土木工程专业英语（带翻译）

State-of-the-art report of bridge health monitoring

Abstract

The damage diagnosis and healthmonitoring of bridge structures are active areas of research in recent years. Comparing with the aerospace engineering and mechanical engineering, civil engineering has the specialities of its own in practice. For example, because bridges, as well as most civil engineering structures, are large in size, and have quite lownatural frequencies and vibration levels, at low amplitudes, the dynamic responses of bridge structure are substantially affected by the nonstructural components, unforeseen environmental conditions, and changes in these components can easily to be confused with structural damage.All these give the damage assessment of complex structures such as bridges a still challenging task for bridge engineers. This paper firstly presents the definition of structural healthmonitoring system and its components. Then, the focus of the discussion is placed on the following sections:①the laboratory and field testing research on the damage assessment;②analytical developments of damage detectionmethods, including (a) signature analysis and pattern recognition approaches, (b) model updating and system identification approaches, (c) neural networks approaches; and③sensors and their optimum placements. The predominance and shortcomings of each method are compared and analyzed. Recent examples of implementation of structural health monitoring and damage identification are summarized in this paper. The key problem of bridge healthmonitoring is damage automatic detection and diagnosis, and it is the most difficult problem. Lastly, research and development needs are addressed.

1 Introduction

Due to a wide variety of unforeseen conditions and circumstance, it will never be possible or practical to design and build a structure that has a zero percent probability of failure. Structural aging, environmental conditions, and reuse are examples of circumstances that could affect the reliability and the life of a structure. There are needs of periodic inspections to detect deterioration resulting from normal operation and environmental attack or inspections following extreme events, such as strong-motion earthquakes or hurricanes. To quantify these system performance measures requires some means to monitor and evaluate the integrity of civil structureswhile in service. Since the Aloha Boeing 737 accident that occurred on April

28, 1988, such interest has fostered research in the areas of structural health monitoring and non-destructive damage detection in recent years.

According to Housner, et al. (1997), structural healthmonitoring is defined as“the use ofin-situ,non-destructive sensing and analysis of structural characteristics, including the structural response, for detecting changes that may indicate damage or degradation”[1]. This definition also identifies the weakness. While researchers have attempted the integration of NDEwith healthmonitoring, the focus has been on data collection, not evaluation. What is needed is an efficient method to collect data from a structure in-service and process the data to evaluate key performance measures, such as serviceability, reliability, and durability. So, the definition byHousner, et al.(1997)should be modified and the structural health monitoring may be defined as“the use ofin-situ,nondestructive sensing and analysis of structural characteristics, including the structural response, for the purpose of identifying if damage has occurred, determining the location of damage, estimatingthe severityof damage and evaluatingthe consequences of damage on the structures”(Fig.1). In general, a structural health monitoring system has the potential to provide both damage detection and condition assessment of a structure.

Assessing the structural conditionwithout removingthe individual structural components is known as nondestructive evaluation (NDE) or nondestructive inspection. NDE techniques include those involving acoustics, dye penetrating,eddy current, emission spectroscopy, fiber-optic sensors, fiber-scope, hardness testing, isotope, leak testing, optics, magnetic particles, magnetic perturbation, X-ray, noise measurements, pattern recognition, pulse-echo, ra-diography, and visual inspection, etc. Mostof these techniques have been used successfullyto detect location of certain

elements, cracks orweld defects, corrosion/erosion, and so on. The FederalHighwayAdministration(FHWA, USA)was sponsoring a large program of research and development in new technologies for the nondestructive evaluation of highway bridges. One of the two main objectives of the program is to develop newtools and techniques to solve specific problems. The other is to develop technologies for the quantitative assessment of the condition of bridges in support of bridge management and to investigate howbest to incorporate quantitative condition information into bridge management systems. They hoped to develop technologies to quickly, efficiently, and quantitatively measure global bridge parameters, such as flexibility and load-carrying capacity. Obviously, a combination of several NDE

techniques may be used to help assess the condition of the system. They are very important to obtain the data-base for the bridge evaluation.But it is beyond the scope of this review report to get into details of local NDE.

Health monitoring techniques may be classified as global and local. Global attempts to simultaneously assess the condition of the whole structure whereas local methods focus NDE tools on specific structural components. Clearly, two approaches are complementaryto eachother. All such available informationmaybe combined and analyzed by experts to assess the damage or safety state of the structure.

