曲线组合箱梁桥考虑多种力学、几何和时变效应的梁单元模型及长期性能分析

Curved steel-concrete composite box girders are widely used in ramp and interchange bridges in cities. Complicated mechanic behavior and significant long-term deflection always occur in curved composite box-girder bridges at their service stages. However, the current one-dimension models for long-term behavior analysis of curved composite box-girder bridges have shortages in two aspects: (1) for mechanical and geometrical effects, the models do not consider comprehensively shear-lag, restrained torsion, distortion behaviors and structural initial curvature influence, and especially longitudinal and radial slip behavior at interface; (2) for concrete time-dependent effect, the models neglect the influence of material nonlinearity, which includes crack of concrete slab and yielding of reinforcement bar in slabs, on the structural long-term behavior. The project will first establish a one-dimension mechanical model considering muti-mechanical and geometrical effects of curved composite box girders and conduct experimental research on long-term behavior of the girders under positive and negative moment. The fiber beam element in OpenSees will be then upgraded to develop a beam element considering multi-mechanical, geometrical and time-dependent effects of the girders for their long-term behavior analysis. The one-dimension mechanical model and the experimental research will provide the development of the beam element with theoretical foundation and material constitutive relation, respectively. The long-term behavior of curved composite box-girder bridges will finally be analyzed based on the beam element model. The project is expected to reveal the developing rule of long-term behavior, propose a beam element model for long-term behavior analysis and provide designers with a simplified formula of the index for evaluating long-term behavior of curved composite box-girder bridges. The project achievements are significant in scientific research and engineering application.

曲线组合箱梁桥作为城市立交桥和匝道桥的主要形式之一，在运营阶段受力行为复杂，长期下挠显著。然而目前其长期性能梁单元模型的研究远不成熟：(1) 力学和几何效应方面，不能全面和准确地考虑剪力滞、约束扭转、畸变行为和初曲率影响，尤其是界面纵向和径向滑移行为；(2) 时变效应方面，不能考虑混凝土板开裂和板内钢筋屈服对结构长期性能的影响。本项目计划确立曲线组合箱型梁可考虑多种力学和几何效应的一维空间受力模型，进行正、负弯矩加载的长期性能试验研究，进而以一维空间受力模型为理论基础，引入试验中获取的材料本构，升级OpenSees软件的纤维梁单元，开发可考虑多种力学、几何和时变效应的长期性能梁单元，开展结构体系的长期性能分析。本项目研究可望揭示曲线组合箱型梁长期性能的发展规律，获得适用于运营阶段全程分析的长期性能梁单元模型，提出用以指导设计的长期性能评估指标简化公式。研究成果具有重要的科学意义和应用价值。

曲线钢-混凝土组合箱梁桥具有自重轻、跨越能力强、抗扭刚度大等优点，目前已逐渐广泛应用于城市公路立交桥和匝道桥的建设中。与直线梁桥相比，曲线组合箱梁桥具有典型的弯扭耦合受力特性，结构受扭时截面会发生明显的纵向翘曲和畸变变形，结构较宽时混凝土顶板和钢梁底板还会表现出明显的剪力滞行为，同时界面还会发生特有的滑移行为。并且由于混凝土的收缩徐变特性，曲线组合箱梁桥会在运营阶段发生典型的长期下挠行为。本课题进行了曲线组合箱型梁正、负弯矩弹性静载试验、负弯矩弹塑性静载试验和正、负弯矩长期堆载试验，通过试验探究了曲线组合箱型梁的弯扭耦合复杂受力机理和长期下挠行为；依据经典的弹性薄壁杆件理论，基于Vlasov一维曲梁力学模型建立了可以考虑剪力滞、界面双向滑移、约束扭转、畸变和初曲率影响的曲线组合箱型梁2节点26自由度有限梁单元；在该单元基础上引入混凝土收缩徐变效应的应力-应变关系，建立了可以同时考虑混凝土时变效应的有限梁单元；基于开发的曲线组合箱型梁考虑4种复杂力学效应、初曲率影响和混凝土收缩徐变效应的有限梁单元，研究了曲线组合箱型梁复杂的空间受力行为和结构长期时变行为。研究结果表明：由于扭转翘曲、畸变翘曲效应和初曲率的影响，曲线组合箱型梁截面应力沿横向分布并不相同，当圆心角增大到60°时弯扭耦合影响显著；曲线组合箱型梁可通过增设横隔板显著控制畸变纵向位移，但对于畸变应力影响有限；在桥梁1年以内的运营期间，结构的长期下挠发展最快，之后长期下挠发展逐渐减缓，直至趋于稳定。本项目开发的模型计算效率高，可直接应用于曲线组合箱梁桥的设计分析；关于结构复杂空间力学性能和长期受力性能的分析结果可指导该类桥梁的设计。