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Volume 22, Number 6, December30 2016

Mega composite structure systems have been widely used in high rise buildings in China. Compared to other structures, this type of composite structure systems has a larger cross-section with less weight. Concrete filled steel tubular (CFST) laced column to box-beam connections are gaining popularity, in particular for the mega composite structure system in high rise buildings. To enable a better understanding of the destruction characteristics and aseismic performance of these connections, three different connection types of specimens including single-limb bracing, cross bracing and diaphragms for core area of connections were tested under low cyclic and reciprocating loading. Hysteresis curves and skeleton curves were obtained from cyclic loading tests under axial loading. Based on these tested curves, a new trilinear hysteretic restoring force model considering rigidity degradation is proposed for CFST laced column to box-beam connections in a mega composite structure system, including a trilinear skeleton model based on calculation, law of stiffness degradation and hysteresis rules. The trilinear hysteretic restoring force model is compared with the experimental results. The experimental data shows that the new hysteretic restoring force model tallies with the test curves well and can be referenced for elastic-plastic seismic analysis of CFST laced column to composite box-beam connection in a mega composite structure system.

Key Words
steel concrete composite connection; concrete filled steel tube (CFST); box-beam column connections; hysteretic restoring force model; seismic performance; connection behavior

(1) Zhi Huang, Li-Zhong Jiang, Wang-Bao Zhou:
School of Civil Engineering, Central South University, Changsha 410075, China;
(2) Zhi Huang:
Department of Civil Engineering, The Pennsylvania State University, Middletown 17057, PA, USA;
(3) Shan Chen:
Hunan institute of nonferrous geological exploration and research, Changsha 410015, China.

The modified couple stress-based third-order shear deformation theory is presented for sigmoid functionally graded materials (S-FGM) plates. The advantage of the modified couple stress theory is the involvement of only one material length scale parameter which causes to create symmetric couple stress tensor and to use it more easily. Analytical solution for dynamic instability analysis of S-FGM plates on elastic medium is investigated. The present models contain two-constituent material variation through the plate thickness. The equations of motion are derived from Hamilton's energy principle. The governing equations are then written in the form of Mathieu-Hill equations and then Bolotin's method is employed to determine the instability regions. The boundaries of the instability regions are represented in the dynamic load and excitation frequency plane. It is assumed that the elastic medium is modeled as Pasternak elastic medium. The effects of static and dynamic load, power law index, material length scale parameter, side-to-thickness ratio, and elastic medium parameter have been discussed. The width of the instability region for an S-FGM plate decreases with the decrease of material length scale parameter. The study is relevant to the dynamic simulation of micro structures embedded in elastic medium subjected to intense compression and tension.

Key Words
dynamic instability; functionally graded materials; elastic medium; plate theory; modified couple stress theory

(1) Weon-Tae Park:
Division of Construction and Environmental Engineering, Kongju National University, 275 Budai, Cheonan, 331-717, Republic of Korea;
(2) Sung-Cheon Han:
Department of Civil & Railroad Engineering, Daewon University College, 316 Daehak, Jecheon, 390-702, Republic of Korea;
(3) Woo-Young Jung:
Department of Civil Engineering, Gangneung-Wonju National University, 7 Jukheon, Gangneung, 210-702, Republic of Korea;
(4) Won-Hong Lee:
Department of Civil Engineering, Gyeongnam National University of Science and Technology, 33 Dongjin,Jinju, 660-758, Republic of Korea.

We study chaotic motion in a nonlinear laminated composite plate under subsonic fluid flow and a simultaneous external load in this paper. We derive equations of motion of the plate using the von-Kármán's hypothesis and the Hamilton's principle. Galerkin's approach is adopted as the solution method. We then conduct a divergence analysis to obtain critical velocities of the transient flow. Melnikov's integral approach is used to find the critical parameters in which chaos takes place. Effects of different parameters including the aspect ratio, plate material and the ply angle in laminates on the critical flow speed are investigated. In a parametric study, we show that how the linear and nonlinear stiffness of the plate and the load frequency and amplitude would influence the chaotic behavior of the plate.

