Abstract
This paper introduces an enhanced version of the Big Bang-Big Crunch (BB-BC) optimization algorithm, based on the theory of parallel universes, to improve its performance in the optimal design of truss structures. The governing equations of the BB-BC optimization algorithm are defined based on the Big Bang phenomenon in our universe. According to the parallel universes theory, it is possible to hypothesize the existence of parallel universes with physical laws that either oppose or differ from those of our universe. These hypothetical physical laws are implemented as transfer functions in the search space of the BB-BC optimization algorithm to enhance its exploration and exploitation phases. This modified approach is termed the Parallel Universes Big Bang-Big Crunch (PUBB) algorithm. In truss size optimization, the cross-sectional areas of the members are used as design variables to reduce the truss's weight, while keeping member stresses and nodal displacements within acceptable limits. The proposed PUBB algorithm is implemented using MATLAB software. To quantitatively evaluate its performance, three groups of truss structures—small-scale (10-, 18-, and 25-member), medium-scale (72-member), and large-scale (200- and
942-member)—are analyzed under diverse loading conditions and multiple design constraints. The results demonstrate that the proposed PUBB algorithm is highly effective and efficient in optimizing truss structures across various scales. Compared to the standard BB-BC algorithm and most population-based algorithms, PUBB exhibits a superior capability to escape local optima, thereby achieving improved convergence and solution quality.
Key Words
Big Bang-Big Crunch optimization algorithm; optimization; parallel universe; truss structures
Address
Mohammad Bagher Sabouri Aghdam, Seyed Arash Mousavi Ghasem, Reza Gholi Ejlali and Adel Ferdousi: Department of Civil Engineering, Ta.C., Islamic Azad University, Tabriz, Iran
Abstract
This paper investigates the effectiveness of layered foundation systems in mitigating railway-induced vibrations using a Finite Element/Infinite Element (FE/IE) model and a scaled-down laboratory model. Traditional single-layer isolators often face bearing capacity limitations, prompting the use of layered under-foundation isolators (LUFI) as a practical alternative. Five different isolator configurations, including single-layer (SUFI) and multi-layer (LUFI) setups, were assessed under varying soil conditions and building characteristics. The study employed a parametric analysis to evaluate vibration reduction performance, measured by the Insertion Loss (IL) index. Results indicate that single-layer isolators generally outperform multilayer isolators of equivalent total thickness, particularly in stiffer soil conditions. However, when the rubber thickness is increased proportionally across multiple layers, multi-layer isolators demonstrate superior vibration attenuation. The effectiveness of the proposed isolation method in a real-world situation was then confirmed by developing a 3D numerical model and a scaled-down laboratory model of a building adjacent to a railway track. The accuracy of the numerical approach was also validated by comparing its results with those from the laboratory model. The study underscores the importance of considering soil-structure interaction, isolation frequency, and isolation layers in the design of effective vibration mitigation systems.
Address
Javad Sadeghi, Ehsan Haghighi, Hiva Rabiee and Nima Hadadi: School of Railway Engineering, Iran University of Science and Technology, Tehran, Iran
Abstract
In this research an experimental study is carried out on four concrete filled double skin steel tubular (CFDST) and
concrete filled double skin corrugated steel tube CFDSCST slender columns. This research is considered as a second part of a previous one done by the authors on CFDST stub columns. A verified finite element (FE) program (ABAQUS) is used to give better understanding of the behavior of CFDSCST under axial load. A parametric analysis was then produced in order to show the axial behavior of these columns while taking into account several affecting elements, including the steel strength, hollow ratio, concrete compressive strength, length, and depth-to-thickness ratio. It was found that using the corrugated steel in the inner tube offer more confinement and a lower ductility compared to using corrugated steel in outer tube. It was found that increasing concrete strength cause reduction in a column ductility, increasing tube thickness and concrete strength increases
column resistance. Increasing hollow ratio result in decreasing columns strength as a result of decreasing the sandwiched concrete. Euro code and AISC is evaluated against FE model results.
