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CONTENTS
Volume 96, Number 2, October25 2025
 

Abstract
This study presents a comprehensive investigation of vibrational behavior in multi-walled carbon nanotube (MWCNT) reinforced glass fiber reinforced polymer (GFRP) composite plates featuring multiple delaminations using explainable artificial intelligence techniques. A displacement-based finite element model incorporating third order shear deformation theory (TSDT) was developed to analyze natural frequencies and modal damping factors in composite plates with double and triple delamination configurations. The mathematical framework considers 12-ply symmetric laminate configurations [(0/90)3]s with clamped boundary conditions, examining 71,280 systematic cases for double delamination and 109,200 cases for triple delamination across six interfaces. The finite element analysis reveals complex frequency-damping interdependencies where MWCNT reinforcement (0.005-0.01 wt%) consistently increases natural frequencies by 1.751-3.53% while simultaneously reducing modal damping factors by 3.003-7.484%. Double delamination configurations exhibit frequency ranges from 134.8-174.82 Hz, while triple delamination scenarios demonstrate more severe degradation with frequencies spanning 124.44-168.75 Hz, representing up to 26.3% reduction between optimal and damage locations. To overcome computational challenges associated with extensive parametric studies, an advanced machine learning framework was implemented using XGBoost regression models achieving exceptional performance with R2 values of 0.993 for natural frequency predictions and 0.997 for modal damping factor predictions for double delaminated case. The explainable AI implementation through SHAP and LIME analysis reveals that interface position dominates frequency behavior while MWCNT concentration significantly influences damping characteristics. The framework enables rapid dual-parameter predictions in less than 0.001 seconds compared to 45 minutes required for finite element analysis, facilitating efficient design space exploration and multi-objective optimization for damage-tolerant composite structures in aerospace, automotive, and marine applications.

Key Words
explainable-AI; FEM; modal damping; multi-delamination; MWCNT; natural frequency

Address
Dhivya Elumalai: Department of Civil Engineering, Greater Noida Institute of Technology, AKTU, Greater Noida, 201310, India
Mohit Gupta: Department of Civil Engineering, Greater Noida Institute of Technology, AKTU, Greater Noida, 201310, India
Ananda B. Arumugam: Department of Mechanical Engineering, SoET, DIT University, Dehradun, Uttarakhand, 248009, India
Muthukumaran Gunasegeran: Project Division, Imeconsys Private limited, Puducherry, 605004, India
Amrita: Center for Cyber Security and Cryptology, CSE, SSCSE, Sharda University, Greater Noida, 201310, India

Abstract
The sliding between the concrete slab and steel beam reduces the flexural bearing capacity of the steel-concrete composite beam. To obtain the flexural bearing capacity of the composite beam, the method based on the equivalent coefficient of compressive area (ECCA) of the concrete slab was proposed in this paper. Finite element models of the composite beams were established to investigate the effects of different parameters on the ECCA of the concrete slab and yield area ratio of the steel beam. The results indicated that the ECCA of the concrete slab, in the partial shear connected composite beam, is mainly affcted by the degree of shear connection and the sliding between the concrete slab and steel beam. The ECCA increases with the increasing of the degree of shear connection, and the ECCA was fitted. In the full and partial shear-connected composite beam, the steel beam is in a full section yield status under ultimate bending load. Comparing the formulas proposed in this paper with those in other literature, this method has a high accuracy and simple form in predicting the flexural bearing capacity of the full and partial shear connected steel-concrete composite beam.

Key Words
degree of shear connection; equivalent coefficient of compressive area; flexural bearing capacity; steelconcrete composite beam; yield area ratio

Address
Hu Ding: School of Civil Engineering, Central South University, 22 South Shaoshan Rd., Changsha, Hunan Provinve, China; Hunan No.6 Engineering Co., Ltd., 788 West Laodong Rd., Changsha, Hunan Province, China
Faxing Ding: School of Civil Engineering, Central South University, 22 South Shaoshan Rd., Changsha, Hunan Provinve, China; Engineering Technology Research Center for Prefabricated Construction Industrialization of Hunan Province, 22 South Shaoshan Rd., Changsha, Hunan Provinve, China
Chang He: School of Civil Engineering, Central South University, 22 South Shaoshan Rd., Changsha, Hunan Provinve, China
Liping Wang: School of Civil Engineering, Central South University, 22 South Shaoshan Rd., Changsha, Hunan Provinve, China
Fei Lyu: School of Civil Engineering, Central South University, 22 South Shaoshan Rd., Changsha, Hunan Provinve, China