Structural health monitoring research can be categorized into the following four levels: (I) detecting the existence of damage, (II) findingthe location of damage, (III) estimatingthe extentof damage, and (IV) predictingthe remaining fatigue life. The performance of tasks of Level (III) requires refined structural models and analyses, local physical examination, and/or traditional NDE techniques. To performtasks ofLevel (IV) requires material constitutive information on a local level, materials aging studies, damage mechanics, and high-performance computing. With improved instrumentation and understanding of dynamics of complex structures, health monitoring and damage assessment of civil engineering structures has become more practical in systematic inspection and evaluation of these structures during the past two decades.

Most structural health monitoringmethods under current investigation focus on using dynamic responses to detect and locate damage because they are global methods that can provide rapid inspection of large structural systems.These dynamics-based methods can be divided into fourgroups:①spatial-domain methods,②modal-domain methods,③time-domain methods, and④frequency- domain methods. Spatial-domain methods use changes of mass, damping, and stiffness matrices to detect and locate damage. Modal-domain methods use changes of natural frequencies, modal damping ratios, andmode shapesto detect damage. In the frequency domain method, modal quantities such as natural frequencies, damping ratio, and model shapes are identified.The reverse dynamic systemof spectral analysis and the generalized frequency response function estimated fromthe nonlinear auto-regressive moving average (NARMA) model were applied in nonlinear system identification. In time domainmethod, systemparameterswere determined fromthe observational data sampled in time. It is necessaryto identifythe time variation of systemdynamic characteristics fromtime domain approach if the properties of structural system

changewith time under the external loading condition. Moreover, one can use model-independent methods or model-referenced methods to perform damage detection using dynamic responses presented in any of the four domains. Literature shows that model independent methods can detect the existence of damage without much computational efforts, butthey are not accurate in locating damage. On the otherhand, model-referencedmethods are generally more accurate in locating damage and require fewer sensors than model-independent techniques, but they require appropriate structural models and significant computational efforts. Although time-domain methods use original time-domain datameasured using conventional vibrationmeasurement equipment, theyrequire certain structural information and massive computation and are case sensitive. Furthermore, frequency- and modal-domain methods use transformed data,which contain errors and noise due totransformation.Moreover, themodeling and updatingofmass and stiffnessmatrices in spatial-domain methods are problematic and difficult to be accurate. There are strong development

trends that two or three methods are combined together to detect and assess structural damages.For example, several researchers combined data of static and modal tests to assess damages. The combination could remove the weakness of each method and check each other. It suits the complexity of damage detection.

Structural health monitoring is also an active area of research in aerospace engineering, but there are significant differences among the aerospace engineering, mechanical engineering, and civil engineering in practice. For example,because bridges, as well as most civil engineering structures, are large in size, and have quite lownatural frequencies and vibration levels, at lowamplitudes, the dynamic responses of bridge structure are substantially affected by the non-structural components, and changes in these components can easily to be confused with structural damage. Moreover,the level of modeling uncertainties in reinforced concrete bridges can be much greater than the single beam or a space truss. All these give the damage assessment of complex structures such as bridges a still challenging task for bridge engineers. Recent examples of research and implementation of structural health monitoring and damage assessment are summarized in the following sections.

2 Laboratory and field testing research

In general, there are two kinds of bridge testing methods, static testing and dynamic testing. The dynamic testing includes ambient vibration testing and forced

vibration testing. In ambient vibration testing, the input excitation is not under the control. The loading could be either micro-tremors, wind, waves, vehicle or pedestrian traffic or any other service loading. The increasing popularity of this method is probably due to the convenience of measuring the vibration

response while the bridge is under in-service and also due to the increasing availability of robust data acquisition and storage systems. Since the input is unknown, certain assumptions have to be made. Forced vibration testing involves application of input excitation of known force level at known frequencies. The excitation manners include electro-hydraulic vibrators, force hammers, vehicle impact, etc. The static testing in the laboratory may be conducted by actuators, and by standard vehicles in the field-testing.

we can distinguish that①the models in the laboratory are mainly beams, columns, truss and/or frame structures, and the location and severity of damage in the models are determined in advance;②the testing has demonstrated lots of performances of damage structures;③the field-testing and damage assessmentof real bridges are more complicated than the models in the laboratory;④the correlation between the damage indicator and damage type,location, and extentwill still be improved.

