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CONTENTS
Volume 88, Number 5, December10 2023
 

Abstract
This paper reveals theoretical research to the nonlinear dynamic response and initial geometric imperfections sensitivity of the spinning graphene platelets reinforced metal foams (GPLRMF) cylindrical shell under different boundary conditions in thermal environment. For the theoretical research, with the framework of von-Karman geometric nonlinearity, the GPLRMF cylindrical shell model which involves Coriolis acceleration and centrifugal acceleration caused by spinning motion is assumed to undergo large deformations. The coupled governing equations of motion are deduced using Euler-Lagrange principle and then solved by a combination of Galerkin's technique and modified Lindstedt Poincare (MLP) model. Furthermore, the impacts of a set of parameters including spinning velocity, initial geometric imperfections, temperature variation, weight fraction of GPLs, GPLs distribution pattern, porosity distribution pattern, porosity coefficient and external excitation amplitude on the nonlinear harmonic resonances of the spinning GPLRMF cylindrical shells are presented.

Key Words
initial geometric imperfections; Modified Lindstedt Poincare technique; nonlinear harmonic resonances; spinning motion

Address
Yi-Wen Zhang and Gui-Lin She: College of Mechanical and Vehicle Engineering, Chongqing University, Chongqing 400044, China

Abstract
The use of reinforced concrete (RC) shear walls (SW) as an efficient lateral load-carrying system has gained recent attention. However, creating openings in RC shear walls is unavoidable due to architectural requirements. This reduces the walls' strength and stiffness, resulting in the development of wall piers. In this study, the cyclic behavior of RC shear walls with openings, reinforced with carbon fiber reinforced polymer (CFRP) sheets in various patterns, was numerically investigated. Finite element analysis (FEA) using ABAQUS software was employed. Additionally, the retrofitting of sub-standard buildings (5, 10, and 15-story structures) designed based on the old and new versions of the Iranian Code of Practice for Seismic-Resistant Structures was evaluated. Nonlinear static analyses, specifically pushover analyses, were conducted on the structures. The best pattern of CFRP wrapping was determined and utilized for retrofitting the sub-standard structures. Various structural parameters, such as load-carrying capacity, ductility, stress contours, and tension damage contours, were compared to assess the efficiency of the retrofit solution. The results indicated that the load-carrying capacity of the sub-standard structures was lower than that of standard ones by 57%, 69%, and 67% for 5, 10, and 15-story buildings, respectively. However, the retrofit solution utilizing CFRP showed promising results, enhancing the capacity by 10-25%. The retrofitted structures demonstrated increased yield strength, ultimate strength, and ductility through CFRP wrapping and effectively prevented wall slipping.

Key Words
CFRP; Finite Element Analysis (FEA); nonlinear static analysis (pushover); Reinforced Concrete (RC) Shear Wall (SW); retrofitting; wall pier

Address
Fatemeh Zahiri, Ali Kheyroddin and Majid Gholhaki: Faculty of Civil Engineering, Semnan University, Iran

Abstract
Non-linear vibration characteristics of functionally graded CNT-reinforced composite (FG-CNTRC) cylindrical shell panel on elastic foundation have not been sufficiently examined. In this situation, this study aims at the profound numerical investigation of the non-linear vibration response of FG-CNTRC cylindrical panels on Winkler-Pasternak foundation by introducing an accurate and effective 2-D meshfree-based non-linear numerical method. The large-amplitude free vibration problem is formulated according to the first-order shear deformation theory (FSDT) with the von Kármán non-linearity, and it is approximated by Laplace interpolation functions in 2-D natural element method (NEM) and a non-linear partial derivative operator HNL. The complex and painstaking numerical derivation on the curved surface and the crucial shear locking are overcome by adopting the geometry transformation and the MITC3+ shell elements. The derived nonlinear modal equations are iteratively solved by introducing a three-step iterative solving technique which is combined with Lanczos transformation and Jacobi iteration. The developed non-linear numerical method is estimated through the benchmark test, and the effects of foundation stiffness, CNT volume fraction and functionally graded pattern, panel dimensions and boundary condition on the non-linear vibration of FG-CNTRC cylindrical panels on elastic foundation are parametrically investigated.

