预应力连续组合梁收缩徐变效应的计算方法研究

With remarkable economic benefits prestressed continuous composite beams are widely used in highway and railway bridges. The negative moment region of continuous beams is complicated by the force because the negative moment, shear force and axial force are interrelated. In the process of long-term use, the shrinkage and creep of concrete lead to the redistribution of the internal forces both in the section and structure, and the secondary internal forces will significantly change the moment, shear force and axial force, causing the bridge slab cracking and the the deflection increasing, which seriously affects the safety and use of structures. The range of crack area is related to many factors, such as load, section and so on, which is uncertain. Underestimating the scope of cracking area means overestimating the scope of the shrinkage and creep. The shear deformation caused by shrinkage in negative moment zone is very large and the shearing deformations of the webs can not be neglected. How to consider these adverse influences on shrinkage and creep effects, on which current research is not sufficient. Theses are also the urgent and important contents need to be supplemented and improved in the code. Considering creep, shear deformation and slip, the analytic calculation methods of the deflection and stiffness of continuous composite beams under the action of prestress and shrinkage are presented, the reasonable range of crack zone is proposed, and the influence law of main factors is revealed. Analytic method will be checked and revised by test and numerical methods. The results can enrich and develop the theory of prestressed continuous composite beams, provide theoretical basis for safe design of relevant specifications, and provide verification means for finite element design software.

预应力连续组合梁具有显著的经济效益，在公路和铁路桥梁中应用广泛。连续梁的负弯矩区受力复杂，负弯矩、剪力和轴力相互关联。在长期使用过程中，混凝土收缩徐变导致了截面和结构的内力重分布，产生的次内力还将显著改变弯矩、剪力和轴力的大小，引发桥面板开裂和下挠增加，严重影响了结构的安全和使用。开裂区范围与荷载、截面等许多因素有关，具有不确定性，低估开裂区范围意味着高估收缩徐变的作用范围。收缩在负弯矩区引起的次剪力很大，型钢梁腹板产生的剪切变形不能被忽略。对收缩徐变效应如何考虑这些不利影响，目前研究尚不充分，也是规范所缺乏和亟待需要补充的重要内容。考虑徐变、剪切变形和滑移，形成连续组合梁挠度和刚度在预应力和收缩等作用下的解析计算方法，提出开裂区的合理范围，揭示主要因素的影响规律。解析法用试验和数值法来校正。成果可进一步丰富和发展预应力连续组合梁理论，为相关设计规范提供理论依据，为有限元软件提供验证手段。

组合梁在公路、铁路桥梁、高层建筑中应用日益广泛。在连续梁的负弯矩区，组合截面的力学优势反转为劣势（钢梁受压，翼板受拉），混凝土受拉开裂可能导致预应力筋锈蚀和疲劳破坏等工程病害，严重影响了结构的安全和使用。在充分调研的基础上，完成了3根简支钢-混组合梁、3根连续钢-混组合梁、3根原位混凝土小梁和3根立式收缩试件的长期荷载试验，得到一批有价值的测试数据。结合试验，考虑预应力连续组合梁长期变形的各种影响因素，构建了徐变影响系数的解析计算模型，形成预应力连续组合梁收缩徐变的内部和外部约束力的解析计算方法，定量分析收缩和徐变对刚度和挠度带来多大的不利影响，探寻刚度与主要影响参数之间的内在规律，给出截面重分布应力和结构次内力的简化计算公式。成果可扩展和完善预应力连续组合梁收缩徐变的分析、计算和简化计算方法理论，为有限元软件分析提供验证手段，确保软件计算结果的正确性和可靠性。