大跨预应力NSC-UHPC连续混合箱梁桥新体系试验与理论研究

Long-span prestressed concrete (PC) box girder bridges have been plauged by two unresolved issues posed by long-term excessive deflection at midspan and cracking of box girder which have already become the major technical bottlenecks restricting the applications and developments of the PC box girder bridges. Since the two issues are generally caused by the large dead weight, low tensile strength and creep effect of normal strength concrete (NSC), an innovative structure system-long-span prestressed NSC-UHPC (Ultra high performance concrete) continuous hybrid box girder is proposed, in which the midspan segments of a conventional PC continuous bridge are replaced by light thin-walled box girders composed of UHPC with super compression and tensile strengths, super toughness, good durability and low creep. The prelimilary researches indicate that the new hybrid structure can benefit from the reduction of light weight and creep deformation, high tensile strength and good durability of UHPC. Therefore, the developed structure system has the potential for solving the afore-metioned two problems (cracking of box girder and excessive deflection of main-span), and exhibits a promising feasibility to extend the span length of continuous box girder bridges to 350m. Through theoretical analyses, experimental studies and numerical simulations, the project aims to carry out the fundamental work as follows: to investigate the reasonable layout and optimization construction of the new NSC-UHPC hybrid box girder bridge, to study the basic performances of the hybrid structure and the purely UHPC box girder, to propose design methods for preventing crack and long-term deflection of the NSC-UHPC hybrid box girder bridge, to study the static and fatigue behaviors of the purpose fully designed connections for NSC-UHPC girder segments and UHPC-UHPC girder segments, and to establish the complete calculation and design methods for the NSC-UHPC hybrid box girder bridge. The achievements are expected to lay a soild foundation for controlling excessive deflection at midspan and box girder cracking of long-span PC box girder bridges for the development of bridge engineering in the future.

大跨PC梁桥普遍存在开裂和下挠两大难题，至今未有效解决，已成为制约其发展的主要技术瓶颈。申请者针对自重过大、混凝土抗拉强度低和徐变效应明显三个病害根本成因，基于UHPC超强、耐久、徐变小的优异性能，研发跨中区段采用UHPC薄壁箱梁的大跨预应力NSC（常规混凝土）-UHPC连续混合箱梁桥新体系。前期研究表明，新体系具有自重轻、徐变变形小、材料抗裂性高、耐久性好等优点，能综合解决上述两个难题、并扩展桥梁跨径至350m。项目结合理论、试验和数值方法完成以下基础性工作：探明NSC-UHPC混合梁桥合理构型，掌握整体结构及UHPC箱梁的基本力学性能与分析理论，提出混合主梁的防止开裂和下挠设计方法，研究UHPC-NSC、UHPC-UHPC梁段新型连接的静力与疲劳性能，建立完备的UHPC-NSC混合梁桥设计方法和计算理论。项目成果将为解决大跨PC梁桥发展的重大需求－控制开裂和下挠－奠定原创性的坚实基础。

大跨PC梁桥普遍存在开裂和下挠两大难题，至今未有效解决，已成为制约其发展的主要技术瓶颈。申请者针对自重过大、混凝土抗拉强度低和徐变效应明显三个病害根本成因，基于UHPC超强、耐久、徐变小的优异性能，研发跨中区段采用UHPC薄壁箱梁的大跨预应力NSC（常规混凝土）-UHPC连续混合箱梁桥新体系。.申请者从大跨UHPC-PC连续混合箱梁桥分析与优化设计、预制UHPC梁段的预应力+螺栓连接组合接缝的抗弯性能、UHPC-RC组合结构界面抗剪性能、UHPC作为NSC之间湿接缝时组合结构的受力性能以及UHPC-RC组合结构的抗弯性能等五个方面进行了课题的研究。研究结果表明项目组充分利用了UHPC的优良性能，实现装配式桥梁跨中梁段轻型化和抗裂性能、耐久性的大幅提高，并通过降低应力水平来减小混凝土梁段徐变变形，有效解决PC梁桥自重过大、主跨过度下挠和梁体开裂等难题，项目组提出的预制UHPC梁段间预应力+螺栓连接键齿接缝的接缝连接形式可以保证结构的安全可靠，验证了UHPC-RC结构界面具有良好的抗剪粘接性能能够确保UHPC层与混凝土结构共同承受荷载，证明了预制拼装普通混凝土构件现浇UHPC接缝的可行性和优越性，且UHPC层可以使原RC结构正常使用状态得到大幅改善。申请者提出了与研究课题相关的设计方法和计算理论，为该技术应用于实际工程提供了技术指导和试验结果支撑。.本项目以解决大跨PC梁桥主跨过度下挠和梁体开裂为基本目的，系统开展大跨预应力UHPC-NC连续混合箱梁桥新体系的基础性研究，有望将这种新型梁桥的跨径拓展至350m。项目研究面向混凝土梁桥大跨、安全、经济、耐久的重大需求，具有重要的科学意义和实用价值。