Key Words
composite laminated plates; vibration; subsonic flow; chaos; Melnikov's method

(1) Hamed Norouzi, Davood Younesian:
School of Railway Engineering, Iran University of Science and Technology, Tehran 16846-13114, Iran;
(2) Davood Younesian:
Department of Mechanical Engineering, UC Berkeley, Berkeley, CA 94720-1740, USA.

This paper deals with the analysis of vibration of antisymmetric angle-ply plates using spline method for higher order shear theory. Free vibration of laminated plates is addressed to show the capability of the present method in the vicinity of higher order shear deformation theory and simply supported edges of plates. The coupled differential equations are obtained in terms displacement and rotational functions. These displacement and rotational functions are approximated using cubic and quantic spline. A generalized eigenvalue problem is obtained and solved numerically for an eigenfrequency parameter and an associated eigenvector of spline coefficients. The antisymmetric angle-ply fiber orientation are taken as design variables. Numerical results enable us to examine the frequencies for various geometric and material parameters and accuracy and effectiveness of the proposed method is also verified by comparative study.

Key Words
antisymmetric angle-ply; free vibration; shear deformation theory; spline approximation; eigenvalue

(1) Saira Javed, K.K. Viswanathan, Z.A. Aziz, K. Karthik:
UTM Centre for Industrial and Applied Mathematics (UTM-CIAM), Ibnu Sina Institiute for Scientific & Industrial Research, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia;
(2) Saira Javed, K.K. Viswanathan, Z.A. Aziz, K. Karthik:
Department of Mathematical Sciences, Faculty of Science Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia;
(3) K.K. Viswanathan:
Kuwait College of Science and Technology, Doha Area, 7th Ring Road, P.O. Box No. 27235, Safat 13133, Kuwait;
(4) J.H. Lee:
Department of Naval Architecture & Ocean Engineering, Inha University, Incheon, South Korea.

In this paper, the free vibrations of a short cylindrical nanotube made of piezoelectric material are studied based on the consistent couple stress theory and using the shear deformable cylindrical theory. This new model has only one length scale parameter and can consider the size effects of nanostructures in nanoscale. To model size effects in nanoscale, and considering the nanotube material which is piezoelectric, the consistent couple stress theory is used. First, using Hamilton's principle, the equations of motion and boundary condition of the piezoelectric cylindrical nanoshell are developed. Afterwards, using Navier approach and extended Kantorovich method (EKM), the governing equations of the system with simple-simple (S-S) and clamped-clamped (C-C) supports are solved. Afterwards, the effects of size parameter, geometric parameters (nanoshell length and thickness), and mechanical and electric properties (piezoelectric effect) on nanoshell vibrations are investigated. Results demonstrate that the natural frequency on nanoshell in nanoscale is extremely dependent on nanoshell size. Increase in size parameter, thickness and flexoelectric effect of the material leads to increase in frequency of vibrations. Moreover, increased nanoshell length and diameter leads to decreased vibration frequency.

Key Words
piezoelectric effect; flexoelectric effect; consistent couple-stress theory; electromechanical size-dependent; first order shear deformable theory; extended Kantorovich method

(1) Narges Ebrahimi:
Mechanical Engineering Department, Shahrekord University, Shahrekord, Iran;
(2) Yaghoub Tadi Beni:
Faculty of Engineering, Shahrekord University, Shahrekord, Iran.

The current study focuses on the assessment and interface response of reinforced concrete elements with composite materials (carbon fiber reinforced polymers-CFRPs, glass fiber reinforced polymers-GFRPs, textile reinforced mortars-TRM's, near surface mounted bars-NSMs). A description of the transfer mechanisms from concrete elements to the strengthening materials is conducted through analytical models based on failure modes: plate end interfacial debonding and intermediate flexural crack induced interfacial debonding. A database of 55 in total reinforced concrete columns (scale 1:1) is assembled containing elements rehabilitated with various techniques (29 wrapped with CFRP's, 5 wrapped with GFRP's, 4 containing NSM and 4 strengthened with TRM). The failure modes are discussed together with the performance level of each technique as well as the efficiency level in terms of ductility and bearing/ bending capacity. The analytical models' results are in acceptable agreement with the experimental data and can predict the failure modes. Despite the heterogeneity of the elements contained in the aforementioned database the results are of high interest and point out the need to incorporate the analytical expressions in design codes in order to predict the failure mechanisms and the limit states of bearing capacities of each technique.

