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CONTENTS
Volume 8, Number 5, October 2008
 

Abstract
In the present study, an efficient method for the optimum design of three-dimensional (3D) steel framed structures is proposed. In this method, in addition to choosing the best position of columns based on architectural requirements, the optimum cross-sectional dimensions of elements are determined. The preliminary design variables are considered as the number of columns in structural plan, which are determined by a direct optimization method suitable for discrete variables, without requiring the evaluation of derivatives. After forming the geometry of structure, the main variables of the cross-sectional dimensions are evaluated, which satisfy the design constraints and also achieve the least-weight of the structure. To reduce the number of finite element analyses and the overall computational time, a new third order approximate function is introduced which employs only the diagonal elements of the higher order derivatives matrices. This function produces a high quality approximation and also, a robust optimization process. The main feature of the proposed techniques that the higher order derivatives are established by the first order exact derivatives. Several examples are solved and efficiency of the new approximation method and also, the proposed method for the best position of columns in 3D steel framed structures is discussed.

Key Words
optimum design; approximation concepts; higher order approximations; steel structures.

Address
P. Torkzadeh, J. Salajegheh and E. Salajegheh: Department of Civil Engineering, University of Kerman, Kerman, Iran

Abstract
The Eurocode 4 presents some negative aspects in the design of composite slabs by the m-k Method or the Partial Connection Method. On one hand, the component chemical adherence is not accounted for in the connection between the profiled steel sheet and the concrete. On the other hand, the application of these methods requires some fitting parameters that must be determined by full scale tests. In this paper, the Eurocode 4 methods are compared with a method developed at the Federal Polytechnic School of Lausanne, based on pullout tests, which can be a valid alternative. Hence, in order to calculate the necessary parameters for the three methods, several tests have been performed such as the full scale test described in Eurocode 4 and pull-out tests. This last type of tests is of small dimensions and implicates lower costs. Finally, a full-scale test of a steelconcrete composite slab with a generic loading is presented, with the goal of verifying the analytical formulation

Key Words
composite slabs; curvature; longitudinal shear; shear span; slip phenomenon; moment-curvature relation; pull-out test; full-scale test; small-scale test.

Address
Emanuel Lopes : Civil Engineering Department, Polytechnic Institute of Castelo Branco, Castelo Branco, Portugal and Rui Simoes ISISE, Civil Engineering Department, University of Coimbra, Coimbra, Portugal

Abstract
In December 2005, one(A) of the two pre-engineered warehouse buildings in the port of K City of Korea was completely destroyed and the other(B) was seriously damaged to be demolished. Over-loaded snow and unexpected blast of wind were the causes of the accident and destructive behavior was brittle fracture caused by web local buckling and lateral torsional buckling at the flange below rafter. However, the architectural design technology of today based on material non-linear method does not consider the tolerances to solve the problem of such brittle fracture. So, geometric non-linear evaluation which includes initial deformation, width-thickness ratio, web stiffener and unbraced length is required. This study evaluates the structural safety of 4 models in terms of width-thickness ratio and unbraced length using ANSYS 9.0 with parameters such as width-thickness ratio of web, existence/non-existence of stiffener and unbraced length. The purpose of this study is to analyze destructive mechanism of the above-mentioned two warehouse buildings and to provide ways to promote the safety of pre-engineered buildings.

Key Words
tapered beam; local buckling; lateral torsional buckling; peb(pre-engineered buildings) system; ductile design.

Address
Seong Hui Lee and Sung Mo Choi:Division Architectural Engineering, School of Architecture and Architectural Engineering University of Seoul, Korea
E.T. Lee and Hyun Ju Shim : Department of Architectural Engineering, School of Architecture and Building Science College of Engineering Chung-Ang University, Korea

Abstract
The design provisions for semi-rigid steel frames have been incorporated in codes of practice for steel structures. In order to do the same, it is necessary to know the experimental moment-relative rotation (M-?r) behaviour of beam-to-column connections. In spite of numerous publications and collection of several connection databases, there is no unified approach for the semi-rigid design of steel frames. Amongst the many connection models available, the Frye-Morris polynomial model, with its limitations reported in the literature, is simple to adopt at least for the linear design space. However this model requires more number of connection tests and regression analyses to make it a realistic prediction model. In this paper, 3D nonlinear finite element (FE) analysis of beam-column connection specimens, carried out using ABAQUS software, for evaluating the M-?r behaviour of semi-rigid top and seat-angle (TSA) bolted connections are described. The finite element model is validated against experimental behaviour of the same connection with regard to their moment-rotation behaviour, stress distribution and mode of failure of the connections. The calibrated FE model is used to evaluate the performance of the Frye-Morris polynomial model. The results of the numerical parametric studies carried out using the validated FE model have been used in proposing modifications to the Frye-Morris model for TSA connection in terms of the powers of the size parameters.

Key Words
semi-rigid analysis; top and seat-angle connection; Frye-Morris polynomial model, Momentrelative rotation (M-?r).

Address
P. Prabha, V. Marimuthu, S. Arul Jayachandran and S. Seetharaman: Strucutural Engineering Research Centre, CSIR campus, Taramani, Chennai 600 113, India
N. Raman : Flour Daniel India Limited, Gurgaon, Haryana, India

Abstract
This paper reports an experimental investigation of the behaviour of concrete-encased composite columns subjected to short-term axial load and biaxial bending. In the study, six square and four L-shaped cross section of both short and slender composite column specimens were constructed and tested to examine the load-deflection behaviour and to obtain load carrying capacities. The main variables in the tests were considered as eccentricity of applied axial load, concrete compressive strength, cross section, and slenderness effect. A theoretical procedure considering the nonlinear behaviour of the materials is proposed for determination of the behaviour of eccentrically loaded short and slender composite columns. Two approaches are taken into account to describe the flexural rigidity (EI) used in the analysis of slender composite columns. Observed failure mode and experimental and theoretical load-deflection behaviour of the specimens are presented in the paper. The composite column specimens and also some composite columns available in the literature have been analysed and found to be in good agreement with the test results.

Key Words
composite column; biaxial bending; slenderness effect; ultimate strength; flexural rigidity.

Address
Serkan Tokgoz : Assist. Professor of Civil Engineering Mersin University 33340 Mersin, Turkey
Cengiz Dundar : Professor of Civil Engineering Cukurova University 01330 Adana, Turkey


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