Structural health monitoring of long-span suspension bridges using wavelet packet analysis

During the service life of civil engineering structures such as long-span bridges, local damage at key positions may continually accumulate, and may finally result in their sudden failure. One core issue of global vibration-based health monitoring methods is to seek some damage indices that are sensitive to structural damage, This paper proposes an online structural health monitoring method for long-span suspension bridges using wavelet packet transform （WPT）. The WPT- based method is based on the energy variations of structural ambient vibration responses decomposed using wavelet packet analysis. The main feature of this method is that the proposed wavelet packet energy spectrum （WPES） has the ability to detect structural damage from ambient vibration tests of a long-span suspension bridge. As an example application, the WPES-based health monitoring system is used on the Runyang Suspension Bridge under daily environmental conditions. The analysis reveals that changes in environmental temperature have a long-term influence on the WPES, while the effect of traffic loadings on the measured WPES of the bridge presents instantaneous changes because of the nonstationary properties of the loadings. The condition indication indices VD reflect the influences of environmental temperature on the dynamic properties of the Runyang Suspension Bridge. The field tests demonstrate that the proposed WPES-based condition indication index VD is a good candidate index for health monitoring of long-span suspension bridges under ambient excitations.

Damage alarming of long-span suspension bridge based on GPS-RTK monitoring

Structure damage identification and alarming of long-span bridge were conducted with three-dimensional dynamic displacement data collected by GPS subsystem of health monitoring system on Runyang Suspension Bridge.First,the effects of temperature on the main girder spatial position coordinates were analyzed from the transverse,longitudinal and vertical directions of bridge,and the correlation regression models were built between temperature and the position coordinates of main girder in the longitudinal and vertical directions;then the alarming indices of coordinate residuals were conducted,and the mean-value control chart was applied to making statistical pattern identification for abnormal changes of girder dynamic coordinates;and finally,the structural damage alarming method of main girder was established.Analysis results show that temperature has remarkable correlation with position coordinates in the longitudinal and vertical directions of bridge,and has weak correlation with the transverse coordinates.The 3%abnormal change of the longitudinal coordinates and 5%abnormal change of the vertical ones caused by structural damage are respectively identified by the mean-value control chart method based on GPS dynamic monitoring data and hence the structural abnormalities state identification and damage alarming for main girder of long-span suspension bridge can be realized in multiple directions.

Advanced aerostatic analysis of long-span suspension bridges

As the span length of suspension bridges increases, the diameter of cables and thus the wind load acting on them, the nonlinear wind-structure interaction and the wind speed spatial non-uniformity all increase consequently, which may have unnegligible influence on the aerostatic behavior of long-span suspension bridges. In this work, a method of advanced aerostatic analysis is presented firstly by considering the geometric nonlinearity, the nonlinear wind-structures and wind speed spatial non-uniformity. By taking the Runyang Bridge over the Yangtze River as example, effects of the nonlinear wind-structttre interaction, wind speed spatial non-uniformity, and the cable＇s wind load on the aerostatic behavior of the bridge are investigated analytically. The results showed that these factors all have important influence on the aerostatic behavior, and should be considered in the aerostatic analysis of long and particularly super long-span suspension bridges.

Study of the aerostatic and aerodynamic stability of super long-span cable-stayed bridges

With the increase of span length, the bridge tends to be more flexible, and the wind stability be- comes an important problem for the design and construction of super long-span cable-stayed bridges. By taking a super long-span cable-stayed bridge with a main span of 1 400 m as example, the aerostatic and aerodynamic stability of the bridge are investigated by three-dimensional nonlinear aerostatic and aerodynamic stability analy- sis, and the results are compared with those of a suspension bridge with a main span of 1 385 m, and from the aspect of wind stability, the feasibility of using cable-stayed bridge in super long-span bridge with a main span above l 000 m is discussed. In addition, the influences of design parameters including the depth and width of the girder, the tower structure, the tower height-to-span ratio, the side-to-main span ratio, the auxiliary piers in the side span and the anchorage system of stay cables, etc on the aerostatic and aerodynamic stability of su- per long-span cable-stayed bridges are investigated numerically; the key design parameters are pointed out, and also their reasonable values are proposed.

Cable flexural rigidity influence on suspension bridges static properties

In order to figure out the cable flexural rigidity influence on suspension bridges,a contrast model experiment is made:a chain cable model with no flexural rigidity and a wire cable model with some flexural rigidity.And then,four finite element models of a same long-span suspension bridge with different cable element are set up to be analyzed.Both experimental and numerical simulation results show that,with the increase of the span and the decrease of sag-span ratio,the influence of the cable flexural rigidity is significant.The difference of nodes displacement reaches more than 10 cm in construction analysis,which will bring some trouble to the construction.And the difference of the maximum section edge normal stress may reach 15%,which may have an adverse impact onto the bridge.Therefore,considering the cable flexural rigidity is necessary on some analysis of suspension bridges.

