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Volume 33, Number 3, March 2024

The fatigue-induced sequential failure of a structure having structural redundancy requires system-level analysis to account for stress redistribution. System reliability-based design optimization (SRBDO) for preventing fatigue-initiated structural failure is numerically costly owing to the inclusion of probabilistic constraints. This study incorporates the Branchand- Bound method employing system reliability Bounds (termed the B3 method), a failure-path structural system reliability analysis approach, with a metaheuristic optimization algorithm, namely grey wolf optimization (GWO), to obtain the optimal design of structures under fatigue-induced system failure. To further improve the efficiency of this new optimization framework, an additional bounding rule is proposed in the context of SRBDO against fatigue using the B3 method. To demonstrate the proposed method, it is applied to complex problems, a multilayer Daniels system and a three-dimensional tripod jacket structure. The system failure probability of the optimal design is confirmed to be below the target threshold and verified using Monte Carlo simulation. At earlier stages of the optimization, a smaller number of limit-state function evaluation is required, which increases the efficiency. In addition, the proposed method can allocate limited materials throughout the structure optimally so that the optimally-designed structure has a relatively large number of failure paths with similar failure probability.

Key Words
failure sequence; fatigue; system reliability; system reliability-based design optimization

Department of Civil, Urban, Earth, and Environmental Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919, Republic of Korea.

To properly extract the strain components under varying operational conditions is very important in bridge health monitoring. The abnormal sensor readings can be correctly identified and the expected operational performance of the bridge can be better understood if each strain components can be accurately quantified. In this study, strain components under varying load conditions, i.e., temperature variation and live-load variation are evaluated based on field strain measurements collected from a real concrete box-girder bridge. Temperature-induced strain is mainly regarded as the trend variation along with the ambient temperature, thus a smoothing technique based on the wavelet packet decomposition method is proposed to estimate the temperature-induced strain. However, how to effectively extract the vehicle-induced strain is always troublesome because conventional threshold setting-based methods cease to function: if the threshold is set too large, the minor response will be ignored, and if too small, noise will be introduced. Therefore, an autoencoder framework is proposed to evaluate the vehicleinduced strain. After the elimination of temperature and vehicle-induced strain, the left of which, defined as the model error, is used to assess the operational performance of the bridge. As empirical techniques fail to detect the degraded state of the structure, a clustering technique based on Gaussian Mixture Model is employed to identify the damage occurrence and the validity is verified in a simulation study.

Key Words
autoencoder; early warning; Gaussian mixture model; strain measurement; structural health monitoring; strain measurement

(1) Huachen Jiang:
Shanghai Key Laboratory of Engineering Structure Safety, SRIBS, Shanghai 200032, China;
(2) Liyu Xie, Songtao Xue:
Department of Disaster Mitigation for Structures, Tongji University, Shanghai 200092, China;
(3) Da Fang, Chunfeng Wan, Shuai Gao, Youliang Ding:
Southeast University, Key Laboratory of Concrete and Prestressed Concrete Structure of Ministry of Education, Nanjing 210096, China;
(4) Kang Yang:
School of Railway Transportation, Shanghai Institute of Technology, Shanghai 201418, PR China;
(5) Songtao Xue:
Department of Architecture, Tohoku Institute of Technology, Sendai, Miyagi 982-8577, Japan.

Spline chirplet transform and local maximum synchrosqueezing are introduced to present a novel structural instantaneous frequency (IF) identification method named local maximum synchrosqueezing spline chirplet transform (LMSSSCT). Namely spline chirplet transform (SCT), a transform is firstly introduced based on classic chirplet transform and spline interpolated kernel function. Applying SCT in association with local maximum synchrosqueezing, the LMSSSCT is then proposed. The index of accuracy and Rényi entropy show that LMSSSCT outperforms the other time-frequency analysis (TFA) methods in processing analytical signals, especially in the presence of noise. Numerical examples of a Duffing nonlinear system with single degree of freedom and a two-layer shear frame structure with time-varying stiffness are used to verify the effectiveness of structural IF identification. Moreover, a nonlinear supported beam structure test is conducted and the LMSSSCT is utilized for structural IF identification. Numerical simulation and experimental results demonstrate that the presented LMSSSCT can effectively identify the IFs of nonlinear structures and time-varying structures with good accuracy and stability.