Key Words
cylindrical shell panels; FG-CNTRC; MITC3+ shell element; non-linear free vibration; three-step iterative scheme; von Kármán non-linearity; Winkler-Pasternak foundation

Address
J.R. Cho: Department of Naval Architecture and Ocean Engineering, Hongik University, Sejong 30016, Korea

Abstract
Lumped Damage Mechanics (LDM) is a theory proposed in the late eighties, which assumes that structural collapse may be analyzed as a two-phase phenomenon. In the first (pre-localization) stage, energy dissipation is a continuous process and it may be modelled by means of the classic versions of the theory of plasticity or Continuum Damage Mechanics (CDM). The second, post-localization, phase can be modelled assuming that energy dissipation is lumped in zones of zero volume: inelastic hinges, hinge lines or localization surfaces. This paper proposes a new LDM formulation for cracking in concrete structures in tension. It also describes its numerical implementation in conventional finite element programs. The results of three numerical simulations of experimental tests reported in the literature are presented. They correspond to plain and fiber-reinforced concrete specimens. A fourth simulation describes also the experimental results of a new test using the digital image correlation technique. These numerical simulations are also compared with the ones obtained using conventional Cohesive Fracture Mechanics (CFM). It is then shown that LDM conserves the advantages of both, CDM and CFM, while overcoming their drawbacks.

Key Words
damage mechanics; fiber-reinforced concrete; finite element analysis; localization bands; mesh independence; plain concrete

Address
Daniel V.C. Teles: Laboratory of Mathematical Modelling in Civil Engineering, Post-graduate Program in Civil Engineering, Federal University of Sergipe, São Cristóvão, Brazil
Rafael N. Cunha: Post-graduate Program in Civil Engineering, Federal University of Alagoas, Maceió, Brazil
Ricardo A. Picón: Departamento de Obras Civiles y Geología, Facultad de Ingeniería, Universidad Católica de Temuco,
Av. Rudecindo Ortega 02950, 4780000 Temuco, Chile
David L.N.F. Amorim: Laboratory of Mathematical Modelling in Civil Engineering, Post-graduate Program in Civil Engineering, Federal University of Sergipe, São Cristóvão, Brazil; Post-graduate Program in Civil Engineering, Federal University of Alagoas, Maceió, Brazil
Yongtao Bai: School of Civil Engineering, Chongqing University, Shapingba-District, 400045, Chongqing, China
Sergio P.B. Proença: Department of Structural Engineering, Engineering School of São Carlos, University of São Paulo,
Av. Trabalhador São-Carlense 400, São Carlos, Brazil
Julio Flórez-López: School of Civil Engineering, Chongqing University, Shapingba-District, 400045, Chongqing, China

Abstract
The buckling-restrained braced frames with eccentric configurations (BRBF-Es) exhibit stable cyclic behavior and possess a high energy absorption capacity. Additionally, they offer architectural advantages for incorporating openings, much like Eccentrically Braced Frames (EBFs). However, studies have indicated that significant residual drifts occur in this system when subjected to earthquakes at the Maximum Considered Earthquake (MCE) hazard level. Consequently, in order to mitigate these residual drifts, it is recommended to employ self-centering systems alongside the BRBF-E system. In our current research, we propose the utilization of the Direct Displacement-Based Seismic Design method to determine the design base shear for a hybrid system that combines BRBF with an eccentric configuration and a self-centering frame. Furthermore, we present a methodology for designing the individual components of this composite system. To assess the effectiveness of this design approach, we designed 3-, 6-, and 9-story buildings equipped with the BRBF-E-SCF system and developed finite element models. These models were subjected to two sets of ground motions representing the Maximum Considered Earthquake (MCE) and Design Basis Earthquake (DBE) seismic hazard levels. The results of our study reveal that although the combined system requires a higher amount of steel material compared to the BRBF-E system, it substantially reduces residual drift. Furthermore, the combined system demonstrates satisfactory performance in terms of story drift and ductility demand.

Key Words
buckling-restrained braced frames with eccentric configurations; direct displacement-based seismic design (DDBSD); hybrid system; seismic level; self-centering frame

Address
Akbar Nikzad, Alireza Kiani and Seyed Alireza Kazerounian: Department of Civil Engineering, Bushehr Branch, Islamic Azad University, Bushehr, Iran

Abstract
The past earthquakes revealed the importance of the design of moment-resisting reinforced concrete framed structures with ductile behavior. Due to seismic activity, failures in framed structures are widespread in beam-column joints. Hence, the joints must be designed to possess sufficient strength and stiffness. This paper investigates the effects of fibers on the ductility of hybrid fiber reinforced self-compacting concrete (HFRSCC) when subjected to seismic actions; overcoming bottlenecks at the beam-column joints has been studied by adding low modulus sisal fiber and high modulus steel fiber. For this, the optimized dose of hooked end steel fiber content (1.5%) was kept constant, and the sisal fiber content was varied at the rate of 0.1%, up to 0.3%. The seismic performance parameters, such as load-displacement behavior, ductility, energy absorption capacity, stiffness degradation, and energy dissipation capacity, were studied. The ductility factor and the cumulative energy dissipation capacity of the hybrid fiber (steel fiber, 1.5% and sisal fiber, 0.2%) added beam-column joint specimen is 100% and 121% greater than the control specimen, respectively. And also the stiffness of the hybrid fiber reinforced specimen is 100% higher than the control specimen. Thus, the test results showed that adding hybrid fibers instead of mono fibers could significantly enhance the seismic performance parameters. Therefore, the hybrid fiber reinforced concrete with 1.5% steel and 0.2% sisal fiber can be effectively used to design structures in seismic-prone areas.

