OPTIMUM DESIGN OF ONE-BAY PORTAL STEEL FRAMES
Osama El-Mahdy
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Abstract
The paper presents optimum design of statically indeterminate two-hinged steel portal frames under multiple loadings. An explicit formulation of the analysis equations using the Virtual Work Method is developed. Loading cases include both gravity loads and wind loads. Design equations involving local buckling, lateral torsional buckling, shear buckling, combined stresses and deflection constraints, as provided by the latest Egyptian Code of Practice for Steel Construction and Bridges, are included. The objective function is chosen as the minimum weight of the structure. The design variables are the cross-sectional dimensions of the built-up sections for rafters and columns. The design constraints cover all cases of discontinuity for compact prismatic sections. Ordinary mild steel and high tensile steel cases are considered. The optimization technique adopted in this research is the Modified Method of Feasible Directions. Several examples are presented to validate the efficiency of the formulation and to prove that the designs obtained in this work are more economical than those provided by other classical design approaches. Savings up to fifty percent of the weight of the frame are achieved for some cases.
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DESIGN SYNTHESIS FOR SINGLE- AND MULTI-BAY STEEL FRAMES ACCORDING TO ECP’ 01
Minimum weight design of single-and multi-bay steel portal frames is presented. The design variables are the dimensions of prismatic built-up sections for beams and columns. Design constraints are considered as per ECP’ 01: shape, buckling, stresses, and deflection constraints. Both compact and non-compact sections are included in the formulation. Cases of loading comprise vertical and lateral loads. Analysis is done using Displacement Stiffness Method. An optimization technique based on the Method of Feasible Directions -through an implicit formulation– is adopted. Several examples are presented in order to assess the advantages of adopting optimization in structural steel design as compared to other classical design approaches.
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Effect of serviceability limits on optimal design of steel portal frames
Journal of Constructional Steel Research, 2013
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Pollack Periodica
Frame structures are defined as structures built of straight, less often curved bars, which are dimensioned to carry a planar or spatial load. These frames are generally considered statically indeterminate structures so that several methods can be used to determine their loads, but all of them require some simplification. This paper is not concerned with investigating these theories for determining the stresses but with the optimum design of a frame structure for a given geometry. Several different loads have been considered, where the value of the wind load in the horizontal direction has been considered. The optimization problem is mathematically formulated so that both compressive forces and bending moments acting on the horizontal beam and the vertical column, and their composite loads, are below the limit set by the material properties. The column connections were assumed to be fully rigid, and welded I-section were considered for both columns. For local bending conditions, the...
Design of Steel Structures
Portal frames are the most commonly used structural forms for single-storey industrial structures. They are constructed mainly using hot-rolled sections, supporting the roofing and side cladding via cold-formed purlins and sheeting rails. They may also be composed of tapered stanchions and rafters fabricated from plate elements. Portal frames of lattice members made of angles or tubes are also common, especially in the case of longer spans.
Structural Evaluation of Semi-Rigid Steel Portal Frames
Proceedings of the …, 2005
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The paper has proposed a mathematical model for parametric optimization problem of the steel lattice portal frame. The design variable vector includes geometrical parameters of the structure (node coordinates), as well as cross-sectional dimensions of the structural members. The system of constraints covers load-carrying capacities constraints formulated for all design sections of structural members of the steel structure subjected to all ultimate load case combinations. The displacements constraints formulated for the specified nodes of the steel structure subjected to all serviceability load case combinations have been also included into the system of constraints. Additional requirements in the form of constraints on lower and upper values of the design variables, constraints on permissible minimal thicknesses, constraints on permissible maximum diameter-to-thickness ratio for the structural members with circle hollow sections, as well as the conditions for designing gusset-less w...
Practical analysis procedures of steel portal frames having different connections rigidities using modified stiffness matrix and end-fixity factor concept
IOP Conference Series: Materials Science and Engineering, 2019
The real behaviour of connections in the steel buildings is often underestimated by designers at the structural analysis and design stages, despite their influences on the structural performance, deflection limits and a possibility of achieving a reduction in the material weights, which can significantly reduce the overall cost and amount of energy embodied. This paper, therefore, described systematic and simplified procedures to conduct a first-order elastic structural analysis of the semi-rigid steel portal frames in order to implement a design optimization using a Generalized Reduced Gradient (GRG) algorithm within Solver Add-in tool in Microsoft Excel. The written program used the robustness and efficiency of the Finite Element (FE) method with the versatility of a spreadsheet format in Excel. To simulate the semi-rigid response of the connections, the mathematical representation through End-Fixity Factor and the Modified Stiffness Matrix were used to incorporate such behaviour ...
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