Time-dependent effect of steel-concrete joints grouted by expansive UHPC in hybrid girder cable-stayed bridges
In order to clarify the influence of shrinkage and creep of expansive Ultra-High-Performance Concrete(UHPC)grouting material on the long-term performance of steel-concrete joints in hybrid girder cable-stayed bridges,tests on material property and structural response were performed based on the engineering background of Wuxue Yangtze River highway bridge in Hubei.A multi-scale finite element method combining whole frame structure and local spatial grid was used to investigate the time-dependent effect of steel-concrete joint with different grouting materials.The results show that the expansive UHPC adopted in the actual bridge exhibits a trend of increasing first and then decreasing in expansive strains and maintaining expansion during the test age.The expansive strain reaches the maximum value of 292.6με on the 5th day approximately,and reaches 83.8με on the 1 080th day.The creep coefficient increases rapidly in the first 50 days,and reaches 1.63 on the 1 080th day.The shrinkage of grouting materials results in significant secondary stresses in the steel-concrete joint,which are manifested in the tensile stress in the filled concrete and the compressive stress in steel cells.The creep causes the stress relaxation of the concrete,and thus a certain amount of compressive stress caused by the dead load is transferred to the steel structure.After 20 years of operation,the ordinary concrete in the steel-concrete joint has a high risk of cracking.The conventional UHPC without any shrinkage control is also subjected to tensile stress,but the peak stress does not exceed tensile strength,and the corresponding safety factor of crack resistance is still more than 1.5.The expansive UHPC is still under compression without any risk of cracking.The application of expansive UHPC not only helps to improve the crack resistance of filled concrete,but also contributes to the structural optimization of conventional steel-concrete joints,greatly reducing the use of materials and structural weight.
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