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CONTENTS
Volume 95, Number 6, September25 2025
 

Abstract
Vibration-based structural damage detection offers a practical method for timely and remotely identifying existing damages in structures before they grow to irrecoverable failures. Nevertheless, challenges such as handling high-dimensional vibration signals, limited data on diverse damage scenarios, and unavoidable environmental and operational confounding factors complicate its application. To tackle these challenges, advanced pattern recognition approaches, particularly, deep-learning models, have become increasingly attractive to structural engineers, thanks to their ability to learn hidden complex patterns within high-dimensional data and map them to structural states. This study conducts a comprehensive comparative analysis of seventeen machine learning/deep learning models for structural damage detection. These models are evaluated using several benchmarks, including numerical and experimental databases ranging from relatively simple beams to complex multi-story frame structures. A modular workflow is designed to ensure a fair comparison, incorporating consistent training/testing splits, hyperparameter optimization, and measurement metrics for assessing model performance, computational time, model complexity, and robustness. Results reveal that modern convolution-based models such as ResNet and FCN consistently emerge as top-performing models, whereas a 1D convolutional neural network demonstrates a notable balance across various perspectives. Transformer-based models, due to their complexity, may not be as practical as machine learning models for structural engineering applications.

Key Words
deep learning; signal processing; structural dynamic; structural health monitoring; vibration data

Address
Truong-Thang Nguyen, Viet-Hung Dang, Trung-Hieu Nguyen, Ngoc-Lam Pham, Quang-Huy Nguyen and Tien-Dung Nguyen: Faculty of Building and Industrial Construction, Hanoi University of Civil Engineering, Hanoi, Vietnam

Abstract
Beams on elastic foundations (BEFs) play a crucial role in modeling many mechanical and civil structures. These beams are often subjected to repetitive loads, like those in railway tracks, or extreme environmental conditions, making them prone to damage such as cracks and corrosion. Additionally, beams may be connected by weakened joints, which can lead to premature failure under reduced buckling loads. Currently, the weakened BEFs (W-BEFs) are modeled as two separate BEFs linked by a spring at the weakened joint. The existing Beam-Spring Model (BSM) requires solving two coupled differential equations through iterative methods, limiting computational efficiency. This work presents a novel Equivalent Moment System (EMS) that replaces weakened joints with concentrated moments, reducing the problem to a single governing equation and enabling closed-form solutions, addressing a critical gap in existing analytical approaches. Beyond W-BEFs, the EMS framework offers a generalizable approach for modeling discontinuities in other mechanical and structural systems. Focusing on pin-ended beams subjected to uniform lateral loading, this study investigates the effects of key parameters, including beam bending stiffness, beam length, weakening location and intensity, and elastic foundation stiffness, on stability and deflection behavior. Results show that as beam length or foundation stiffness increases, the elastic foundation carries more load, causing mid-span deflections to stabilize. When the weakened section of the beam is located within this stabilized deflection region, its effect on overall beam deflection becomes minimal. Furthermore, it was observed that the buckling capacity is most sensitive to weakening in high-moment regions, though foundation stiffness partially mitigates this reduction. The results from the derived solution are compared with those from benchmark problems and finite element models, demonstrating its high accuracy.

Key Words
closed-form solution; differential equation; elastic foundation; equivalent moment technique; structural stability; weakened beam

Address
Vahid Akrami and Tooba Makaremi: Faculty of Engineering, University of Mohaghegh Ardabili, Ardabil, Iran

Abstract
Tuned mass dampers (TMDs) are widely adopted for vibration control of tall engineering structures subjected to lateral loads such as earthquakes and winds. Although the design, implementation, and performance of TMD for structural vibration control have been widely investigated in the literature, determining the optimum parameters of TMD is contested. As an example, disregarding the effects of soil-structure interaction (SSI) may result in suboptimal design parameters of TMDs, especially for tall buildings. This is why soil structure parameters were recently considered for a more realistic optimum design of TMDs. Nevertheless, because of the unpredictable variations in soil's mechanical characteristics, assessing the reliability of the system necessitates addressing a probabilistic problem. In this paper, the optimum design of TMD parameters is performed in a deterministic and probabilistic framework employing metaheuristic techniques and optimization approaches based on reliability in design. The objective function of this study is the transfer function of the top story displacement. Mass, stiffness, and damping of the TMD are considered as design variables. An enhanced metaheuristic algorithm is comparatively employed to find the most efficient solution of the deterministic optimization problem. Finally, the TMD optimum parameters considering uncertainty in soil parameters are identified by a novel double-loop combination of reliability-based design optimization (RBDO) and Big-Bang Big-Crunch optimization (BB-BC). The effectiveness of the proposed procedure is assessed concerning a 40-story shear building equipped with TMD, considering soil-structure interaction. Numerical results show that the uncertainty in soil-structure interaction significantly affects the optimum design of TMD for tall buildings. The accuracy of the proposed RBDO method is validated by performance indexes under some natural ground motions.

