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CONTENTS
Volume 47, Number 2, April25 2023
 

Abstract
The paper contrasts conventional seismic design with a design that incorporates buckling-restrained bracing in three-dimensional reinforced concrete buildings (BRBs). The suboptimal structures may be found using the multi-objective chimp optimization algorithm (MEN-ChOA). Given the constraints and dimensions, ChOA suffers from a slow convergence rate and tends to become stuck in local minima. Therefore, the ChOA is improved by niching and evolutionary operators to overcome the aforementioned problems. In addition, a new technique is presented to compute seismic and dead loads that include all of a structure's parts in an algorithm for three-dimensional frame design rather than only using structural elements. The performance of the constructed multi-objective model is evaluated using 12 standard multi-objective benchmarks proposed in IEEE congress on evolutionary computation. Second, MEN-ChOA is employed in constructing several reinforced concrete structures by the Mexico City building code. The variety of Pareto optimum fronts of these criteria enables a thorough performance examination of the MEN-ChOA. The results also reveal that BRB frames with comparable structural performance to conventional moment-resistant reinforced concrete framed buildings are more cost-effective when reinforced concrete building height rises. Structural performance and building cost may improve by using a nature-inspired strategy based on MENChOA in structural design work.

Key Words
buckling-restrained braces; evolutionary multi-objective chimp optimization; niching concept; reinforced concrete; seismic structure design

Address
Shouhua Liu:Faculty of Architecture and Civil Engineering, Huaiyin Institute of Technology, Huaian, Jiangsu 223001, China

Jianfeng Li:1)Faculty of Engineering, China University of Geosciences (Wuhan), Wuhan 430000, Hubei, China
2)Zhongjiao Yuanzhou Transportation Technology Group Co., Ltd, Fujian Branch, Fuzhou 350109, Fujian, China
3)Hainan Cloud Spacetime Information Technology Co.,Ltd, Danzhou571700, Hainan, China

Hamidreza Aghajanirefah:Department of Civil Engineering, Faculty of Engineering, Qazvin Branch Islamic Azad University, Qazvin, Iran

Mohammad Khishe:Department of Electrical Engineering, Imam Khomeini Marine Science University, Nowshahr, Iran

Abbas Khishe:Department of Civil Engineering, Iran University of Science and Technology, Iran

Arsalan Mahmoodzadeh:Rock Mechanics Division, School of Engineering, Tarbiat Modares University, Tehran, Iran

Banar Fareed Ibrahim:Department of Information Technology, College of Engineering and Computer Science, Lebanese French University, Kurdistan Region, Iraq

Abstract
In this study, a new recentering friction device (RFD) to retrofit steel moment frame structures is introduced. The device provides both self-centering and energy dissipation capabilities for the retrofitted structure. A hybrid performance-based seismic design procedure considering multiple limit states is proposed for designing the device and the retrofitted structure. The design of the RFD is achieved by modifying the conventional performance-based seismic design (PBSD) procedure using computational intelligence techniques, namely, genetic algorithm (GA) and artificial neural network (ANN). Numerous nonlinear time-history response analyses (NLTHAs) are conducted on multi-degree of freedom (MDOF) and single-degree of freedom (SDOF) systems to train and validate the ANN to achieve high prediction accuracy. The proposed procedure and the new RFD are assessed using 2D and 3D models globally and locally. Globally, the effectiveness of the proposed device is assessed by conducting NLTHAs to check the maximum inter-story drift ratio (MIDR). Seismic fragilities of the retrofitted models are investigated by constructing fragility curves of the models for different limit states. After that, seismic life cycle cost (LCC) is estimated for the models with and without the retrofit. Locally, the stress concentration at the contact point of the RFD and the existing steel frame is checked being within acceptable limits using finite element modeling (FEM). The RFD showed its effectiveness in minimizing MIDR and eliminating residual drift for low to mid-rise steel frames models tested. GA and ANN proved to be crucial integrated parts in the modified PBSD to achieve the required seismic performance at different limit states with reasonable computational cost. ANN showed a very high prediction accuracy for transformation between MDOF and SDOF systems. Also, the proposed retrofit showed its efficiency in enhancing the seismic fragility and reducing the LCC significantly compared to the un-retrofitted models.