Abstract
In this study, the effectiveness of reinforcement with steel diagonal elements in a reinforced concrete building was investigated. A typical reinforced concrete building with ground floor+4 floors was designed for the numerical study. All column dimensions were 400x400 mm, all beam dimensions were 250x500 mm, transverse reinforcement spacing in column and beam elements was 100 mm and floor heights were 3 meters. The existing building was strengthened with X steel diagonal elements and two models were obtained. Nonlinear static pushover and incremental dynamic analyses of the buildings were performed. 11 earthquake records were used for incremental dynamic analyses. The acceleration amplitudes of these records were increased from 0.1 g to 1.0 g by 0.1 g and the analyses were performed. In order to model the nonlinear behaviour, lumped plastic hinges were assumed at the ends of the structural elements. As a result of nonlinear static pushover and incremental dynamic analyses of the buildings, capacity curves, maximum responses, inter-storey drifts, hysteretic curves at the ends of selected columns and damage patterns were obtained. Fragility curves were created by considering the damage levels in the buildings. According to the results, the average inter-storey drifts of the building strengthened using X steel diagonal elements decreased by approximately 90% compared to its current condition for 1.0 g PGA, while the damage probability and vibration period were also significantly reduced. In addition, the base shear force encountered by the strengthened building increased more than 4 times compared to its current condition.

Key Words
fragility curve; incremental dynamic analysis; inter-storey drift; pushover analysis; RC buildings

Address
Gürkan Tam and Burak Yön: Department of Civil Engineering, Munzur University, Tunceli, 62000, Türkiye

Abstract
This paper presents a study on the effect of composite patch repair on the fatigue life of an aluminum alloy plate containing two lateral cracks and subjected to cyclic tensile stresses applied to its upper and lower parts. The investigation considers several parameters, including the load ratio between minimum and maximum stresses (0, 0.3, 0.6, and 0.7), the cracking speed as a function of the stress intensity factor (tK), and the influence of the plate material. Among the alloys examined were 2024-T3, 2024-T351, and 7075-T73. The study identifies the material most resistant to cyclic loading. The plate is analyzed in both unrepaired and repaired conditions, with repairs performed using two different composite patches: boron/epoxy and graphite/epoxy. The results demonstrate that patch reinforcement significantly improves fatigue resistance, with boron/epoxy patches providing the greatest enhancement. The study concluded that the AL 2024-T3 material presents better results compared to the other two materials. These findings confirm the effectiveness of composite patching as a promising technique for extending the service life of cracked structures.

Key Words
cracking; lifetime; load ratio; patches; plate; stress

Address
Moulgada Abdelmadjid: Department of Mechanical Engineering, University of Ibn Khaldoun Tiaret, City Zaaroura BP 78 Tiaret, 14000, Algeria; Laboratory of Mechanical and Physics of Materials LMPM, University of Djillali Liabes Sidi Bel Abbes, 22000, Algeria
Zagane Mohammed El Sallah: Department of Mechanical Engineering, University of Ibn Khaldoun Tiaret, City Zaaroura BP 78 Tiaret, 14000, Algeria; Laboratory of Mechanical and Physics of Materials LMPM, University of Djillali Liabes Sidi Bel Abbes, 22000, Algeria
Ait kaci Djafar: Laboratory of Mechanical and Physics of Materials LMPM, University of Djillali Liabes Sidi Bel Abbes, 22000, Algeria; Department of Mechanical Engineering, University of Djillali Liabes Sidi Bel Abbes, 22000, Algeria
Sahli Abderahmane: Laboratory of Mechanical and Physics of Materials LMPM, University of Djillali Liabes Sidi Bel Abbes, 22000, Algeria; Department of Mechanical Engineering, University of Djillali Liabes Sidi Bel Abbes, 22000, Algeria
Murat Yaylaci: Department of Civil Engineering, Recep Tayyip Erdogan University, 53100, Rize, Turkey; Turgut K

