A frequency response function change method for damage localization and quantification in a shear building under ground excitation

A frequency response function change (FRFC) method to detect damage location and extent based on the change in the frequency response functions of a shear building under the effects of ground excitation was proposed in this paper. The damage identification equation was derived from the motion equations of the system before and after the occurrence of the damage. Efforts to make the FRFC method less model‐dependent were made. Intact system matrices, which could be estimated using the measured data without the need for an analytical model, and the frequency response functions were required for the FRFC method. The effects of measurement noise and model parameter error in the FRFC method were studied numerically. The proposed FRFC method was validated by experimental studies of a six‐story steel building structure with single and multiple damage cases. Copyright © 2012 John Wiley & Sons, Ltd.     

Earthquake-induced damage detection and localization in masonry structures using smart bricks and Kriging strain reconstruction: A numerical study

The intrinsic vulnerability of masonry structures to seismic events makes structural health monitoring of the utmost importance for the conservation of the built heritage. The development of piezoresistive bricks, also termed smart bricks, is an innovative technology recently proposed by the authors for the monitoring of such structures. Smart bricks exhibit measurable variations in their electrical properties when subjected to external loads or, alternatively, strain self-sensing capabilities. Therefore, the deployment of a network of smart bricks into a masonry structure confers self-diagnostic properties to the host structure. In this light, this paper presents a theoretical investigation on the application of smart bricks to full-scale masonry structures for seismic assessment. This includes the study of the convenience of providing electrical isolation conditions to the sensors, as well as the effectiveness of smart bricks when installed into either new constructions or in pre-existing structures. Secondly, numerical results are presented on the seismic analysis of a three-dimensional masonry building equipped with a network of smart bricks. Finally, in order to map the strain field throughout the structure exploiting the outputs of a limited number of sensors, an interpolation-based strain reconstruction approach is proposed.     

Effects of excitation frequency on detection accuracy of orthogonal wavelet decomposition for structural health monitoring

Accurate estimation of stiffness loss is a challenging problem in structural health monitoring. In this study orthogonal wavelet decomposition is used for identifying the stiffness loss in a single degree of freedom spring-mass-damper system. The effects of excitation frequency on accuracy of damage detection is investigated. Results show that pseudo-alias effects caused by the orthogonal wavelet decomposition (OWD), affect damage detectability. It is demonstrated that theproposed approach is sunable for damage detection when the excitation frequency is relatively low. This study shows how a priori knowledge about the signal and ability to control the sampling frequency can enhance damage detectability.     

An energy‐based damage model for seismic response of steel structures

This paper proposes a new model for quantifying the damage in structural steel components subjected to randomly applied flexural/shear stress reversals, such those induced by earthquakes. In contrast to existing approaches that consider the damage as a combination of the global amount of dissipated energy and maximum displacement, the proposed model represents the damage by two parameters: (a) the total dissipated energy and (b) the portion of the energy consumed in the skeleton part of the load–displacement curve. These parameters are employed to define a single ‘damage index’, which measures the level between 0 (no damage) and 1 (failure). The proposed model takes into account that the ultimate energy dissipation capacity of the steel component is path‐dependent and can change throughout the entire response duration. The new model is derived from low‐cycle fatigue static tests of round steel rods and steel plates subjected to bending and shear. The accuracy of the model is verified experimentally through dynamic real‐time shaking table tests. From these tests, it is observed that the proposed model measures the level of damage at any stage of the loading process reasonably well and predicts the failure of the structural component accurately. The model can be easily implemented in a computer program to assess the level of seismic damage and the closeness to failure in new structures or to evaluate the safety of existing ones. Copyright © 2007 John Wiley & Sons, Ltd.     

小波分析在结构损伤识别中的应用

为提高结构损伤识别方法的准确性和适用性,将小波分析引入到结构损伤识别中。本文首先介绍了小波分析的基本原理,然后详细论述了小波分析用于结构损伤识别的三种方法:基于时域响应的方法、基于空间域响应的方法和小波分析与其他方法联合使用,接着分析了各种方法的应用现状、适用范围和存在的问题。通过比较可以看出小波分析用于结构损伤识别有着广阔的应用前景,本文最后针对进一步研究的方向提出了五点建议。     

建筑物震害预测模糊震害指数法

建筑物震害预测是城市防震减灾的基础工作之一。本文在分析现有震害预测方法的基础上，提出了一种新的震害预测方法－模糊震害指数法。模糊震害指数法以现有震害预测资料为基础，采用模糊数学方法实现。本文详细阐述了模糊震害指数法的理论模型，推导了其数学公式，最后给出了实例分析。     

