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CONTENTS
Volume 68, Number 2, October25 2018
 

Abstract
This paper aims to develop response modification factors for stiffness degrading structures by incorporating soil-structure interaction effects. A comprehensive parametric study is conducted to investigate the effects of key SSI parameters, natural period of vibration, ductility demand and hysteretic behavior on the response modification factor of soil-structure systems. The nonlinear dynamic response of 6300 soil-structure systems are studied under two ensembles of accelograms including 20 recorded and 7 synthetic ground motions. It is concluded that neglecting the stiffness degradation of structures can results in up to 22% underestimation of inelastic strength demands in soil-structure systems, leading to an unexpected high level of ductility demand in the structures located on soft soil. Nonlinear regression analyses are then performed to derive a simplified expression for estimating ductility-dependent response modification factors for stiffness degrading soil-structure systems. The adequacy of the proposed expression is investigated through sensitivity analyses on nonlinear soil-structure systems under seven synthetic spectrum compatible earthquake ground motions. A good agreement is observed between the results of the predicted and the target ductility demands, demonstrating the adequacy of the expression proposed in this study to estimate the inelastic demands of SSI systems with stiffness degrading structures. It is observed that the maximum differences between the target and average target ductility demands was 15%, which is considered acceptable for practical design purposes.

Key Words
response modification factor; degrading structures; soil-structure interaction; practical equation; sensitivity analysis

Address
Behnoud Ganjavi: Department of Civil Engineering, University of Mazandaran, Babolsar, Iran
Majid Bararnia: Department of Civil, Water & Environmental Engineering, Shahid Beheshti University, Tehran, Iran
Iman Hajirasouliha: Department of Civil and Structural Engineering, University of Sheffield, Sheffield, UK

Abstract
For the first time, nonlocal damped vibration and buckling analyses of arbitrary tapered bidirectional functionally graded solid circular nano-plate (BDFGSCNP) are presented by employing modified spectral Ritz method. The energy method based on Love-Kirchhoff plate theory assumptions is applied to derive neutral equilibrium equation. The Eringen\'s nonlocal continuum theory is taken into account to capture small-scale effects. The characteristic equations and corresponding first mode shapes are calculated by using a novel modified basis in spectral Ritz method. The modified basis is in terms of orthogonal shifted Chebyshev polynomials of the first kind to avoid employing adhesive functions in the spectral Ritz method. The fast convergence and compatibility with various conditions are advantages of the modified spectral Ritz method. A more accurate multivariable function is used to model two-directional variations of elasticity modulus and mass density. The effects of nanoscale, in-plane pre-load, distributed dashpot, arbitrary tapering, pinned and clamped boundary conditions on natural frequencies and buckling loads are investigated. Observing an excellent agreement between results of current work and outcomes of previously published works in literature, indicates the results\' accuracy in current work.

Key Words
non-local continuum mechanics; damped vibration; buckling; bidirectional functionally graded material; circular nano-plate; arbitrary thickness variation

Address
Abbas Heydari: Young Researchers and Elite Club, Ardabil Branch, Islamic Azad University, Ardabil, Iran

Abstract
In this paper, harmonic responses of infilled multi-storey frames are obtained by using a single variable shear deformation theory (SVSDT) and dynamic stiffness formulations. Two different planar frame models are used which are fully infilled and soft storey. The infill walls are modeled by using equivalent diagonal strut approach. Firstly, free vibration analyses of bare frame and infilled frames are performed. The calculated natural frequencies are tabulated with finite element solution results. Then, harmonic response curves (HRCs) of frame models are plotted for different infill wall thickness values. All of the results are presented comparatively with Timoshenko beam theory results to reveal the effectiveness of SVSDT which considers the parabolic shear stress distribution along the frame member cross-sections.

Key Words
dynamic stiffness; harmonic response; infilled frame; natural frequency; single variable shear deformation theory

Address
Baran Bozyigit and Yusuf Yesilce: Department of Civil Engineering, Dokuz Eylul University, 35160, Buca, Izmir, Turkey

Abstract
This paper describes an experimental study on the seismic performance of steel reinforced concrete (SRC) T-shaped columns. The lateral loads were applied along the web of the column with different loading histories, such as monotonic loading, mixed loading of variable amplitude cyclic loading and monotonic loading, constant amplitude cyclic loading and variable amplitude cyclic loading. The failure modes, load-displacement curves, characteristic loads and displacements, ductility, strength and stiffness degradations and energy dissipation capacity of the column were analyzed. The effects of loading history on the seismic performance were focused on. The test results show that the specimens behaved differently in the aspects of the failure mode subject to different loading history, although all the failure modes can be summarized as flexural failure. The hysteretic loops of specimens are plump, and minimum values of the failure drift angles and ductility coefficients are 1/24 and 4.64, respectively, which reflect good seismic performance of SRC T-shaped column. With the increasing numbers of loading cycles, the column reveals lower bearing capacity and ductility. The strength and stiffness of the column with variable amplitude cyclic loading degrades more rapidly than that with constant amplitude cyclic loading, and the total cumulative dissipated energy of the former is less.

