Structural health monitoring

About: Structural health monitoring is a research topic. Over the lifetime, 11727 publications have been published within this topic receiving 186231 citations.

A Review of NDT/Structural Health Monitoring Techniques for Hot Gas Components in Gas Turbines

Abstract: The need for non-destructive testing/structural health monitoring (SHM) is becoming increasingly important for gas turbine manufacturers. Incipient cracks have to be detected before catastrophic events occur. With respect to condition-based maintenance, the complex and expensive parts should be used as long as their performance or integrity is not compromised. In this study, the main failure modes of turbines are reported. In particular, we focus on the turbine blades, turbine vanes and the transition ducts of the combustion chambers. The existing monitoring techniques for these components, with their own particular advantages and disadvantages, are summarised in this review. In addition to the vibrational approach, tip timing technology is the most used technique for blade monitoring. Several sensor types are appropriate for the extreme conditions in a gas turbine, but besides tip timing, other technologies are also very promising for future NDT/SHM applications. For static parts, like turbine vanes and the transition ducts of the combustion chambers, different monitoring possibilities are identified and discussed.

Application of low-profile piezoceramic transducers for health monitoring of concrete structures

Abstract: Using piezoceramic patches bonded on concrete beams to perform structural health monitoring is investigated in this paper. To evaluate the performance of piezoceramic sensors and ultrasonic wave methods, two series of tests were carried out on 100×100×500 mm 3 concrete prisms. In the first series of tests, the influence of the frequency of the input signal on the waveforms was investigated and the optimum frequency to generate ultrasonic waves was evaluated. From the velocity of Rayleigh waves and longitudinal waves, the dynamic modulus of elasticity and dynamic Poisson's ratio of the concrete were obtained. In the second series, the effect of uniaxial compressive stress and the resulting internal cracking of the concrete on the amplitude of the waveforms received by piezoceramic sensors was investigated. It is shown that differences in amplitude between two wave packets are sensitive to the cracking process of concrete with externally applied loads. The results confirm that piezoceramic sensors and corresponding ultrasonic waves methods have the potential to monitor cracking and the long-term deterioration of concrete structures.

Influence of axial loads on the health monitoring of concrete structures using embedded piezoelectric transducers

Abstract: Piezoceramic-based smart aggregate has been widely used to evaluate early-age concrete strength and to detect damage in concrete structures. In these structural health monitoring systems, they are generally verified and calibrated through experiments under load-free condition. However, the stress levels of actual concrete members are different. The microstructures of concrete will change with the variation of external load, and the high-frequency waves used in the monitoring system may be highly sensitive to these changes. In this study, the effects of axial compressive loading on the monitoring results are investigated. Specifically, three loading cases, that is, single cycle load, cyclic load, and step-by-step load, are employed to stress the concrete specimens embedded with smart aggregates. The amplitude and velocity of monitoring signals were measured before, during, and after each loading case. The test results show that the axial load lower than 30% of failure load still have a significant impact on the received signals. The amplitude attenuation is dependent on both frequency and load history, while the velocity is highly stress-dependent. The results indicate that the baselines of monitoring signals obtained from the same concrete structure in its healthy state can vary under different stress levels. The axial load variation should be carefully considered during the monitoring process. This study also provides a potential method to assess stress state in concrete structures using smart aggregates.

Analysis of non-stationary structural systems by using a band-variable filter

Abstract: One of the main tools used to study the dynamic response of structural systems is certainly the Fourier Transform. This tool is very useful and reliable to investigating the response of a stationary system, i.e. a generic system that does not changes its characteristics over time. Conversely, the Fourier Transform is no longer reliable if the main goal is to study the evolution of the dynamic response of a system whose features rapidly vary with time. To this regard, several mathematical tools were developed to analyze time-variable dynamic responses. Soil and buildings, subject to transient forcing such as an earthquake, may change their characteristics over time with the initiation of nonlinear phenomena. This paper proposes a new methodology to approach the study of non-stationary response of soil and buildings: a band-variable filter based on S-Transform. In fact, with the possibility of changing the bandwidth of each filtering window over time, it becomes possible to extract from a generic record only the response of the system focusing on the variation of individual modes of vibration. Practically, it is possible to extract from a generic non-stationary signal only the phase of interest. The paper starts from examples and applications on synthetic signals, then examines possible applications to the study of the non-stationary response of soil and buildings. The last application focuses on the possibility to evaluate the mode shapes over time for both numerical and scaled model subjected to strong motion inputs.

Vision-Based Bridge Deformation Monitoring

Abstract: Optics-based tracking of civil structures is not new, due to historical application in surveying, but automated applications capable of tracking at rates that capture dynamic effects are now a hot research topic in structural health monitoring. Recent innovations show promise of true non-contacting monitoring capability avoiding the need for physically attached sensor arrays. The paper reviews recent experience using the Imetrum Dynamic Station (DMS) commercial optics-based tracking system on Humber Bridge and Tamar Bridge, aiming to show both the potential and limitations. In particular the paper focuses on the challenges to field application of such a system resulting from camera instability, nature of the target (artificial or structural feature) and illumination. The paper ends with evaluation of a non-proprietary system using a consumer grade camera for cable vibration monitoring to emphasise the potential for lower cost systems where if performance specifications can be relaxed.