Abstract
This paper proposes a new recycled aggregate concrete (RAC) beam model on a foundation that incorporates damage. The damage models are derived based on composite damage mechanics, considering three phases: cement paste, recycled concrete aggregate (RCA), and nano inclusions. Three damage models are used to represent damage in the RAC beam: the Voigt parallel model, the Reuss serial model, and the generalized self-consistent model. The Voigt parallel model represents the upper bound responses, while the lower bound responses are represented by the Reuss serial model. The beam model is developed using the virtual displacement principle, with the kinematic assumption based on Euler-Bernoulli beam theory. The Winkler-Pasternak foundation model is employed to account for the interaction between the beam and foundation. Two numerical simulations were conducted to investigate the effects of damage and system parameters on static bending analysis. Both simulations reveal that damage parameters lead to a degradation of system stiffness, resulting in increased beam deflection. Conversely, the foundation parameters increase system stiffness, leading to a reduction in beam deflection.

Key Words
composite materials; damage model; Euler-Bernoulli beam theory; generalized self-consistent model; Pasternak foundation; three-phase damage model

Address
Suchart Limkatanyu: Department of Civil and Environmental Engineering, Faculty of Engineering, Prince of Songkla University, Songkhla 90110, Thailand
Worathep Sae-Long: Civil Engineering Program, School of Engineering, University of Phayao, Phayao 56000, Thailand
Nattapong Damrongwiriyanupap: Civil Engineering Program, School of Engineering, University of Phayao, Phayao 56000, Thailand
Piti Sukontasukkul: Construction and Building Materials Research Center, Department of Civil Engineering, King Mongkut's University of Technology North Bangkok, Bangkok 10800, Thailand
Tanakorn Phoo-Ngernkham: Department of Civil Engineering, Faculty of Engineering and Technology, Rajamangala University of Technology Isan, Nakhon Ratchasima 30000, Thailand
Chayanon Hansapinyo: Excellence Center in Infrastructure Technology and Transportation Engineering, Department of Civil Engineering, Faculty of Engineering, Chiang Mai University, Chiang Mai 50200, Thailand
Tosporn Prasertsri: Department of Civil Engineering, Faculty of Engineering and Architecture, Rajamangala University of Technology Tawan-ok, Bangkok 10330, Thailand
Panumas Saingam: Department of Civil Engineering, School of Engineering, King Mongkut's Institute of Technology Ladkrabang, Bangkok 10520, Thailand

Abstract
The strengthening of concrete structures with carbon fiber-reinforced polymers (CFRP) has become an attractive alternative to other conventional methods due to its characteristics, including low density, versatility, speed of application, high elastic modulus, high tensile and fatigue strengths, and corrosion resistance. More complex analyses are typically demanded when evaluating the behavior of a CFRP-strengthened structural element. Numerical methods, such as the Finite Element Method, allow highly complex processes, including nonlinear analyses of concrete structural elements. In this context, this work aims to perform computational modeling through the Finite Element Method of reinforced concrete beams strengthened in shear with CFRP sheets using customized ANSYS software. Special attention is given to the bonding stresses that develop at the interface between the CFRP sheets and the concrete, considering contact finite elements and bilinear Cohesive Zone models. Therefore, the computational simulations enabled the identification of premature rupture modes associated with CFRP sheet debonding and the inadequate utilization of its strengthening properties. Twelve simply supported beams, laboratory tested and with results reported in the literature, were simulated, both with and without CFRP strengthening to enhance shear. The numerical model developed proved to be capable of predicting their behavior in terms of load versus displacement, load versus strain, as well as their rupture modes with good accuracy.

Key Words
ANSYS; carbon fiber reinforced polymers; finite element method; reinforced concrete structures; structural strengthening

Address
Palloma B. Soares, Américo Campos Filho, Paula M. Lazzari, Bruna M. Lazzari and Alexandre R. Pacheco: Civil Engineering Graduate Program, Federal University of Rio Grande do Sul, 99 Oswaldo Aranha Ave, 90035-190, Porto Alegre, RS, Brazil

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