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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14 MPa和2 MPa,6 MPa和2 MPa,对比开展了单轴压应力为6 MPa、14 MPa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,360 d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。
In order to obtain the law of shrinkage and creep of long-span prestressed concrete box girder under bidirectional prestress, the effect of different prestressing combinations on the shrinkage and creep effect is analyzed. Stress combination, the biaxial creep test of high-strength concrete under two kinds of stress combinations was carried out by using crossed beams. The stress combinations were 14 MPa and 2 MPa, 6 MPa and 2 MPa respectively. The uniaxial compressive stress Shrinkage and Creep Test of High Strength Concrete at 6 MPa and 14 MPa respectively. The effects of single and biaxial creep and stress combination on shrinkage and creep of high strength concrete are analyzed. The results show that the stress combination has a significant effect on the creep of high-strength concrete, and the creep coefficient under 360-day biaxial stress is only 75% of the corresponding uniaxial creep coefficient. Using the existing shrinkage and creep prediction model can not predict the high strength Concrete creep development process, and the use of exponential function has good fitting accuracy. It is suggested that in the design and construction of long-span continuous box girders, the vertical pre-stress level of the webs should be controlled within the designed allowable range.