long-term deformation performance of UHPC box girder is further revealed.