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CONTENTS
Volume 31, Number 1, January 2023
 

Abstract
In this paper, Timoshenko-beam model is developed for the vibration of double carbon nanotubes. The resulting frequencies are gained for axial wave mode and length-to-diameter ratios. The natural frequency becomes more prominent for lower length-to-diameter ratios and diminished for higher ratios. The converse behavior is observed for axial wave mode with clamped-clamped and clamped-free boundary conditions. The frequencies of clamped-free are lower than that of clampedclamped boundary condition. The eigen solution is obtained to extract the frequencies of double walled carbon nanotubes using Galerkin's method through axial deformation function. Computer softer MATLAB is used for formation of frequency values. The frequency data is compared with available literature and found to be in agreement.

Key Words
axial wave mode; double walled carbon nanotubes; frequency data; Timoshenko-beam model

Address
Emad Ghandourah: Nuclear Engineering Department, Faculty of Engineering, King Abdulaziz University, Jeddah, Saudi Arabia
Muzamal Hussain: Department of Mathematics, Govt. College University Faisalabad, 38000, Faisalabad, Pakistan
Mohamed A. Khadimallah: Department of Civil Engineering, College of Engineering in Al-Kharj, Prince Sattam Bin Abdulaziz University, Al-Kharj, 11942, Saudi Arabia
Mashhour Alazwari: Mechanical Engineering Department, Faculty of Engineering, King Abdulaziz University, Jeddah, Saudi Arabia
Mohamed R. Ali: Faculty of Engineering and Technology, Future University in Egypt New Cairo 11835, Egypt; Basic Engineering Science Department, Benha Faculty of Engineering, Benha University, Benha, Egypt
Mohammed A. Hefni: Mining Engineering Department, Faculty of Engineering, King Abdulaziz University, Jeddah, Saudi Arabia

Abstract
The published studies usually used analytical method, numerical methods or experimental method to determine the stress-strain state and displacement of the single-layer or multi-layer curved shell types, but with a small scale model. However, a full scale multi-layer doubly curved concrete shell roof model should be researched. This paper presents the results of the experiment and simulation analysis involving stress-strain state, sliding between layers, the formation and development of the full scale double-layer doubly curved concrete shell roof when this shell begins to crack. The results of the this study have constructed the load-sliding strain relationship; strain diagram; stress diagram in the shell layers; the Nx, Ny membrane force diagram and deflection of shell. This results by experimental method on a full scale model of concrete have clarified the working of multi-layer doubly curved concrete shell roof. The experimental and simulation results are compared with each other and compared with the Sap2000 software.

Key Words
cracking; doubly curved shell; multi-layer shell; sliding; steel fiber concrete; stress-strain; thin shell

Address
Thanh Quang Khai Lam and Thi My Dung Do: Faculty of Civil Engineering, Mien Tay Construction University, 20B Pho Co Dieu, Ward 3, Vinh Long, Vietnam

Abstract
Reinforced concrete flat slab (RCFS) with columns is a standard gravity floor system for tall buildings in North America. Typically, RCFS-column connections are designed to resist gravity loads, and their contribution to resisting seismic forces is ignored. However, past experimental research has shown that RCFS-column connections have some strength and ductility, which may not be ignored. Advanced numerical models have been developed in the past to determine the nonlinear cyclic behavior of RCFS-column connections. However, these models are either too complicated for nonlinear dynamic analysis of an entire building or not developed to model the behavior of modern RCFS-column connections. This paper proposes a new nonlinear model suitable for modern RCFS-column connections. The numerical model is verified using experimental data of specimens with various material and reinforcement properties. A 40-story RC shear wall building was designed and analyzed to investigate the influence of RCFS on the global response of tall concrete buildings. The seismic responses of the building with and without the RCFS were modelled and compared. The results show that the modelling of RCFS has a significant impact on the inter-story drifts and force demands on both the seismic force-resisting and gravity elements.

Key Words
40-story RC shear wall building; advanced numerical models; nonlinear cyclic behavior; RCFS column connection

Address
T.Y. Yang: Department of Civil Engineering, University of British Columbia, Vancouver, Canada
O. AlHarras, L. Tobber, O. Sargazi: School of Engineering, University of British Columbia, Kelowna, Canada

Abstract
This paper proposes and validates the extension of two models, previously formulated for the evaluation of the shear strength of reinforced concrete members with un-corroded reinforcements, to the case of beams with corroded stirrups. These extended models are based on the plasticity theory (this model has been proposed in the past by one of the authors) and on the simplified modified compression field theory. The response of these models is compared with that of the compression chord capacity model, which has recently been embedded with modifications that simulate the effects of steel corrosion. These latter modifications are first discussed and then introduced into the other two models. An existing database of slender and non-slender beams tested in laboratory by other researchers is revised and improved. Finally, all the considered models are applied to the selected specimens and a comparison is drawn between the shear strength resulting from the considered models and the shear strength resulting from the laboratory tests. The effects of corrosion on some important parameters of the ultimate shear response of the reinforced concrete beams are also discussed.

