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CONTENTS
Volume 44, Number 6, September25 2022
 


Abstract
In this study, a graphical automatic system is developed in order to investigate the stress redistribution of structural members in a steel cable-stayed bridge. The generalized Maxwell model is selected for stress relaxation estimation, and it is carefully verified and applied to all the cable members of a steel cable-stayed bridge to investigate its stress relaxation. A set of stress relaxation parameters in all cables is determined using the fmincon optimization function. The stress redistribution of the steel cable-stayed bridge is then analyzed using ABAQUS. To shorten the investigation time, all the aforementioned phases are built up to be an automatic system. The automatic system is then employed to investigate the effect of cable cross-section areas and girder spans on stress redistribution. The findings from these studies show that the initial tension in the cables of a steel cable-stayed bridge should be kept to less than 55% of the cable's ultimate strength to reduce the effect of cable stress relaxation. The cable space in a steel cable-stayed bridge should be limited to 15,000 mm to minimize the effect of cable stress relaxation. In comparison to other structural members of a steel cable-stayed bridge, the girders experience a significant stress redistribution.

Key Words
automated system; cable-stayed bridge; cable stress relaxation; high strength steel cable; long-term deformation

Address
Tien-Thang Hong,Duc-Kien Thai and Seung-Eock Kim: Department of Civil and Environmental Engineering, Sejong University, 98 Gunja-dong, Gwangjin-gu, Seoul 05006, South Korea

Jung J. Kim:Department of Civil and Environmental Engineering, Kyungnam University, Changwon-si, South Korea


Abstract
In this paper a mathematical model for the prediction of the fire resistance of slim-floor steel beams based on an Artificial Neural Network modeling procedure is presented. The artificial neural network models are trained and tested using an analytical database compiled for this purpose from analytical results based on FEM. The proposed model was selected as the optimum from a plethora of alternatives, employing different activation functions in the context of Artificial Neural Network technique. The performance of the developed model was compared against analytical results, employing several performance indices. It was found that the proposed model achieves remarkably improved predictions of the fire resistance of slim-floor steel beams. Moreover, based on the optimum developed AN model a closed-form equation for the estimation of fire resistance is derived, which can prove a useful tool for researchers and engineers, while at the same time can effectively support the teaching of this subject at an academic level.

Key Words
activation functions; artificial neural networks; slim-floor steel beams; fire resistance; soft computing

Address
Panagiotis G. Asteris:Computational Mechanics Laboratory, School of Pedagogical and Technological Education, 14121 Athens, Greece

Chrysanthos Maraveas:Department of Natural Resources and Agricultural Engineering, Agricultural University of Athens, Greece

Athanasios T. Chountalas:Computational Mechanics Laboratory, School of Pedagogical and Technological Education, 14121 Athens, Greece

Dimitrios S. Sophianopoulos and Naveed Alam: Department of Civil Engineering, University of Thessaly, Volos, Greece 4 FireSERT,
School of Built Environment, Ulster University, Belfast, UK

Abstract
In order to study the influence of loading angles on seismic performance of steel reinforced concrete (SRC) specialshaped columns, cyclic loading tests and finite element analysis (FEA) were both carried out. Seven SRC special-shaped columns, including two L-shaped columns, three T-shaped columns and two cross-shaped columns, were tested, and the failure patterns of the columns with different loading angles were obtained. Based on the tests, the FEA models of SRC special-shaped columns with different loading angles were established. According to the simulation results, hysteretic curves and seismic performance indexes, including bearing capacity, ductility, stiffness and energy dissipation capacity, were analyzed in detail. The results showed that the failure patterns were different for the columns with the same section and different loading angles. With the increasing of loading angles, the hysteretic curves became fuller and the bearing capacity and initial stiffness appeared increasing tendency, but the energy dissipation capacity changed insignificantly. When the loading angle changed, the ductility got better with the larger area of steel at the failure side for the unsymmetrical section and near the neutral axis for the symmetrical section, respectively.