Key Words
axial resistance; corrugated steel; double skin tubes; ductility; finite elements
Address
Aya M. Handousa: Department of Structural Engineering, Higher Future Institute for Engineering and Technology in Mansoura, Egypt; Structural Engineering Department, Faculty of Engineering, Mansoura University, Egypt
Fikry A. Salem: Structural Engineering Department, Faculty of Engineering, Mansoura University, Egypt
Nabil Sayed Mahmoud: Structural Engineering Department, Faculty of Engineering, Mansoura University, Egypt
Mohamed Ghannam: Structural Engineering Department, Faculty of Engineering, Mansoura University, Egypt
Abstract
This study presents a new analytical model for predicting the full torsional response of reinforced concrete (RC) beams strengthened with fiber-reinforced polymer (FRP) composites. The proposed approach extends the Modified Softened Variable Angle Truss Model by incorporating the confinement effects of FRP materials on concrete and accounting for the softened compressive and tensile behavior of concrete. These enhancements improve the accuracy in predicting the torsional response. An iterative trial-and-error algorithm, implemented in MATLAB, based on the modified constitutive relationships of concrete under the influence of external FRP reinforcement and the equilibrium conditions of the beam. The validity and reliability of the proposed model were assessed using 38 experimental RC beam specimens strengthened with carbon-FRP (CFRP) or glass-FRP (GFRP) in various practical configurations reported in the literature. For comparative evaluation, the torsional strengths of the same specimens were also predicted using the fib Bulletin 90 strut-and-tie approach. The analytical results show closely match experimental results, capturing complete torque-twist curves of the tested beams. In contrast, predictions obtained from fib Bulletin 90 were found to be conservative, yielding an average strength ratio of approximately 0.81 relative to the experimental results.
Address
Vinh Sang Nguyen, Anh Dung Nguyen and Ngoc Thang Nguyen: Faculty of Civil Engineering, Thuyloi University, 175 Tay Son, Kim Lien, Hanoi, Vietnam
Abstract
The PVC-CFRP tube-reinforced concrete column (PCTRCC) overcomes the challenging connection issue between beam members and PVC-CFRP tube confined concrete columns. To study the crack development law of the PCTRCC under axial compression and determine a calculation model of cracking load, the axial compression tests are conducted for fourteen
PCTRCCs and three RC comparison columns. The influences of stirrup form and stirrup ratio outside the core column, CFRP strips spacing and layers, concrete strength grade inside the core column, and diameter-to-width ratio on crack development law, cracking load, ultimate strain, and initial stiffness of the specimens are analyzed. The research results indicate that the "H"- shaped crack or "N"-shaped crack is formed when the specimens with octagonal stirrup or diamond stirrup are damaged, but the surface of the specimens with the square stirrup has only a diagonal crack. As the the CFRP strips spacing decreases or concrete strength grade, stirrup ratio, CFRP strips layers, diameter-to-width ratio increase, the crack development rate of the specimens is reduced, and the ultimate strain and bearing capacity are improved. Compared with square stirrup, the crack development rate of the specimens with octagonal stirrups or diamond stirrups are reduced, and the ultimate strain and bearing capacity increases. Finally, based on the experimental study, the effect of concrete strength grade on cracking load is considered, and the calculation model for cracking load is proposed.
Abstract
Mechanical design workflow typically involves iterative cycles of computer-aided design (CAD) modeling, finite element analysis, and optimization, each requiring significant expertise and manual effort. Recent advances in large language models (LLMs) have enabled the automation of individual stages, including CAD modeling and finite element analysis. Moreover, several studies have utilized LLMs for mechanical design. However, fully integrated end-to-end automation remains limited. Therefore, this study proposes a novel end-to-end framework based on LLM agents that achieves full automation of the entire design–analysis–optimization workflow. Driven entirely by natural language inputs, the framework integrates automatic parameter extraction, CAD modeling, meshing, structural analysis, and optimization. The proposed framework performs structural analyses and achieves optimization goals while preserving design constraints. This is demonstrated through four case studies: a cantilever beam, two-section bar, desk, and flanged pipe. Notably, the proposed approach preserves critical design parameters that are often implicit, thereby mimicking the decision-making of experienced engineers. These results demonstrate the feasibility of democratizing mechanical design by enabling non-experts to perform sophisticated tasks. Although the current implementation is confined to linear analysis and exhibits reduced robustness in highly complex scenarios, this work provides a promising foundation for AI-driven automation in engineering design.
Key Words
automated mechanical design; computer-aided design; design optimization; finite element analysis; large language model
Address
Hojun Lee: Department of Mechanical Engineering, Chungbuk National University, 1 Chungdae-ro, Seowon-Gu, Chungbuk 28644, Republic of Korea
Hyo-Jin Kim: KAIST InnoCORE PRISM-AI Center, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
Jaeho Jung: Department of Mechanical Engineering, Chungbuk National University, 1 Chungdae-ro, Seowon-Gu, Chungbuk 28644, Republic of Korea
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