Key Words
corrosion; mechanical model; plasticity; reinforced concrete beams; shear strength; stirrups

Address
Pier Paolo Rossi and Nino Spinella: Department of Civil Engineering and Architecture, University of Catania, Via Santa Sofia 64, 95125 Catania, Italy

Abstract
The rotational stiffness of a semi-rigid beam-to-column connection plays an important role in the reduction of the second-order effects in the precast concrete skeletal frames. The aim of this study is to present a detailed nonlinear finite element study to reproduce the experimental response of a semi-rigid precast beam-to-column connection composed by corbel, dowel bar and continuity tie bars available in the literature. A parametric study was carried using four arrangements of the reinforcing tie bars in the connection, including high ratio of the continuity tie bars passing around the column in the cast-in-place concrete. The results from the parametric study were compared to analytical equations proposed to evaluate the secant rotational stiffness of beam-to-column connections. The good agreement with the experimental results was obtained, demonstrating that the finite element model can accurately predict the structural behaviour of the beam-to-column connection despite its complex geometric configuration. The secant rotational stiffness of the connection was good evaluated by the analytical model available in the literature for ratio of the continuity tie bars of up to 0.69%. Precast beam-to-column connection with a ratio of the continuity tie bars higher than 1.4% had the secant stiffness overestimated. Therefore, an adjustment coefficient for the effective depth of the crack at the end of the beam was proposed for the analytical model, which is a function of the ratio of the continuity tie bars.

Key Words
beam-to-column connection; computational modelling; design method; precast concrete; semi-rigid

Address
Sérgio A. Coelho: Instituto Federal de Goiás-Câmpus Goiânia, Rua 75, no 46, Centro, Goiânia/GO, CEP: 74055-110, Brazil
Daniel L. Araújo: Escola de Engenharia Civil e Ambiental, Universidade Federal de Goiás, Rua Universitária, no 1488, Qd 86, Setor Universitário, Goiânia/GO, CEP: 74605-220, Brazil

Abstract
In this paper, the effects of the thickness of cubic samples on the tensile strength of concrete blocks were studied using experimental tests in the laboratory and numerical simulation by the particle flow code in three dimensions (PFC3D). Firstly, the physical concrete blocks with dimensions of 150 mmx190 mm (widthxheight) were prepared. Then, three specimens for each of seven different samples with various thicknesses were built in the laboratory. Simultaneously with the experimental tests, their numerical simulations were performed with PFC3D models. The widths, heights, and thicknesses of the numerical models were the same as those of the experimental samples. These samples were tested with a new tensile testing apparatus. The loading rate was kept at 1 kg/sec during the testing operation. Based on these analyses, it is concluded that when the thickness was less than 5 cm, the tensile strength decreased by increasing the sample thickness. On the other hand, the tensile strength was nearly constant when the sample thickness was raised to more than 5 cm (which can be regarded as a threshold limit for the specimens' thickness). The numerical outputs were similar to the experimental results, demonstrating the validity of the present analyses.

Key Words
new tensile testing apparatus; PFC3D; simulation; tensile strength; thickness effect

Address
Lei Zhou: State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, China; MOE Key Laboratory of Deep Earth Science and Engineering, College of Architecture and Environment, Sichuan University, Chengdu 610065, China; Failure Mechanics and Engineering Disaster Prevention, Key Laboratory of Sichuan Province, College of Architecture and Environment, Sichuan University, Chengdu 610065, China
Hadi Haeri: Department of Mining Engineering, Higher Education Complex of Zarand, Zarand, Iran
Vahab Sarfarazi: Department of Mining Engineering, Hamedan University of Technology, Hamedan, Iran
Mohammad Fatehi Marji: Department of Mine Exploitation Engineering, Faculty of Mining and Metallurgy, Institute of Engineering, Yazd University, Yazd, Iran
A.A. Naderi: Department of Mining Engineering, Hamedan University of Technology, Hamedan, Iran
Mohammadreza Hassannezhad Vayani: Department of CIvil Engineering, University of Tabriz, Tabriz, Iran

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