混合梁斜拉桥微膨胀UHPC灌注钢混结合段的时变效应

Time-dependent effect of steel-concrete joints grouted by expansive UHPC in hybrid girder cable-stayed bridges

为明确微膨胀超高性能混凝土(Ultra-High-Performance Concrete,UHPC)灌注材料的收缩徐变对混合梁斜拉桥钢混结合段长期性能的影响,以湖北武穴长江公路大桥为工程背景,开展材性试验与结构反应实测。基于一种全桥杆系+局部空间网格的多尺度有限元建模方法,对不同灌注材料收缩徐变下钢混结合段的时变效应进行分析研究。研究结果表明:实桥所采用的微膨胀UHPC在测试龄期内膨胀应变呈现出先增后减且始终保持膨胀的趋势,在约5 d龄期时达到最大膨胀应变292.6με,至1 080 d时为83.8με;徐变系数在前50 d龄期内增长较快,至1 080 d时为1.63。灌注材料的收缩可在结合段内部产生显著的次应力,表现为内填混凝土的拉应力和钢格室的压应力;徐变则会导致混凝土应力松弛而使一部分恒载压应力向钢结构转移。运营20 a后,钢混结合段内填普通混凝土存在较高的开裂风险。未作收缩控制的普通UHPC虽亦出现拉应力,但未超过其抗拉强度,抗裂安全系数仍可达到1.5以上。而微膨胀UHPC处于受压状态,不存在开裂问题。微膨胀UHPC的应用,既可改善内填混凝土的抗裂性能,又有助于常规钢混结合段的结构优化,大幅减少材料用量和结构自重。

In order to clarify the influence of shrinkage and creep of expansive UItra-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 292.6ue on the 5th day approximately,and reaches 83.8με on the 1080th day.The creep coefficient increases rapidly in the first 50 days,and reaches 1.63 on the 1080th 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.