3 Analytical development

The bridge damage diagnosis and health monitoring are both concerned with two fundamental criteria of the bridges, namely, the physical condition and the structural function. In terms of mechanics or dynamics, these fundamental criteria can be treated as mathematical models, such as response models, modal models and physical models.Instead of taking measurements directly to assess bridge condition, the bridge damage diagnosis and monitoring systemevaluate these conditions indirectly by using mathematical models. The damage diagnosis and health monitoring are active areas of research in recentyears. For example, numerous papers on these topics appear in the proceedings of Inter-national Modal Analysis Conferences (IMAC) each year, in the proceedings of International Workshop on Structural HealthMonitoring (once of two year, at Standford University), in the proceedings of European Conference on Smart materials and Structures and European Conference on Structural Damage AssessmentUsing Advanced Signal Processing Procedures, in the proceedings ofWorld Conferences of Earthquake Engineering, and in the proceedings of International Workshop on Structural Control, etc.. There are several review papers to be referenced, for examples,Housner, et al. (1997)provided an extensive summary of

the state of the art in control and health monitoring of civil engineering structures[1].Salawu (1997)discussed and reviewed the use of natural frequency as a diagnostic parameter in structural assessment procedures using vibration monitoring.Doebling, Farrar, et al. (1998)presented a through review of the damage detection methods by examining changes in dynamic properties.Zou, TongandSteven (2000)summarized the methods of vibration-based damage and health monitoring for composite structures, especially in delamination modeling techniques and delamination detection.

4 Sensors and optimum placement

One of the problems facing structural health monitoring is that very little is known about the actual stress and strains in a structure under external excitations. For example, the standard earthquake recordings are made ofmotions of the floors of the structure and no recordings are made of the actual stresses and strains in structural members. There is a need for special sensors to determine the actual performance of structural members. Structural health monitoring requires integrated sensor functionality to measure changes in external environmental conditions, signal processing functionality to acquire, process, and combine multi-sensor and multi-measured information. Individual sensors and instrumented sensor systems are then required to provide such multiplexed information.

FuandMoosa (2000)proposed probabilistic advancing cross-diagnosis method to diagnosis-decision making for structural health monitoring. It was experimented in the laboratory respectively using a coherent laser radar system and a CCD high-resolution camera. Results showed that this method was promising for field application. Another new idea is thatneural networktechniques are used to place sensors. For example,WordenandBurrows (2001)used the neural network and methods of combinatorial optimization to locate and classify faults.

The static and dynamic data are collected from all kinds of sensorswhich are installed on the measured structures.And these datawill be processed and usable informationwill be extracted. So the sensitivity, accuracy, and locations,etc. of sensors are very important for the damage detections. The more information are obtained, the damage identification will be conducted more easily, but the price should be considered. That’s why the sensors are determined in an optimal ornearoptimal distribution. In aword, the theory and validation ofoptimumsensor locationswill still being developed.

5 Examples of health monitoring implementation

In order for the technology to advance sufficiently to become an operational system for the maintenance and safety of civil structures, it is of paramount importance that new analytical developments are ultimately verified with appropriate data obtained frommonitoring systems, which have been implemented on civil structures, such as bridges.

Mufti (2001)summarized the applications of SHM of Canadian bridge engineering, including fibre-reinforced polymers sensors, remote monitoring, intelligent processing, practical applications in bridge engineering, and technology utilization. Further study and applications are still being conducted now.FujinoandAbe(2001)introduced the research and development of SHMsystems at the Bridge and Structural Lab of the University of Tokyo. They also presented the ambient vibration based approaches forLaser DopplerVibrometer (LDV) and the applications in the long-span suspension bridges.

The extraction of the measured data is very hard work because it is hard to separate changes in vibration signature duo to damage form changes, normal usage, changes in boundary conditions, or the release of the connection joints.

