【作者】 何天涛；

【导师】 颜东煌； 李学文；

【作者基本信息】 长沙理工大学 ， 桥梁与隧道工程， 2008， 硕士

【摘要】 随着科学技术和交通事业的发展,大跨度预应力连续梁(刚构)桥以其施工简便、造价经济、受力合理、行车舒适等独特优势在近年来得到了迅速崛起。但由于它出现较晚,其理论和经验还不是十分完善,在修建过程中也存在一些技术上的问题。国内大跨径预应力混凝土梁桥存在的主要病害是主梁跨中下挠过大和箱梁梁体裂缝,分析大跨径预应力混凝土梁桥挠度的影响因素,并研究如何控制主梁跨中下挠是十分有意义的。在现代预应力混凝土结构中,预应力损失的大小和徐变的准确计算直接影响着结构的挠度,而对于多跨连续刚构桥,合龙顺序对成桥内力及结构后期变形的影响也不容忽视。因此本文第一步从混凝土徐变的角度出发,通过对徐变机理、影响徐变的各种因素、徐变理论及计算方法等的分析,阐述了它们对主梁下挠的影响。第二步再从预应力损失的角度,包括长束预应力、纵向和竖向预应力三个方面,探讨其对挠度的一些影响并得出相应结论。第三步再对不同的施工合龙顺序进行比较,分析其对主梁后期变形的影响。然后对目前控制大跨径预应力混凝土梁桥挠度的普遍方法进行研究,包括短期挠度和长期挠度两个方面。长期变形的传统控制方法是设置预拱度,本文通过对预拱度设置方法的分析以及不同方法的比较,为成桥预拱度提供准确的设置方法;短期挠度则依靠对施工线形的监控来调整,而目前大跨径混凝土梁桥施工控制方法的理论都比较抽象,在实际过程中难于操作。本文结合平寨桥的实际监控经验摸索出更实用的线形控制方法,如采用回归分析方法确定挂篮变形挠度的真实值,利用相对高差法来避免施工荷载和温度荷载对立模的影响等。最后为控制主梁跨中长期下挠提出新的方法,首先,采用顶板预应力控制跨中长期下挠,根据最大悬臂状态预应力弯矩与自重弯矩大致相等的原则,重新配置顶板束,将重配束后的内力、位移及顶板束用量与原设计作比较分析;其次,可以增加跨中底板束用量,增加专门用来减小长期下挠的后期束,本文分析了增加跨中底板束后应力及位移变化,比较了不同位置底板束控制跨中下挠的效率,研究后期束合理张拉时期;再次,对合龙预顶力进行优化,以改善结构内力和主梁的后期变形;提出临时斜拉索辅助合龙与重配预应力束相结合控制跨中长期下挠的设想,做到施工期间箱梁不下挠,则成桥以后长期收缩徐变变形都较小,从而实现对主梁跨中长期下挠进行有效控制。更多还原

【Abstract】 With the development of science technology and traffic enterprise the long-span continuous girder (rigid frame) bridge has been growing up rapidly in the recent years with it’s unique predominance of handy construction, economical cost, reasonable interal force and comfortable traveling. But the theories and experience in it are not very perfect because of it’s short appearance. There are still several questions in the construction. In our country, main problems of large span prestressed concrete girder bridges are excessive midspan lag and cracks in box girder. So, it is quite necessary to study how to control long-term deflection of large span prestressed concrete girder bridges.For prestressed concrete structures, it is important to know how much the prestress loss is occurred and calutate the concrete creep exactly for the deflection of the structures. For multi-span continuous rigid frame bridge, the closure order to bridge internal forces and structural deformation of late should not be overlooked. Firstly, this thesis starts from the point of concrete creep analyses the creep mechanism and the factors affecting the creep, creep theory and the calculation method, discusses their impact on the deformation of girder. Secondly, starting from the prestress loss disicusses its influence to the deflection and derives the corresponding conclusions. Thirdly, comparison the re-construction of a different order of closure, and analysis its main beam deformation of late.Then study the current control of long-span prestressed concrete girder bridge deflection of a common method,including short-term and long-term.The traditional way that control the long-term deformation is to set up pre-camber. Based on analysis the different methods of pre-camber settings, to provide accurate methods for bridge. Short-term deflection relying on control the construction line to adjust. At present the theory of long-span concrete bridge in the construction control methods are more abstract, which of the process are difficult to operate in practice. This paper will explore more useful of the linear control methods, that combine the practical experience of the Pingzhai bridge monitoring. For example, using regression analysis to determine basket deformation of the true value of deflection,and use of the relative height difference law to avoid the effects of working-load and temperature-load .Last, using temporary cables together with designing prestress according to integral cast construction to control long-term midspan deflection is studied. Longitudinal prestress tendons are designed according to internal force of integral cast construction, sum of prestress bending moment, selfweight bending moment and bridge deck pavement bending moment is approximately zero. Then to optimize the prejacking force to improve the structure of the internal forces and the main beam late deformation. During construction stage, with the help of temporary cables, box girder will not deflect, so that displacement during construction is very little. After the construction, long-term shrinkage and creep displacement will be very little as well, as a result, long-term midspan deflection is controlled.更多还原