Key Words
cyclic loading; loading angle; seismic performance; special-shaped column; steel reinforced concrete

Address
Qu Pengfei, Zuqiang Liu and Jianyang Xue: 1)School of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China
2)Key Lab of Structural Engineering and Earthquake Resistance, Ministry of Education (XAUAT), Xi'an 710055, China

Abstract
Composite materials are effective in forming externally bonded reinforcements which find applications related to existing structures repair, attributed to their high strength-to-weight ratio and ease of installation. Among various composites, fibre reinforced polymers (FRP) have somewhat been largely accepted as a commonly utilized composite for such purposes. It is only recently that steel fibres have been considered as additional members of the FRP fibre family, intuitively termed as steel reinforced polymer (SRP). Owing to its low cost and permissibility of fibre bending at sharp corners, SRP is rapidly becoming a viable contender to other FRP systems. This paper investigates the bond behaviour of SRP-concrete joints with different bonded lengths (50, 75, 100, 150 and 300 mm) and widths (15, 30, 40, 50, and 75 mm) using single-lap shear tests. The experimental specimens contain SRP strips with a fixed density of steel fibres (0.472 cords/mm) bonded to the face of concrete prisms. The load responses were obtained and compared in terms of corresponding load and slip boundaries of the constant region and the peak loads. The failure modes of SRP composites are discussed, and the range of effective bonded length is evaluated herein. In the end, a new analytical model was proposed to estimate the SRP-concrete bond strength using a genetic algorithm, which outperforms 22 existing FRP-concrete bond strength models.

Key Words
bond properties; composite materials; Fibre Reinforced Polymers (FRP); Genetic Algorithm (GA); Steel Reinforced Polymers (SRP)

Address
Hashem Jahangir:1Department of Civil Engineering, University of Birjand, University Blvd., Birjand, Southern Khorasan, Iran


Danial Rezazadeh Eidgahee and Mohammad Reza Esfahani:Department of Civil Engineering, Ferdowsi University of Mashhad, Azadi Square, Mashhad, Razavi Khorasan, Iran

Abstract
In this study, considering dissipated energy in fracture process zone (FPZ), a novel criterion based on maximum strain energy release rate (SER) for orthotropic materials is presented. General case of in-plane loading for cracks along the fibers is assumed. According to the experimental observations, crack propagation is supposed along the fibers and the reinforcement isotropic solid (RIS) concept is employed as a superior model for orthotropic materials. SER in crack initiation and propagation phases is investigated. Elastic properties of FPZ are extracted as a function of undamaged matrix media and micro-crack density. This criterion meaningfully links between dissipated energy due to toughening mechanisms of FPZ and the macroscopic fracture by defining stress intensity factors of the damaged zone. These coefficients are used in equations of maximum SER criterion. The effect of crack initiation angle and the damaged zone is considered simultaneously in this criterion and mode II stress intensity factor is extracted in terms of stress intensity factors of damage zone and crack initiation angle. This criterion can evaluate the effects of FPZ on the fracture behavior of orthotropic material. Good agreement between extracted fracture limit curves (FLC's) and available experimental data proves the ability of the new proposed criterion.

Key Words
crack initiation angle; fracture process zone; orthotropic materials; reinforcement isotropic solid model; strain energy release rate

Address
Zahra Khaji and Mahdi Fakoor:Faculty of New Sciences and Technologies, University of Tehran, Tehran, Iran

Abstract
This manuscript work presents a comprehensive continuum model capable to investigate the effect of porosity on vibro-acoustic behaviour of functionally graded (FG) beams resting on an elastic foundation subjected to thermal and mechanical loadings. Effects of uniform temperature rise and edge compressive load on the sound radiation characteristics are studied in a comparative manner. The numerical analysis is carried out by combining finite element method with Rayleigh's integral. Detailed parametric studies are accomplished, and influences of power law index, porosity volume, porosity distribution and boundary conditions on the vibro-acoustic response characteristics are analyzed. It is found that the vibroacoustic response under mechanical edge compression is entirely different compared to from that under the thermal load. Furthermore, nature of grading of porosity affects the sound radiation behaviour for both the loads. The proposed model can be used to obtain the suppression performance of vibration and noise FG porous beams under thermal and mechanical loads.