Key Words
artificial neural network; disc-springs; FEM; fragility analysis; genetic algorithm; incremental dynamic analysis; life-cycle cost; PBSD; seismic retrofit; self-centering

Address
Mohamed Noureldin, Masoum M. Gharagoz and Jinkoo Kim:Department of Global Smart City, Sungkyunkwan University, Suwon Korea

Abstract
Despite the high lateral stiffness and strength of the Concentrically Braced Frame (CBF), due to the buckling of its diagonal members, it is not a suitable system in high seismic regions. Among the offered methods to overcome the shortcoming, utilizing a metallic damper is considered as an appropriate idea to enhance the behavior of Concentrically Braced Frames (CBFs). Therefore, in this paper, an innovative steel damper is proposed, which is investigated experimentally and numerically. Moreover, a parametrical study was carried out to evaluate the effect of the mechanism (shear, shear-flexural, and flexural) considering buckling mode (elastic, inelastic, and plastic) on the behavior of the damper. Besides, the necessary formulas based on the parametrical study were presented to predict the behavior of the damper that they showed good agreement with finite element (FE) results. Both experimental and numerical results confirmed that dampers with the shear mechanism in all buckling modes have a better performance than other dampers. Accordingly, the FE results indicated that the shear damper has greater ultimate strength than the flexural damper by 32%, 31%, and 56%, respectively, for plates with elastic, inelastic, and plastic buckling modes. Also, the shear damper has a greater stiffness than the flexural damper by 43%, 26%, and 53%, respectively, for dampers with elastic, inelastic, and plastic buckling modes.

Key Words
buckling; Concentrically Braced Frame (CBF); steel plate-based damper; stiffness; strength

Address
Denise-Penelope N. Kontoni:1)Department of Civil Engineering, School of Engineering, University of the Peloponnese, GR-26334 Patras, Greece
2)School of Science and Technology, Hellenic Open University, GR-26335 Patras, Greece

Ali Ghamari:Department of Civil Engineering, Ilam Branch, Islamic Azad University, Ilam, Iran

Chanachai Thongchom:Department of Civil Engineering, Faculty of Engineering, Thammasat School of Engineering, Thammasat University,
Pathumthani 12120, Thailand

Abstract
The composite beam connections often encountered fracture failure in the welded bottom flange joint, and a bottom flange bolted connection has been proposed to increase the deformation ability of the bottom flange joint. The seismic performance of the bottom flange bolted composite beam connection was suffered from both the composite action of concrete slab and the asymmetric load transfer mechanisms between top and bottom beam flange joints. Thus, this paper presents a comprehensive numerical study on the working mechanism of the bottom flange bolted composite beam connections. Three available modelling methods and a new modelling method on the flange-stud-slab interactions were compared. The efficient numerical modeling method was selected and then applied to the parametric study. The influence of the composite slab, the bottom flange bolts, the shear composite ratio and the web hole shape on the seismic performance of the bottom flange bolted composite beam connections were investigated. A hogging strength calculation method was then proposed based on numerical results.

Key Words
composite beam; connections; finite element model; hysteretic behavior; moment strength

Address
Xiaoxiang Wang:1)School of Civil Engineering, Central South University, Changsha 410075, China
2)Hunan Construction Engineering Group Co., Ltd., Changsha Hunan 410004, China

Yujie Yu and Lizhong Jiang:1)School of Civil Engineering, Central South University, Changsha 410075, China 2) National Engineering Research Center of High-speed Railway Construction Technology, Changsha 410075, China

Zhiwu Yu:National Engineering Research Center of High-speed Railway Construction Technology, Changsha 410075, China

Abstract
In this study, a parametric study was performed considering material properties of concrete, material properties of steel, the number of longitudinal reinforcement (reinforcement ratio), CFRP ply orientations, a number of layers as variables by using ABAQUS. Firstly, the parameters used in the Hashin failure criteria were verified using four coupon tests of CFRP. Secondly, the numerical models of the beams strengthened by CFRP were verified using five experimental data. Finally, eighty numerical models and eighty analytic calculations were developed to investigate the effects of the aforementioned variables. The results revealed that in the case of using fibrous polymer to prevent shear failure, the variables related to reinforced concrete significantly affected the behavior of specimens, whereas the variables related to CFRP composite have a slight effect on the behavior of the specimens. As a result of numerical analysis, while the increase in the longitudinal tensile and compression reinforcement, load bearing capacity increases between 23.6%-70.7% and 5.6%-12.2%, respectively. Increase in compressive strength (29 MPa to 35 MPa) leads to a slight increase in the load-carrying capacity of the specimens between 4.6% and 7.2%. However, the decrease in the compressive strength (29 MPa to 20 MPa) significantly affected (between 6.4% and 8.1% decrease observed) the behavior of the specimens. As the yield strength increases or decreases, the capacity of specimens increase approximately 27.1% or decrease 12.1%. The effects of CFRP ply orientation results have been obtained as a negligible well approximately 3.7% difference. An increasing number of CFRP layers leads to almost no effect (approximately 2.8%) on the behavior of the specimen. Finally, according to the numerical analysis, the ductility values obtained between 4.0 and 6.9 indicate that the beams have sufficient ductility capacity.

