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CONTENTS
Volume 40, Number 1, July10 2021
 

Abstract
In recent years, earthquake resilient structures have become a research focus in the field of seismic engineering. In order to improve the resilience of steel frame - concrete wall panel structures, an innovative self-centering SRC wall panels with replaceable energy dissipaters is presented in the paper. For this purpose, the tested subassembly involving the self-centering SRC walls with frame beams as boundary was presented. The wall panels used in steel moment frames can provide the lateral resistance for structures. Test models of the wall panels with partial framed beams as boundary were suggested. The full-scale specimens were tested under cyclic lateral loads. The configuration of energy dissipaters and initial force of PT steel bars were varied to study their impacts on lateral behavior of the walls. Furthermore, the numerical models based on ABAQUS were developed. The parameter studies, including diameter of PT tendons, beam profile, beam span and wall width, were then conducted. The PT tendons can provide self-centering ability and the dampers are used to dissipate energy. The failure of the wall panels is mainly concentrated on energy dissipaters. This case makes it possible to repair the walls easily.

Key Words
self-centering; wall panels; dampers; mild steel; replaceable

Address
Lu Sui, Hanheng Wu, Penghui Tang, Tao Gong and Yifan Wang: School of Civil Engineering, Chang'an University, Xi

Abstract
The use of steel-concrete composites (SCCs) is growing rapidly in the construction industry because of their improved constructability, decreased labor cost, improved bond to reinforcing steel, improved structural integrity and accelerated project schedules compared to conventional composites. Fire is a constant danger to these structural composites. Therefore, the effect of fire on the behavior of SCCs must be evaluated and included in design provisions. Slim-floor beams (SFBs) are cost-effective systems which permit a major decrease in the thickness of industrial and commercial buildings floors. The present study reviews the recent advancements and history of SCCs together with recent studies investigating the fire performance of SFBs. First, the evolution of SCC systems is briefly discussed. Then, the fire resistance and specific thermal definitions of the main structural members are presented. Finally, analytical and numerical methods for predicting fire resistance, as well as the relevant experimental results are presented. The main focus of this study is on analyzing the performance of SFBs as a flooring system under fire. It is found that further investigation is required to improve Eurocode 4 provisions for enabling the rapidly growing construction industry to benefit from the advantages provided by composite construction methods with safety considerations. Numerous studies have so far been conducted in terms of enhancing the design quality of these systems, among which some will be discussed in this study.

Key Words
steel-concrete composite; slim-floor beams; fire resistance; thermal behavior; construction

Address
Armin Memarzadeh, Amir Ali Shahmansouri and Mahdi Nematzadeh: Department of Civil Engineering, Faculty of Engineering and Technology, University of Mazandaran, Babolsar, Iran
Aliakbar Gholampour: College of Science and Engineering, Flinders University, South Australia, Australia

Abstract
Based on finite element software, a simulation programme is used to evaluate the seismic behaviour of new-type steel-reinforced concrete (SRC) columns, called enlarged cross steel-reinforced concrete (ECSRC) columns. With abundant simulations, the effects of the loading paths, number of loading cycles, incremental amplitude of displacement and variable axial load on the seismic response of the ECSRC columns were investigated. The results indicate that the seismic behaviour of the column is highly dependent on the loading paths, and it was observed that the loading paths produced a significant effect on the hysteretic response of the columns. Compared with those under uniaxial loading, the yield load, maximum load, ultimate displacement and ductility coefficient of the ECSRC columns under biaxial loading are reduced by 13.47%, 18.01%, 12.17% and 32.64%, respectively. The energy dissipation capacity of the columns is highly dependent on the loading paths. The skeleton curves are not significantly influenced by the number of loading cycles until the yield point of steel and longitudinal reinforcement is reached. With an increase in loading cycles, the yield load, yield displacement, ductility coefficient and maximum load, as well as the corresponding horizontal displacement of the column, are reduced, while the energy dissipation grows. In addition, the yield displacement, yield load, and ductility coefficient increase with an increase in the incremental amplitude of displacement; however, the energy dissipation decreases under these conditions. The seismic performance of the SRC column under variable axial loads clearly exhibits asymmetry that is worse than that observed under constant axial loads.