Parameter effects on the dynamic characteristics of a super-long-span triple-tower suspension bridge

A 3D finite element model for the Taizhou Yangtze River Bridge,the first triple-tower long-span suspension bridge in China,is established based on the nonlinear finite element software ABAQUS,and the dynamic characteristics of the bridge are analyzed using the LANCZOS eigenvalue solution method. The study focuses on the effects of the vertical,lateral and torsional stiffness of the steel box girder,the rigid central buckle and the elastic restraints connecting the towers and the steel box girder on the dynamic characteristics of the triple-tower suspension bridge. Our results show that,in general,the dynamic characteristics of the triple-tower suspension bridge are similar to those of two-tower suspension bridges. The vertical,lateral and torsional stiffness of the steel box girder have different effects on the dynamic characteristics of triple-tower suspension bridges. The elastic re-straints have a more significant effect on the dynamic characteristics than the central buckle,and decreasing the stiffness of the elastic restraints results in the appearance of a longitudinal floating vibration mode of the bridge. Also,rigid central buckles have a greater influence on the dynamic characteristics of triple-tower suspension bridges than on those of two-tower suspension bridges. The results obtained could serve as a valuable numerical reference for analyzing and designing super-long-span triple-tower suspension bridges.

Aerodynamic stability evolution tendency of suspension bridges with spans from 1000 to 5000 m

Aerodynamic instability owing to aerostatic and flutter-related failures is a significant concern in the wind-resistant design of long-span suspension bridges.Based on the dynamic characteristics of suspension bridges with spans ranging from 888 to 1991 m,we proposed fitted equations for increasing spans and base frequencies.Finite element models of suspension bridges with increasing span from 1000 to 5000 m were constructed.The structural parameters were optimized to follow the fitted tendencies.To analyze the aerodynamic instability,streamlined single-box section(SBS),lattice truss section(LTS),narrow slotted section(NSS),and wide slotted section(WSS)were considered.We performed three-dimensional(3-D)full-mode flutter analysis and nonlinear aerostatic instability analysis.The flutter critical wind speed continuously decreases with span growth,showing an unlimited approaching phenomenon.Regarding aerostatic instability,the instability wind speed decreases with span to approximately 3000 m,and increases when the span is in the range of 3000 to 5000 m.Minimum aerostatic instability wind speed with SBS or LTS girder would be lower than observed maximal gust wind speed,indicating the probability of aerostatic instability.This study proposes that suspension bridge with span approximately 3000 m should be focused on both aerostatic instability and flutter,and more aerodynamic configuration optimistic optimizations for flutter are essential for super long-span suspension bridges with spans longer than 3000 m.

超长大跨度公铁合建桥梁结构体系研究

新建甬舟铁路西堠门公铁两用大桥连接金塘岛和册子岛,桥位处海域宽2.7 km,最大水深93 m,地形复杂,桥梁设计难度大。为研究超长大跨度公铁合建桥梁合理结构体系,结合地形地质条件,选取主跨1500 m悬索桥、斜拉桥及斜拉悬索协作体系3种桥型方案,对上部结构设计进行详细介绍,并从静力性能、动力性能、经济性能等方面对不同结构体系进行对比分析。研究表明:(1)与斜拉体系相比,协作体系桥可减小30%~50%的主梁内力和60%的桥塔内力,一定程度上解决了加劲梁承受巨大轴压力造成屈曲问题,并有效减小了桥塔规模;(2)与悬索桥相比,协作体系可减小50%的主缆内力,主缆钢丝和锚碇的工程量相应减小,施工难度得以降低,同时协作体系扭转频率更高,降低了结构在较低风速下发生涡激振动的可能性;(3)斜拉悬索协作体系能够充分发挥斜拉结构和悬索结构的组合优势,实现超大跨度的同时具有较大的纵向刚度和竖向刚度,满足铁路行车对结构刚度的要求;(4)对于主跨1500 m级超长大跨度公铁合建桥梁,斜拉悬索协作体系经济性更好。

Multi-type sensor placement and response reconstruction for structural health monitoring of long-span suspension bridges

This study is devoted to the experimental validation of the multi-type sensor placement and response reconstruction method for structural health monitoring of long-span suspension bridges. The method for multi-type sensor placement and response reconstruction is briefly described. A test bed, comprising of a physical model and an updated finite element （P-E） model of a long-span suspension bridge is also concisely introduced. The proposed method is then applied to the test bed; the equation of motion of the test bed subject to ground motion, the objective function for sensor location optimization, the principles for mode selection and multi-type response reconstruction are established. A numerical study using the updated FE model is performed to select the sensor types, numbers, and locations. Subsequently, with the identified sensor locations and some practical considerations, fiber Bragg grating （FBG） sensors, laser displacement transducers, and accelerometers are installed on the physical bridge model. Finally, experimental investigations are conducted to validate the proposed method. The experimental results show that the reconstructed responses using the measured responses from the limited number of multitype sensors agree well with the actual bridge responses. The proposed method is validated to be feasible and effective for the monitoring of structural behavior of longspan suspension bridges.