Key Words
steel reinforced concrete (SRC); T-shaped column; loading history; seismic performance; experimental study

Address
J. Wang, Z.Q. Liu, J.Y. Xue and C.M. Hu: College of Civil Engineering, Xi

Abstract
This paper presents a study of geometric nonlinear forced vibration of carbon nano-tubes (CNTs) reinforcement composite plates on nonlinear elastic foundations. The plate is bonded with piezoelectric layers. The von Karman geometric nonlinearity assumptions with classical plate theory are employed to obtain the governing equations. The Galerkin and homotopy perturbation method (HPM) are utilized to investigate the effect of carbon nano-tubes volume fractions, large amplitude vibrations, elastic foundation parameters, piezoelectric applied voltage on frequency ratio and primary resonance. The results indicate that the carbon nano-tube volume fraction, applied voltage and elastic foundation parameters have significant effect on the hardening response of carbon nanotubes reinforced composite (CNTRC) plates.

Key Words
nonlinear forced vibration; carbon nano-tube; elastic foundation, Homotopy Perturbation method

Address
Ali A. Yazdi: Department of Mechanical Engineering, Quchan University of Technology, P. O. Box 94717-84686, Quchan, Iran

Abstract
In this article, the theory of fractional order two temperature generalized thermoelasticity is employed to study the wave propagation in a fiber reinforced anisotropic thermoelastic half space in the presence of moving internal heat source. The whole space is assumed to be under the influence of gravity. The surface of the half-space is subjected to an inclined load. Laplace and Fourier transform techniques are employed to solve the problem. Expressions for different field variables in the physical domain are derived by the application of numerical inversion technique. Physical fields are presented graphically to study the effects of gravity and heat source. Effects of time, reinforcement, fractional parameter and inclination of load have also been reported. Results of some earlier workers have been deduced from the present analysis. 2010MSC: 74A15, 80A20.

Key Words
fiber reinforcement; gravity; heat source; two temperature; fractional order theory

Address
Kavita Jain, Kapil Kumar Kalkal and Sunita Deswal: Department of Mathematics, Guru Jambheshwar University of Science and Technology, Hisar-125001, Haryana, India

Abstract
Cables are the main load-bearing members of prestressed structure and other tensegrity structures. Based on the static equilibrium principle, a new cable force identification method considering cable flexural rigidity is proposed. Its computational formula is derived and the strategy to solve its implicit formula is introduced as well. In order to improve the reliability and practicality of this method, the influence of the cable flexural rigidity on cable force identification accuracy is also investigated. Through cable force identification experiments, the relationships among certain parameters including jacking force, jacking displacement, initial cable force, and sectional area (flexural rigidity) are studied. The results show that the cable force calculated by the proposed method considering flexural rigidity is in good agreement with the finite element results and experimental results. The proposed method with high computational accuracy and resolution efficiency can avoid the influences of the boundary condition and the length of the cable on calculation accuracy and is proven to be conveniently applied to cable force identification in practice.

Key Words
prestressed structure; flexural rigidity; cable force identification method; static equilibrium; experimental research

Address
Long Wang:
1) School of Civil Engineering and Transportation, South China University of Technology, Guangzhou, 510641, P. R. China
2) Guangzhou Construction Co., Ltd, Guangzhou, 510030, P. R. China
Bo Wu, Kairong Shi, Wenzhi Pan, Zhuoyi He, Zhijian Ruan and Quanpan Lin: School of Civil Engineering and Transportation, South China University of Technology, Guangzhou, 510641, P. R. China
Junyue Gao: Guangzhou Construction Co., Ltd, Guangzhou, 510030, P. R. China

Abstract
This study proposes an empirical formulation to predict the maximum deformation of offshore blast wall structure that is subjected to impact loading caused by hydrocarbon explosion. The blast wall model is assumed to be supported by a simply-supported boundary condition and corrugated panel is modelled. In total, 1,620 cases of LS-DYNA simulations were conducted to predict the maximum deformation of blast wall, and they were then used as input data for the development of the empirical formulation by regression analysis. Stainless steel was employed as materials and the strain rate effect was also taken into account. For the development of empirical formulation, a wide range of parametric studies were conducted by considering the main design parameters for corrugated panel, such as geometric properties (corrugation angle, breadth, height and thickness) and load profiles (peak pressure and time). In the case of the blast profile, idealised triangular shape is assumed. It is expected that the obtained empirical formulation will be useful for structural designers to predict maximum deformation of blast wall installed in offshore topside structures in the early design stage.

