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CONTENTS
Volume 17, Number 5, November 2014
 

Abstract
The paper provides the test results and analysis on the behavior of steel 1.7147 at different temperatures. Mechanical uniaxial tests were used to determine mechanical properties, resistance to creep and Charpy impact tests to determine impact energy. Test results are presented in the form of engineering stress-strain diagrams, creep curves as well as numerical data related to impact energy. The results show that the tensile strength has the highest value at room temperature, and the same goes for the yield strength as well as for modulus of elasticity. After room temperature both of mentioned properties decrease with temperature increasing. Some of creep curves were modeled using rheological models and analytical equation. Based on Charpy impact energy an assessment of fracture toughness was made.

Key Words
1.7147 steel; material properties; creep; creep modeling; fracture toughness calculation

Address
Faculty of Engineering, University of Rijeka, Vukovarska 58, 51000 Rijeka, Croatia.

Abstract
In this paper, we present the scattering characteristics of infinite and finite array using method of moment (MoM) with Floquet harmonics and asymptotic waveform evaluation (AWE) technique. First, infinite cylindrical dipole array is analyzed using the MoM with entire domain basis function and cylindrical Floquet harmonics. To provide the validity of results, we fabricated the cylindrical dipole array and measured the transmission characteristics. The results show good agreements. Second, we analyzed the scattering characteristics of finite array. A large simulation time is needed to obtain the scattering characteristics of finite array over wide frequency range because Floquet harmonics cant be applied. So, we used the MoM with AWE technique using Taylor series and Pade approximation to overcome the shortcomings of conventional MoM. We calculated the radar cross section (RCS) as scattering characteristics using the proposed method in this paper and the conventional MoM for finite planar slot array, finite spherical slot array, and finite cylindrical dipole array, respectively. The compared results agree well and show that the proposed method in this paper is good for electromagnetic analysis of finite FSS.

Key Words
frequency selective surface; finite and curved array; cylindrical Floquet harmonics; asymptotic waveform evaluation (AWE) technique; RCS; transmission

Address
(1) Yi-Ru Jeong, Jong-Gwan Yook:
School of Electrical and Electronics Engineering, Yonsei University, Seoul, Korea;
(2) Ic-Pyo Hong:
Department of Information and Communication Engineering, Kongju National University, Cheonan, Korea;
(3) Heoung-Jae Chun:
School of Mechanical Engineering, Yonsei University, Seoul, Korea;
(4) Yong Bae Park:
Department of Electrical and Computer Engineering, Ajou University, Suwon, Korea;
(5) Youn-Jae Kim:
Agency for Defense and Development, Daejon, Korea.

Abstract
A new type of connection for steel-concrete composite bridges was developed by the Steel Structures Laboratory of Ecole Poytechinque Fédérale de Lausanne. Resistance to longitudinal shear is based on the development of shear stresses in the confined interfaces which form the connection. Confinement is provided by the reinforced concrete slab which encloses the connection and restrains the uplift (lateral separation) of the interfaces by developing normal stresses. The experimental investigation of the interfaces, under static and cyclic loading, enabled the development of the laws describing the structural behaviour of each interface. Those laws were presented by the authors in previous papers. The current paper focuses on the continuity of the research. It presents the experimental investigation on the new connection by means of push-out tests on specimens submitted to static and cyclic shear loading. Investigation revealed that the damage in the connection, due to cyclic loading, is expressed by the accumulation of a residual slip. A safe fatigue failure criterion is proposed for the connection which enabled the verification of the connection for the fatigue limit state with respect to the limit of fatigue. A numerical model is developed which takes into account the laws describing the interface behaviour and the analytical expressions for the confinement effect, the latter obtained by performing finite element analysis. This numerical model predicts the shear resistance of the connection and enables to assess its fatigue limit which is necessary for the fatigue design proposed.

Key Words
steel-concrete connection; interfaces; shear; slip; uplift; confinement; cyclic loading; fatigue damage; composite bridges

Address
(1) Dimitrios Papastergiou:
DIC s.a. ingénieurs, Aigle, Switzerland;
(2) Jean-Paul Lebet:
Steel Structures Laboratory, EPFL Ėcole Polytechnique Fédérale de Lausanne, Switzerland.

Abstract
Repairing and strengthening structural members by bonding composite materials have received a considerable attention in recent years. The major problem when using bonded FRP or steel plates to strengthen existing structures is the high interfacial stresses that may be built up near the plate ends which lead to premature failure of the structure. As a result, many researchers have developed several analytical methods to predict the interface performance of bonded repairs under various types of loading. In this paper, a numerical solution using finite . difference method (FDM) is used to calculate the interfacial stress distribution in beams strengthened with FRP plate having a tapered ends under thermal loading. Different thinning profiles are investigated since the later can significantly reduce the stress concentration. In the present theoretical analysis, the adherend shear deformations are taken into account by assuming a parabolic shear stress through the thickness of both beam and bonded plate. The shear correction factor for I-section beams is also included in the solution. Numerical results from the present analysis are presented to demonstrate the advantages of use the tapers in design of strengthened beams.

