截面收缩徐变非一致性分布与T梁桥腹板竖向开裂的时变相关性

Time-dependent Correlation between Non-uniformity Distribution of Cross-section Shrinkage and Creep and Vertical Cracking in Web of T-shaped Beam Bridge

在钢筋混凝土或预应力混凝土T梁桥的腹板竖向裂缝中,有一些并非在施工时出现,而是在长达1-2 a后才逐渐出现。为解释这些T梁桥腹板竖向裂缝形成过程中具有时间依赖性的现象,研究了截面收缩、徐变不一致分布与T梁竖向开裂的相关性。根据T梁截面的特点,考虑结构截面不同部位实际的配筋与理论厚度对收缩、徐变的不同影响。根据轴力等效转换及截面钢筋和混凝土变形协调的原则,推导了钢筋对收缩、徐变应变影响的理论系数,采用截面分层的方法考虑截面理论厚度沿梁高的变化,最后依据截面应变的平截面假定,推导了T梁截面收缩、徐变非一致分布效应导致的截面收缩、徐变自应力及其随时间变化的分层计算方法。实桥参数计算结果表明,T梁梁体纤薄,其顶板、腹板和马蹄的配筋和理论厚度存在较大差异,收缩、徐变在截面上容易形成不同步或差异较大的不一致分布情况。T梁截面收缩、徐变非一致分布是导致腹板竖向裂缝具有时间依赖性的重要因素,利用本文方法得到的竖向裂缝在时间轴上的形成过程与实际桥梁的裂缝出现的时间和位置情况基本吻合,验证了本文方法的有效性,为结构设计中考虑此因素提供了理论工具。

In web vertical cracks of reinforced concrete or prestressed concrete T-shaped beam bridge, there are some cracks do not appear during construction, but gradually appear 1 to 2 years later. In order to explain the time-dependent phenomena of forming of web vertical cracks in T-shaped beam bridge, the correlation between non-uniform distribution of shrinkage and creep （NUDSC） in cross-section and the web vertical cracking is studied. According to the characteristics of the T-shaped beam cross-section, the influence of reinforcements and theoretical thicknesses of different parts of the structure section on shrinkage and creep is considered. Based on the principle of axial force equivalent transformation and deformation compatibility for steel and concrete on the same section, the theoretical coefficient for influence of reinforcement on shrinkage and creep strain is derived. By using the theory of sectional layered approach and considering the change of the theoretical sectional thickness along the beam height, on the basis of the plane assumption of section strain, a layered calculation method of self-stresses of sectional shrinkage and creep and their changes with time caused by the NUDSC of T-shaped beam is derived. The result of real bridge parameter calculationshows that （ ! ） T-shaped beam has slender section, the reinforcement and theoretical thickness of top flange, web and bulb have larger differences, the sectional shrinkage and creep are easily to form un-synchronization or a significant non-uniformity distribution; （2） the NUDSC on the T-shaped beam section is the important factor for time-dependent vertical cracking on the web. The theoretical formation process of vertical cracks on the timeline obtained by the proposed method is consistent with the actual bridge cracking time and location, which verified the effectiveness of the proposed method, and provided a theoretical tool for considering NUDSC in structure design.