Key Words
concrete column; retrofit; fiber reinforced polymers; interface; force transfer mechanism

Reinforced Concrete Laboratory, Civil Engineering Department, Democritus University of Thrace (D.U.Th.), Vas. Sofias 12, 67100, Xanthi, Greece.

Buckling and free vibration behavior of a laminated cylindrical panel exposed to non-uniform thermal load is addressed in the present study. The approach comprises of three portions, in the first portion, heat transfer analysis is carried out to compute the non-uniform temperature fields, whereas second portion consists of static analysis wherein stress fields due to thermal load is obtained, and the last portion consists of buckling and prestressed modal analyzes to capture the critical buckling temperature as well as first five natural frequencies and associated mode shapes. Finite element is used to perform the numerical investigation. The detailed parametric study is carried out to analyze the effect of nature of temperature variation across the panel, laminate sequence and structural boundary constraints on the buckling and free vibration behavior. The relation between the buckling temperature of the panel under uniform temperature field and non-uniform temperature field is established using magnification factor. Among four cases considered in this study for position of heat sources, highest magnification factor is observed at the forefront curved edge of the panel where heat source is placed. It is also observed that thermal buckling strength and buckling mode shapes are highly sensitive to nature of temperature field and the effect is significant for the above-mentioned temperature field. Furthermore, it is also observed that the panel with antisymmetric laminate has better buckling strength. Free vibration frequencies and the associated mode shapes are significantly influenced by the non-uniform temperature variations.

Key Words
cylindrical panel; thermal buckling; non-uniform heating; finite element analysis; free vibration

Department of Mechanical Engineering, National Institute of Technology Karnataka, Surathkal, Mangalore, 575025, India.

Limit load of pressure bearing structures was reviewed in this article. By means of the finite element analysis, limit load of pressurized cylinder with nozzle was taken as an example. Stress classification method and Elastic-plastic finite element analysis combining with limit load determination methods were used to determine limit load of cylinder with nozzle. Comparison of limit load determined by different methods, the results indicated that limit load determined by linearization method was the smallest. Limit load determined by twice elastic slope criterion was the nearest than experimental results. Elastic-plastic finite element analysis had comparably computational precision, but required time consuming. And then the requirements of computer processing and storage capacity by power system became higher and higher. Most of criteria for limit load estimation included any human factors based on a certain substantive characteristics of experimental results. The reasonable criterion should be objective and operational.

Key Words
pressure vessel; limit load; estimation criteria; ANSYS

(1) Xiaohui Chen, Xingang Wang:
School of Control Engineering, Northeastern University, Qinhuangdao, 066004, China;
(2) Xiaohui Chen:
College of Mechanical Engineering, Yanshan University, Qinhuangdao, 066004, China;
(3) Bingjun Gao:
School of Chemical Engineering and Technology, Hebei University of Technology, Tianjin, 300000, China.

Cellular and castellated steel beams are used to obtain higher stiffness and bending capacity using the same weight of steel. In addition, the beam openings may be used as a pass for different mechanical fixtures such as ducts and pipes. The aim of this study is to investigate the effect of different parameters on both elastic and inelastic critical buckling stresses of steel web plates with openings. These parameters are plate aspect ratio; opening shape (circular or rectangular); end distance to the first opening; opening spacing; opening size; plate slenderness ratio; steel grade; and initial web imperfection. The web/flange interaction has been simplified by web edge restraints representing simply supported boundary conditions. A numerical parametric study has been performed through linear and nonlinear finite element (FE) models, where the FE results have been verified against both experimental and numerical results in the literature. The web plates are subject to in-plane linearly varying compression with different loading patterns, ranging from uniform compression to pure bending. A buckling stress modification factor (β-factor) has been introduced as a ratio of buckling stress of web plate with openings to buckling stress of the corresponding solid web plate. The variation of β-factor against the aforementioned parameters has been reported. Furthermore, the critical plate slenderness ratio separating elastic buckling and yielding has been identified and discussed for two steel grades of DIN-17100, namely: ST-37/2 and ST-52/3. The FE results revealed that the minimum β-factor is 0.9 for web plates under uniform compression and 0.7 for those under both compression and tension.