Key Words
enlarged cross steel-reinforced concrete columns; various loadings; numerical simulation; biaxial coupling effect; seismic behaviour

Address
Peng Wang, Qingxuan Shi and Qiuwei Wang: State Key Laboratory of Green Building in Western China of Xi'an University of Architecture & Technology, Xi'an 710055, China;
College of Civil Engineering, Xi'an University of Architecture & Technology, Xi'an 710055, China
Key Laboratory of Structural Engineering and Seismic Resistance Education, Xi'an University of Architectural & Technology, Xi'an 710055, China
Feng Wang: College of Civil Engineering, Xi'an University of Architecture & Technology, Xi'an 710055, China

Abstract
Recently, the elliptic-braced moment resisting frame (ELBRF) which is a new lateral bracing system installed in the middle bay of the frame in the facade of buildings is introduced. This system not only prevents a solution for opening space problem in view of architectural aspects, but also improves the structural behavior. The main drawback of its using in view of numerical modeling in multistory buildings is lack of curved frame element in design and analysis software. To overcome this shortcoming, in this paper, for the first time, an equivalent element for elliptic brace is presented for ELBRF through a laboratory program and nonlinear finite element analysis, which will contribute to its accurate and easy modelling and design. To evaluate the hysteresis behavior of the equivalent element, an experimental test on a 1/2 scale was conducted for a single-story single-bay ELBRF specimen under cyclic quasi-static loading and the results were compared with those for the equivalent element in a story base model. Good agreement was observed between the experimental and analytical outcomes. The seismic demand analyses of ELBRF and frame with equivalent bracing system in 3, 5, 7, and 10 stories were carry out through different loading patterns in Nonlinear Static Pushover Analysis (NSPA) and Nonlinear Time History Analysis (NTHA) with 20 earthquake records using OpenSees software. Story drift, displacement, and story shear were evaluated. Relatively accurate estimations were achieved by NSPA in comparison with NTHA. Also, the seismic performance of the equivalent element for the ELBRF system against earthquake was examined and then response modification factor (R factor) was acquired. The values of 8.5 and 12.2 for the R factor were calculated at the ultimate and the allowable stress limit states, respectively.

Key Words
elliptic braced moment resisting frame; equivalent element; seismic demand; nonlinear static pushover analysis; nonlinear time history analysis; response modification factor

Address
Habib Ghasemi Jouneghani and Abbas Haghollahi: Department of Civil Engineering, Faculty of Civil Engineering, Shahid Rajaee Teacher Training University, Tehran, Iran
Mohammad Talebi Kalaleh: Department of Civil Engineering, Sharif University of Technology, Tehran, Iran
S. Bahram Beheshti-Aval: Department of Civil Engineering, Faculty of Civil Engineering, K. N. Toosi University of Technology, Tehran, Iran

Abstract
A segmental concrete-filled basalt fiber-reinforced polymer (BFRP) tube was proposed, whose lightweight characteristic promoted convenient bridge column transportation and construction. A special connecting component between the adjacent BFRP segments ensured effective transfer of sectional forces. Four specimens, including three segmental specimens and one comparative integral concrete-filled BFRP tube, were tested to investigate the mechanical performance of the BFRP tube under cyclic loading. Damage patterns, load-deformation response, and strain development were observed, showing that the segmental concrete-filled BFRP tube presented satisfactory load-carrying and deformation capacities. Further, the connecting component effectively guaranteed a satisfactory hysteretic performance. Based on the test results, the overall load-carrying capacity was mainly determined by the moment resistance of the interface. Furthermore, the segmental structure weakened the confining effect on the core concrete, though applying multiple stirrups could compensate for the reduced confining effect. Finally, design methods were proposed for the connecting component.

