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CONTENTS
Volume 17, Number 4, October 2014
 

Abstract
In this experimental and numerical study, the effect of plate thickness, the diameter of circular cutout, the distance between circular cutouts and rowing orientation angle effect (θ) on the buckling load of E-glass/vinylester pultruded composite beams with single and double circular cutouts, were investigated. The composite beam having 2, 4, and 6 mm thicknesses was produced as [Mat/θ/Mat/θ/Mat] by using pultrusion technique. Seven different fiber angles as 0°, 15°, 30°, 45°, 60°, 75°, and 90° were chosen for investigation of rowing orientation angle. The distances between each circular cutout were selected as 15, 30, 45, 60, and 75 mm in the case of double circular cutouts. The diameters of circular cutouts were chosen as 2, 4, 6, 8, and 10 mm to investigate the effect of cutout size. The experimental buckling loads were compared with the results calculated from the numerical analysis. ANSYS 11 commercial software was used for numerical study. A good agreement was obtained between numerical and experimental results.

Key Words
buckling load; diameter of circular cutout; pultruded E-glass/vinylester; finite element method

Address
Uşak University, Department of Mechanical Engineering, 64200, Uşak, Turkey.

Abstract
This paper presents a tri-linear restoring force model based on the test results of 12 circular RC columns strengthened by CFRP strips under low cyclic loading. The pre-stress of CFRP strips and axial load ratio of specimens are considered as the affect parameters of the proposed model. All essential characteristics of the hysteretic behavior of the proposed model, including the hysteretic rules, main performance points, strength degradation, stiffness degradation and confinement effects are explicitly analyzed. The calculated results from the proposed model are in good agreement with the experimental results, which shows that the recommended model can be reliably used for seismic behavior predictions of circular RC columns strengthened by pre-stressed CFRP strips.

Key Words
restoring force model; circular reinforced concrete column; pre-stressed fiber reinforced polymer; seismic behavior; active confinement

Address
(1) Changdong Zhou, Hui Li, Teng Tian:
School of Civil Engineering, Beijing Jiaotong University, Beijing, 100044, China;
(2) Xilin Lu:
State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai, 200092, China.

Abstract
This paper presents a high accuracy Finite Element approach for delamination modelling in laminated composite structures. This approach uses multi-layered shell element and cohesive zone modelling to handle the mechanical properties and damages characteristics of a laminated composite plate under low velocity impact. Both intralaminar and interlaminar failure modes, which are usually observed in laminated composite materials under impact loading, were addressed. The detail of modelling, energy absorption mechanisms, and comparison of simulation results with experimental test data were discussed in detail. The presented approach was applied for various models and simulation time was found remarkably inexpensive. In addition, the results were found to be in good agreement with the corresponding results of experimental data. Considering simulation time and results accuracy, this approach addresses an efficient technique for delamination modelling, and it could be followed by other researchers for damage analysis of laminated composite material structures subjected to dynamic impact loading.

Key Words
composite materials; intralaminar damage; interlaminar damage; delamination; cohesive zone modelling; impact loading

Address
(1) Masoud Kharazan, M.H. Sadr:
Aerospace Engineering Department & Center of Excellence in Computational Aerospace Engineering, Amirkabir University of Technology, Tehran, Iran;
(2) Morteza Kiani:
Center for Advanced Vehicular Systems, Mississippi State University, Starkville, Mississippi, USA;
(3) Morteza Kiani:
Engineering Technology Associate (ETA), Troy, MI 48083, USA.

Abstract
In this paper, it is aimed to determine the structural behavior of suspension bridges considering construction stages and different soil conditions. Bosporus Suspension Bridge connecting the Europe and Asia in Istanbul is selected as an example. Finite element model of the bridge is constituted using SAP2000 program considering existing drawings. Geometric nonlinearities are taken into consideration in the analysis using P-Delta large displacement criterion. The time dependent material strength of steel and concrete and geometric variations is included in the analysis. Time dependent material properties are considered as compressive strength, aging, shrinkage and creep for concrete, and relaxation for steel. To emphases the soil condition effect on the structural behavior of suspension bridges, each of hard, medium and soft soils are considered in the analysis. The structural behavior of the bridge at different construction stages and different soil conditions has been examined. Two different finite element analyses with and without construction stages are carried out and results are compared with each other. At the end of the analyses, variation of the displacement and internal forces such as bending moment, axial forces and shear forces for bridge deck and towers are given in detail. Also, displacement and stresses for bridge foundation are given with detail. It can be seen from the analyses that there are some differences between both analyses (with and without construction stages) and the results obtained from the construction stages are bigger. It can be stated that the analysis without construction stages cannot give the reliable solutions. In addition, soil condition have effect on the structural behavior of the bridge. So, it is thought that construction stage analysis using time dependent material properties, geometric nonlinearity and soil conditions effects should be considered in order to obtain more realistic structural behavior of suspension bridges.