桥梁健康监测及诊断研究综述

本文分析了桥梁结构健康监测和诊断的必要性和紧迫性，对桥梁结构损伤探测的方法进行了详细的分类及论述。提出了桥梁健康监测和诊断的研究新领域——无线监测系统。最后指出了桥梁健康监测和诊断中存在的问题及发展趋势。     

对结构损伤识别中曲率模态方法的改进

曲率模态在结构损伤识别中有很好的应用。针对模态分析中某几阶曲率模态曲线未能有效地反映损伤的情况,本文提出对曲线进行一次数值微分的处理方法,计算结果表明这种方法能进一步提高曲率模态对损伤的敏感性,是一种很好的辅助处理数据方法。     

Optimal maintenance strategies for structures in seismic zones

In this paper an approach is developed for establishing optimal maintenance (repair) strategies of structures in seismic zones. The approach is based on expected future costs and the main decision variable is a damage threshold for repair given an acceptable reliability level. It is considered that structural damage accumulates over a number of earthquakes until a threshold is reached or exceeded, after which the structure is repaired so that there is no remaining damage. A Markov model is implemented for such a process of damage accumulation during future earthquakes. An algorithm is proposed for computing non‐linear structural response to earthquakes using a damage function model. This algorithm is used to evaluate transition probabilities between damage states based on simulations of future earthquakes of given intensities. Expressions are derived for evaluating expected life‐cycle damage costs and structural reliability as a function of time and of the damage threshold for repair. As an application, a single‐degree‐of‐freedom structural system is studied. In addition, the paper addresses the case of instrumented structures where information from earthquake response records is available. Such information is incorporated into the formulation for maintenance strategies by means of a Bayesian approach for updating the probability distribution of structural damage and of non‐linear behaviour parameters so that predictions about costs and reliability are improved. Copyright © 2002 John Wiley & Sons, Ltd.     

土木工程结构安全性评估、健康监测及诊断述评

阐述了土木工程结构的安全性评估、健康监测及损伤诊断的必要性和迫切性，系统论述了结构健康监测和诊断的概念、理论和方法，重点讨论了传感器的优化布置、损伤识别等健康监测中的关键问题，介绍了光纤等新型传感器的应用情况，最后指出了值得进一步研究的问题。     

Theoretical models and recorded response in the estimation of cumulative seismic damage on non‐linear structures

A damage‐function model is proposed for the inelastic response of structures in terms of initial damage and of displacement amplitudes and secant stiffnesses of response cycles. The model is used to obtain an analytical closed‐form solution for the probability distribution of cumulative damage after an earthquake ground motion given the distribution prior to such excitation and information on the inelastic structural response. The formulation is applied to a reinforced concrete frame and the results show the capabilities of the method to yield updated distributions of damage. Copyright © 2000 John Wiley & Sons, Ltd.     

结构动力分析中多点激励问题的研究综述

针对结构多点激励问题的研究现状,分别介绍了地震动时空变化性、多点激励分析基本方法、地震动记录校正以及多点激励对结构的影响.首先阐述了地震动时空变化性及主要表现形式,并提出了最不利行波概念;其次介绍了多点激励分析的基本方法,并指出了3种确定性方法的优缺点和适用性;然后论述了多点激励对地震动时程的基本要求:地震动加速度记录的校正问题;接着简要介绍了多点激励对结构的复杂影响,并指出这种影响取决于拟静力反应项和动反应项的相互关系.最后,对结构多点激励分析有关问题提出了展望和建议.     

Probabilistic neural networks for seismic damage mechanisms prediction

The procedure commonly employed to assess the seismic vulnerability of buildings uses simplified qualitative and quantitative observations obtained from the measured data entered into report forms. In Italy, the data sheets adopted by the National Defence Group against Earthquakes (Gruppo Nazionale per la Difesa dai Terremoti—GNDT) play a unifying and reference role. This paper proposes a method for the processing of the data contained in such report forms which is based on probabilistic neural networks producing a Bayesian classification. The final goal is to exploit the fundamental learning and generalization capabilities of neural networks to obtain an estimate of the vulnerability of structural systems. In particular, the aim is to be able to predict the damage mechanisms which may be triggered in the macro-elements of public worship buildings. Copyright © 1999 John Wiley & Sons Ltd.     

