A data-driven approach based on wavelet analysis and deep learning for identification of multiple-cracked beam structures under moving load

Coastal environmental changes in Southeast Asia: A study from Quang Nam Province, Central Vietnam

This research proposes a correlation coefficient for detecting and evaluating defects in beams, which brings about a positive outcome in terms of accuracy and efficiency. This parameter surpasses other parameters, such as natural frequency and damping coefficient, thanks to its sensitivity to structural changes. Our results show that although the damping coefficient had more variation than the natural frequency value in the same experiment, its changes were insufficient and unstable at different levels of defects. In addition, the proposed correlation coefficient parameter has a linear characteristic and always changes significantly according to increasing levels of defects. The results outweigh damping coefficient and natural frequency values. Furthermore, this value is always sensitive to measurement channels, which could be an important factor in locating defects in beams. The testing index is statistically evaluated by a normal distribution of the amplitude value of vibration measurement signals. Changes and shifts in this distribution are the basis for evaluating beam defects. Thus, the suggested parameter is a reliable alternative for assessing the defects of a structure.

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Detecting and Evaluating Defects in Beams by Correlation Coefficients

In this paper, we investigate changes in the mechanical properties of complex structures using a combination of the discrete model, Fast Fourier Transform (FFT) analysis and deep learning. The first idea from this research utilizes the discrete model from a perspective that is different from the finite element method (FEM) of previous works. As the method in this paper only models the mechanical properties of structures with finite degrees of freedom instead of dividing them into smaller elements, it reduces error in evaluation and produces more realistic results compared to the FEM model. Another advantage is how it allows the research to survey both parameters that affect the mechanical properties of structures—the overall stiffness (K) and the damping coefficient (c)—during vibration, while previous researches focus only on one of these two parameters. The second idea is to use FFT analysis to increase the sensitivity of the signal received during vibration. FFT analysis simplifies calculations, thereby reducing the effect of noise or errors. The sensitivity achieved in FFT analysis increases by 25% compared to traditional Fourier Transform (FT) analysis; moreover, the error in FFT analysis compared to experimental results is quite small, less than 2%. This shows that FFT is a suitable method to identify sensitive characteristics in evaluating changes in the mechanical properties. When FFT is combined with the discrete model, results are much better than those of several existing approaches. For the last idea, the manuscript applies deep learning (FFT-deep learning) in the noise reduction process for the original data. This makes the results much more accurate than in previous studies. The results of this research are shown through the monitoring of spans of the Saigon Bridge—the biggest and most important bridge in Ho Chi Minh City, Vietnam—during the past 11 years. The correspondence between the theoretically obtained result and the experimental one at the Saigon Bridge suggests a new area for development in evaluating and forecasting structural changes in the future.

A Data-Driven Approach to Structural Health Monitoring of Bridge Structures Based on the Discrete Model and FFT-Deep Learning

We propose a novel representative power spectrum density as a specific characteristic for showing responses of spans during a long operational period. The idea behind this method is to use the representative power spectrum density as a powerful tool to evaluate the stiffness decline of spans during their operation period. In addition, a new measurement method has been introduced to replace the traditional method of monitoring the health conditions of bridges through a periodic measurement technique. This helps to reduce costs when carrying out testing bridges. Besides, the proposed approach can be widely applied not only in Vietnam but also in many other underprivileged countries around the world. Obtained results show that, during the operational process of spans, there is not only a pure vibration evaluation such as bending vibration and torsion vibration tests but also a combination of various vibration types including bending-torsion vibration or high-level vibrations like first-mode bending and first-mode torsion. Depending on each type of structure and material properties, different types of vibrations will appear more or less during the operational process of spans under a random moving load. Furthermore, the representative power spectrum density is also suitable for evaluating and determining many different fundamental vibrations through the same measurement time as well as various measurement times.

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A New Insight to Vibration Characteristics of Spans under Random Moving Load: Case Study of 38 Bridges in Ho Chi Minh City, Vietnam

A novel approach based on viscoelastic parameters for bridge health monitoring: A case study of Saigon bridge in Ho Chi Minh City – Vietnam

A Correlation Coefficient Approach for Evaluation of Stiffness Degradation of Beams Under Moving Load

This paper introduces a newly proposed “loss factor function (LF)” and its application to bridge condition assessment based on the structure monitoring data. First, a viscoelastic model is integrated in the equation of motion of a beam. In this model, material characteristics contained two components such as elastic modulus and viscous coefficient. Viscoelastic model, different with linear elastic model, is nonlinear, and therefore, it reflects real state of the structure precisely. Secondly, LF is calculated from amplitudes and frequencies of power spectral density of random vibration signals and is concerned with mechanical parameters in detecting structural changes. Vibration of beams was investigated in case different random excitations are used to simulate ambient load in the process of varying material properties. Based on theoretical analysis and simulation result, this study reveals more effective in condition assessment of structure.

A Novel Proposal in Using Viscoelastic Model for Bridge Condition Assessment

Erosion and rising sea level represent important challenges to the Vietnamese society, especially around coastal areas in the middle of the country. A significant length of this coastline has been protected by coastal revetments against natural disasters. Further increases in sea levels will allow higher waves to reach the coastline and thus, will require coastal defenses and breakwaters to be reinforced and strengthened. In this paper, the authors attempt to describe the current erosion situation that has been observed and learned at Cua Dai Beach, which is located in Central Vietnam. The GIS application with satellite images is also used to estimate how coastlines suffer from erosion and other disasters. The effect that future sea level rise might have on coastal structures in Cua Dai Beach is investigated by calculating the expansion in cross section and armor units under several scenarios of sea level rise.

Thao D. Nguyen

Papers

A novel approach based on viscoelastic parameters for bridge health monitoring: A case study of Saigon bridge in Ho Chi Minh City – Vietnam

A Correlation Coefficient Approach for Evaluation of Stiffness Degradation of Beams Under Moving Load

A New Insight to Vibration Characteristics of Spans under Random Moving Load: Case Study of 38 Bridges in Ho Chi Minh City, Vietnam

A Novel Proposal in Using Viscoelastic Model for Bridge Condition Assessment

Coastal Erosion in Cua Dai Beach: Future Influence of Climate Change and Sea Level Rise on Coastal Protection