Key Words
plate bonding; FRP composite; interfacial stresses; repaired beam; taper

Address
(1) Benaoumeur El Mahi, Kouider Halim Benrahou, Khalil Belakhdar, Abdelouahed Tounsi, El Abbes Adda Bedia:
Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria;
(2) Sofiane Amziane:
Clermont University, Institut Pascal, Polytech'Clermont-Ferrand, 63174 Aubière Cedex, France.

Abstract
Due to recent advancements in the area of Artificial Intelligence (AI) and computational intelligence, the application of these technologies in the construction industry and structural analysis has been made feasible. With the use of the Adaptive-Network-based Fuzzy Inference System (ANFIS) as a modelling tool, this study aims at predicting the shear strength of channel shear connectors in steel concrete composite beam. A total of 1200 experimental data was collected, with the input data being achieved based on the results of the push-out test and the output data being the corresponding shear strength which were recorded at all loading stages. The results derived from the use of ANFIS and the classical linear regressions (LR) were then compared. The outcome shows that the use of ANFIS produces highly accurate, precise and satisfactory results as opposed to the LR.

Key Words
shear connector; channel; composite beam; shear strength; ANFIS; LR

Address
Department of Civil Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia.

Abstract
This paper presents the analytical solutions for the size-dependent static analysis of the functionally graded (FG) beams with various boundary conditions based on the nonlocal continuum model. The nonlocal behavior is described by the differential constitutive model of Eringen, which enables to this model to become effective in the analysis and design of nanostructures. The elastic modulus of beam is assumed to vary through the thickness or longitudinal directions according to the power law. The governing equations are derived by using the nonlocal continuum theory incorporated with Euler-Bernoulli beam theory. The explicit solutions are derived for the static behavior of the transversely or axially FG beams with various boundary conditions. The verification of the model is obtained by comparing the current results with previously published works and a good agreement is observed. Numerical results are presented to show the significance of the nonlocal effect, the material distribution profile, the boundary conditions, and the length of beams on the bending behavior of nonlocal FG beams.

Key Words
functionally graded beam; nonlocal theory; analytical solution; power series method

Address
Department of Architectural Engineering, Sejong University, 98 Kunja Dong, Kwangjin Ku, Seoul 143-747, Republic of Korea.

Abstract
Tapered concrete filled double skin steel tubular (CFDST) columns have been used in China for structures such as electricity transmission towers. In practice, the bearing capacity related to the connection details on the top of the column is not fully understood. In this paper, the experimental behaviour of tapered CFDST stub columns subjected to axial partial compression is reported, sixteen specimens with top endplate and ten specimens without top endplate were tested. The test parameters included: (1) tapered angle, (2) top endplate thickness, and (3) partial compression area ratio. Test results show that the tapered CFDST stub columns under axial partial compression behaved in a ductile manner. The axial partial compressive behaviour and the failure modes of the tapered CFDST stub columns were significantly influenced by the parameters investigated. Finally, a simple formula for predicting the cross-sectional capacity of the tapered CFDST sections under axial partial compression is proposed.

Key Words
concrete filled steel tube (CFST); concrete filled double skin steel tube (CFDST); tapered column; axial partial compression; cross-sectional capacity

Address
(1) Qing-Xin Ren:
School of Civil Engineering, Shenyang Jianzhu University, Shenyang 110168, PR China;
(2) Qing-Xin Ren, Chao Hou, Lin-Hai Han:
Department of Civil Engineering, Tsinghua University, Beijing 100084, PR China;
(3) Dennis Lam:
School of Engineering, University of Bradford, Bradford BD7 1DP, UK.

Abstract
A great number of moment-resisting steel structures collapsed due to ductile crack initiation at welded beam-column connections, followed by explosive brittle fracture in the Kobe (Hyogoken-Nanbu) earthquake in 1995. A series of experimental and numerical studies on cracking behaviors of beam-column connections in steel bridge piers were carried out by the authors

Key Words
ductile fracture; post weld treatment; burr grinding; R-finish; beam-column connection; steel bridge pier

Address
(1) Liang-Jiu Jia:
Advanced Research Center for Natural Disaster Risk Reduction, Meijo University, 1-501 Shiogamaguchi, Tenpaku-ku, Nagoya, 468-8502, Japan;
(2) Hanbin Ge:
Deptartment of Civil Engineering, Meijo University, 1-501 Shiogamaguchi, Tenpaku-ku, Nagoya, 468-8502, Japan;
(3) Toshimitsu Suzuki:
Hiroshima Machinery Works, Mitubishi Heavy Industries, Ltd., 5-1 Ebaokimachi, Naka-ku, Hiroshima, 730-8642, Japan.