Temperature-induced structural static responses of a long-span steel box girder suspension bridge

Temperature is a significant load on bridges,particularly for long-span steel box girder bridges.This study investigates the temperature-induced static responses of a long-span suspension bridge under real service environmental conditions using numerical simulations and field measurements.Detailed 2 D finite element(FE)models of a typical section for the box girder,main cable,hanger,tower column,and crossbeam are constructed.The thermal boundary conditions are determined strictly according to the surrounding environments of a typical sunny day and applied to the FE models.A transient heat-transfer analysis is performed and the time-dependent temperature and its distribution on the bridge are obtained.In addition,a fine,3 D FE model of the bridge is developed for a structural analysis.The calculated temperatures are applied to the 3 D model and the temperature-induced structural responses are simulated.The simulated temperatures and the associated static responses have good agreement with the measured counterparts and support the numerical simulation method.The main cable and bridge deck make the greatest contributions to the temperature effects on the suspension bridge.The static responses of bridge caused by the design vehicle load are also calculated.The daily variation of the temperature-induced static responses is comparable with,even higher than,that of the design vehicle load.

并置双缆超大跨悬索桥缆索系统振动异步性研究

大跨度悬索桥在风荷载和大交通流的作用下,极易发生振动.为规避采用并置双缆结构的超大跨度悬索桥在运营期间产生的双缆碰撞风险,研究并置双缆间的振动异步性问题.建立包括车辆子系统、桥梁子系统、风场子系统的风-汽车-桥梁耦合系统动力分析模型,并以某超大跨悬索桥并置双缆方案为例,对比研究横风和随机车流作用下,分离式吊索、共用吊索-缆间铰接和共用吊索-缆间刚接3种吊索方案的主缆振动异步性.研究结果表明:横风是并置双缆振动异步性的主要诱因,并主要呈现为横向振动异步性;共用吊索方案可有效降低横向振动异步性,但会略微增加竖向振动异步性;分离式吊索方案的风致横向振动异步性最大,并置双缆横向靠近量约为净距的1/4,初步判别不存在碰撞风险.

超大跨径缆索承重桥梁新型结构体系研究与实践

文章以正在建设的常泰长江大桥和张靖皋长江大桥为例,对超大跨径斜拉桥和悬索桥的结构体系进行分析,讨论了超大跨径斜拉桥的塔梁约束、索塔锚固及沉井基础,超大跨径悬索桥的缆塔约束、索塔形式、锚碇基础及正交异性桥面板等结构体系设计的关键技术问题,给出了相应的解决方案,以期为我国其它超大跨径缆索承重桥梁的建设提供借鉴。

山区悬索桥超大倾斜式隧道锚施工技术研究

针对油溪长江大桥悬索桥超大倾斜式隧道锚施工技术问题,结合山区地形条件和场地位置,对隧道锚开挖、支护及衬砌进行研究。隧道锚锚洞开挖采用微振动光面爆破法施工;初期支护超前小导管、热轧无缝钢管和锁脚锚;二次衬砌施工采用支架模板方案进行混凝土浇筑。通过这些施工技术加快了施工进度,有效节约了成本,保证了超大倾角隧道锚的施工安全和质量,为同类工程施工建设提供指导。

贝雷梁下挂模法浇筑混凝土桥板施工技术

以有轨电车蓉2号线南北大道还建排洪渠桥超宽型现浇桥板施工为例,基于贝雷梁组合形式多样,且组合后的截面力学特性能得到明显提高这些特点,设计了悬吊式现浇支架。从现浇桥板的设计形式、施工制约因素、支架结构设计、工作原理、力学检算、主要施工工艺流程等方面进行了阐述,并利用有限元分析软件对结构进行检算,希望能为类似工程提供借鉴。

杨泗港长江大桥模态参数识别与分析

建立了杨泗港长江大桥的有限元模型,进行了基于环境随机激励的模态测试。采用基于参考点的随机子空间模态参数识别法对该桥的模态参数进行了识别,并将测试结果与有限元模型计算的结果进行比对,评价了该桥的设计与施工质量,为该桥安全有效运行提供了依据。