Key Words
acoustics; buckling; finite element method; porous FGM beams; shear influence; vibration

Address
Lenin Babu Mailan Chinnapandi:1)School of Mechanical Engineering, Vellore Institute of Technology, Chennai 600127, Tamil Nadu, India
2)Electric Vehicles-Incubation, Testing and Research Centre, Vellore Institute of Technology, Chennai 600127, Tamil Nadu, India

Jeyaraj Pitchaimani:Advanced Dynamics Lab, Department of Mechanical Engineering, National Institute of Technology Karnataka,
Surathkal, Mangalore 575 025, India

Mohamed A. Eltaher: 1)Mechanical Design and Production Dept., Faculty of Engineering, Zagazig University, P.O. Box 44519, Zagazig, Egypt
2)Mechanical Engineering Department, Faculty of Engineering, King Abdulaziz University (KAU), P.O. Box 80204, Jeddah, Saudi Arabia

Abstract
In this study, the performance of shear deficient reinforced concrete (RC) beams with rectangular cross-sections, which were externally bonded reinforced (EBR) with high strength CFRP and GFRP strips composite along shear spans, has been experimentally and analytically investigated under vertical load. In the study, the minimum CFRP and GFRP strips width over spacing were considered. The shear beam with turned end to a bending beam was investigated by applying different composite strips. Therefore various arising in each of strength, ductility, rigidity, and energy dissipation capacity were obtained. A total of 12 small-scaled experimental programs have been performed. Beam dimensions have been taken as 100x150x1000 mm. Four beams have been tested as unstrengthened samples. This paper focuses on the effect of minimum CFRP and GFRP strip width on behaviours of RC beams shear-strengthened with full-wrapping, U-wrapping, and U-wrapping+longitudinal bonding strips. Strengthened beams showed significant increments for flexural ductility, energy dissipation, and inelastic performance. The full wrapping strips applied against shear failure have increased the load-carrying capacity of samples 53%- 63% interval rate. Although full wrapping is the best strengthening choice, the U-wrapping and U-wrapping+longitudinal strips of both CFRP and GFRP bonding increased the shear capacity by 53%~75% compared to the S2 sample. In terms of ductility, the best result has been obtained by the type of strengthening where the S5 beam was completely GFRP wrapped. The experimental results were also compared with the analytically given by ACI440.2R-17, TBEC-2019 and FIB-2001. Especially in U-wrapped beams, the estimation of FIB was determined to be 81%. The estimates of the other codes are far from meeting the experimental results; therefore, essential improvements should be applied to the codes, especially regarding CFRP and GFRP deformation and approaches for longitudinal strip connections. According to the test results, it is suggested that GFRP, which is at least as effective but cheaper than CFRP, may be preferred for strengthening applications.

Key Words
damage analysis; experimental study; CFRP and GFRP strip width; minimum CFRP and GFRP; shear deficient beam

Address
Ceyhun Aksoylu: Department of Civil Engineering, Konya Technical University, 42075 Konya, Turkey


Abstract
Predicting the compressive strength of concrete (CSoC) is of high significance in civil engineering. The CSoC is a highly dependent and non-linear parameter that requires powerful models for its simulation. In this work, two novel optimization techniques, namely evaporation rate-based water cycle algorithm (ER-WCA) and equilibrium optimizer (EO) are employed for optimally finding the parameters of a multi-layer perceptron (MLP) neural processor. The efficiency of these techniques is examined by comparing the results of the ensembles to a conventionally trained MLP. It was observed that the ER-WCA and EO optimizers can enhance the training accuracy of the MLP by 11.18 and 3.12% (in terms of reducing the root mean square error), respectively. Also, the correlation of the testing results climbed from 78.80% to 82.59 and 80.71%. From there, it can be deduced that both ER-WCA-MLP and EO-MLP can be promising alternatives to the traditional approaches. Moreover, although the ER-WCA enjoys a larger accuracy, the EO was more efficient in terms of complexity, and consequently, time-effectiveness.

