Health Monitoring Based on Dynamic Flexibility Matrix: Theoretical Models versus <i>In-Situ</i>Tests

The paper focuses on damage detection of civil engineering structures and especially on concrete bridges. A method for structural health monitoring based on vibrational measurements is presented and discussed. Experimentally identified modal parameters (eigenfrequencies, mode shapes and modal masses) of bridge structures are used to calculate the inverse stiffness matrix, the so-called flexibility matrix. By monitoring of the stiffness matrix, damage can easily be detected, quantified and localized by tracking changes of its individual elements. However, based on dynamic field measurements, the acquisition of the flexibility matrix instead of the stiffness matrix is often the only choice and hence more relevant for practice. But the flexibility-based quantification and localisation of damage are often possible but more difficult, as it depends on the type of support and the location of the damage. These issues are discussed and synthetized, that is an originality of this paper and is believed useful for engineers in the damage detection of different bridge structures. First the theoretical background is briefly repeated prior to the illustration of the differences between stiffness and flexibility matrix on analytical and numerical examples. Then the flexibility-based detection is demonstrated on two true bridges with real-time measurement data and the results are promising.

高架桥梯形轨枕轨道不平顺测量

北京地铁5号线天通苑站至天通苑北站之间铺设了一段长为171 m的梯形轨枕轨道试验段.为了得出符合城市轨道交通实际情况的轨道不平顺谱,对梯形轨枕轨道试验段进行了轨道不平顺测量,并对轨道不平顺功率谱进行了拟合,得出了拟合曲线的特征参数.通过对测量结果进行幅值分析和功率谱分析可知,北京地铁5号线梯形轨枕轨道试验段的轨道平顺状态较好.

Dynamic analysis of rail transit elevated bridge with ladder track

In this paper,a dynamic analysis model of an elevated bridge with ladder tracks under moving train load is established.The whole process of a train running through an elevated bridge at different speeds is simulated.The dynamic responses of the elevated bridge with ladder track and the running safety and comfort index of train vehicles are evaluated.Compared with the dynamic responses of an elevated bridge with ordinary nonballasted slab track,the ladder track’s effect on reducing the vibration of an elevated bridge is analyzed.The analysis results show that the ladder track has good vibration reduction characteristics as compared to ordinary non-ballasted track.

Damage detection in steel plates using feed-forward neural network coupled with hybrid particle swarm optimization and gravitational search algorithm

Over recent decades,the artificial neural networks(ANNs)have been applied as an effective approach for detecting damage in construction materials.However,to achieve a superior result of defect identification,they have to overcome some shortcomings,for instance slow convergence or stagnancy in local minima.Therefore,optimization algorithms with a global search ability are used to enhance ANNs,i.e.to increase the rate of convergence and to reach a global minimum.This paper introduces a two-stage approach for failure identification in a steel beam.In the first step,the presence of defects and their positions are identified by modal indices.In the second step,a feedforward neural network,improved by a hybrid particle swarm optimization and gravitational search algorithm,namely FNN-PSOGSA,is used to quantify the severity of damage.Finite element(FE)models of the beam for two damage scenarios are used to certify the accuracy and reliability of the proposed method.For comparison,a traditional ANN is also used to estimate the severity of the damage.The obtained results prove that the proposed approach can be used effectively for damage detection and quantification.

Running train induced vibrations and noises of elevated railway structures and their influences on environment

The vibrations and noises of elevated railway structures have been cause for concern due to their effects on the environment and the people living near elevated lines.In this paper,the main structural features of some new elevated bridges and station hall were introduced.The generation mechanism of vibrations and noise of elevated structures induced by trains were investigated.The noise induced by different types of elevated bridges,their influences on the environment and the theoretical method for the analysis of structure borne noise was analyzed.Finally,several field measurements on train induced noises at the platforms of elevated subway stations and bridges were presented.