独塔混合梁斜拉桥摘要

摘要
混合梁斜拉桥是指斜拉桥的主梁沿梁的长度方向由两种不同材料组成,主跨的梁体为钢梁,边跨(或伸入主跨的一部分)的梁体为混凝土梁。

混合梁斜拉桥由于其主跨采用钢梁,所以具有跨越能力大的优点,而边跨采用混凝土梁从而起到了很好的锚固作用且兼有可降低建桥成本的特点。

斜拉桥与其它一般梁式桥在结构体系、材料受力性能等方面都有明显的差异，其抗风、抗震性能以及车振性能等均有其自身的特点。

桥梁结构的动力学特性主要包括桥跨结构的自振频率、振型、阻尼比以及在车辆、风、地震等动荷载作用下的动力响应等。

斜拉桥的动力特性分析是研究斜拉桥动力行为的基础，其自振特性决定其动力反应特性，分析斜拉桥自振特性意义重大。

近半个世纪以来，斜拉桥的设计理论、结构风动稳定试验和减振控制、计算机技术的应用、有限元分析和施工质量的控制、检测技术日趋成熟，与上述较成熟的理论相比，斜拉桥的动力特性分析方面较落后。

目前，斜拉桥正不断的向大跨度、轻型化方向发展，对其在动荷载(如车辆、风和地震等)作用下的动力响应研究更显得十分迫切。

桥梁结构的地震反应分析是一个抗震动力学问题。

对桥梁结构进行地震反应分析，必须从抗震动力学出发来思考问题、解决问题，而桥梁结构的地震反应分析必须以地震场地的运动为依据。

但是由于实际强震记录的不足，这个关键问题还未能很好的解决，因此仍然是结构抗震设计计算中最薄弱的环节。

斜拉桥动力学分析的方法大致可以分为两类，一类为传统的理论解析方法，对结构作一定的简化后作解析分析，最后得出解析公式。

另一类是有限元数值分析方法，利用电子计算机强大的计算功能采用有限单元法分析，该方法能够更为真实地模拟实际结构，分析结果精度高。

本桥采用有限元数值分析方法。

本文在现有研究的基础上，以广州东沙特大桥为背景，围绕独塔混合梁斜拉桥动力特性及地震响应的分析，展开进一步的研究。

混合梁斜拉桥由于其主梁沿梁的长度方向由两种不同材料组成,主跨的梁体为钢梁,边跨为混凝土梁。

因此混合梁斜拉桥的动力特性及抗震性能方面与混凝土斜拉桥及钢箱梁斜拉桥相比，有其相似处，但亦有其自身的特色。

本文在现有研究的基础上，以广州东沙特大桥作为计算背景，围绕混合梁斜拉桥动力特性及混合梁斜拉桥地震响应的计算分析，展开了以下几个方面的工作：
1、以广州东沙特大桥为背景，运用大型通用软件ANSYS建立该桥的动力分析模型，对设置辅助墩和不设置辅助墩情况下的动力特性做比较分析。

2、建立考虑在不同的参数影响下对其自振频率的影响程度。

如斜拉索的稀密程度、索塔、钢混比等。

3、基于地震响应时程反应分析基本理论，对独塔混合梁斜拉桥分别在横向+竖向地震波、纵向+竖向地震波、三向地震波作用下的地震时程影响做出分析，并对比考虑辅助墩相互作用和不考虑辅助墩相互作用两种模型的地震时程影响本文以东沙大桥为例,利用ANSYS建立空间动力计算模型，分析了桥梁主要结构参数对其振动特性的影响，结果表明：对于独塔混合梁斜拉桥，边垮辅助墩可以大幅提高结构的整体刚度，而且斜拉索的稀密程度、索塔、钢混比对其自振频率均有不同程度影响。

独塔混合梁斜拉桥根据自身结构形式的不同,其动力特性也随之变化。

1,辅助墩的设置使得结构的整体刚度有较大的提高,改善了结构的动力性能; 除个别振型外(例如第六阶主塔侧弯耦合主跨主梁侧弯振型有无辅助墩其频率基本相同) ,有无辅助墩对整体振型的出现次序及对应频率影响较大。