Key Words
BFRP tube; segmental structure; jointed reinforcement; cyclic test; crack resistance; seismic performance

Address
Yuehan Sun, Kailai Deng, Wenfeng Huang and Chao Yin: Department of Bridge Engineering, Southwest Jiaotong University, Chengdu 610031, China
Yulin Zhan: Department of Bridge Engineering, Southwest Jiaotong University, Chengdu 610031, China;
Institute of Civil Engineering Materials, Southwest Jiaotong University, Chengdu 610031, China

Abstract
A fiber-reinforced polymer (FRP)-confined concrete core that provides high strength and ductility under axial compression can act as strength enhancement in a hybrid column. In the present study, ordinary concrete was replaced with ultra-high-performance concrete (UHPC) to form an FRP-confined UHPC core (FCUC). The FCUC was embedded in square concrete-filled steel tube (CFST) columns to form a high-performance hybrid column (SCF-UHPC column for short). The axial compressive behavior of the SCF-UHPC was experimentally investigated using 12 SCF-UHPC columns and two ordinary CFST columns for comparison. The advantages of the SCF-UHPC include excellent axial load-bearing capacity, good ductility, and stable residual load-bearing capacity. The results show that failure of an SCF-UHPC column was caused by FRP rupture of FCUC, which occurred after steel tube buckling that results in the degraded stiffness. It was also shown that the load-displacement behavior of the SCF-UHPC composite column was determined by the UHPC core diameter and the corresponding confinement provided by the outer steel tube and inner FRP jacket. A hardening effect could be achieved when the confinement demand of the UHPC core was satisfied, whereas a plateau effect appeared if the confinement was insufficient. Furthermore, the load-bearing capacity and ductility of the SCF-UHPC columns improved with increased thickness of the steel tube and the FRP.

Key Words
FRP; UHPC; composite column; axial compression behavior; experimental study

Address
Yi Tao: School of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an, Shaanxi, China;
State Key Laboratory of Green Building in Western China, Xi'an University of Architecture and Technology, Xi'an, Shaanxi, China
Jin-Ben Gu: College of Civil Engineering, Tongji University, Shanghai, China
Jian-Fei Chen: Department of Ocean Science and Engineering, Southern University of Science and Technology, Shenzhen, Guangdong, China
Peng Feng: Department of Civil Engineering, Tsinghua University, Beijing, China


Abstract
In this study, an analytical model is developed for the analysis of transient temperature, displacements, and stresses in simply supported layered beams. The beam is suddenly heated from the top and bottom surfaces by external steady heat sources and is subjected to a mechanical load. The temperature in each layer is variable along the thickness and follows the one-dimensional (1-D) transient heat transfer equation. The Laplace transform approach is used to obtain the transient temperature field in the beam. The thermoelastic constants of the beam are temperature-dependent. Dividing every layer into a series of thin slices, the temperature and the thermoelastic constants for each slice can be considered uniform. The two-dimensional (2-D) thermoelasticity theory is adopted to derive the governing equations of displacements and stresses in each slice. The transfer matrix method is applied to obtain the displacement and stress solutions for the beam. As an example, the distributions of transient temperature, displacements, and stresses in a three-layer beam are studied. The effects of the temperature dependent thermoelastic constants on the mechanical behavior of the beam are discussed in detail.

Key Words
layered beam; Laplace transform; transient temperature field; thermoelasticity; transfer matrix method

Address
Zhong Zhang, Ding Zhou, Jiandong Zhang and Hai Fang: College of Civil Engineering, Nanjing Tech University, Nanjing 211816, China
Huixuan Han: College of Civil Engineering and Architecture, Jiangsu University of Science and Technology,
Zhenjiang 212000, China

