基于组合式模型的箱梁横向预应力张拉顺序分析

为了研究混凝土箱梁横向预应力合理的张拉顺序,利用体梁组合单元建立了南京长江第二大桥北汊桥悬臂施工的空间有限元模型,分析了采用不同张拉顺序施加横向预应力对箱梁顶板横向正应力分布的影响.分析结果表明:分段立即张拉会造成顶板中部下缘横向压应力沿纵向近似线性增加,从与前一梁段交界处的2.9 MPa增加到与后一梁段交界处的10.1 MPa;采用滞后张拉时,顶板中部下缘产生约6.7 MPa的均匀压应力,表明滞后张拉能更合理地发挥横向预应力的效应.据此提出了基于滞后张拉的施工方法,以克服横向压应力沿纵向分布不均的缺点,并进一步指出了滞后张拉在设计和施工中的注意事项,为改进现有大跨预应力混凝土箱梁的设计理论提供参考.

Analysis on tensioning sequence of transverse prestressing in box girder based on combined element model

In order to study the reasonable tensioning sequence of transverse prestressing in concrete box girders,a spatial finite element model simulating the cantilever construction process of the North Bridge of Nanjing Second Yangtze River Bridge is established based on the brick-beam combination element.The influence of the tensioning sequence of transverse prestressing on the transverse normal stress distribution in the top plate of the box girder is analyzed.The analysis results show that when the transverse prestressing is tensioned immediately,the transverse compressive stress at the lower center of the top plate approximately linearly increases along the longitudinal coordinate,from 2.9MPa at the point connecting the previous segment to 10.1MPa at the point connecting the following segment.When the transverse prestressing is delay-tensioned,the uniform transverse compressive stress of about 6.7MPa is produced at the lower center of the top plate,demonstrating that delay-tensioning can more effectively play the role of transverse prestressing.According to the results,the construction method based on the delay-tensioning is proposed to solve the problem of non-uniform distribution of the transverse compressive stresses along the longitudinal coordinate.Furthermore,the notes of the delay-tensioning in design and construction are given,which can be used as a reference for improving the design theory of the existing large span prestressed concrete box girder.