Key Words
numerical study; web plate with openings; elastic and inelastic buckling; buckling stress modification factor

Department of Structural Engineering, Faculty of Engineering, Cairo University, Egypt.

The effects of moisture and temperature on buckling of laminated composite cylindrical shell panels are investigated both numerically and experimentally. A quadratic isoparametric eight-noded shell element is used in the present analysis. First order shear deformation theory is used in the present finite element formulation for buckling analysis of shell panels subjected to hygrothermal loading. A program is developed using MATLAB for parametric study on the buckling of shell panels under hygrothermal field. Benchmark results on the critical loads of hygrothermally treated woven fiber glass/epoxy laminated composite cylindrical shell panels are obtained experimentally by using universal testing machine INSTRON 8862. The effects of curvature, lamination sequences, number of layers and aspect ratios on buckling of laminated composite cylindrical curved panels subjected to hygrothermal loading are considered. The results are presented showing the reduction in buckling load of laminated composite shells with the increase in temperature and moisture concentrations.

Key Words
hygrothermal effects; buckling; woven fiber; Glass/Epoxy; laminated cylindrical shell panels; FSDT; FEM

(1) Madhusmita Biswal:
School of Civil Engineering KIIT University, Bhubaneswar, Odisha 751024, India;
(2) Shishir Kr. Sahu, A.V. Ash:
Department of Civil Engineering National Institute of Technology, Rourkela, Odisha 769008, India;
(3) Namita Nanda:
Department of Applied Mechanics, Indian Institute of Technology, Delhi 110016, India.

Conventional plate I-girders are sensitive to local buckling of the web when they are subjected mainly to shear action because the slenderness of the web in out-of-plane direction is much bigger. The local buckling of the web can also cause the distorsion of the plate flange under compression as a thin-walled plate has very low torsional stiffness due to its open section. A new I-girder consisted of corrugated web, a concrete-filled rectangular tubular flange under compression and a plate flange under tension is presented to improve its resistance to local buckling of the web and distorsion of the flat plate flange under compression. Experimental tests on a conventional plate I-girder and a new presented I-girder are conducted to study the failure process and the failure mechanisms of the two specimens. Strain developments at some critical positions, load-lateral displacement curves, and load-deflection curves of the two specimens have all be measured and analyzed. Based on these results, the failure mechanisms of the two kinds of I-girders are discussed.

Key Words
I-girder; shear behavior; corrugated web; concrete-filled tubular flange; failure mechanism

School of Mechatronic Engineering, Southwest Petroleum University, Xindu Road 8#, Xindu District, Chengdu 610500, P.R. China.

This paper presents the results of an experimental study on the behavior of a new type of composite FRP-concrete-steel member subjected to bi-axial eccentric loading. This new type of composite member is in the form of concrete-filled square steel tube slender columns with inner CFRP (carbon fiber-reinforced polymer) circular tube, composed of an inner CFRP tube and an outer steel tube with concrete filled in the two tubes. Tests on twentysix specimens of high strength concrete-filled square steel tube columns with inner CFRP circular tube columns (HCFST-CFRP) were carried out. The parameters changed in the experiments include the slenderness ratio, eccentric ratio, concrete strength, steel ratio and CFRP ratio. The experimental results showed that the failure mode of HCFSTCFRP was similar to that of HCFST, and the specimens failed by local buckling because of the increase of lateral deflection. The steel tube and the CFRP worked together well before failure under bi-axial eccentric loading. Ductility of HCFST-CFRP was better than that of HCFST. The ultimate bearing capacity of test specimen was calculated with simplified formula, which agreed well with test results, and the simplified formula can be used to calculate the bearing capacity of HCFSTF within the parameters of this test.

Key Words
CFRP tube; high strength concrete-filled square steel tube; bi-axial eccentric; slenderness ratio; slender column

(1) Guochang Li, Zhijain Yang:
School of Civil Engineering, Shenyang Jianzhu University, Shenyang, 110168, China;
(2) Yan Lang:
cDepartment of Building Engineering, Suqian College, Jiangsu Province, 223800, China;
(3) Chen Fang:
Department of Civil Engineering, University of Texas at El Paso, El Paso, TX 79968, USA.

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