【作者】 朱巍志；

【导师】 张哲；

【作者基本信息】 大连理工大学 ， 桥梁与隧道工程， 2009， 博士

【摘要】 自锚式斜拉—悬索协作体系桥作为一种新型的桥梁结构形式,具有结构新颖,受力合理,抗风性能好,施工安全和工程造价低等优点,具备了传统的缆索承重桥所具备的许多优点,并且由于取消了庞大的锚碇,使其在软土地基、强风地区具有突出的优越性,在大跨桥型尤其是跨海大桥中极具竞争力。目前国内外关于自锚式斜拉—悬索协作体系桥的相关研究较少,而该桥型在特定条件下有其独特的优势,因此有必要对该桥型展开系统的研究,本文结合交通部西部交通建设科技项目“斜拉—悬索协作体系桥梁的研究”课题,以拟建的大连跨海大桥为工程背景,对自锚式斜拉—悬索协作体系桥的合理成桥状态计算方法、非线性随机静力响应、非线性动力响应及减震设计优化进行了深入的研究,主要研究内容如下:1.由于自锚式斜拉—悬索协作体系桥这种桥型比较特殊,它结合了斜拉桥和自锚式悬索桥的受力特点和结构特征,利用现有的斜拉桥和悬索桥计算合理成桥状态的方法已经无法得到理想的结果,推导了不变形预张力的索力不变原理,在现有方法的基础上,基于几何非线性计算,结合该原理提出了自锚式斜拉—悬索协作体系桥合理成桥状态确定的分步算法。利用相关有限元计算程序及自行编制的辅助程序MCFS可以方便地实现该计算方法。计算实例表明利用该方法计算得到的成桥状态下加劲梁位于设计曲线上并且恒载弯矩较为均匀,分布合理,主塔弯矩较小且塔顶水平变位接近于零,斜拉索索力分布均匀。计算时主缆、斜拉索和吊索均采用弹性悬链线索单元模拟,得到的不变形预张力(或无应力索长)结果可以直接应用于施工阶段的分析计算。2.考虑结构构件的材料、几何尺寸等各项参数的随机性,应用响应面法对自锚式斜拉-悬索协作体系桥的加劲梁跨中挠度以及结构的整体稳定性进行了随机静力分析,其中针对加劲梁跨中挠度为研究对象的随机静力分析采用了非线性有限元计算模型,研究了自锚式-斜拉悬索协作体系桥加劲梁跨中挠度和结构整体稳定性在各项基本随机变量变化下的变化规律,结果表明主缆的各项参数为自锚式-斜拉悬索协作体系桥结构整体刚度的主要影响因素:而混凝土加劲梁的各项参数对其稳定性影响最为显著。通过这一研究结果可以使设计者能清楚地了解各种随机因素对自锚式斜拉—悬索协作体系桥结构响应的影响程度,为合理设计提供理论依据。3.通过大连跨海大桥的空间有限元动力分析,讨论了漂浮体系的自锚式斜拉—悬索协作体系桥的动力特性:利用修正的反应谱分析了结构在纵向、横向、竖向及三向正交分两组合作用下的地震反应;采用国际常用实录波和人工生成的地震波进行了非线性动力时程分析,取其结果平均值作为非线性动力时程的分析结果。将其结果与反应谱分析结果进行了对比,揭示了对于该类大跨度桥梁进行非线性动力时程分析的必要性,所得结论可以作为该类桥梁的抗震设计参考,地震反应分析的结果表明结构需要进行减、隔震设计。4.采用Maxwell模型来模拟阻尼器对结构进行了考虑几何非线性和边界非线性的动力时程分析,从阻尼器参数变化和安装位置的选择出发,对结构在地震荷载作用下的响应展开了具体研究,结果表明:当阻尼器的速度指数α一定时,随着阻尼系数C的增加,阻尼器的耗能能力增加,阻尼器位移、梁端位移以及塔顶位移单调减小,但是在阻尼系数较高的区域,较低的速度指数对应的位移值非常接近且变化平缓;而塔底弯矩的变化则是在阻尼系数达到一定数值以后趋于平缓,且速度指数在一定范围内对应的弯矩值非常接近,甚至影响曲线存在交叉的现象,这说明对于塔底弯矩来说并非速度指数越小减震效果就越好:阻尼器对塔底剪力的影响很小,但从其变化规律来看塔底剪力的变化有一个低谷,在阻尼系数较小时塔底剪力随阻尼系数的增大而减小,但是在低谷之后塔底剪力随阻尼系数的增大而增大。根据这一变化规律确定了合理有效的减震设计方案。采用该减震方案可以在不改变结构静力性能的前提下使加劲梁及主塔纵向位移的地震响应最大值均减小近60%,塔底纵向弯矩地震响应最大值也减小近50%,表明该方案具有显著的减震效果,能够有效的减小地震对结构引起的危害。更多还原