Key Words
beam; CFRP; composite; concrete; fiber orientations; hashin failure; numerical study; strengthening; wrapping

Address
Ceyhun Aksoylu, Mohammed Alsdudi and Musa Hakan Arslan:Department of Civil Engineering, Konya Technical University, 42130, Konya, Turkey

Yasin Onuralp Ozkilic:Department of Civil Engineering, Necmettin Erbakan University, 42100, Konya, Turkey

Şakir Yazman:IIgin Vocational School, Selcuk University, 42615, Konya, Turkey

Lokman Gemi:Meram Vocational School, Necmettin Erbakan University, 42100, Konya, Turkey

Abstract
The stiffness evaluation of cracked base metal is of great guidance to fatigue crack reinforcement. By carrying out fatigue tests and numerical simulation of typical cracking details in steel box girder, the strain-degradation law of cracked base metal was analyzed and the relationship between base metal stress and its displacement (stiffness) was explored. The feasibility of evaluating the stress of cracked base metal based on the stress field at the crack tip was verified. The results demonstrate that the stiffness of cracked base metal shows the fast-to-slow degradation trend with fatigue cracking and the base metal at 50mm or more behind the crack tip basically lose its bearing capacity. Drilling will further accelerate stiffness degradation with the increase of hole diameters. The base metal stress has a negative linear relation with its displacement (stiffness), The stress of cracked base metal is also related to stress intensity factor and its relative position (distance, included angle) to the crack tip, through which the local stiffness can be effectively evaluated. Since the stiffness is not uniformly distributed along the cracked base metal, the reinforcement patch is suggested to be designed according to the stiffness to avoid excessive reinforcement for the areas incompletely unloaded.

Key Words
drilling stop-hole; fatigue cracking; roof-vertical stiffener; steel bridge deck; stiffness degradation

Address
Liang Fang, Zhongqiu Fu, Bohai Ji and Xincheng Li:College of Civil and Transportation Engineering, Hohai University, No. 1 Xikang Road, Nanjing, China

Abstract
The bearing capacities resisted by the two-bay beams of multi-story planar frames with unequal spans under column removal scenarios differ considerably owing to the asymmetric stress on the left and right beams connected to the failed column and cause the potential for beams with larger span-to-depth ratios to be unable to exert effectively, which is disadvantageous for resisting the vertical load in unequal-span frame structures. To address this problem, the structural measure of adding braces to the weak bays of multi-story unequal-span frames was proposed, with the objective of achieving a coordinated stress state in two-bay beams with unequal spans, thereby improving the collapse resistance of unequal-span frame structures. Before conducting the numerical simulation, the modeling methods were verified by previous experimental results of two multi-story planar frames with and without steel braces. Thereafter, the effects of the tensile and compressive braces on the collapse behavior of the frame structures were elucidated. Then, based on the mechanical action laws of the braces throughout the collapse process, a detailed design method for improving the collapse resistance of unequal-span frame structures was proposed. Finally, the proposed design method was verified by using sufficient example models, and the results demonstrated that the design method has good application prospects and high practical value.

Key Words
cooperative working; multi-story steel frame; progressive collapse; resistance improvement; unequal span

Address
Zheng Tan, Bao Meng, Shi-chao Duan,Yu-hui Zheng:School of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China

Wei-hui Zhong: 1)School of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China
2)Key Laboratory of Structural Engineering and Earthquake Resistance, Ministry of Education,
Xi'an University of Architecture and Technology, Xi'an 710055, China

Hong-chen Wang:China Northwest Architecture Design and Research Institute Co., Ltd, Xi'an 710018, China

Xing-You Yao:Jiangxi Province Key Laboratory of Hydraulic and Civil Engineering Infrastructure Security,
Nanchang Institute of Technology, Nanchang, 330000, China