Key Words
instantaneous frequency; local maximum synchrosqueezing; local maximum synchrosqueezing spline chirplet transform; spline chirplet transform

(1) Ping-Ping Yuan, Zhou-Jie Zhao:
School of Civil Engineering and Architecture, Jiangsu University of Science and Technology, Zhenjiang, 212100, Jiangsu, China;
(2) Ya Liu:
The First Construction Engineering Company Ltd. of China Construction Second Engineering Bureau, Beijing, 100176, China;
(3) Zhong-Xiang Shen:
School of Naval Architecture and Ocean Engineering, Jiangsu University of Science and Technology, Zhenjiang, 212100, Jiangsu, China.

In this study, an electromagnetic dynamic vibration suppressor and energy harvester is designed and studied. In this system, a gear mechanism is used to convert the linear motion to continuous rotary motion. Governing equations of motion for the system are derived and validated using the experimental results. Effects of changing the main parameters of the presented system, such as mass ratio, stiffness ratio and gear ratio on the electro-mechanical behavior of system are investigated. Moreover, using so-called Weighted Cost Function, the optimum parameters of the system are obtained. Finally, it is shown that the presented electromagnetic dynamic vibration absorber not only can reduce the undesired vibration of the main system but also it can harvest acceptable electrical energy.

Key Words
dynamic vibration absorber; electromagnetic energy harvesting; gear mechanism

(1) Aref Afsharfard:
Department of Mechanical Engineering, Ferdowsi University of Mashhad, Mashhad, Iran;
(2) Hooman Zoka:
Department of Mechanical Engineering, Concordia University, Montreal, Canada;
(3) Aref Afsharfard, Kyung Chun Kim:
Eco-friendly Smart Ship Parts Technology Innovation Center, Pusan National University, Busan, South Korea.

Safety and structural integrity of civil structures, like bridges and buildings, can be substantially enhanced by employing appropriate structural health monitoring (SHM) techniques for timely diagnosis of incipient damages. The information gathered from health monitoring of important infrastructure helps in making informed decisions on their maintenance. This ensures smooth, uninterrupted operation of the civil infrastructure and also cuts down the overall maintenance cost. With an early warning system, SHM can protect human life during major structural failures. A real-time online damage localization technique is proposed using only the vibration measurements in this paper. The concept of the 'Degree of Scatter' (DoS) of the vibration measurements is used to generate a spatial profile, and fractal dimension theory is used for damage detection and localization in the proposed two-phase algorithm. Further, it ensures robustness against environmental and operational variability (EoV). The proposed method works only with output-only responses and does not require correlated finite element models. Investigations are carried out to test the presented algorithm, using the synthetic data generated from a simply supported beam, a 25-storey shear building model, and also experimental data obtained from the lab-level experiments on a steel I-beam and a ten-storey framed structure. The investigations suggest that the proposed damage localization algorithm is capable of isolating the influence of the confounding factors associated with EoV while detecting and localizing damage even with noisy measurements.

Key Words
damage localization; environmental and operational variability; fractal dimension; laboratory framed structure; model-free SHM; shear building

CSIR-Structural Engineering Research Centre, CSIR Campus, Taramani, Chennai-600113, Tamilnadu, India.

Modeling of vibrations of a rotating pendulum with working shape memory alloy rod has been performed in the frames of a microstructural model taking into account the latent heat release, absorption and the heat exchange during direct and reverse martensitic transformation. It has been shown that the influence of the latent heat, the rate of preliminary deviation of the pendulum from the equilibrium, the rate of heating and cooling can have a significant impact on the vibrations and damping characteristics of the system.

Key Words
damping; heat exchange conditions; latent heat; microstructural modeling; shape memory alloys; TiNi; vibration protection

(1) Fedor S. Belyaev:
Laboratory of Mathematical Methods in Mechanics of Materials, Institute for Problems in Mechanical Engineering of the RAS, V.O., Bolshoj pr. 61, St. Petersburg, 199178, Russia;
(2) Fedor S. Belyaev, Margarita E. Evard, Aleksandr E. Volkov, Maria S. Starodubova:
Saint Petersburg State University, Universitetskaya Nab. 7-9, St. Petersburg, 199034, Russia.

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