考虑中面剪切变形的预应力混凝土U型薄壁梁弯剪扭复合作用性能研究

Urban railway transit engineering is growing rapidly along with the tide of the new socialist era, which leads to the wide application of prestressed concrete U-shaped beams (PCUBs). PCUBs has the advantages of bearing, noise reduction, operation and protection. In the actual application, PCUBs are under the coupling effects of bending, shear and torsion due to the curved track, eccentric loads, transvers wind loads and earthquake actions. The interaction of bending, shear and torsion may induce early cracking of concrete, deterioration of structural rigid and even the collapse of the structure. However, theoretical and experimental studies on torsional property of PCUBs are quite scarce and no relevant design specification can be consulted, which restrict the structures’ further applications in engineering construction. Therefore, in order to meet the urgent engineering needs, this project studies the mechanical performance of PCUBs, which are under the coupling effects of bending, shear and torsion, by means of the combined research methods of theoretical derivation, experimental study and the finite element method. The interaction of bending, shear and torsion is detailed studied, meanwhile the shear deformation is specially considered. In this project, a calculation method for the mechanical performance of PCUBs in the entire loading process with the consideration of shear deformation is theoretically derived. Experimental studies focus on the variation of concrete cracks, stresses of prestressed reinforcement and regular reinforcement, failure modes and rigid of the beams. Parametric analysis explores the effect of span-depth ratio, boundary conditions and loading ratio on the mechanical performance of PCUBs. Finally, a set of simple formulas are proposed to obtain the bearing capacity of PCUBs under combined loadings. All efforts in this project are made to provide a technical reference for the application and promotion of PCUBs.

社会主义新时代的浪潮下，城市轨道交通工程迅猛发展，集承载、降噪、运营、防护等功能于一身的预应力混凝土U型梁得到广泛应用。实际工程应用中，预应力混凝土U型梁处于弯剪扭复合作用状态，弯扭、剪扭的相互作用会导致混凝土提前开裂、刚度退化，甚至结构破坏。然而，预应力混凝土U型梁弯剪扭复合作用性能的研究严重滞后，现存的规范也缺乏对该结构的条文说明。因此，本项目针对实际工程需要，以弯剪扭复合作用下的预应力U型梁为对象，采用理论推导、试验验证和有限元模拟三种方法，重点探究弯剪扭的耦合作用和中面剪切变形的影响，推导考虑中面剪切变形的预应力混凝土U型梁在弯剪扭复合作用下力学性能的全过程计算方法，探究结构的抗裂性、钢筋及混凝土的应变、破坏模式及刚度等变化规律，探究荷载比例、边界条件和跨高比对U型梁力学性能的影响。最终，提出预应力混凝土U型梁在弯剪扭复合作用下的承载力计算公式，为U型梁的推广及应用提供技术参考。

随着国内轨道交通事业的迅猛发展，近年来，钢筋混凝土U型薄壁梁基于其建筑高度低、外形美观、施工迅速等独特的特点得到广泛应用。在实践应用中，由于偏载、横向风载、车辆摇摆和地震等作用，U型薄壁梁会处于承受弯剪扭的复合受力状态。然而，对于钢筋混凝土开口薄壁构件的扭转、弯扭复合作用性能的相关研究严重匮乏。本项目针对实际及理论研究需要，通过理论计算、试验研究和有限元计算三种方法对钢筋混凝土U型梁在不同弯扭比例条件下的力学性能和破坏机理展开研究。本项目理论研究建立了考虑中面剪切变形影响的U型梁弹性扭转计算方法，并提出了弯剪扭复合作用下U型梁的非线性性能计算方法；基于翘曲弯矩和弯矩耦合作用，建立U型梁混凝土弯曲开裂荷载计算公式。试验研究表明U型梁混凝土裂缝开展分为垂直的弯曲裂缝和斜向剪切裂缝，弯曲裂缝由翘曲弯矩和弯矩作用控制，剪切裂缝由翘曲扭矩、剪力和自由扭矩控制；试验试件发生典型的弯曲型破坏特征，纯扭矩作用试件两侧腹板均形成塑性铰（由翘曲弯矩控制），而弯扭复合作用试件的塑性铰发生于加载侧腹板（由弯矩和翘曲弯矩控制）；破坏截面处钢筋的应变沿截面底板或者腹板基本呈线性分布，单板满足平截面假定。混凝土U型梁的力学性能与构件的边界条件（简支或者固支）、跨高比、弯扭比例等条件密切相关，直接影响剪切变形的作用效果、裂缝形式、构件的破坏方式，设计中应对使用条件加以限定。最终，提出混凝土U型梁的承载力计算公式。本项目的研究成果，能够U型梁在实际应用中的弯扭复合作用效果做出定量的评估，为U型梁的设计应用提供技术参考，同时，充分发挥U形梁的结构性能，拓宽U型梁的使用范围，为单槽双线及市政高架桥的应用实施提供技术支持。