Shuichi Mikami

Wavelet packet based damage detection in beam-like structures without baseline modal parameters

In this paper, a new approach for damage detection in beam-like structures is presented. The method can be used without the need for baseline modal parameters of the undamaged structure. Another advantage of the proposed method is that it can be implemented using a small number of sensors. In the proposed technique, the measured dynamic signals are decomposed into the wavelet packet decomposition (WPD) components, the power spectrum density (PSD) of each component is estimated and then a damage localisation indicator is computed to indicate the structural damage. The proposed method is firstly illustrated with a simulated beam and the identified damage is satisfactory with assumed damage. Then, the method is applied to a steel beam. The effect of damage location and the effects of wavelet type and the decomposition level are examined. The results show that the proposed method has great potential in crack detection of beam-like structures.

Damage identification in a lightly reinforced concrete beam based on changes in the power spectral density

This paper deals with the detection of damage in a lightly reinforced concrete beam using dynamic measurements. An algorithm based on changes in the power spectral density (PSD) is presented. The algorithm is used to detect damage, predict the location and assess the extent of damage in the reinforced concrete beam. The method is based on the measured data on the beam after introducing some damage at salient locations. A tuneable piezoelectric actuator was used to produce additional peaks in the dynamic response of the system in the frequency domain. These additional peaks were adjusted over the frequency band by tuning the actuator. It was noticed from the results, that the PSD method detected the damage, determine the location and could monitor the increase in damage in the beam

Seismic retrofit of square reinforced concrete piers by ferrocement jacketing

An experimental investigation was conducted to strengthen shear deficient reinforced concrete columns using ferrocement jacketing. Three scale model specimens, identical to the actual bridge piers, were tested. One of the piers was tested under as-built condition while the other two were strengthened with layers of wire mesh before being tested. All the specimens were subjected to a simulated seismic loading and constant axial load. It was observed from the experimental results that the ferrocement-jacketed specimens exhibited enhanced stiffness, strength, energy dissipation and ductility and the mode of failure changed from brittle shear failure to a ductile flexural failure. The control specimens failed by shear at a relatively low lateral displacement. A finite element model was developed and the results obtained from the numerical analysis compared well with the experimental results. A design methodology for strengthening piers with square/rectangular columns with inadequate shear strength using ferrocement jackets is also presented.

Application of smart materials and systems to long-term bridge health monitoring

An efficient monitoring system is essential to avoid catastrophic structural failure and reduce retrofit cost on structures at aging time. The objective of this paper is to develop a diagnostic system to monitor structural integrity of bridge by stain sensing using fiber optic sensor (FOS). A number of laboratory tests were carried out in the process of this research for steel and concrete members with attached and embedded type fiber optic sensors. Strain data obtained from cracked area as an estimation of crack propagation and survivability performance of fiber optic sensor due to cyclic loading experience are concerned. Electrical strain gages co- located with fiber optic sensor to verify functioning of fiber optic sensor and finally compared results obtained from both sensors with numerical calculations. Our research results revealed that, fiber optic sensor and strain gage respond same way at transition zone and significant variation in strain response observed when crack propagates from notch tips. In this series of investigation by bringing new experimental system about fatigue crack evaluation and wireless health monitoring we could develop smart system to apply to field assessment.

Damage Identification for Civil Infrastructure Employing a Strain Energy Based Approach

The identification of structural damage is an essential goal of health monitoring for civil infrastructures. Damage of a structure reflects on a change of modal parameters, such as natural frequencies, mode shapes and modal damping. A method of damage identification for civil infrastructures based on strain energy is proposed in this paper. The method is described theoretically and applied to the experimental data from a steel bridge. Several damage scenarios were introduced to the members of the test structure. Experimental results show that the proposed approach may be successfully implemented to detect damage and to locate regions where damage occurred. This research also aims at establishment of experimental environment to enable the verification of applicability and the effective evaluation of the structural health monitoring (SHM) technology that uses the high performance sensor system on real bridges. The primary goal of the project is the development of test beds that meet wider requests for SHM experiments. Several steel bridges on an abolished railway in Hokkaido, Japan will be available for the establishment of the test beds. The test beds can be utilized by not only researchers of this project but also other researchers. The final goal of the project is international contribution by means of cooperative utilization of the test beds.

Accuracy Improvement of Ultrasonic Inspection for Civil Structures and Materials

When we want to extend the life of an actual infrastructure and improve its serviceability adjusting the change of environmental situation, we need to evaluate its structural integrity quantitatively by using an appropriate inspection procedure on it. It is, therefore, important for a civil engineer to set up an effective inspection procedure to get the quantitative integrity evaluation of an infrastructure. The procedure of inspection for an infrastructure in Japan is divided into two types, that is, a periodical inspection and occasional (eventwise) inspection just after an earthquake. Inspector is chosen to have his experience career as a civil engineer more than 5 years and inspects infrastructures to classify the integrity level by five ranks on the each part of the structure by using the visual inspection according to the inspection manual tentatively provided by the Public Works Research Institute, Ministry of Construction. In the case if an inspector found any important damage or defect by the visual inspection, the precise inspection will be done by using a nondestructive testing to evaluate the size, shape and location of the damage or defect on the infrastructure. And if we could identify the damage or defect with an accurate information, we can evaluate its remaining life time by means of fracture mechanics and fatigue analysis and decide whether the damage or defect will propagate further or not. Thus we can, eventually, evaluate the structural integrity of the infrastructure by using the analysis of quantification theory [3] to classify the structures into four groups of integrity as A (Keep Watching), B (Need Small Repair), C (Need Large Repair) and D (Need Replace or Reconstruction).

Imaging of Small Defect and Fracture Process Zone by Using Scientific Visual Analysis in Ultrasonic Inspection

When we diagnose the structural integrity of a material in service and evaluate its remaining life time, we need to improve analyzing method to get the accurate information for a internal damage of a material. And by the recent demand for high level quality control of structural joint the accuracy improvement of detected image became essential in nondestructive evaluation (NDE)1. So far several methods like X-ray, EMAT and ultrasonics are used to detect an internal defect and 3D image of a damage is obtained only by CAT scan method of X-ray inspection.

EVALUATION METHOD IN MAINTENANCE INSPECTION OF A BRIDGE BY MEANS OF COMPUTER GRAPHICS AND QUANTIFICATION THEORY

橋梁の維持点検データに基づいて健全度を診断する手法として数量化理論とコンピュータ・グラフィクスを組み合わせた解析方法を提案した. 橋梁健全度の総合評価を機能的評価と物理的評価に大別し, 機能的健全度評価においては幅員, 線形, 交通混雑度など7項目のアイテム, また物理的健全度評価においては主部材, 床版など17項目のアイテムを設定して数量化理論による解析を行っている. またコンピュータ・グラフィクスの 3D Rotation 法を用いて評価の解析結果を明確に表示できることを示した.

Accuracy Improvement of Small Defect Detection for Ultrasonic Inspection by Using Scientific Visual Analysis

When we diagnose the structural integrity of a steel member in service and evaluate its remaining life time, we need to improve analyzing method to get the accurate information of a internal defect of a member. And by the recent demand for high level quality control of welding of steel joint the accuracy improvement of defect detection in the image display became essential in nondestructive evaluation (NDE)[1][2][3]. So far the defect information obtained by an ultrasonic test is displayed in several ways and A-scan and B-scan displays are commonly used in a field inspection and C-scan display is used in laboratory test of the steel structural member[4][5].