Abstract
In this study, a nonlocal Layerwise theory is presented for free vibration analysis of nanobeams resting on an elastic foundation. Eringen's nonlocal elasticity theory is used to consider the small-scale effect on behavior of nanobeam. The governing equations are obtained by employing Hamilton's principle and Layerwise theory of beams and Eringen's nonlocal constitutive equation. The presented theory takes into account the in-plane and transverse normal and shear strain in the modeling of the nanobeam and can predict more accurate results. The governing equations of the beam are solved by Navier's method for Simple-Simple boundary conditions and semi-analytical methods to obtain the natural frequency for various boundary conditions including Clamped-Simple (C-S), Clamped-Clamped (C-C) and Free-Free (F-F) boundary conditions. Predictions of the present theory are compared with benchmark results in the literature. Effects of nonlocal parameter, Pasternak shear coefficient, Winkler spring coefficient, boundary conditions, and the aspect ratio on the free vibration of nanobeams are studied. The flexural mode and thickness mode natural frequencies of the nanobeam are predicted. It is shown that the predictions of present method are more accurate than the equivalent single layer theories. The theoretical developments and formulation presented herein should also be served to analyze the mechanical behavior of various nanostructures with various loading and boundary conditions.

Key Words
free vibration; nanobeam; nonlocal elasticity theory; layerwise theory; winkler-pasternk foundation

Address
Mahsa Najafi and Isa Ahmadi: Advanced Materials and Computational Mechanics Lab., Department of Mechanical Engineering, University of Zanjan, University Blvd,
P.O Box: 45371-38791, Zanjan, Iran

Abstract
A structure undergoes progressive collapse when a primary structural element fails, leading to damage of either a large part or even the entire structure. Beam-column connections are one of the major contributing structural elements which significantly affect the performance of the structure. Undesirable performance and damage to these connections can result in local failure and, in turn, lead to progressive failure. In the present research, behaviors of some beam-column connections were empirically and numerically assessed subject to column removal scenario. A number of tests were performed on some welded top and seat angle connections. Then, numerical models were created and validated by the experimental results. It was observed that the results of finite element analyses very well correspond to the test results. Moreover, parametric studies were done using finite element analysis. Behavior, failure limit states, and formation of the catenary action were investigated. Results demonstrate that adding a web plate or a web angle could be an appropriate method for upgrading the connection behavior. Furthermore, an increase in the angle thickness and length of the angle leg attached to the column can result in higher resistance to progressive collapse.

Key Words
progressive collapse; top and seat angle connections; catenary action; failure mode; finite element analysis

Address
Mohammad Ali Hadianfard, Mahboobe Namjoo, Morteza Boroumand and Sareh Akbarpoor: Department of Civil and Environmental Engineering, Shiraz University of Technology,
P.O. Box 71555-313, Modarres Blvd, Shiraz, Iran

Abstract
The goal of this study is to fill this apparent gap in the area about investigating free vibration of Functionally Graded Piezoelectric Materials (FGPMs) nanobeams with porosity resting on two-parameter elastic foundations, under voltage load considering Timoshenko beam model and nonlocal theory. The elastic foundation is considered as a Pasternak model with adding a shear layer to the Winkler model. The electromechanical and mechanical properties of the nanobeam (such as elastic, piezoelectric, dielectric coefficients and mass density) are FG in the thickness direction of the beam. Based on Hamilton principle, governing equations of the problem are derived. The Differential Quadrature Method (DQM) for solution of these equations are employed to determine the natural frequencies of the FGPM nanobeams at different Boundary Conditions (B.C.s). The influences of supporting conditions, the porosity coefficient and patterns including even and uneven, nonlocal parameter, Winkler foundation modulus, shear elastic foundation modulus, external voltage and power-law index on the electromechanical vibration characteristics of the FGPM nanobeams are discussed in details. It is found that the FG index and nonlocal parameter will reduce the natural frequencies of the FG nanobeam, while the Winkler and Pasternak moduli of the foundation show an opposite tendency.

Key Words
vibration analysis; porosity; functionally graded piezoelectric materials; two-parameter elastic foundations; Timoshenko beam model

Address
Wenhua Huang: School of Civil Engineering and Architecture, Shaanxi University of Technology, Han zhong, Shaanxi, 723001, China
Vahid Tahouneh: Young Researchers and Elite Club, Islamshahr Branch, Islamic Azad University, Islamshahr, Iran

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