【Abstract】 As a new type of bridge structure, self-anchored cable-stayed suspension bridge has not only many advantages as new structure, reasonable load, well wind resistant, safety of construction and low cost, but also has the merits just like that of traditional cable-supported bridge has. Owing to huge anchorage being canceled, this type of bridge structure becomes outstanding superior in soft soil base and strong wind areas, and also highly competitive in large-span bridge construction, especially in the cross-sea bridge construction. At present, there is little related research on self-anchored cable-stayed suspension bridge home and abroad. While because this type of bridge structure has its unique advantages in some special conditions, it is necessary to develop systematic research on it. Combining the scientific research project-the study on cable-stayed suspension bridges, which is the transportation construction scientific item for western regions held by the Ministry of Communications, with the engineering background of Dalian Gulf Bridge to be built, this paper focuses on calculating method for the reasonable finished dead state of the self-anchored cable-stayed suspension bridge and damping optimization design. Moreover, nonlinear stochastic static response and nonlinear dynamic response are both investigated systematically in the paper. The research work mainly covers the following aspects:1. Self-anchored cable-stayed suspension bridge structure is different from other bridge structures, which combines both stress characteristics and structural characteristics of cable-stayed bridge and self-anchored suspension bridge. According to the present available calculating methods for reasonable finished dead state of cable-stayed bridges and suspension bridges, the reasonable result couldn’t be got. Under this condition, unreformed pretension principle of how to keep the internal Force of the cable remaining unchanged is deduced in this paper. Based on this principle and geometric nonlinear calculation, the step-by-step calculating method for the reasonable finished dead state of the self-anchored cable-stayed suspension bridge is proposed on the basis of some available methods. Utilizing related finite element calculating program and the self-developed MCFS program, the step-by-step calculating method could be conveniently carried out. It is shown from the practical calculation examples that the stiffening girder under finished dead state drawn through the step-by-step calculating method lies on the design curve and the dead load bending moment is well distributed. Moreover, the bending Moment of main tower is relatively small, horizontal displacement of pylon top is coming to zero and the cable force is even distributed. During calculation, the main cable and the stay cable as well as the sling are all simulated by using elastic catenaries cable elements. The results drawn from the calculation about undeformed pretension or unstressed cable length can be directly used in analyzing construction phases. 2. Considered the randomness in material properties, physical dimensions and other parameters of structural elements, the response surface approach is utilized to analyze mid-span deflection in stiffening girder and the whole stability of self-anchored cable-stayed suspension bridge structure. Taken mid-span deflection in stiffening girder as the research object, the nonlinear finite element calculation model is utilized in the stochastic static analysis. The variation of random variables for the mid-span deflection in stiffening girder and the whole stability of self-anchored cable-stayed suspension bridge structure is also analyzed. The result shows that the parameters of main cable have a great effect on the whole rigidity of self-anchored cable-stayed suspension bridge structure. The parameters of the concrete stiffening girder significantly influence the stability of the bridge structure. The above research results will help designers clearly know how different kinds of random parameters affect the response of self-anchored cable-stayed suspension bridge structure and provide reasonable theoretical evidence for bridge designing.3. Through the space finite element dynamic analysis for Dalian Gulf Bridge, the dynamic characteristic of self-anchored cable-stayed suspension bridge structure is analyzed. The modified response spectrum is utilized to analyze the structural seismic response in longitudinal, vertical, horizontal and under the effect of the two from the above three. Based on the memoir wave commonly used and the seismic wave artificial generated, the nonlinear dynamic time-history is analyzed. The average of the result is taken as the analysis result for the whole nonlinear dynamic time-history analysis. Compared this analysis result with the result from response spectrum analysis, it is obviously shown that the nonlinear dynamic time-history analysis is of great importance for this kind of bridge structure with huge span. The conclusion drawn from the analysis can provide reference for seismic design of the similar bridge structure and the analysis result shows that shock absorption design and isolation design are both necessary.4. Considered both geometric nonlinearity and boundary nonlinearity, the nonlinear dynamic time-history is analyzed by using Maxwell model to simulate damper. Proceeded from parameter variation of damper and option of installation position, the structural response under the effect of seismic load is specifically studied.The result from the study shows that energy dissipation of damper will be enhanced with the increase of damping coefficient C when velocity indexes a keeps certain and the displacement of damper, beam end and tower top will decrease monotonously. But in the area where the damper parameter is higher, the displacements for the lower velocity index are very similar and change mildly. While the variation for bending moment of pylon bottom remains slight only when damping coefficient comes to a certain value. The bending moments corresponding to velocity index are so similar in certain extend that they may affect the curves cross over each other. This suggests that, for bending moment, it doesn’t mean that the smaller the velocity index, the better the damping effect. Damper has little effect on shear of Pylon bottom, but it is shown from the change of shear that there is a declining period. When damping coefficient is smaller, shear of pylon bottom will decrease with the increase of damper coefficient. While except the declining period, shear of Pylon bottom will increase along with the damper coefficient. According to this change, the reasonable and efficient shock absorption design scheme is studied. Based on shock absorption design scheme, the longitudinal displacement of gird and pylon under earthquake action can be reduced nearly 60% on the premise of no change static structural performance. The longitudinal bending Moment of Pylon bottom also can be reduced nearly 50%. All of this proves that shock absorption design scheme has significant effect on damping and it can efficiently minimize the harm caused by earthquake on bridge structure.更多还原