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CONTENTS
Volume 51, Number 2, April 25 2024
 


Abstract
Based on the consistent couple stress theory (CCST), we develop a unified formulation for analyzing the static bending and free vibration behaviors of functionally graded (FG) microscale beams (MBs). The strong forms of the CCSTbased Euler-Bernoulli, Timoshenko, and Reddy beam theories, as well as the CCST-based sinusoidal, exponential, and hyperbolic shear deformation beam theories, can be obtained by assigning some specific shape functions of the shear deformations varying through the thickness direction of the FGMBs in the unified formulation. The above theories are thus included as special cases of the unified CCST. A comparative study between the results obtained using a variety of CCST-based beam theories and those obtained using their modified couple stress theory-based counterparts is carried out. The impacts of some essential factors on the deformation, stress, and natural frequency parameters of the FGMBs are examined, including the material length-scale parameter, the aspect ratio, and the material-property gradient index.

Key Words
consistent couple stress theory; deformation; microscale beams; modified couple stress theory; unified shear deformation theory; vibration

Address
Chih-Ping Wu and Zhen Huang:Department of Civil Engineering, National Cheng Kung University, 1 University Road, Tainan 70101, Taiwan

Abstract
There are many challenges in the construction of large-section tunnels, such as extremely soft rock and fractured zones. In order to solve these problems, the confined concrete support technology is proposed to control the surrounding rocks. The large-scale laboratory test is carried out to clarify mechanical behaviours of the combined confined concrete and traditional I-steel arches. The test results show that the bearing capacity of combined confined concrete arch is 3217.5 kN, which is 3.12 times that of the combined I-steel arch. The optimum design method is proposed to select reasonable design parameters for confined concrete arch. The parametric finite element (FE) analysis is carried out to study the effect of the design factors via optimum design method. The steel pipe wall thickness and the longitudinal connection ring spacing have a significant effect on the bearing capacity of the combined confined concrete arch. Based on the above research, the confined concrete support technology is applied on site. The field monitoring results shows that the arch has an excellent control effect on the surrounding rock deformation. The results of this research provide a reference for the support design of surrounding rocks in large-section tunnels.

Key Words
combined confined concrete arch; design optimization; large-section tunnels; on-field experimental tests; parametric finite element analysis

Address
Jiang Bei,Xu Shuo, Wei Hua Yong and Ma Feng Li:State Key Laboratory for Tunnel Engineering, China University of Mining & Technology-Beijing, Beijing 100083, China

Wang Qi:1)State Key Laboratory for Tunnel Engineering, China University of Mining & Technology-Beijing, Beijing 100083, China
2)Geotechnical and Structural Engineering Research Center, Shandong University, Jinan 250061, China

Xin Zhong Xin:Geotechnical and Structural Engineering Research Center, Shandong University, Jinan 250061, China

Abstract
In this paper, structural behavior under fire conditions is comprehensively examined, and a novel software interface for testing interfaces efficiently is developed and validated. In order to accurately assess the response of structures to fire scenarios, advanced simulation techniques and modeling approaches are incorporated into the study. This interface enables accurate heat transfer analysis and thermo-mechanical simulations by integrating software tools such as CSI ETABS, CSI SAP2000, and OpenSees. Heat transfer models can be automatically generated, simulation outputs processed, and structural responses interpreted under a variety of fire scenarios using the proposed technique. As a result of rigorous testing and validation against established methods, including Cardington tests on scales and hybrid simulation approaches, the software interface has been proven to be effective and accurate. The analysis process is streamlined by this interface, providing engineers and researchers with a robust tool for assessing structural performance under fire conditions.