Key Words
empirical formulation; offshore blast wall; explosion; deformation; structural design

Address
Do Kyun Kim:
1) Ocean and Ship Technology Research Group, Department of Civil and Environmental Engineering, Universiti Teknologi PETRONAS, 32610 Seri Iskandar, Perak, Malaysia
2) Graduate Institute of Ferrous Technology, POSTECH, 37673 Pohang, Republic of Korea
William Chin Kuan Ng: Ocean and Ship Technology Research Group, Department of Civil and Environmental Engineering, Universiti Teknologi PETRONAS, 32610 Seri Iskandar, Perak, Malaysia
Oeju Hwang: McDermott Asia Pacific, 50250 Kuala Lumpur, Malaysia

Abstract
In this study (Part I), an advanced empirical formulation was proposed to predict the ultimate strength of initially deflected steel plate subjected to longitudinal compression. An advanced empirical formulation was proposed by adopting Initial Deflection Index (IDI) concept for plate element which is a function of plate slenderness ratio (Beta) and coefficient of initial deflection. In case of initial deflection, buckling mode shape, which is mostly assumed type in the ships and offshore industry, was adopted. For the numerical simulation by ANSYS nonlinear finite element method (NLFEM), with a total of seven hundred 700 plate scenarios, including the combination of one hundred (100) cases of plate slenderness ratios with seven (7) representative initial deflection coefficients, were selected based on obtained probability density distributions of plate element from collected commercial ships. The obtained empirical formulation showed good agreement (R2 = 0.99) with numerical simulation results. The obtained outcome with proposed procedure will be very useful in predicting the ultimate strength performance of plate element subjected to longitudinal compression.

Key Words
ultimate strength; plate; unstiffened panel; initial deflection; empirical formulation

Address
Do Kyun Kim:
1) Ocean and Ship Technology Research Group, Department of Civil and Environmental Engineering, Universiti Teknologi PETRONAS, 32610 Seri Iskandar, Perak, Malaysia
2) Graduate Institute of Ferrous Technology, POSTECH, 37673 Pohang, Republic of Korea
Bee Yee Poh and Jia Rong Lee: Ocean and Ship Technology Research Group, Department of Civil and Environmental Engineering, Universiti Teknologi PETRONAS, 32610 Seri Iskandar, Perak, Malaysia
Jeom Kee Paik:
1) The Korea Ship and Offshore Research Institution (The Lloyd\'s Register Foundation Research Centre of Excellence), Pusan National University, Busan, Republic of Korea
2) Department of Mechanical Engineering, University College London, London, UK

Abstract
A comprehensive study was provided to investigate the buckling behavior of the steel plates with and without through-thickness holes subjected to uniaxial compression using ABAQUS. The method was validated by the results reported in the literature. Using the critical stresses, the buckling coefficients (K_c) were calculated. The effects of inclusion of material nonlinearity, plate thickness (t), aspect ratio (AR), and initial imperfection on buckling resistance of the plate was studied. Besides, the effects of having the hole in the plate were also studied. The diameter of the hole was normalized by dividing by plate breadth and was given in the form of a. Results showed that perforating one hole in the center of a plate increases the plate buckling resistance while the having two holes resulted in a decrease in the plate buckling resistance. The effects of hole eccentricity (Ecc) on the buckling resistance of the plate was studied. The position of the hole center was normalized by half of the plate breadth and length in X- and Y-directions, respectively. In this study, four cases of boundary conditions were considered, and the corresponding buckling behavior were studied combined with plate aspect ratio. It was observed that the boundary condition of the case I resulted in the highest buckling resistance. Finally, a comparison was made between the buckling behavior of the uniaxially and biaxially loaded plate. It was revealed that the buckling resistance of a biaxially loaded plate is lower half than half of that of the uniaxially loaded plate.

Key Words
buckling analysis; post-buckling; plates; through-thickness hole; buckling coefficient; material nonlinearity; geometrical nonlinearity; hole eccentricity

Address
Behzad Mohammadzadeh and Eunsoo Choi: Department of Civil Engineering, Hongik University, Seoul 04066, Republic of Korea
Woo Jin Kim: Department of Materials Science and Engineering, Hongik University, Seoul 04066, Republic of Korea

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