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CONTENTS
Volume 37, Number 5, December10 2020
 


Abstract
A novel spiral confined angle-steel reinforced concrete (SCARC) column was developed in this study. A total of 16 specimens were prepared and tested (eight of them were tested under axial loading, the other eight were tested under eccentric loading). The failure processes and load-displacement relationships of specimens under axial and eccentric loads were examined, respectively. The load-carrying capacity and ductility were evaluated by parametric analysis. A calculation approach was developed to predict the axial and eccentric load-carrying capacity of these novel columns. Results showed that the spiral reinforcement provided enough confinement in SCARC columns under axial and low eccentric loads, but was not effective in that under high eccentric loads. The axial load-carrying capacity and ductility of SCARC columns were improved significantly due to the satisfactory confinement from spirals. The outer reinforcement and other construction measures were necessary for SCARC columns to prevent premature spalling of the concrete cover. The proposed calculation approach provided a reliable prediction of the load-carrying capacity of SCARC columns.

Key Words
steel reinforced concrete columns; spiral reinforcement; axial loading; eccentric loading; load-carrying capacity; ductility

Address
Chunheng Zhou and Junhua Li: School of Civil and Environmental Engineering, Ningbo University, 818 Fenghua Road, Ningbo, China
Zongping Chen: College of Civil Engineering and Architecture, Guangxi University, 100 Daxue Road, Nanning, China;
Guangxi Key Laboratory of Disaster Prevention and Engineering Safety, Guangxi University, 100 Daxue Road, Nanning, China
Liping Cai and Zhenhua Huang: Department of Mechanical Engineering, University of North Texas, 3940 N. Elm St., Denton, Texas, U.S.A.



Abstract
This paper firstly developed a new type of Double Skin Composite (DSC) beams using novel enhanced C-channels (ECs). The shear behaviour of novel ECs was firstly studied through two push-out tests. Eleven full-scale DSC beams with ECs (DSCB-ECs) were tested under four-point loading to study their ultimate strength behaviours, and the studied parameters were thickness of steel faceplate, spacing of ECs, shear span, and strength of concrete core. Test results showed that all the DSCB-ECs failed in flexure-governed mode, which confirmed the effective bonding of ECs. The working mechanisms of DSCB-ECs with different parameters were reported, analysed and discussed. The load-deflection (or strain) behaviour of DSCB-ECs were also detailed reported. The effects of studied parameters on ultimate strength behaviour of DSCB-ECs have been discussed and analysed. Including the experimental studies, this paper also developed theoretical models to predict the initial stiffness, elastic stiffness, cracking, yielding, and ultimate loads of DSCB-ECs. Validations of predictions against 11 test results proved the reasonable estimations of the developed theoretical models on those stiffness and strength indexes. Finally, conclusions were given based on these tests and analysis.

Key Words
double skin composite beam; shear connectors; ultimate strength behaviour; bending tests; theoretical model; parametric study; stiffness and strength

Address
Jia-Bao Yan and Huining Guan: School of Civil Engineering / Key Laboratory of Coast Civil Structure Safety of Ministry of Education,
Tianjin University, Tianjin 300350, China
Tao Wang: Key Laboratory of Earthquake Engineering and Engineering Vibration, Institute of Engineering Mechanics,
CEA, Harbin 150080, China



Abstract
Recently, Concrete-filled double skin steel tubular (CFDST) columns have proven an exceptional structural resistance in terms of strength, stiffness, and ductility. However, the resistance of these column members can be severely affected by the type of loading in which bending stresses increase in direct proportion with axial load and eccentricity value. This paper presents a non-linear finite element based modeling approach that studies the behavior of slender CFDST columns under biaxial loading. Finite element models were calibrated based on the outcomes of experimental work done by other researchers. Results from simulations of slender CFDST columns under axial loading eccentric in one direction showed good agreement with the experimental response. The calibrated models are expanded to a total of thirty models that studies the behavior of slender CFDST columns under combined compression and biaxial bending. The influences of parameters that are usually found in practice are taken into consideration in this paper, namely, eccentricity-to-diameter (e/D) ratios, slenderness ratios, diameter-to-thickness (D/t) ratios, and steel contribution ratios. Finally, an analytical study based on current code provisions is conducted. It is concluded that South African national standards (2011) provided the most accurate results contrasted with the Eurocode 4 (2004) and American Institute of Steel Construction (2016) that are found to be conservative. Accordingly, correction factors are proposed to the current design guidelines to provide more satisfactory results.

Key Words
slender composite columns; concrete-filled steel tubes; double-skin; CFDST; eccentric loading; buckling; non-linear finite elements; biaxial

Address
Awni Abu-Shamah: Independent researcher, Amman, Jordan
Rabab Allouzi: Department of Civil Engineering, The University of Jordan, Aljubeiha, Amman, Jordan

Abstract
Vibration of vertically aligned-monolayered-nonuniform nanorods consist of functionally graded materials with elastic supports has not been investigated yet. To fill this gap, the problem is examined using the elasticity theories of Eringen and Gurtin-Murdoch. The geometrical and mechanical properties of the surface layer and the bulk are allowed to vary arbitrarily across the length. The nonlocal-surface energy-based governing equations are established using differential-type and integro-type formulations, and solved by employing the Galerkin method by exploiting admissible modes approach and element-free Galerkin (EFG). Through various comparison studies, the effectiveness of the EFG in capturing both nonlocal-differential/integro-based frequencies is proved. A constructive parametric study is also conducted, and the roles of nanorods' diameter, length, stiffness of both inter-rod's elastic layer and elastic supports, power-law index of both constituent materials and geometry, nonlocal and surface effects on the dominant frequencies are revealed.