有辅助墩情况下，边垮主梁没有振动现象，而没有辅助墩的情况下，边垮有振动现象，如模型B的3、5、7、9、10阶。

2，斜拉索的稀密程度对结构面外振动频率影响不明显，而面内振动频率影响稍大．这说明斜拉索布置的稀密程度对提高结构的横向刚度作用很小，而对全桥的竖向刚度作用很大。

密索还能大大增加塔和梁的耦合现象。

3，索塔刚度的加大对桥梁的面内频率提高不明显，对面外的频率的提高显著。

4，钢混比的减小会增大基础频率，但却明显的降低了其他振型的频率。

斜拉桥动力学特性的研究为桥梁的抗震设计、抗风设计以及车辆振动分析等方面的内容提供理论基础。

通过动力学分析能够更真实地揭示斜拉桥的桥跨结构在汽车车辆荷载作用下的受力与变形状况，并能够描述桥跨结构在地震作用和风荷载作用下的结构响应。

时程分析，建立了考虑辅助墩相互作用和不考虑辅助墩相互作用两种模型，比较并分析了在三组地震波作用下，两种模型的时程响应情况。

基于地震响应时程反应分析基本理论，对独塔混合梁斜拉桥分别在横向+竖向地震波、纵向+竖向地震波、三向地震波作用下的地震时程影响做出分析，并对比考虑辅助墩相互作用和不考虑辅助墩相互作用两种模型的地震时程影响，得出以下结论：
1、比较三组地震波情况下的位移及受力情况，对于独塔混合梁斜拉桥塔梁墩固结体系，在地震波作用下，主要以竖向及纵向地震时程的影响为主，横向地震时程影响相对较小。

这是因为本桥的一阶基本振型是主跨主梁竖弯，所以此结论符合本桥的振型规律。

2、对比考虑辅助墩相互作用和不考虑辅助墩相互作用两种模型，考虑辅助墩
相互作用时，本桥刚度明显增大，使得在三种地震类型激励下本桥的位移、轴力、剪力、弯矩峰值增量较不考虑辅助墩相互作用时有不同程度减小。

3、某些峰值大小与在何种类型地震激励影响下有密切关系，例如无横向地震波激励情况下的塔底面外弯矩峰值和塔顶横向位移峰值明显小于有横向地震波激励情况下的塔底面外弯矩峰值和塔顶横向位移峰值。

4、对三组地震波情况下，独塔混合梁斜拉桥关键截面处的应力进行了验算，经验算，部分关键截面处的应力已超出允许范围，因此，在地震活动比较活跃的地区应用此种桥型时应慎重考虑，且应做进一步的抗震分析。

本文以广州东沙特大桥为背景，借助有限元软件ANSYS，重点分析了独塔混合梁斜拉桥的动力特性、独塔混合梁斜拉桥的地震时程反应特性。

考虑了桥梁主要结构参数对其振动特性的影响。

并对有无辅助墩相互作用情况下的动力特性进行了对比分析；在地震时程反应特性中分别分析了三种地震波情况下，不考虑辅助墩相互作用和考虑辅助墩相互作用时对独塔混合梁斜拉桥地震反应的影响，并进行了横向比较。

根据本文的研究，结合前人研究的成果，得出以下结论：
1、考虑辅助墩作用时独塔混合梁斜拉桥的基频比不考虑辅助墩时普遍偏大，这是因为边跨没有辅助墩的约束, 使得主梁竖弯刚度降低。

2、斜拉索布置的稀密程度对本桥的自振频率也有影响，密索可以降低基频即面内振动频率，稀索提高了面外振动频率。

但是这种变化非常的小。

索塔刚度的加大可以有效的提高独塔混合梁斜拉桥的自振频率。

钢混比的减小增大基础频率，但却明显的降低了其他振型的频率。

3、比较三组地震波情况下的位移及受力情况，对于独塔混合梁斜拉桥塔梁墩固结体系，在地震波作用下，主要以竖向及纵向地震时程的影响为主，横向地震时程影响相对较小。

这是因为本桥的一阶基本振型是主跨主梁竖弯，所以此结论符合本桥的振型规律。

4、对比考虑辅助墩相互作用和不考虑辅助墩相互作用两种模型，考虑辅助墩相互作用时，本桥刚度明显增大，使得在三种地震类型激励下本桥的位移、轴力、剪力、弯矩值较不考虑辅助墩相互作用时有不同程度减小。

5、某些峰值大小与在何种类型地震激励影响下有密切关系，例如无横向地震波激励情况下的塔底面外弯矩峰值和塔顶横向位移峰值明显小于有横向地震波激励情况下的塔底面外弯矩峰值和塔顶横向位移峰值。

6、对三组地震波情况下，独塔混合梁斜拉桥关键截面处的应力进行了验算，经验算，部分关键截面处的应力已超出允许范围，因此，在地震活动比较活跃的地区应用此种桥型时应慎重考虑，且应做进一步的抗震分析。