Key Words
computer-aided design; finite element method; opensees fire; thermal analysis

Address
Seong-Hoon Jeong:Department of Architectural Engineering, Inha University, Incheon, South Korea

Ehsan Mansouri:2)Institute of Research and Development, Duy Tan University, Da Nang 550000, Vietnam
3)Faculty of Natural Sciences, Duy Tan University, Da Nang 550000, Vietnam

Nadia Ralston:Department of Civil and Environmental Engineering, Princeton University, United State

Jong-Wan Hu:1)Department of Civil and Environmental Engineering, Incheon National University, South Korea
2)Incheon Disaster Prevention Research Center, Incheon National University, South Korea

Abstract
In this research, a semi-analytical solution is presented for computing mechanical displacements and thermal stresses in rotating thick cylindrical pressure vessels made of functionally graded material (FGM). The modulus of elasticity, linear thermal expansion coefficient, and density of the cylinder are assumed to change along the axial direction as a power-law function. It is also assumed that Poisson's ratio and thermal conductivity are constant. This cylinder was subjected to nonuniform internal pressure and thermal loading. Thermal loading varies in two directions. The governing equations are derived by the first-order shear deformation theory (FSDT). Using the multilayer method, a functionally graded (FG) cylinder with variable thickness is divided into n homogenous disks, and n sets of differential equations are obtained. Applying the boundary conditions and continuity conditions between the layers, the solution of this set of equations is obtained. To the best of the researchers' knowledge, in the literature, there is no study carried out bi-directional thermoelastic analysis of clamped-clamped rotating FGM thick-walled cylindrical pressure vessels under variable pressure in the longitudinal direction.

Key Words
First-Order shear Deformation Theory (FSDT); Functionally Graded Material (FGM); rotating cylinder; thermoelastic; two-direction

Address
Fatemeh Ramezani and Mohammad Zamani Nejad:Department of Mechanical Engineering, Yasouj University, Yasouj, Iran

Abstract
Due to the fast development of constructions in recent years, there has been a rapid consumption of fresh water and river sand. In the production of concrete, alternatives such as sea water and sea sand are available. The near surface mounted (NSM) technique is one of the most important methods of strengthening. Aluminum alloy (AA) bars are non-rusting and suitable for usage with sea water and sand concrete (SSC). The goal of this study was to enhance the shear behaviour of SSCbeams strengthened with NSM AA bars. Twenty-four RC beams were cast from fresh water river sand concrete (FRC) and SSC before being tested in four-point flexure. All beams are the same size and have the same internal reinforcement. The major factors are the concrete type (FRC or SSC), the concrete degree (C25 or C50 with compressive strength = 25 and 50 MPa, respectively), the presence of AA bars for strengthening, the direction of AA bar reinforcement (vertical or diagonal), and the AA bar ratio (0, 0.5, 1, 1.25 and 2 %). The beams' failure mechanism, load-displacement response, ultimate capacity, and ductility were investigated. Maximum load and ductility of C25-FRC-specimens with vertical and diagonal AA bar ratios (1%) were 100,174 % and 140, 205.5 % greater, respectively, than a matching control specimen. The ultimate load and ductility of all SSCbeams were 16-28 % and 11.3-87 % greater, respectively, for different AA bar methods than that of FRC-beams. The ultimate load and ductility of C25-SSC-beams vertically strengthened with AA bar ratios were 66.7-172.7 % and 89.6-267.9 % higher than the unstrengthened beam, respectively. When compared to unstrengthened beams, the ultimate load and ductility of C50- SSC-beams vertically reinforced with AA bar ratios rose by 50-120 % and 45.4-336.1 %, respectively. National code proposed formulae were utilized to determine the theoretical load of tested beams and compared to matching experimental results. The predicted theoretical loads were found to be close to the experimental values.

Key Words
aluminum alloy bars; deformations; experimental; near-surface mounted technique; seawater sea-sand concrete beam; shear behavior; shear strengthening

Address
Yasin Onuralp Ozkilic:1)Department of civil engineering, Necmettin Erbakan University, 42090 Konya, Turkey
2)Department of Civil Engineering, Lebanese American University, Byblos 1102-2801, Lebanon

Emrah Madenci:Department of civil engineering, Necmettin Erbakan University, 42090 Konya, Turkey

Ahmed Badr:Department of Civil Engineering, Faculty of Engineering, Damanhur University, Egypt

Walid Mansour and Sabry Fayed:Department of Civil Engineering, Faculty of Engineering, Kafrelsheikh, Egypt

