摘要
在现代桥梁设计中,箱形截面构件以其良好的空间受力性能和稳定性而成为许多桥梁设计者首选的结构形式,虽然混凝土箱梁应用极为普遍,但其设计理论并非十分完善,混凝土箱梁的抗剪设计问题就是有待完善的内容之一。影响箱梁受剪性能的因素是多方面的,需要大量的试验研究和理论分析。基于此,本文选取竖向预应力这一影响因素,对配置竖向预应力筋混凝土箱梁的抗剪性能开展研究。主要完成了以下工作：
(1)对国内外混凝土箱梁抗剪研究的发展和现状以及桁架理论的发展进行了综述,并结合对箱梁抗剪性能的相关研究,提出了本文研究的主要内容。
(2)以广西来宾市红水河二桥为原型,运用有限元程序分析其腹板在竖向预应力作用下的压应力水平,并以此为依据,设计并制作了本文的试验梁模型。
(3)以配置竖向预应力筋钢筋混凝土薄壁箱梁的抗剪承载力试验为基础,分析了不同参数下试验梁的破坏形态、裂缝行为以及试验梁随荷载变化下的挠度、混凝土主拉应变、腹板平均应变、箍筋应变、腹板纵向钢筋应变等的发展规律。采用国内外几种具代表性的规范进行抗剪承载力计算,并将计算值与试验值进行比较分析,结果表明：就所比较的几本典型规范而言,除我国铁路桥涵设计规范和前苏联设计规范外,采用各国其他规范计算钢筋混凝土箱梁抗剪承载力具有一定的安全储备。
(4)编制了适用于箱梁抗剪承载力分析的软化桁架理论计算程序,并用试验结果对程序进行了验证,结果表明该程序能够较好地模拟试验粱的受剪性能。在此基础上,运用验证过的非线性程序,对影响抗剪强度的竖向预应力布置参数如竖向预应力的大小、竖向预应力筋的间距等进行了参数分析,研究了不同参数下箱梁的受剪性能。
For its good mechanical properties and stability of space, the box beam, in modern bridge design, has become a first choice for many bridge designers. Although the concrete box girders are very popular, the design theory is not perfect, the Shear design of concrete box beams is one of the elements need to be improved. As the shear performance of box girders is affected by many factors, it requires a lot of tests and theoretical analysis. Based on these, the paper which takes the vertical prestressing as a factor, presents the researches on the shear capacity of vertical prestressed concrete box girder. And the main research work is summarized as follows:
(1) Both the domestic and foreign research and development of shear strength of concrete box girder and the status and development of the truss theory are reviewed, then combining some researches of shear performance of the box girder, the main contents of this paper are presented.
(2) Taking Red River Bridge in Laibin Guangxi as the prototype, finite element method is used to analyze its principal compressive stress level of webs under vertical prestressed, then taking it as the design standard, the test beams are designed.
(3) Based on shear tests of the vertical prestressed thin-walled box girders, the main mechanics of test beams with different parameters such as fracture behaviors and failure modes and the beam deflection, concrete-principal tensile strain, the average web strain, hoop strain, web reinforcement strain are analyzed. Then the shear capacity of the test is calculated with several different typical norms at home and abroad, and it is compared with experimental data, results show that the norms present a safe capacity calculation for reinforced concrete box girder except Railway Bridge design specification and of Soviet Union code.
(4) A softened truss program is developed to predict the shear capacity of the box girder and it is verified by experimental results. It is proved that the truss program can simulate the beam shear test performance very well. On this basis, using validated non-linear process, the parametric analysis is carried out to study the box girder shear properties with the different parameters, which select the vertical prestressed strength and spacing of vertical tendon as factors.
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