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By using a piezoelectric actuator, a real steel bridge can be accelerated locally to detect the effect of small damage like fatigue crack and connection damage as a response to change of vibration. Power spectrum density (PSD) function of the response can give us the indication of the extent of damage before and after the damage. Detailed analysis of PSD before and after damage can give us the location and size (area) of damage. This paper shows the experimental result of damage detection by using local excitation method on a real bridge.

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

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.

This paper presents structural damage detection method based on changes in Transfer Function Estimate (TFE) for detecting damage, predicting its location and monitoring the growth in damage. This method assumes that the displacement or the acceleration response time histories at various locations along the structure both before and after damage are available for damage assessment These responses are used to estimate TFE. The change of TFE between the baseline state and the current state is then used to identify the location of possible damage in the structure. TI1e method is applied to the experimental and numerical data obtained from a railway steel bridge that is no longer in service. Several damage scenarios were introduced to the main girder of the test structure. Results show the method can be used to detect the damage, determine the exact location and measure the growth in damage with very good accuracy. The use of piezoelectric actuators as a local excitation source for large structures such as steel bridges is also presented. Experimental and numerical results show that the proposed approach may be successfully implemented on-line to detect the damage and to locate regions where damage occurred., application/pdf

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 ferro...

The sophisticated arrangement of confinement in columns using closely spaced stirrups not only interrupts the continuity and creates a plane of weakness between core and concrete cover, but also adds to the problem of congestion. This is the reason why most of the time it may not be possible to confine the structure sufficiently by providing laterals alone, and supplementary confinement such as ferrocement composites may be necessary. The success of the ferrocement technology is attributed to the ready availability of its component materials, low level of technology needed for construction and low cost. In the past decades, ferrocement has emerged as a very good rehabilitating/restrengthening material because of its superior mechanical properties, high in-plane strength and mouldability. In the present paper a review of the research on ferrocement confinement of plain and reinforced concrete with applications to column retrofitting is presented.

In order to obtain a physical interpretation of experimental data obtained in ultrasonic-acoustic measurements, we simulate the experiment by numerical calculation on a supercomputer. The composite we discuss here is a two dimensional rectangular beam which has one reinforcement layer located at middepth. The Finite Strip Method (FSM) is used to formulate the composite and modal analysis and Duhatnel integral equation are also used to obtain its dynamic response for the impulsive incident wave. Making use of the Visualization Technique of Stress Wave Propagation (VTSWP) we obtain the animated simulation of stress wave propagation in a composite. The effect of gradient distribution of the stiffness in the interphase layer on the wave energy transmission from matrix to fiber is also analyzed as an amplitude transmission coefficient (ATC).

A wavelet-based technique is proposed for structural damage detection and health monitoring. In this technique, characteristics of representative vibration signals under the wavelet transformation are examined for damage identification. The proposed method is based on only the output data without the need for measuring the excitation forces, any modal identification or numerical models. The method is described theoretically and verified both experimentally and numerically using a railway steel bridge. The applicability of utilizing piezoelectric actuators for exciting large structures such as steel bridges is also investigated in this paper. Several damage scenarios were introduced to the test structure by removing bolts from some stiffeners located on the web of the main girder. Similar damage scenarios were introduced to the finite element model of the test structure. The results indicate that the current approach can identify the location of small damage effectively. The proposed method combined with the use of piezoelectric actuators is shown to be very suitable for continuous health monitoring of steel bridges. Copyright © 2009 John Wiley & Sons, Ltd.

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.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.