超大跨径单向预应力UHPC连续箱梁桥新体系研究

For continuous long-span prestressed concrete (PC) box girder bridge, the ever-existing problems, such as the concrete beam being subject to cracks and the difficulty in controlling the long-term deflection at mid-span, has posed a challenge to bridge engineers and has become a technical bottleneck of a further breakthrough of this type of bridge. A new structure system of super-long-span continuous box girder bridge composed of one-way prestressed UHPC is proposed by the applicant with independent-intelligence-right. Using the excellent performance of UHPC, a new box girder system that can match the high performance of UHPC is established. The new box girder system is a thin-walled box girder with dense diaphragms, whose structure construction and mechanical characteristics lie between traditional concrete box girder and steel box girder, and transform the traditional three-dimensional pre-stresses into a new one-way prestress in longitudinal direction. The preliminary research demonstrates that the proposed new system has advantages of light weight, high stiffness, high tensile and compressive strength, and small long-term deformation. The new system has the potential to solve the afore-mentioned challenges simultaneously (the crack of concrete beam and down deflection of main-span), and exhibits promising feasibility to expand the span length of continuous box girder bridge to 400m. The project aims to complete the fundamental work as follows: to investigate the basic performances of the new UPHC box girder bridge; to understand the critical technologies of UHPC box girder such as the shear behavior of web plate, the torsion resistance performance, and the control on creep deflection of the main girder; and to establish the design method of the UHPC box girder bridge system. The achievements of this project would lay original solid foundation for understanding the core technologies of super-long-span concrete beam bridge with sufficient durability, which is also a great demand of bridge development.

大跨径预应力混凝土连续箱梁桥存在着梁体易开裂及跨中长期下挠难控制等热点问题，已成为其跨径进一步突破的技术瓶颈。为综合解决上述难题，申请者研发了一种具备独立知识产权的单向预应力超高性能混凝土（UHPC）连续箱梁桥新体系，即利用UHPC的优异性能，构建与这种新材料相匹配的新型箱梁结构体系：采用结构构造和受力特性介于传统混凝土箱梁与钢箱梁之间的密集隔板薄壁箱梁结构，并将传统三向预应力变为单纵向预应力。前期研究表明，新结构具有自重轻、刚度大、抗拉压强度高、长期变形小等优点，能同时解决开裂和下挠两个难题，并可使连续梁桥跨径扩展到400m级。本项目将完成以下基础性工作：探明新体系UHPC箱梁桥的基本性能；掌握UHPC箱梁桥腹板抗剪、箱梁抗扭和控制主梁徐变下挠等关键技术；形成新体系UHPC箱梁桥的设计方法。本项目成果将为解决桥梁发展的重大需求－掌握大跨径长耐久混凝土梁桥的核心技术－奠定原创性的坚实基础。

传统大跨预应力混凝土箱梁桥在国内外应用广泛，但长期存在梁体开裂下挠等技术难题，严重影响其经济性、安全性和耐久性，增加了桥梁的维护成本。. 为综合解决上述难题，项目组原创性地提出了一种与超高性能混凝土（UHPC）材料力学性能相适应的大跨径单向预应力UHPC箱梁结构体系。本项目在以下研究内容方面取得了进展：. UHPC材料组分优化及其基本力学性能。研发了适用于UHPC箱梁结构体系的具有高抗拉强度和自密实特性的UHPC；研究了钢纤维的增强增韧作用，得到了其对UHPC抗压性能、弯拉性能和轴拉性能的影响规律；研究了UHPC梁的徐变性能，结果表明UHPC梁的徐变变形仅为常规梁的20%，有望解决大跨度混凝土梁桥过度下挠问题。. UHPC箱梁结构体系基本受力性能。研究了UHPC桥面板局部受力性能、腹板抗剪性能、抗扭特性、承压稳定性能等。结果表明：UHPC箱梁桥面板为双向受力传力构件，主受力方向为纵向，5.5倍设计车轮局部荷载作用下试验工况桥面板仍处于线弹性受力阶段；UHPC箱梁腹板的抗剪切开裂强度、承载能力、剪切稳定性均完全满足桥梁设计要求，主跨400m的新型UHPC连续箱梁桥的抗裂安全度可达184.4%；UHPC箱形内设置密集横隔板对于提高UHPC箱梁抗扭特性和底板承压稳定性具有明显的效果；此外，提出了牛腿式箱梁节段接缝和H形体外预应力锚固齿块的构造形式。. UHPC箱梁结构体系优化设计及合理跨径范围。优化了UHPC箱梁结构体系的整体构型和桥面体系并研究了其合理跨径范围，给出了UHPC箱梁各尺寸建议范围以方便设计，提出了正交异性UHPC矮肋桥面体系以减轻结构自重和方便布置体内预应力，证明了UHPC箱梁结构体系在300~500m跨径范围内具有良好的竞争力。. 设计方法。提出了新型UHPC箱梁的设计方法，并形成了《UHPC箱梁专用技术规程》。. 本研究针对大跨预应力混凝土箱梁桥的典型病害问题提出了新的解决方案，理论和试验研究均表明，新型UHPC箱梁结构受力性能良好，有望解决大跨预应力混凝土箱梁桥难题，并具有良好的经济性能。因而本项目研究意义重大，将产生巨大的社会和经济效益。

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