Abstract
Composite steel-concrete box girders are frequently used in bridge construction for their economic and structural advantages. An integrated metaheuristic based optimization procedure is proposed for discrete size optimization of straight multi-span steel box girders with the objective of minimizing the self-weight of girder. The metaheuristic algorithm of choice is the Cuckoo Search (CS) algorithm. The optimum design of a box girder is characterized by geometry, serviceability and ultimate limit states specified by the American Association of State Highway and Transportation Officials (AASHTO). Size optimization of a practical design example investigates the efficiency of this optimization approach and leads to around 15% of saving in material.

Key Words
composite box girder; size-optimization; optimal design; cuckoo search algorithm

Address
Centre of Excellence for Fundamental Studies in Structural Engineering, Iran University of Science and Technology, Narmak, Tehran-16, Iran.

Abstract
In the current study, we consider a new class of analytical periodic solution for free nonlinear vibration of mechanical systems. Hamiltonian approach is applied to analyze nonlinear problems which occur in dynamics. The proposed method doesn\'t have the limitations of the classical methods and leads us to a high accurate solution by only one iteration. Two well known examples are studied to show the convenience and effectiveness of this approach. Runge-Kutta\'s algorithm is also applied and the results of it are compared with the Hamiltonian approach. High accuracy of the proposed approach reveals that the Hamiltonian approach can be very useful for other nonlinear practical problems in engineering.

Key Words
non-linear vibration; Hamiltonian approach; Runge-Kutta\'s algorithm

Address
(1) Mahmoud Bayat, Mahdi Bayat:
Department of Civil Engineering, College of Engineering, Mashhad Branch, Islamic Azad University, Mashhad, Iran;
(2) Iman Pakar:
Young Researchers and Elites Club, Mashhad Branch, Islamic Azad University, Mashhad, Iran.

Abstract
Concrete-filled steel tube (CFT) composite columns, either circular (CCFT) or rectangular (RCFT), have many economical and aesthetic advantages but the behavior of their connections are complicated. This study aims to investigate, through an experimental program, the performance and behavior of different connections configurations between circular concrete filled steel tube columns (CCFT) and gusset plates subjected to shear and axial compression loadings. The study included seventeen connection subassemblies consisting of a fixed length steel tube and gusset plate connected to the tube end with different details tested under half cyclic loading. A notable effect was observed on the behavior of the connections due to its detailing changes with respect to capacity, failure mode, ductility, and stress distribution.

Key Words
concrete filled tube (CFT) columns; connections; ductility; strength; connection detailing

Address
(1) M.M. Hassan, H.M. Ramadan, S.A. Mourad:
Faculty of Engineering (Steel Department), Cairo University, Cairo, Egypt;
(2) M. Naeem:
Faculty of Engineering (Structural Department), Cairo University, Cairo, Egypt.

Abstract
In this paper, nonlinear vibration and post-buckling analysis of beams made of functionally graded materials (FGMs) resting on nonlinear elastic foundation subjected to thermo-mechanical loading are studied. The thermo-mechanical material properties of the beams are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents, and to be temperature-dependent. The assumption of a small strain, moderate deformation is used. Based on Euler-Bernoulli beam theory and von-Karman geometric nonlinearity, the integral partial differential equation of motion is derived. Then this PDE problem which has quadratic and cubic nonlinearities is simplified into an ODE problem by using the Galerkin method. Finally, the governing equation is solved analytically using the variational iteration method (VIM). Some new results for the nonlinear natural frequencies and buckling load of the FG beams such as the influences of thermal effect, the effect of vibration amplitude, elastic coefficients of foundation, axial force, end supports and material inhomogenity are presented for future references. Results show that the thermal loading has a significant effect on the vibration and post-buckling response of FG beams.

Key Words
functionally graded beams; thermal and axial loadings; nonlinear free vibration; postbuckling; Galerkin method; variational iteration method

Address
(1) Hessameddin Yaghoobi, Mohammad Sadegh Valipour, Abdolhossein Fereidoon:
Faculty of Mechanical Engineering, Semnan University, Semnan, Iran;
(2) Pooria Khoshnevisrad:
Department of Biomedical Engineering, Amirkabir University of Technology, Tehran, Iran.


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