Key Words
metaheuristics; optimum design; reliability-based design optimization; soil-structure interaction; tuned mass damper; uncertainty

Address
Touraj Heydari: Department of Civil Engineering, Mahabad Branch, Islamic Azad University, Mahabad, Iran
Bahman Farahmand Azar: Faculty of Civil Engineering, University of Tabriz, Tabriz, Iran
Omid Haddad: Department of Civil Engineering, Mahabad Branch, Islamic Azad University, Mahabad, Iran

Abstract
Compressive strength (fc) evaluation of concrete traditionally relies on non-destructive tests (NDT) such as ultrasonic pulse velocity and rebound hammer number, or their combination, known as SonReb. However, the accuracy of these methods is influenced by concrete conditions. Digital image processing (DIP) techniques have emerged as less sensitive alternatives to these conditions. In this paper, a novel approach that combines NDT and DIP to establish a reliable and generalizable relationship for estimating the fc of concrete is presented. 135 cylindrical samples were prepared, allowing NDT, compressive tests, and DIP feature extraction from their cut surfaces. The results were used to train and validate a regression model for estimating fc. Additionally, similar tests were conducted on cores, with a diameter of 95 mm, drilled from three levels of two column specimens, with a dimension of 1800x300x300 mm, to test the generalizability of the proposed equations in structural elements. The findings revealed that the innovative combination of conventional NDT and DIP outperforms SonReb in estimating fc, with R2 values of 0.90 and 0.94 for training and validation, respectively, compared to SonReb's R2 values of 0.83 and 0.91. Furthermore, the proposed model estimated the fc of cores with R2=0.88.

Key Words
concrete column; concrete strength assessment; digital image processing; non-destructive test; Schmidt rebound hammer; SonReb; ultrasonic pulse velocity

Address
Hassan Araghi, Rahmat Madandoust and Meysam Effati: Department of Civil Engineering, University of Guilan, 5th Kilometer of Persian Gulf Highway, Rasht, Guilan, Iran

Abstract
This study presents a comprehensive numerical analysis of Un-Reinforced Masonry (URM) walls retrofitted with Fiber-Reinforced Polymer (FRP) materials under in-plane static cyclic loading. Utilizing a three-dimensional macro-modeling approach, the research investigates the influence of various retrofitting configurations, wall geometries, and FRP ply counts on seismic performance. The finite element model, developed in ANSYS, incorporates the SOLID65 and SHELL181 elements with the Tsai-Wu failure criterion to simulate complex failure mechanisms in both masonry and FRP layers. Model verification was conducted using experimental data from ElGawady et al. (2004), demonstrating a strong correlation. Parametric studies revealed that full-coverage and H-frame FRP configurations significantly enhance lateral load capacity, energy dissipation, and ductility. The results provide practical insights into efficient retrofitting strategies for seismic upgrading of masonry structures.

Key Words
finite element modeling; GFRP; retrofitting; static cyclic loading; Tsai-Wu criterion; un-reinforced masonry wall

Address
Majid Farrin: Department of Civil Engineering, Ara.C. Islamic Azad University, Jolfa, Iran

Abstract
The increasing deployment of autonomous systems, such as autonomous underwater vehicles (AUVs), highlights a critical need for robust and efficient recovery mechanisms. A significant challenge in extended autonomous operations is the limited onboard battery capacity, which necessitates reliable docking solutions. This paper presents a transformable underwater docking mechanism based on origami-inspired deployable and bistable structures, which can be mounted on a submarine. The proposed docking station system is divided into two components, which are the deployable funnel, and the landing station, respectively. The deployable funnel and landing station employe the Sarrus linkage and bistable structure, respectively. Additionally, the applied structures help reduce the burden on system control, enabling the use of a minimal number of actuators. The grasping forces of both components are analyzed, and the structural stability is simulated. The performance of the proposed mechanism is verified by conducting five underwater docking experiments in a circulation water tunnel with a free-stream velocity of 0.6 m/s.

Key Words
autonomous underwater vehicle; bistable structure; origami; Sarrus linkage; transformable mechanism; underwater docking

Address
Gagyeong Park, Ki-Hoon Lee, Sung-Jin Lee, Seongjun Lee, Dae-Young Lee: Department of Aerospace Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
Minseop Lee, Daegyoum Kim: Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea

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