Newbridges offer opportunities for developing complete structural health monitoring systems for bridge inspection and condition evaluation from“cradle to grave”of the bridges. Existing bridges provide challenges for applying state-of-the-art in structural health monitoring technologies to determine the current conditions of the structural element,connections and systems, to formulate model for estimating the rate of degradation, and to predict the existing and the future capacities of the structural components and systems. Advanced health monitoring systems may lead to better understanding of structural behavior and significant improvements of design, as well as the reduction of the structural inspection requirements. Great benefits due to the introduction of SHM are being accepted by owners, managers, bridge engineers, etc..

6 Research and development needs

Most damage detection theories and practices are formulated based on the following assumption: that failure or deterioration would primarily affect the stiffness and therefore affect the modal characteristics of the dynamic response of the structure. This is seldom true in practice, because①Traditional modal parameters (natural frequency, damping ratio and mode shapes, etc.) are not sensitive enough to identify

and locate damage. The estimation methods usually assume that structures are linear and proportional damping systems.②Most currently used damage indices depend on the severity of the damage, which is impractical in the field. Most civil engineering structures, such as highway bridges, have redundancy in design and large in size with low

natural

frequencies.

Any

damage

index

should

consider

these

factors.③Scaledmodelingtechniques are used in currentbridge damage detection. Asingle beam/girder models cannot simulate the true behavior of a real bridge. Similitude

laws

for

dynamic

simulation

and

testing

should

be

considered.④Manymethods usually use the undamaged structural modal parameters as the baseline comparedwith the damaged information. This will result in the need of a large data storage capacity for complex structures. But in practice,there are majority of existing structures for which baseline modal responses are not available. Only one developed method(StubbsandKim (1996)), which tried to quantify damagewithout using a baseline, may be a solution to this difficulty. There is a lot of researchwork to do in this direction.⑤Seldommethods have the ability to distinguish the type of damages on bridge structures. To establish the direct relationship between the various damage patterns and the changes of vibrational signatures is not a simple work.

Health monitoring requires clearly defined performance criteria, a set of corresponding condition indicators and global and local damage and deterioration indices, which should help diagnose reasons for changes in condition indicators. It is implausible to expect that damage can be reliably detected or tracked by using a single damage index. We note that many additional localized damage indiceswhich relate to highly localized properties ofmaterials or the circumstances may indicate a susceptibility of deterioration such as the presence of corrosive environments around reinforcing steel in concrete, should be also integrated into the health monitoring systems.

There is now a considerable research and development effort in academia, industry, and management department regarding global healthmonitoring for civil engineering structures. Several commercial structural monitoring systems currently exist, but further development is needed in commercialization of the technology. We must realize that damage detection and health monitoring for bridge structures by means of vibration signature analysis is a very difficult task. It

contains several necessary steps, including defining indicators on variations of structural physical condition, dynamic testing to extract such indication parameters,

defining the type of damages and remaining capacity or life of the structure, relating the parameters to the defined damage/aging. Unfortunately, to date, no one has accomplished the above steps. There is a lot of work to do in future.

桥梁健康监测应用与研究现状

摘要

桥梁损伤诊断与健康监测是近年来国际上的研究热点,在实践方面,土木工程和航空航天工程、机械工程有明显的差别,比如桥梁结构以及其他大多数土木结构,尺寸大、质量重,具有较低的自然频率和振动水平,桥梁结构的动力响应极容易受到不可预见的环境状态、非结构构件等的影响,这些变化往往被误解为结构的损伤,这使得桥梁这类复杂结构的损伤评估具有极大的挑战性.本文首先给出了结构健康监测系统的定义和基本构成,然后集中回顾和分析了如下几个方面的问题:①损伤评估的室内实验和现场测试;②损伤检测方法的发展,包括:(a)动力指纹分析和模式识别方法, (b)模型修正和系统识别方法, (c)神经网络方法;③传感器及其优化布置等,并比较和分析了各自方法的优点和不足.文中还总结了健康监测和损伤识别在桥梁工程中的应用,指出桥梁健康监测的关键问题在于损伤的自动检测和诊断,这也是困难的问题;最后展望了桥梁健康监测系统的研究和发展方向.

