体外预应力混凝土曲线桥复杂空间力学行为及失效机理

As a new trend of development, precast segmental externally prestressed bridge has made a prominent and brilliant rise in the construction of global urban viaducts. But because of the lack of research on complex dimensional mechanical behavior and failure mechanism of curved externally prestressed bridge , there are some problems in its development. The spatial arrangement of external tendons and the bending and twisting coupling characteristics of curved bridge make its limit state design many urgent problems to be solved. This project will explore the structural dimensional mechanical behavior, the failure mechanism and the ultimate bearing capacity through the theoretical deducing, finite element analysis and model experiments, quantify the influence of curve radius and radial layout of external tendons to the ultimate stress, second-effect of external tendons and the internal force distribution in structure, then reveal failure mechanism of segmental joints in curved bridge and develop a spatial truss-arch model for the ultimate state, finally propose design theory for externally prestressed curved bridge. This project will first put forward theoretical research on externally prestressed concrete curved bridge, innovatively develop a spatial truss-arch mechanical model, propose the failure morphology developmental path, criteria and methods. The research results will be beneficial to the further understanding of externally prestressed curved bridge, and has important theoretical and practical significance.

节段预制拼装的体外预应力桥梁当前在全球城市高架桥建设中崭露头角、优势突出，成为发展的新趋势。但当前对曲线体外预应力梁桥复杂空间力学行为和失效机理缺乏研究，制约了体外预应力的大范围推广应用。体外索空间布置和曲线梁弯扭耦合的特性使其极限状态设计存在诸多迫切需要解决的问题。本项目将从探索结构空间力学行为、失效机理和极限承载力的角度出发，采用理论推导、有限元分析和模型试验的方法展开研究，量化曲线半径和体外索径向布置等因素对体外索极限应力、两次效应和结构内力分布的影响，揭示曲线桥节段接缝失效机理，发展极限状态空间桁架-拱模型，最终提出体外预应力曲线桥设计理论。本项目将首次提出体外预应力混凝土曲线桥的复杂空间力学行为和失效机理的理论研究，创新性发展空间桁架-拱力学模型，提出多失效形态的发展路径、判别标准和方法，研究成果将有利于深入理解体外预应力曲线桥受力性能，具有重要的理论和现实意义。

曲线梁桥受曲率的影响，梁体中作用大扭矩荷载效应，而弯扭耦合使得曲梁受力更为复杂。本项目提出采用体外预应力作为曲线梁桥中的抗扭束，提供直接而高效的抗扭力。通过理论推导和数值模拟，认为在适当的空间体外索线形布置下，体外索能提供的抗扭力比体内索更为有效。空间有限元分析结果表明，正常使用极限状态下曲线半径、边中跨比和连续梁中支点边界条件等对体外预应力曲线梁的受力性能影响与体内预应力曲梁差异较小。基于前期直梁桥的研究成果，NFEM空间分析结果表明曲线实验梁的曲率对体外索应力增量和二次效应的影响有限。首次设计了4片三跨体外预应力混凝土曲线连续箱梁受力全过程模型试验。为实现缩尺模型荷载形式上的合理缩尺等效，提出了缩尺模型荷载优化的计算算法并应用于实验。实验结果表明受曲率和偏载作用影响，关键破坏截面呈现弯扭剪的复合受力破坏形态；实验梁为三跨连续梁，作用我国桥规荷载，随着裂缝的出现，弯矩内力重分布现象明显，与直梁桥的内力重分布存在显著差异，提出综合的受压区高度系数概念可用于曲线梁桥的内力重分布计算。建立了弯扭剪共同作用的箱梁空间塑性桁架模型，用该模型推导的理论破坏包络面与实验曲梁的实验值吻合较好。本项目中提出的采用体外预应力筋进行曲线梁的抗扭设计方法高效，且受力明确；全过程破坏试验对连续曲线梁的受力性能和破坏机理有了更进一步的认识。