Key Words
concrete compressive strength; high-performance concrete; multi-layer perceptron; non-linear analysis

Address
Hossein Moayedi: 1)Institute of Research and Development, Duy Tan University, Da Nang, Vietnam 2)School of Engineering & Technology, Duy Tan University, Da Nang, Vietnam

Amirali Eghtesad: Department of Engineering, Islamic Azad University Science and Research Branch, Tehran, Iran

Mohammad Khajehzadeh: Department of Civil Engineering, Anar Branch, Islamic Azad University, Anar, Iran

Suraparb Keawsawasvong: Department of Civil Engineering, Thammasat School of Engineering, Thammasat University, Bangkok, Thailand

Mohammed M. Al-Amidi: Information Technology Unit, Al-Mustaqbal University College, Babylon, 51001, Iraq

Bao Le Van: 1)Institute of Research and Development, Duy Tan University, Da Nang, Vietnam 2)School of Engineering & Technology, Duy Tan University, Da Nang, Vietnam


Abstract
A hollow-core partially-encased composite beam, named HPEC beam, is investigated in this paper. HPEC beam comprises Ibeam, longitudinal reinforcement, stirrup, foam formwork, and cementitious grout. The foam formwork is located on both sides of the web, and cementitious grout is cast within the steel flange. To investigate the shear performance of HPEC beams, static loading tests of six HPEC beams and three control beams were conducted. The shear span ratio and the number of studs on the shear behavior of the HPECspecimens were studied. The failure mechanism was studied by analyzing the curves of shear force versus both deflection and strain. Based on the shear span ratio (λ), two typical shear failure modes were observed: shear compression failure when 1.6 ≤ λ ≤ 2; and diagonal compression failure when λ ≤ 1.15. Shear studs welded on the flange can significantly increase the shear capacity and integrity of HPEC beams. Flange welded shear studs are suggested. Based on the deformation coordination theory and superposition method, combined with the simplified modified compression field model and the Truss-arch model, Modified Deformation Coordination Truss-arch (M.D.C.T.) model was proposed. Compared with the shear capacity from YB9038-2006 and JGJ138-2016, the calculation results from M.D.C.T. model could provide reasonable predictions.

Key Words
diagonal compression failure; hollow-core partially-encased composite beam; Modified Deformation Coordination Truss-arch (M.D.C.T.) model; shear compression failure

Address
Yanxia Ye, Yifan Yao and Yue Gao:School of Civil Engineering, Chang

Abstract
To study the seismic performance of the all-steel buckling-restrained brace (BRB) using the novel soft steel LY315 for core member, a total of three identical BRBs were designed and a series of experimental and numerical studies were conducted. First, monotonic and cyclic loading tests were carried out to obtain the mechanical properties of LY315 steel. In addition, the parameters of the Chaboche model were calibrated based on the test results and then verified using ABAQUS. Second, three BRB specimens were tested under cyclic loads to investigate the seismic performance. The failure modes of all the specimens were identified and discussed. The test results indicate that the BRBs exhibit excellent energy dissipation capacity, good ductility, and excellent low-cycle fatigue performance. Then, a finite element (FE) model was established and verified with the test results. Furthermore, a parametric study was performed to further investigate the effects of gap size, restraining ratio, slenderness ratio of the yielding segment, and material properties of the core member on the load capacity and energy dissipation capacity of BRBs.

Key Words
Buckling-restrained brace (BRB); finite element analysis; LY315 steel; parametric study; seismic performance

Address
Xuan Wei:1)The Key Laboratory of Urban Security and Disaster Engineering of Ministry of Education,
Beijing University of Technology, Beijing 100124, China
2)School of Civil Engineering, Chongqing University, Chongqing 400045, China

Lu Yang:The Key Laboratory of Urban Security and Disaster Engineering of Ministry of Education,
Beijing University of Technology, Beijing 100124, China

Yohchia Frank Chen:School of Civil Engineering, Chongqing University, Chongqing 400045, China

Meng Wang:School of Civil Engineering, Beijing Jiaotong University, Beijing, 100044, China


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