关键词:健康监测系统;损伤检测;状态评估;模型修正;系统识别;传感器优化布

置;神经网络方法;桥梁结构

1概述

由于不可预见的各种条件和情况下，设计和建造一个结构将永远不可能或无实践操作性，它有一个失败的概率百分之零。结构老化，环境条件和回用情况的例子，可能会影响可靠性和结构的使用寿命。有定期检查需要检测恶化，正常运行和环境造成的攻击或检查下列极端事件，如强震地震或飓风。为了量化这些系统性能的措施，当其还在使用中，需要一些手段来监测和评估土木工程的完整性。由于波音737阿罗哈意外，04月28日1988年发生，这些利息也助长了近年来在结构健康监测和非破坏性的损伤检测领域的研究。

根据Housner等编著（1997年），结构健康监控被定义为“使用奥芬原位，无损检测和结构特点，包括结构检测变化的响应可能表明损坏或退化的分析”。这个定义还确定了弱点。虽然研究人员已经尝试了NDE与健康监控一体化，重点是收集数据，而不是评价。我们需要的是一种有效的方法来从使用中的结构中收集数据和处理数据以评估关键性能的措施，如可用性，可靠性和耐用性。因此，由Housner定义（1997）应被修改，并且结构健康监测可以定义为“使用奥芬原位，无损检测及结构特点的分析，包括结构反应分析，以识别的目的，损害发生后，确定损害的部位，评估结构的安全性并评估结构上被毁坏的结果.”一般来

说，结构健康监测系统有潜力提供条件，不仅对于毁坏的发现还有结构的定位。

在除去个别构件以外评估结构被称为无损评价方法(NDE)或无损检验。NDE技术包括那些涉及声学 ，染料渗透，涡流，发射光谱，光纤传感器，光纤范围，硬度测试，同位素，泄漏检测，光学，磁粒，磁扰动，X射线，噪声测量，模式识别，脉冲回波,摄影和视觉检查等。这些技术大部分已被成功用于检测某些位置元素，裂缝或焊接缺陷，腐蚀/侵蚀等。联邦公路管理局（美国）曾赞助一个巨大就公路桥梁的无损害评价技术的研究和发展的项目。这两个方案的主要目标之一是发展新工具和新技术以解决具体问题。另一种是制定了在桥梁管理支持和桥梁技术状况的定量评估，以及如何更好的将定量条件下的信息合并到桥梁管理系统中去。他们希望开发技术，以快速，高效，并定量测量全球桥梁参数，如桥梁灵活性和承载能力。显然，多种无损检测技术的结合可用于协助评估系统的状况。他们对于获取桥梁评估的数据是非常重要的，但是NDE的具体细节超出了本书的范围。

健康监测技术可分为全局的和局部的。全局的试图同时评估整个结构的条件，而局部的方法侧重于具体的构件无损检测工具。显然，两种方法是相辅相成的。所以这些可获得的信息可被专家整合和分析，以评估损失或结构安全状态。

结构健康监测的研究可分为以下四个层次：（一）检测损害的存在，（二）检测位置损伤，（三）估计损害程度（四）预测剩余寿命。(三)的任务需要细微的结构模型,分析计算,当地的体格检查,和传统无损探伤技术。（四）需要当地水平上的材料组成信息、材料老化研究、损伤力学和高性能计算。用改进后的仪器仪表和复杂结构的动力学理解，健康监测和工程结构的损伤评估在过去20年里已成为更切合系统检查和评估结构的方式。

根据目前调查大部分结构健康监控方法聚焦在使用动态反应来检测和定位的危害，因为它们是可提供大型结构系统快速检查的全球性的方法。这些以动力学为基础的方法可分为四组：①空间域的方法，②模态域方法，③时域方法，④频域方法。空间域方法利用质量阻尼和刚度矩阵的改变以检测和定位损害。模态域方法利用自然频率的变化，模态阻尼比的改变和模态振型的改变以查明是否有损伤。在频域法，模态量，如自然频率，阻尼比，和模型形状进行辨识。反向动态系统的频谱分析和广义频率响应函数由非线性回归滑动平均(尘垢NARMA)模型中评估应用于非线性系统辨识。在时间域的方法,系统参数从观测数据样本中决定。如果在外部加载条件下结构系统随时间改变，那么从时间域的方法识别系统的动态性变化的时间是非常有必要的。此外,可以采用模态独立法或模态参考法在四个领域中的任意一个用动态反应进行损伤检测。方法文献表明模态独立法能探测到危害存在与否,无需太多的计算,但是他们并没有准确到定位损伤。另一

