桥用高强混凝土双轴徐变试验研究

为获得大跨度预应力混凝土箱梁腹板在双向预应力作用下的收缩徐变发展规律，分析不同预应力组合对收缩徐变效应的影响，研究了大跨度预应力箱梁腹板的常遇应力组合，并采用十字交叉梁开展了2种应力组合条件下的高强混凝土双轴徐变试验，即应力组合分别为14MPa和2MPa，6MPa和2MPa，对比开展了单轴压应力为6MPa、14MPa的高强混凝土收缩徐变试验，分析单、双轴徐变和应力组合对高强混凝土收缩徐变的影响。研究结果表明：应力组合对高强混凝土徐变影响显著，360d双轴应力条件下的徐变系数仅为相应单轴徐变系数的75%；采用现有收缩徐变预测模型不能较好预测高强混凝土的实际徐变发展过程，而采用指数函数具有较好的拟合精度。建议在大跨度连续箱梁设计和施工中，确保腹板竖向预应力水平控制在设计允许范围内。

Biaxial creep experiment for high strength concrete in bridge engineering

To obtain the shrinkage and creep development law of high strength concrete in bridge engineering,reinforced concrete cross beams were used as creep samples for biaxial creep test.Normal stress condition(14 MPa plus 2 MPa,6 MPa plus 2 MPa) with two combinations were considered.The comparison between creep with single stress and biaxial stress were analyzed.It is indicated that the creep of high strength concrete is highly affected by stress combination.Creep coefficient of biaxial stress is 75% of that of single stress.Accuracy of exiting creep prediction models is unsatisfactory to predict the development of concrete creep with biaxial stress status.Exponential function creep model has higher prediction accuracy.Since vertical stress distribution in box beam is highly effected on concrete creep,it is suggested that vertical prestressing for web plate must be controlled during designing and construction.