Abstract
The WGJ420 fire-resistant weathering (FRW) steel is developed and manufactured with standard yield strength of 420 MPa at room temperature, which is expected to significantly enhance the performance of steel structures with excellent fire and corrosion resistances, strong seismic capacity, high strength and ductility, good resilience and robustness. In this paper, the mechanical properties of FRW steel plates and buckling behavior of columns are investigated through tests at elevated temperatures. The stress-strain curves, mechanical properties of FRW steel such as modulus of elasticity, proof strength, tensile strength, as well as corresponding reduction factors are obtained and discussed. The recommended constitutive model based on the Ramberg-Osgood relationship, as well as the relevant formulas for mechanical properties are proposed, which provide fundamental mechanical parameters and references. A total of 12 FRW steel welded I-section columns with different slenderness ratios and buckling load ratios are tested under standard fire to understand the global buckling behavior in-depth. The influences of boundary conditions on the buckling failure modes as well as the critical temperatures are also investigated. In addition, the temperature distributions at different sections/locations of the columns are obtained. It is found that the buckling deformation curve can be divided into four stages: initial expansion stage, stable stage, compression stage and failure stage. The fire test results concluded that the residual buckling capacities of FRW steel columns are substantially higher than the conventional steel columns at elevated temperatures. Furthermore, the numerical results show good agreement with the fire test results in terms of the critical temperature and maximum axial elongation. Finally, the critical temperatures between the numerical results and various code/standard curves (GB 51249, Eurocode 3, AS 4100, BS 5950 and AISC) are compared and verified both in the buckling resistance domain and in the temperature domain. It is demonstrated that the FRW steel columns have sufficient safety redundancy for fire resistance when they are designed according to current codes or standards.

Key Words
buckling resistance; critical temperature; Fire-resistant weathering (FRW) steel; mechanical properties; standard fire test; Welded I-section column

Address
Yiran Wu, Xianglin Yu, Yongjiu Shi, Yonglei Xu and Huiyong Ban:Department of Civil Engineering, Tsinghua University, 30 Shuangqing Road, Beijing 100084, P. R. China


Abstract
The failure of a thin-walled tube was studied in this paper based on three failure models. Both proportional and nonproportional loading paths were applied. Proportional loading consisted of combined tension-torsion. Cyclic non-proportional loading was also applied. It was a circular out-of-phase axial-shear stress loading path. The third loading path was a combination of a constant internal pressure and a bending moment. The failure models under study were equivalent plastic strain, modified Mohr-Coulomb (Bai-Wierzbicki) and Tearing parameter models. The elasto-plastic analysis was conducted using J2 criterion and nonlinear kinematic hardening. The return mapping algorithm was employed to numerically solve the plastic flow relations. The effects of the hydrostatic stress on the plastic flow and the stress triaxiality parameter on the failure were discussed. Each failure model under study was utilized to predict failure. The failure loads obtained from each model were compared with each other. The equivalent plastic strain model was independent from the stress triaxiality parameter, and it predicted the highest failure load in the bending problem. The modified Mohr-Coulomb failure model predicted the lowest failure load for the range of the stress triaxiality parameter and Lode's angle.

Key Words
bending; ductile failure models; kinematic hardening; non-proportional loading; thin-walled tube; Torsion

Address
Mohammad Hossein Iji and Ali Nayebi:Mechanical Engineering School, Shiraz University, Shiraz, Iran

Abstract
This study aims to extend the application of the spectral element method (SEM) to wave propagation and free vibration analysis of functionally graded (FG) plates integrated with thin piezoelectric layers, plates with tapered thickness and structure on elastic foundations. Also, the dynamic response of the smart FG plate under impact and moving loads is presented. In this paper, the dynamic stiffness matrix of the smart rectangular FG plate is determined by using the exact dynamic shape functions based on Mindlin plate assumptions. The low computational time and results' independence with the number of elements are two significant features of the SEM. Also, to prove the accuracy and efficiency of the SEM, results are compared with Abaqus simulations and those reported in references. Furthermore, the effects of boundary conditions, power-law index, piezoelectric layers thickness, and type of loading on the results are studied.

Key Words
elastic foundation; moving load; piezoelectric layer; spectral element method; tapered thickness; wave propagation

Address
Farhad Abad:1)Department of Mechanical and Aerospace Engineering, Shiraz University of Technology, Shiraz, PO Box-71555-313, Iran
2)Department of Naval Architecture, Ocean and Marine Engineering, University of Strathclyde, Glasgow G4 0LZ, UK

Jafar Rouzegar:Department of Mechanical and Aerospace Engineering, Shiraz University of Technology, Shiraz, PO Box-71555-313, Iran

Saeid Lotfian:Department of Naval Architecture, Ocean and Marine Engineering, University of Strathclyde, Glasgow G4 0LZ, UK

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