方面,模态参考法通常能更准确的定位危害并要求比模态独立法更少的伤害，但是他们需要适当的结构模式和重大的计算方面所做的努力。虽然时域方法采用原来的用传统的振动测量设备所测量得出的时域测量数据，他们要求有一定的结构信息和巨大的计算，以及对大小写敏感性的。此外,使用频率和模态域转化后的数据,这些数据由于转化包含错误和噪声。此外,建模和质量矩阵和刚度矩阵的更新在空间域方法上存在问题并且很难达到准确。两种方法结合在一起来检测和评估结构性破坏有很大的趋势。譬如说,有些研究人员结合数静态数据和模态测试来评估损失。这种结合可以舍去每种方法的缺点,互相制约。它适合复杂的损伤检测。

结构健康监测也是航天工程研究活跃的领域，但在航天工程，机械工程，土木工程实践中还有显着差异。例如，由于桥梁，和大多数国内工程建筑一样，规模大，并有相当低的固有频率和振动水平在，桥梁结构的动力反应受到非结构构件严重影响，并且在这些组件中的变化可以很容易与结构破坏混淆。此外，在钢筋混凝土桥梁模型的不确定性水平比单束或空间桁架更大。所有这些使桥梁等复杂结构损伤评估的桥梁工程师仍然具有挑战性的任务。研究和结构健康监测和损伤评估实施最近的例子由以下几个部分所总结。

2实验室和现场测试研究

一般来说,有两种桥试验方法、静态测试、动态测试。动态测试包括环境振动测试和受迫振动测试。在环境振动测试,输入激励不低于控制。负载可能是微震、风、海浪、车辆和行人或其他加载。该方法的日益普及的原因可能是由于当桥在负载条件下测量振动反应的便利性，还有就是日益增长的粗野数据采集与存储系统的可靠性。既然输入是未知的,也要有一定的假设。受迫震动测试包括已知频率下的已知受迫水平的激励输入的应用。激振力方式包括电液振动器,锤子、车辆冲击力等。在实验室的静态测试可能由执行机构和通过标准的汽车的现场测试进行。

我们能区分出,①在实验室的模型主要是梁、柱、桁架和/或框架结构,以及位置和预先被检测到的模型的严重程度;②测试已经表明许多损伤结构的性能;③现场测试和真正的桥梁损伤评估的模型要比实验室的模型更复杂;④损伤指标和损害类型,位置和程度上之间的相关性仍将得到改善。

3分析发展

桥梁损伤诊断与健康监测都具有两个方面的桥梁基本标准，即身体状况和结构功能。在力学或动力学方面，这些基本条件可以被视为数学模型，如响应模型，模态模型和物理模型。桥梁损伤诊断和健康监控系统可直接利用数学模型来评估

状态，而不是直接采取措施评估桥梁状态。损伤诊断与健康监测近几年成为了研究的活跃领域。例如，大量这些主题的论文出现在了每年的国际模态分析会议（IMAC）诉讼中，国际研讨会关于结构健康监控中的诉讼（在斯坦福大学每二年一次）中，在欧洲会议关于智能材料和结构，预先使用高级信号处理程序评估结构损伤的诉讼中，在世界地震工程会议中，并在研究结构控制程序的国际研讨会中。有几篇文章值得被借鉴，例如Housner等编著（1997年）提供了对国家工程控制和结构健康监测方面广泛的总结[1]。Salawu（1997）讨论并审查了在利用震动监控的结构评估程序中将固有频率作为诊断参数。 Doebling，法拉等编著中（1998）提出了通过动力学方面的改变来回顾损伤检测方法。Zou Tong和Steven（2000）总结了复合材料结构振动的损伤与健康监测的方法，尤其是在分层建模技术和分层检测。

4 传感器和最佳位置

所面临的结构健康监测的一个问题是，在外部激励下的结构的实际应力和应变了解甚少。例如，标准的地震是在结构层的真是压力和应变所导致的。需要有一个特殊传感器，以确定结构成员的实际表现。结构健康监测需要集成传感器的功能来衡量外部环境条件，信号处理功用于获取，处理，并结合多传感器和多种测量信息。各个传感器和传感器系统的仪器要求能够提供多元化的信息。