环境激励下基于波动能量法的结构损伤识别

目前作为结构健康监测系统核心的损伤识别大多是基于模态参数变化而进行的,但模态参数对局部损坏不敏感,导致损伤识别精度不够。波在结构中的传播状态可以更好地反映局部损伤状况,波动能量可以作为损伤识别的有效指标。为了提高环境激励下结构损伤识别的精度,采用S变换分析了结构输出信号,建立波动能量指标,从而使波动能量指标的使用领域扩展到非平稳信号范围。最后通过三层钢框架试验及弹性分层剪切梁的数值模型对该方法进行了验证,结果表明:该方法不仅能够有效识别结构损伤位置,而且能够识别出损伤程度。     

Shaking table tests on a masonry building monitored using smart bricks: Damage detection and localization

The seismic behavior of unreinforced masonry buildings is typically characterized by premature brittle collapse mechanisms that can cause serious consequences for the protection of human lives and for the preservation of historical and cultural heritage. Structural health monitoring can be a powerful tool enabling a quick post-earthquake assessment of the structure's performance, but its applications are still scarce as a consequence of the severe limitations affecting off-the-shelf sensing technologies, in terms of local nature of the measurements, costs, as well as long-term behavior, installation, and maintenance. To overcome some of these limitations, the authors have recently proposed a new sensing technology, called “smart brick,” that is a durable clay brick doped with stainless steel microfibers, working as a smart strain sensor for masonry buildings. This paper presents the first full-scale application of smart bricks, used for detecting and localizing progressive earthquake-induced damage in an unreinforced masonry building subjected to shaking table tests. Smart bricks are employed to detect changes in load paths on masonry walls, comparing strain measurements acquired after each step of the seismic sequence with those referring to the undamaged structure. Experimental results are interpreted using a 3D finite element model built to reproduce the shaking table tests. Overall, the results demonstrate that the smart bricks can effectively reveal local permanent changes in structural conditions following a progressive damage, therefore being apt for earthquake-induced damage detection and localization.     

环境激励下一种基于免疫机制的结构损伤诊断方法

结构状况发生改变时,结构的振动特性将发生变化。免疫算法能有效检测出振动特性的变化。本文将环境激励下的结构响应重构相空间,对其进行奇异值分解后,选择适当个数的奇异值构造特征参数集合,应用反向选择算法进行异常值检测,以ASCE学会提出的基准结构为对象进行研究,讨论了不同个数的特征参数对检测结果的影响。分析表明,该算法能有效地判断结构状况的变化。     

Seismic health monitoring of an instrumented multistory building using the interpolation method

In this paper, a new approach to structural damage localization is presented using as damage feature the interpolation error related to the use of a spline function in modeling the operational deformed shapes of the structure. Statistically significant variations of the interpolation error between the undamaged and the inspection phase indicate the onset of damage. A threshold value of the damage feature is defined in terms of the tolerable probability of false alarm to select variations of the interpolation error because of damage from those due to random sources. The method is successfully applied to a calibrated model of the factor building a real densely instrumented building at the University of California, Los Angeles. Results show that the method is effective for damage localization for both single and multiple locations of damage also in case of responses corrupted by noise. Copyright © 2014 John Wiley & Sons, Ltd.     

The dynamic response of seabed anchored floating tunnels under seismic excitation

In this paper a procedure for analysing the seismic response of seabed anchored floating tunnels is presented. The first step of the research was the development of an ‘ad hoc’ finite element for modelling the behaviour of anchor elements, with particular reference to the problem of transverse oscillations under time varying axial loads. The element was subsequently inserted in a step‐by‐step procedure for the numerical analysis of non‐linear response to multiple‐support seismic input; the procedure encompasses simplified modelling of fluid–structure and soil–structure interaction effects. An example of an application is given concerning two 4680 m long floating tunnels with different seabed profiles. Copyright © 2000 John Wiley & Sons, Ltd.     

Global damage indexes for the seismic performance assessement of RC structures

When performing the seismic risk assessment of new or existing buildings, the definition of compact indexes able to measure the damaging and safety level of structures is essential, also in view of the economic considerations on buildings rehabilitation. This paper proposes two series of indexes, named, respectively, Global Damage Indexes (GDIs), which are representative of the overall structure performance, and Section Damage Indexes (SDIs), which assess the conditions of reinforced concrete (RC) beam‐column sections. Such indexes are evaluated by means of an efficient numerical model able to perform nonlinear analyses of the RC frame, based on the continuum damage mechanics theory and fiber approach. An improvement of a two‐parameter damage model for concrete, developed by some of the authors, which guarantees a better correlation between the Local Damage Indexes (LDIs) and the material's mechanical characteristics, is also presented. For the reinforcement, a specific LDI, named ‘steel damage index’, which takes into account the plastic strain development and the bar buckling effect, is proposed. The numerical model has been employed to simulate several experimental tests, in order to verify the accuracy of the proposed approach in predicting the RC member's behavior. Nonlinear static and dynamic analyses of two RC frames are carried out. The robustness of the method, as well as the effectiveness of the GDIs in assessing the structural conditions, are demonstrated here. Finally, comparisons between the evolution of GDIs and the achievement of the performance levels as proposed in FEMA 356 are reported. Copyright © 2009 John Wiley & Sons, Ltd.