Key Words
construction stage analysis; Bosporus suspension bridge; finite element analysis; soil condition effect; time dependent material properties

Address
(1) Murat Gűnaydin:
Gűműşhane University, Civil Engineering Department, 29000, Gűműşhane, Turkey;
(2) Sűleyman Adanur, Ahmet Can Altunişik, Emel Tűrker:
Karadeniz Technical University, Civil Engineering Department, 61080, Trabzon, Turkey;
(3) Barş Sevı:
Yildiz Technical University, Civil Engineering Department, Istanbul, Turkey.

Abstract
The present study focuses on the mechanical behaviour of concrete filled double skin steel tubular (CFDST) stub columns confined by fiber reinforced polymer (FRP). A series of axial compression tests have been conducted on two CFDST stub columns, eight CFDST stub columns confined by FRP and a concrete-filled steel tubular (CFST) stub column confined by FRP, respectively. The influences of hollow section ratio, FRP wall thickness and fibre longitudinal-circumferential proportion on the load-strain curve and the concrete stress-strain curve for stub columns with annular section were discussed. The test results displayed that the FRP jacket can obviously enhance the carrying capacity of stub columns. Based on the test results, a new model which includes the effects of confinement factor, hollow section ratio and lateral confining pressure of the outer steel tube was proposed to calculate the compressive strength of confined concrete. Using the present concrete strength model, the formula to predict the carrying capacity of CFDST stub columns confined by FRP was derived. The theoretically predicted results agree well with those obtained from the experiments and FE analysis. The present method is also adapted to calculate the carrying capacity of CFST stub columns confined by FRP.

Key Words
FRP; concrete filled steel tubular column; double skin; axial compression

Address
College of Civil Engineering, Nanjing Tech University, Nanjing 211816, People's Republic of China.

Abstract
This article is the result of an investigation on the influence of a Pasternak elastic foundation on the stability of exponentially graded (EG) cylindrical shells under hydrostatic pressure, based on the first-order shear deformation theory (FOSDT) considering the shear stresses. The shear stresses shape function is distributed parabolic manner through the shell thickness. The governing equations of EG orthotropic cylindrical shells resting on the Pasternak elastic foundation on the basis of FOSDT are derived in the framework of Donnell-type shell theory. The novelty of present work is to achieve closed-form solutions for critical hydrostatic pressures of EG orthotropic cylindrical shells resting on Pasternak elastic foundation based on FOSDT. The expressions for critical hydrostatic pressures of EG orthotropic cylindrical shells with and without an elastic foundation based on CST are obtained, in special cases. Finally, the effects of Pasternak foundation, shear stresses, orthotropy and heterogeneity on critical hydrostatic pressures, based on FOSDT are investigated.

Key Words
buckling; composite structures; functionally graded; instability/stability; material properties

Address
(1) A.M. Najafov:
Institute for Machine Elements and Lifting-and-Shifting Machines of Azerbaijan Technical University, Baku, Azerbaijan;
(2) A.H. Sofiyev:
Department of Civil Engineering, Engineering Faculty, Suleyman Demirel University, Isparta, Turkey;
(3) D. Hui:
Department of Mechanical Engineering, University of New Orleans, New Orleans, USA;
(4) Z. Karaca:
Department of Civil Engineering, Ondokuz Mayis University, Samsun, Turkey;
(5) V. Kalpakci:
Department of Civil Engineering, Hasan Kalyoncu University, Gaziantep, Turkey;
(6) M. Ozcelik:
Department of Geological Engineering, Suleyman Demirel University, Isparta, Turkey.