Abstract
This study investigates a new seismic retrofit system that utilizes rotational friction dampers and axial springs. The retrofit system involves a steel frame with rotational friction dampers (RFD) at beam-column joints and linear springs at the corners, providing energy dissipation and self-centering capabilities to existing structures. The axial spring acts as a selfcentering mechanism that eliminates residual deformations, while the friction damper mitigates seismic damage. To evaluate the seismic performance of the proposed retrofit system, a series of cyclic loading tests were carried out on a steel beam-column subassembly equipped with the proposed devices. An analytical model was then developed to validate the experimental results. A performance point ratio (PPR) was presented to optimize the design parameters of the retrofit system, and a performancebased seismic design strategy was developed based on the PPR. The retrofit system's effectiveness and the presented performance-based design approach were evaluated through case study models, and the analysis results demonstrated that the developed retrofit system and the performance-based design procedure were effective in retrofitting structures for multi-level design objectives.

Key Words
performance-based seismic design; seismic retrofit; self-centering; steel frame

Address
Masoum M. Gharagoz:1)Department of Civil Engineering, School of Engineering, Aalto University, Finland
2)Department of Global Smart City, Sungkyunkwan University, South Korea

Seungho Chun:Department of Global Smart City, Sungkyunkwan University, South Korea

Mohamed Noureldin:Department of Civil Engineering, School of Engineering, Aalto University, Finland

Jinkoo Kim:Department of Global Smart City, Sungkyunkwan University, South Korea


Abstract
In this research paper, and for the first time, wave propagations in sigmoidal imperfect functionally graded material plates are investigated using a simplified quasi-three-dimensionally higher shear deformation theory (Quasi-3D HSDTs). By employing an indeterminate integral for the transverse displacement in the shear components, the number of unknowns and governing equations in the current theory is reduced, thereby simplifying its application. Consequently, the present theories exhibit five fewer unknown variables compared to other Quasi-3D theories documented in the literature, eliminating the need for any correction coefficients as seen in the first shear deformation theory. The material properties of the functionally graded plates smoothly vary across the cross-section according to a sigmoid power law. The plates are considered imperfect, indicating a pore distribution throughout their thickness. The distribution of porosities is categorized into two types: even or uneven, with linear (L)-Type, exponential (E)-Type, logarithmic (Log)-Type, and Sinus (S)-Type distributions. The current quasi-3D shear deformation theories are applied to formulate governing equations for determining wave frequencies, and phase velocities are derived using Hamilton's principle. Dispersion relations are assumed as an analytical solution, and they are applied to obtain wave frequencies and phase velocities. A comprehensive parametric study is conducted to elucidate the influences of wavenumber, volume fraction, thickness ratio, and types of porosity distributions on wave propagation and phase velocities of the S-FGM plate. The findings of this investigation hold potential utility for studying and designing techniques for ultrasonic inspection and structural health monitoring.

Key Words
even and uneven porosity; guided wave; phase velocity; Qausi-3D HSDTs; S-FGM

Address
Mokhtar Nebab:1)Department of Civil Engineering, Faculty of Technology, University of M

Abstract
This study shows functionally graded material structural topology optimization under buckling constraints. The SIMP (Solid Isotropic Material with Penalization) material model is used and a method of moving asymptotes is also employed to update topology design variables. In this study, the quadrilateral element is applied to compute buckling load factors. Instead of artificial density properties, functionally graded materials are newly assigned to distribute optimal topology materials depending on the buckling load factors in a given design domain. Buckling load factor formulations are derived and confirmed by the resistance of functionally graded material properties. However, buckling constraints for functionally graded material topology optimization have not been dealt with in single material. Therefore, this study aims to find the minimum compliance topology optimization and the buckling load factor in designing the structures under buckling constraints and generate the functionally graded material distribution with asymmetric stiffness properties that minimize the compliance. Numerical examples verify the superiority and reliability of the present method.

Key Words
buckling constrains; Finite Element Method; functionally graded materials; topology optimization

Address
Minh-Ngoc Nguyen:Department of Architectural Engineering, Sejong University, Seoul, 05006, Republic of Korea

Dongkyu Lee:Department of Architectural Engineering, Sejong University, Seoul, 05006, Republic of Korea

Soomi Shin:Research Institute of Industrial Technology, Pusan National University, Busan, 46241, Republic of Korea


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