关键词：独塔混合梁斜拉桥；动力特性；有限元法；ANSYS；动力响应
ABSTRACT
The girder of hybrid girder cable-stayed bridge is composed of two different materials along the length of beam direction. The material of the main span is steel , while the side bay (or part of the main span) is concrete. Hybrid girder cable-stayed bridge has the advantage of large capacity across because of it’s main span is steel, and the characteristics of playing the anchor role and reducing the cost of bridge construction because of the side span is concrete. Cable-stayed bridge have significant differences in the general structure of the system and mechanical properties of materials with the other beam bridge, which has its own characteristics about the wind, seismic performance, as well as vehicle vibration performance, and so on.
The dynamics of the bridge structure includes a bridge structure of natural frequencies, mode shapes, damping ratio, and the dynamic response in vehicles, wind, earthquake and other dynamic loads . The dynamic characteristics of cable-stayed bridge is the foundation to study the dynamic behavior of cable-stayed bridge, determine the vibration characteristics of its dynamic response characteristics, vibration characteristics of cable-stayed bridge is significant. Nearly half a century, cable-stayed bridge design theory, structural stability tests and wind vibration control, computer technology, finite element analysis and construction quality control, detection technology has matured, and compared to the more mature theory , Dynamic analysis of cable-stayed bridge over backward. At present, the cable-stayed bridge span is constantly to light in the direction of development, its in the dynamic load (such as vehicles, wind and earthquakes) under the dynamic response of more particularly pressing.
Seismic response analysis of bridge structures is a seismic dynamics problem. Regarding the structure of the bridge seismic response analysis, we must proceed from the earthquake dynamics to think, solve problems, and seismic response analysis of bridge structure to earthquake sites must be based on the movement. However, due to lack of actual earthquake records, the key issue is also not well resolved, so calculation of seismic design is still the weakest link.
Bridge dynamic analysis methods can be divided into two categories, one for the traditional method of theoretical analysis, simplified the structure to be made after analysis of a certain conclusion that analytical formulas. The other is the finite element numerical analysis method, using powerful computing computer using the finite element method analysis, the method could be more true to simulate the actual structure, analysis and high precision. The bridge by finite element numerical analysis.
Taking the Dongsha super major bridge in Guangzhou as an instance, this paper has a further research around the analysis of dynamic characteristic and Seismic Response of hybrid girder cable-stayed bridge with single pylon on the foundation of existing research.
Hybrid girder cable-stayed bridge due to the length of the main beam along the beam direction by two different materials, a main span of the beam to beam, side spans of concrete beams. Therefore, the dynamic characteristics of hybrid girder cable-stayed bridge and seismic performance of concrete and steel box girder cable-stayed bridge in comparison with their similarities, but it have their own characteristics. In this paper, based on existing research to the calculation of Guangzhou bridge in the background, around the hybrid girder cable-stayed bridge dynamic characteristics and seismic response of mixed-beam calculation and analysis, carried out the following areas:
1 Taking Guangzhou Dongsha bridge in the background, Use large-scale general-purpose software ANSYS dynamic analysis model to establish the bridge, on the set does not set the auxiliary supporting piers and pier in case of a comparative analysis of dynamic characteristics.
2, Establishes under the influence of different parameters of the natural frequencies of its extent. the cable density level, tower, steel mixing ratio.
3, Based on time history analysis of seismic response of the basic theory of single tower cable-stayed bridge beams were mixed in the horizontal + vertical seismic waves, vertical + vertical seismic waves, seismic waves under three-time history of seismic effects make analysis and comparison consider the auxiliary pier pier supporting the interaction and does not consider the interaction of the two models affect the earthquake process
DongSha bridge in GuangZhou City is taken as an example to establish space dynamic calculaing models with ANSYS. and the influence of primary structural parameters to the self-vibration characteristics is analyzed through the application of the finite element analysis software. The results show that the arrangements of the auxiliary piers in the side spans can increase the structure rigidity greatly. And dilute the extent of cable stayed、tower、steel-concrete ratio have varying degrees of influence on self-vibration frequency.
Hybrid single tower cable-stayed bridge girder structure according to their own different characteristics also change its momentum.
1, Supporting piers set makes the whole structure has greatly improved rigidity and improved the dynamic properties; addition to individual modes of foreign (eg, the sixth-order main tower main span girder bending coupled lateral bending mode with
or without auxiliary Piers the same frequency), with or without auxiliary pier on the overall appearance of the order of vibration mode and the corresponding frequency greater impact. With auxiliary pier case, the edge collapse is not the main beam vibration phenomenon, where no auxiliary pier, side collapse with vibration phenomena, such as the Model B, 3,5,7,9,10-order.
2, Cable of thin dense level was not obvious to inside vibration frequency on the structure, and the vibration frequency of the larger plane. This shows that the cable arrangement of the thin dense level of lateral rigidity on the role of improving the structure of very small, while the full bridge vertical rigidity markedly. Cable can also greatly increase the density towers and beam coupling.
3, Increase the stiffness of the bridge tower the inside frequency did not differ, across the outside of the frequency increased significantly.