Key Words
axial vibration; vertically aligned-monolayered-nanorods; functionally graded materials (FGMs); nonlocal-integro-based model; surface energy; element-free Galerkin

Address
Yuan Yuan, Ke Zhao and Yafei Zhao: School of Mechanical and Precision Instrument Engineering,
Xi'an University of Technology, Xi'an, P.O. Box 710048, China
Keivan Kiani: Department of Civil Engineering, K.N. Toosi University of Technology,
Valiasr Ave., P.O. Box 15875-4416, Tehran, Iran



Abstract
In this article the seismic demand and performance of two recent braced steel frames named steel moment frames with the elliptic bracing (ELBRFs) are assessed through a laboratory program and numerical analyses of FEM. Here, one of the specimens is without connecting bracket from the corner of the frame to the elliptic brace (ELBRF-E), while the other is with the connecting brackets (ELBRF-B). In both the elliptic braced moment resisting frames (ELBRFs), in addition to not having any opening space problem in the bracing systems when installed in the surrounding frames, they improve structure' ss behavior. The experimental test is run on 1/2 scale single-story single-bay ELBRF specimens under cyclic quasi-static loading and compared with X-bracing and SMRF systems in one story base model. This system is of appropriate stiffness and a high ductility, with an increased response modification factor. Moreover, its energy dissipation is high. In the ELBRF bracing systems, there exists a great interval between relative deformation at the yield point and maximum relative deformation after entering the plastic region. In other words, the distance from the first plastic hinge to the collapse of the structure is fairly large. The experimental outcomes here, are in good agreement with the theoretical predictions.

Key Words
elliptic braced moment resisting frame; lateral bracing system; experimental behavior; seismic demand; seismic performance; nonlinear static pushover analysis; energy absorption

Address
Habib Ghasemi Jouneghani and Abbas Haghollahi: Department of Civil Engineering, Faculty of Civil Engineering, Shahid Rajaee Teacher Training University, Tehran, Iran

Abstract
This paper presents an investigation of the thermal performance of composite floor slabs with profiled steel decking exposed to fire effects from floor. A detailed finite-element model has been developed by representing the concrete slab with steel decking under of it and steel beam both steel parts protected by intumescent coating. Although this type of floor systems offers a better fire resistance, passive fire protection materials should be applied when a higher fire resistance is desired. Moreover, fire exposed side is so crucial for composite slab systems as the total fire behaviour of the floor system changes dramatically. When the fire attack from steel parts, the temperature rises rapidly resulting in a sudden decrease on the strength of the beam and decking. Herein this paper, the fire attack side is assumed from the face of the concrete floor (top of the concrete assembly). Therefore, the heat is transferred through concrete to the steel decking and reaching finally to the steel beam both protected by intumescent coating. In this work, the numerical model has been established to predict the heat transfer performance including material properties such as thermal conductivity, specific heat and dry film thickness of intumescent coating. The developed numerical model has been divided into different layers to understand the sensitivity of steel temperature to the number of layers of intumescent coating. Results show that the protected composite floors offer a higher fire resistance as the temperature of the steel section remains below 60C even after 60-minute Standard (ISO) fire and Fast fire exposure. Obtaining lower temperatures in steel due to the great fire performance of the concrete itself results in lesser reductions of strength and stiffness hence, lesser deflections.

Key Words
fire resistance; composite floor; steel decking; steel beam; finite element modelling; intumescent coating

Address
Burak K. Cirpici, Suleyman N. Orhan and Turkay Kotan: Erzurum Technical University, Department of Civil Engineering, Erzurum, Turkey, 25050

Abstract
An innovative Partially Precast Steel Reinforced Concrete (PPSRC) beam is presented in this paper. To study the shear behavior of PPSRC beams, static loading experiments were conducted on 10 specimens, including 4 T-beam specimens and 4 PPSRC inverted T-beam specimens together with 2 PPSRC rectangular section beams. In the tests, the shear behaviors of the PPSRC beams were emphasized. On the basis of the experiments, the failure mode and ultimate bearing capacity were thoroughly examined. The calculation methods for shear capacity are also presented in this paper. The analysis of mechanical behavior and the calculation methods presented can be used as a reference to design these innovative composite PPSRC beams and provide a significant foundation for further research.

Key Words
steel reinforced concrete structure; PPSRC beams; shear behavior; shear capacity; experimental study

Address
Yong Yang and Hui Li: School of Civil Engineering, Xi'an University of Architecture & Technology, Xi'an, Shanxi, 710055, China

Abstract
This research deals with the study of vibrational behavior of armchair and zigzag single-walled carbon nanotubes invoking extended Love shell theory. The effects of different physical and material parameters on the fundamental frequencies are investigated. By using volume fraction for power law index, the fundamental natural frequency spectra for two forms of single-walled carbon nanotubes are calculated. The influence of frequencies against length-to-diameter ratios with varying power law index are investigated in detail for these tubes. To discretize the governing equation in eigen-value form, wave propagation approach is developed. Complex exponential functions have been used and the axial model depends on boundary condition that has been described at the edges of carbon nanotubes to calculate the axial modal dependence. Computer software MATLAB is utilized for the frequencies of single-walled carbon nanotubes and current results shows a good stability with comparison of other studies.

Key Words
power law index; armchair and zigzag; MATLAB; volume fraction

Address
Mohamed Amine Khadimallah: Prince Sattam Bin Abdulaziz University, College of Engineering, Civil Engineering Department, BP 655, Al-Kharj, 11942, Saudi Arabia;
Laboratory of Systems and Applied Mechanics, Polytechnic School of Tunisia, University of Carthage, Tunis, Tunisia
Muzamal Hussain: Department of Mathematics, Govt. College University Faisalabad, 38000, Faisalabad, Pakistan



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