Key Words
beam column joint; ductility; forward and reverse cyclic loading; hybrid fibers; sisal fiber

Address
S.M. Kavitha: Department of Civil Engineering, Alagappa Chettiar Government College of Engineering &Technology, Karaikudi 630 003, Tamil Nadu, India
G. Venkatesan: Department of Civil Engineering, University College of Engineering Tiruchirapalli (BIT Campus), Anna University, Tiruchirapalli -620024, India
Siva Avudaiappan: Departamento de Ciencias de la Construcción, Facultad de Ciencias de la Construccion y Ordenamiento Territorial, Universidad Tecnológica Metropolitana, Santiago, Chile
Chunwei Zhang: Multidisciplinary Center for Infrastructure Engineering, Shenyang University of Technology, Shenyang 110870, China

Abstract
The multiparameter eigenvalue method can be used to solve the damped finite element model updating problems. This method transforms the original problems into multiparameter eigenvalue problems. Comparing with the numerical methods based on various optimization methods, a big advantage of this method is that it can provide all possible choices of physical parameters. However, when solving the transformed singular multiparameter eigenvalue problem, the proposed method based on the generalised inverse of a singular matrix has some computational challenges and may fail. In this paper, more details on the transformation from the dynamic model updating problem to the multiparameter eigenvalue problem are presented and the structure of the transformed problem is also exposed. Based on this structure, the rigorous mathematical deduction gives the upper bound of the number of possible choices of the physical parameters, which confirms the singularity of the transformed multiparameter eigenvalue problem. More importantly, we present a row and column compression method to overcome the defect of the proposed numerical method based on the generalised inverse of a singular matrix. Also, two numerical experiments are presented to validate the feasibility and effectiveness of our method.

Key Words
dynamic analysis; finite element model updating; generalised inverse; row and column compression method; singular multiparameter eigenvalue problem

Address
Zhijun Wang: School of Mathematical Science, Dalian University of Technology, Dalian, Liaoning 116024, China
Bo Dong: School of Mathematical Science, Dalian University of Technology, Dalian, Liaoning 116024, China
Yan Yu: Business School, Dalian University of Foreign Languages, Dalian 116044, China
Xinzhu Zhao: School of Mathematics, Liaoning University, Shenyang, China
Yizhou Fang: School of Mathematical Science, Dalian University of Technology, Dalian, Liaoning 116024, China

Abstract
This paper introduces a new hybrid structural connection joint that combines shear walls with section steel beams, fundamentally resolving the construction complexity issue of requiring pre-embedded connectors in the connection between shear walls and steel beams. Initially, a quasi-static loading scheme with load-deformation dual control was employed to conduct low-cycle repeated loading experiments on five new connection joints. Data was acquired using displacement and strain gauges to compare the energy dissipation coefficients of each specimen. The destruction process of the new connection joints was meticulously observed and recorded, delineating it into three stages. Hysteresis curves and skeleton curves of the joint specimens were plotted based on experimental results, summarizing the energy dissipation performance of the joints. It's noteworthy that the addition of shear walls led to an approximate 17% increase in the energy dissipation coefficient. The energy dissipation coefficients of dog-bone-shaped connection joints with shear walls and cover plates reached 2.043 and 2.059, respectively, exhibiting the most comprehensive hysteresis curves. Additionally, the impact of laminated steel plates covering composite concrete floors on the stiffness of semi-rigid joint ends under excessive stretching should not be disregarded. A comparison with finite element analysis results yielded an error of merely 2.2%, offering substantial evidence for the wide-ranging application prospects of this innovative joint in seismic performance.

Key Words
connection joint; finite element analysis; hysteretic curve; seismic performance; skeleton curve

Address
Weicheng Su, Weihua Ye, Yaojun Deng: School of Civil Engineering, Guangzhou University, Guangzhou 510006, China
Jian Liu: School of Civil Engineering, Guangzhou University, Guangzhou 510006, China; Research Center of Complex Steel Structure Engineering Technology, Guangzhou University, Guangzhou 510006, China
Changjiang Liu: School of Civil Engineering, Guangzhou University, Guangzhou 510006, China; Research Center of Complex Steel Structure Engineering Technology, Guangzhou University, Guangzhou 510006, China; Guangdong Provincial Key Laboratory of Earthquake Engineering and Applied Technology, Guangzhou University, Guangzhou 510006, China
Chiyu Luo: Guangdong Architectural Design & Research Institute Co. LTD, Guangzhou 510145, China

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