4, Reduce the steel-concrete ratio increase the basis of frequency, but significantly reduced the frequency of other modes.
The study of cable-stayed bridge dynamic property provides fundamental theory for aseismatic design, wind resistance and analysis of vehicle vibration. Through the analysis of dynamic, it can reveal more truly the structure stresses and deflection under the effect of vehicles. Then it can figure the responses of bridge structure when earthquake and wind loads affected.
The time-history analysis applied to the hybrid girder cable-stayed bridge, establish two kinds of model, which one consider the the auxiliary piers interaction and another not, compare and analyze the situation of the time analysis of them under three groups of seismic waves.
Based on seismic response analysis of the basic theory ,single tower cable-stayed bridge beams were mixed in the horizontal + vertical seismic waves, vertical + vertical seismic waves, seismic waves under three-time history of seismic effects make analysis and comparison to consider supporting Tun Tun interaction and does not consider supporting the interaction of the two models affect the earthquake process, the following conclusions:
1, Compared three groups of seismic waves in case of displacement and force conditions, the single tower cable-stayed bridge tower Piers hybrid beam consolidation system, the seismic waves, mainly in the vertical and longitudinal range of the main earthquake, horizontal earthquake process was relatively small. This is because the bridge of the first order fundamental mode shape is a main span girder vertical bending, so this conclusion is consistent with the law of the bridge mode.
2, Compared to consider supporting piers supporting the interaction and does not consider the interaction of two model pier, consider the interaction between auxiliary
pier, the bridge stiffness significantly increased, making the three types of excitation of the bridge seismic displacement, axial force, shear force, peak moment to consider supporting pier increment less interaction reduced to varying degrees.
3, Some of the peak size and what type of influence of earthquake excitation is closely related to, for example, no case of transverse earthquake waves tower and the tower bottom bending moment peak lateral displacement of the peak is smaller than a transverse earthquake waves tower case bottom and top of the tower outside the peak moment of peak lateral displacement.
4,Three sets of seismic waves on the circumstances, the key single tower cable-stayed section of mixed beam was checking the stress, experience counted, some of the key section of the stress is beyond the allowable range, therefore, more active in the areas of seismic activity apply should carefully consider the bridge is, and should do further seismic analysis.
In this paper, Guangzhou bridge in the background, using finite element software ANSYS, focused analysis of the single tower cable-stayed bridge in the dynamic characteristics of hybrid girder, single girder cable-stayed bridge tower mixed-time history characteristics of the earthquake. Considered the main structural parameters of the bridge vibration characteristics. And the interaction with or without supporting piers under the dynamic characteristics were analyzed; the earthquake response characteristics of the process were analyzed under three different seismic waves, do not take into account the interaction and to consider supporting piers supporting the interaction between pairs of single tower pier hybrid girder bridge seismic response, and had horizontal comparison. According to this study, combined with the results of previous studies, the following conclusions:
1, Consider the role of supporting piers single tower cable-stayed bridge of the fundamental frequency of composite beam than not generally too large when considering supporting piers, because there is no supporting pier side cross-bound, so the main girder vertical bending stiffness decreased.
2, Cable layout level sparse density of the natural frequency of the bridge also have an impact, secret cable that can reduce the baseband frequency plane, thin Suoti plane high frequency. But this change is very small. Tower stiffness increase can effectively improve the single tower cable-stayed bridge mixed beam natural frequency. Steel and larger than the decrease of the fundamental frequency, but significantly reduced the frequency of other modes.
3, Compared three groups of seismic waves in case of displacement and force conditions for the single tower cable-stayed bridge tower Piers hybrid beam consolidation system, the seismic waves, mainly in the vertical and longitudinal range
of the main earthquake, horizontal earthquake process was relatively small. This is because the bridge of the first order fundamental mode shape is a main span girder vertical bending, so this conclusion is consistent with the laws of the bridge mode.
4, Compared to the interaction and consider the auxiliary pier pier interaction does not consider supporting the two models, consider the auxiliary pier interaction, significantly increased the stiffness of the bridge, making the three types of excitation of the bridge seismic displacement, axial force, shear bending moment than the value does not consider the interaction between auxiliary pier reduced to varying degrees.
5, Some of the peak size and what type of influence of earthquake excitation is closely related to, for example, no case of transverse earthquake waves tower and the tower bottom bending moment peak lateral displacement of the peak is smaller than a transverse earthquake waves tower case bottom and top of the tower outside the peak moment of peak lateral displacement.
6, Three sets of seismic waves on the circumstances, the single tower cable-stayed bridge key sections mixed beam was checking the stress, experience counted, some of the key section of the stress is beyond the allowable range, therefore, more active in the areas of seismic activity apply kind of bridge should be carefully considered and should further seismic analysis.
Key Words：hybrid girder cable-stayed bridge with single tower；dynamic characteristics；finite element method；ANSYS ；dynamic respons。