超大跨悬索桥地震响应的综合最优控制研究

超大跨缆索支承桥梁通常选择隔震体系以减小桥塔的地震内力,但隔震体系会使得结构在强震下的梁端位移很大,必须采取控制措施以保证整体结构的抗震安全性。本文以主跨1 490 m的润扬悬索桥为研究对象,在对其地震响应特性进行分析的基础上,从振动控制的原理出发,探讨了控制超大跨悬索桥地震响应的具体的措施及参数选择,结合改进的层次分析法提出了地震响应综合最优控制的概念,构造了综合最优控制效果评估模型,并给出了该桥在给定地震输入下的综合最优控制措施。结果表明,对于超大跨悬索桥,在塔、梁间设置弹性连接装置或阻尼器都能减小梁端位移响应,但综合考虑其它部位的响应,阻尼器的减震效果更为全面。

超大跨径CFRP主缆悬索桥合理结构体系研究

采用非线性有限元软件BNLAS进行超大跨径CFRP主缆悬索桥与超大跨径钢主缆悬索桥的静动力特性对比分析,从加劲梁约束体系、主缆安全系数、主缆矢跨比、主缆弹性模量4个方面进行超大跨径CFRP主缆悬索桥合理结构体系研究。结果表明:采用CFRP做超大跨径悬索桥主缆可大幅提高主缆应力中活载应力百分比和自振频率,但活载挠度大幅增加;随着跨径增大,加劲梁约束体系对超大跨径悬索桥的动力特性影响减小,3跨连续漂浮体系作为超大跨径CFRP主缆悬索桥加劲梁的约束体系较优;增大主缆安全系数可提高结构的竖向刚度、竖弯基频和扭转基频,但对横向刚度和横弯基频基本无影响;减小矢跨比可提高结构的竖向和横向刚度以及竖弯基频和横弯基频,但会降低扭转基频;增大CFRP主缆的弹性模量可大幅减小活载竖向挠度,提高竖弯基频和扭转基频,但对横向刚度、横弯基频以及主缆线形和应力基本无影响。

交叉吊索对超大跨CFRP主缆悬索桥颤振性能的改善作用

颤振一旦发生,将给桥梁结构带来毁灭性灾难,颤振稳定性是大跨桥梁重要的抗风控制指标。交叉吊索可显著提高超大跨悬索桥的扭转刚度,从而提高其颤振性能。该文以某主跨3500m的超大跨径CFRP(carbon fiber reinforced plastics)主缆悬索桥为工程背景,从频率和振型两方面分析了水平交叉吊索和竖向交叉吊索对其动力特性的影响,并绘制与颤振相关的弯频和扭频随交叉吊索设置位置的变化曲线(简称"影响曲线"),进而针对提高结构颤振稳定性提出11种交叉吊索设置方案。基于耦合颤振的分步分析法,分析这11种方案的颤振稳定性。分析结果表明,在中跨满布水平交叉吊索的同时,在中跨L/3和边跨跨中各对称设置一对竖向交叉吊索,结构的颤振稳定性最好,颤振临界风速提高达49%。

超大跨度公铁悬索桥结构体系参数分析

研究目的：公铁合建悬索桥是大跨度海湾桥梁的优先选择，是经济与社会发展的需要。然而，超大跨度公铁悬索桥超出了目前的设计规范，并且还没有主跨超过2 000 m的悬索桥实例，一些关键技术有待研究。本文以某海湾双塔三跨悬索桥的可行性研究为背景，分析了主要设计参数对结构体系的影响规律，为今后的理论研究和工程设计提供参考。 研究结论：（1）合理的主缆边中跨比为0．22～0．33，合理的加劲梁边中跨比为0．05～0．10；（2）加大加劲梁恒载对结构体系的竖向和横向刚度均有较大的改善，但是以增加主缆量为代价；（3）增加列车长度，有利于使主缆受力均匀，不至于加劲梁局部变形过大；（4）减小主缆矢跨比，有利于提高结构的刚度，但主缆轴力与锚碇规模相应增大，需综合考虑；（5）本文分析归纳的一般性规律，对类似超大跨度桥梁具有参考价值。

交叉吊索对施工中悬索桥的静风稳定性影响

为探明超大跨悬索桥在施工过程中的静风稳定性,采用三维非线性分析方法,对主跨3 500 m的超大跨CFRP(carbon fibre reinforced plastic)主缆悬索桥进行了施工阶段的静风稳定性分析,研究了3种交叉吊索对施工阶段静风性能和变形形态的影响.研究结果表明:随着加劲梁吊装逐步完成,结构静风稳定性不断降低,加劲梁合龙但尚未刚接阶段的静风稳定性最差;仅安装水平交叉吊索作用不大,竖向交叉吊索和综合交叉吊索可显著提高施工阶段的静风稳定性;加劲梁吊装完成率位于9.8%~60.6%时,安装综合交叉吊索可取得较好的抗风效果,其余施工阶段可只安装竖向交叉吊索.