Abstract
The responses of steel buildings with perimeter moment resisting frames (PMRF) with medium size columns (W14) are estimated and compared with those of buildings with deep columns (W27), which are selected according to two criteria: equivalent resistance and equivalent weight. It is shown that buildings with W27 columns have no problems of lateral torsional, local or shear buckling in panel zone. Whether the response is larger for W14 or W27 columns, depends on the level of deformation, the response parameter and the structural modeling under consideration. Modeling buildings as two-dimensional structures result in an overestimation of the response. For multiple response parameters, the W14 columns produce larger responses for elastic behavior. The axial load on columns may be significantly larger for the buildings with W14 columns. The interstory displacements are always larger for W14 columns, particularly for equivalent weight and plane models, implying that using deep columns helps to reduce interstory displacements. This is particularly important for tall buildings where the design is usually controlled by the drift limit state. The interstory shears in interior gravity frames (GF) are significantly reduced when deep columns are used. This helps to counteract the no conservative effect that results in design practice, when lateral seismic loads are not considered in GF of steel buildings with PMRF. Thus, the behavior of steel buildings with deep columns, in general, may be superior to that of buildings with medium columns, using less weight and representing, therefore, a lower cost.

Key Words
steel buildings; moment resisting frames; AISC code; deep columns; nonlinear seismic analysis; structural modeling; local and global parameters

Address
Facultad de Ingeniería, Universidad Autónoma de Sinaloa, Ciudad Universitaria, Culiacán, Sinaloa, México.

Abstract
The ultimate carrying capacity of axially loaded welded square box section members made of medium and high strength steels (nominal yield stresses varying from 345 MPa to 460 MPa), with large width-to-thickness ratios ranging from 35 to 70, is analyzed by finite element method (FEM). At the same time, the numerical results are compared with the predicted results using Direct Strength Method (DSM), modified DSM and Effective Yield Strength Method (EYSM). It shows that curve a, rather than curve b recommended in Code for design of steel structures GB50017-2003, should be used to check the local-overall interaction buckling strength of welded square section columns fabricated from medium and high strength steels when using DSM, modified DSM and EYSM. Despite all this, EYSM is conservative. Compared to EYSM and modified DSM, DSM provides a better prediction of the ultimate capacities of welded square box compression members with large width-thickness ratios over a wide range of width-thickness ratios, slenderness ratios and steel grades. However, for high strength steels (nominal yield strength greater than 460 MPa), the numerical and existent experimental results indicate that DSM overestimates the load-carrying capacities of the columns with width-thickness ratio smaller than 45 and slenderness ratio less than 80. Further, for the purpose of making it suitable for a wider scope, DSM has been modified (called proposed modified DSM). The proposed modified DSM is in excellent agreement with the numerical and existing experimental results.

Key Words
medium and high strength steel; welded square box section; compression member; local-overall interaction buckling; ultimate carrying capacity; direct strength method; effective yield strength method, FEM

Address
School of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, PR China.

Abstract
Experimental results of 39 specimens including concrete columns, RC columns, hollow steel tube columns, concrete filled steel tubular (CFT) columns, and reinforced concrete filled steel tubular (RCFT) columns are presented. Based on the experimental results, the load-carrying capacity, confined effect, ductility, and failure mode of test columns are investigated. The effects of the main factors such as width-thickness ratio (the ratio of external diameter and wall thickness for steel tubes), concrete strength, steel tube with or without rib, and arrangement of reinforcing bars on the mechanical characteristics of columns are discussed as well. The differences between CFT and RCFT are compared. As a result, it is thought that strength, rigidity and ductility of RCFT are improved; especially strength and ductility are improved after the peak of load-displacement curve.

Key Words
reinforced concrete filled steel tubular column; compression test; bearing capacity; ductility ratio; strength

Address
(1) Wei Hua, Hai-Jun:
College of Architectural Engineering, Shenyang University of Technology, No.111, Shenliao West Road, Economic & Technological Development Zone, Shenyang,110870, P.R. China.
(2) Akira Hasegawa:
Dept. of Environmental and Civil Engineering, Hachinohe University of Technology, 88-1 Ohbiraki, Hachinohe 031-8501, Japan.

Abstract
In this paper, the exact closed-form solutions for torsional analysis of heterogeneous magnetostrictive circular cylinder are derived. The cylinder is subjected to the action of a magnetic field produced by a constant longitudinal current density. It is also acted upon by a particular kind of shearing stress at its upper base. The rigidity of the cylinder is graded through its axial direction from one material at the lower base to another material at the upper base. The distributions of circumferential displacement and shear stresses are presented through the radial and axial directions of the cylinder. The influence of the agnetostrictive parameter is discussed. The effects of additional parameters are investigated.

Key Words
circular cylinder; torsion; magnetostrictive; heterogeneous

Address
(1) Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia;
(2) Department of Mathematics, Faculty of Science, Kafrelsheikh University, Kafr El-Sheikh 33516, Egypt.


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