FuandMoosa（2000）提出推进交叉概率诊断方法为结构健康监测做出决策。这是在实验室分别用相干激光雷达系统和CCD高清晰度摄像机所做的实验。结果表明，该方法具有现场应用前景。另一项新的想法人工神经网络技术被用来放置传感器。例如，Worden和Burrows（2001）利用了神经网络和组合优化方法来查找故障并进行分类。

静态和动态数据来自各种被安装的用于实测结构的传感器。这些数据将被处理,并且可用的信息将被提取出来。所以的传感器灵敏度、准确度、和地点等方面对损失的识别是非常重要的。得到信息越多,进行损伤识别越容易,但价格应该考虑。这就是为什么这个传感器是最优或接近最优的。总之,理论和验证优化传感器位置将仍继续发展。

5健康监测实施范例

为了使这一技术及早进行，成为维护和土木结构安全的运作体系，发展新的分析最终由监控系统中所获得的数据所证实是极为重要的，该系统已经土木结构中实施，例如桥梁。

穆夫提（2001）总结了加拿大桥梁结构健康监测技术的应用，包括纤维聚合物传感器，远程监控，智能处理，在桥梁工程中的实际应用和技术的利用。进一

步的研究和应用仍在进行.Fujino和Abe（2001）介绍了东京大学的桥梁与结构实验中的SHM系统的研究和发展。他们基于LDV方法和大跨度悬索桥的应用还提出了环境振动。

所测数据的提取是非常辛苦的工作，因为由于损害形式改变，正常使用，在边界条件的变化，或连接的接头释放单独的变化使得它是很难在振动信号间区分变化。

新桥梁为发展完整的结构监控系统去检测桥梁和评估状态提供了机会。现有的桥梁为申请结构健康监测最先进技术以确定结构元素,连接和体系,制定了推算率模型及预测土壤退化,现有和未来的能力结构的零部件和系统提出了挑战。先进的健康监测系统可能会导致更好的了解结构的行为和显着的改善设计,以及降低了结构的检验要求。巨大的利益由于SHM的引入被人们普遍接受的，例如企业的所有者、管理者、桥梁工程师,等等?

6研究和发展的需要

大多数损伤检测理论与实践,特制定基于以下假设:失败或恶化主要影响系统的刚度，影响模态特征结构的动态响应。这是在实践中真的很少,因为①传统模态参数(固有频率、阻尼比和振型等)都没有足够的灵敏度,以识别和定位的伤害。估算方法通常假定结构是线性比例阻尼系统。②多数目前使用的破坏指标取决于损伤的严重程度,这是不切实际的。大多数土木工程结构,如公路桥梁,有冗余设计和低固有频率的大尺寸。任何损伤指标应考虑这些因素。③建模技术使用于当前桥梁损伤检测。单一光束模型不能模拟真正桥的真实的行为。相似的法律进行动态仿真和测试应被考虑。④许多方法通常用无损坏的结构模型参数作为基线与损害信息相比。这将会导致需要的是为复杂结构的一个大的数据存储容量。但是在实践中,有大部分现有结构的模态响应基线不可获得。只有一个发达的方法(StubbsandKim(1996年)),它试图不使用基线量化损坏，可能是解决这一困难的方法。有大量的研究工作要朝这个方向前进。⑤很少方法有能力分辨桥梁结构损坏的类型。为建立各种损伤模式及其变化的振动信号之间的关系不是一件简单的工作。

健康监测需要明确的性能标准,提出了一套相应的状态指标和全局和局部损伤和恶化,这应该帮助诊断出状态指标的变化情况。利用单损伤指标期待损坏可被检出或跟踪是难以令人信服。我们注意到与高度局部材料性质或情况的恶化相关联的许多额外的局部破坏指标可能表明恶化的易感性，例如钢筋混凝土周围腐蚀性环境的存在,也应该是融入健康监测系统。

在学术界,或者工业界,和管理部门对全球健康监测在土木工程结构有一个相当大的研究和开发工作。几个商业结构监测系统目前存在的,但商业化的技术

需要进一步发展。我们必须认识到,损伤检测,健康监测通过振动信号分析对于桥梁结构是一项非常艰巨的任务。它包含一些必要的步骤,包括在结构物理条件变化下定义指标、动态测试以提取参数,定义了损害类型的和剩余产能或生活相关联的结构参数,界定老化。不幸的是,到目前为止,没有人完成了以上步骤。在未来还有很多工作要做。

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