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Über dieses Buch

This book helps designers and manufacturers to select and develop the most suitable and competitive steel structures, which are safe, fit for production and economic. An optimum design system is used to find the best characteristics of structural models, which guarantee the fulfilment of design and fabrication requirements and minimize the cost function. Realistic numerical models are used as main components of industrial steel structures.

Chapter 1 containts some experiences with the optimum design of steel structures

Chapter 2 treats some newer mathematical optimization methods.

Chapter 3 gives formulae for fabrication times and costs.

Chapters 4 deals with beams and columns. Summarizes the Eurocode rules for design.

Chapter 5 deals with the design of tubular trusses.

Chapter 6 gives the design of frame structures and fire-resistant design rules for a frame.

In Chapters 7 some minimum cost design problems of stiffened and cellular plates and shells are worked out for cases of different stiffenings and loads.

Chapter 8 gives a cost comparison of cylindrical and conical shells.

The book contains a large collection of literatures and a subject list and a name index.

Inhaltsverzeichnis

Frontmatter

Experiences with the Optimum Design of Steel Structures

Abstract
A brief history of the structural optimization is given. The developed system of minimum cost design is described. In 1970’s a school has been found for structural optimization in the University of Miskolc. The advantages and disadvantages are compared for the design by routine and those of optimum design. The problem of interaction of two instabilities is treated with the conclusion that the optimum design is safe when the used stability constraints take into account the effect of initial imperfections and residual stresses. Some own results are detailed about the optimum design for different structural types such as compressed and bent columns, stiffened plates as well as wind turbine towers. A literature survey is given for optimum design of trusses, frames and industrial applications.
József Farkas, Károly Jármai

Newer Mathematical Methods in Structural Optimization

Abstract
Structural optimization means finding the best solution while considering several design constraints. The optimization can be topology, shape and size optimization. Our activity is related mainly to sizing optimization. These constraints can be the behaviour of the structure, like the stresses, fatigue, deformations, stability, eigenfrequency, damping, etc. These constraints are usually highly nonlinear, so to find the optimum it is not an easy task. It is as important to have a reliable optimization technique. There are many optimization algorithms available. Non of the algorithm is superior. All of them can have benefits and disadvantages.
József Farkas, Károly Jármai

Cost Calculations

Abstract
This Chapter describes the importance of cost calculations when we optimize a structure. These cost calculations are founded on material costs and those fabrication costs, which have direct effect on the sizes, dimensions or shape of the structure. The cost function includes the cost of material, assembly, welding as well as surface preparation, painting and cutting, edge grinding, forming the shell and is formulated according to the fabrication sequence. Other costs, like amortization, investment, transportation, maintenance are not considered here. Sometimes we can predict the cost of design and inspection, but usually they are proportional to the weight of the structure.
József Farkas, Károly Jármai

Beams and Columns

Abstract
The present study shows the difference between structures optimized for minimum volume and minimum cost. The cost function contents the cost of material, assembly, welding and painting. A simply supported welded box section beam is investigated. The design constraints are as follows: limitation of the maximum stress from the maximum bending moment, limitation of plate slendernesses to avoid local buckling of flange and web. The minimization of the volume and cost results in different beam sizes, but the cost difference between the two optima is small.
József Farkas, Károly Jármai

Tubular Trusses

Abstract
The present study shows the difference between structures optimized for minimum volume and minimum cost. The cost function contents the cost of material, assembly, welding and painting. A cantilever tubular truss with parallel chords is investigated. The compression rods are designed against overall buckling so that the required cross-sectional areas are calculated with approximate closed formulae. In the cost function also the cost of cutting and edge grinding of the circular hollow section rod ends is included. The heights of the truss corresponding to minimum volume and cost are different, but the cost difference between the two optima is not high.
József Farkas, Károly Jármai

Frames

Abstract
The calculation of the absorbed energy i.e. the area of the hysteretic loop for rods of circular and square hollow sections (CHS and SHS) has been worked out. The limiting points of the hysteretic loop have been determined on the basis of experimental results published in the literature.
A square symmetric portal frame with four horizontal beams and four columns, carrying a silo is designed for vertical and seismic loads. Design rules of Eurocodes 3 and 8 are used. X-bracing is applied, in which the compressive member absorbs the energy by a hysteretic cycle with overall buckling. The cost function for the braced portal frame is expressed in function of unknown dimensions of beams, columns and braces.
The beams and columns are constructed from SHS profiles. All joints are fully welded. The design constraints are formulated for beams and columns on stress, overall buckling and admissible sway for unbraced frame. This sway has two main components: the sway of the vertical frames and the deformation of the beam due to bending in horizontal plane. The constraint on slenderness of braces is also important.
József Farkas, Károly Jármai

Stiffened Plates

Abstract
An assembly desk is constructed as a square plate stiffened by an orthogonal grid of ribs. The residual welding deflection is calculated applying the Okerblom’s method. When the ribs are tacked to each other and to the base plate before welding, then the deflection is decreased by grid effect. The base plate thickness and the dimensions of stiffeners are optimized to minimize the cost and to fulfil the deflection constraint.. The optimization is performed with and without grid effect and it is shown that the grid effect decreases the cost significantly.
József Farkas, Károly Jármai

Cylindrical and Conical Shells

Abstract
The problem is to find the optimum dimensions of a ring-stiffened circular cylindrical shell subject to external pressure, which minimize the structural cost. The calculation shows that the cost decreases when the shell diameter decreases. The decrease of diameter is limited by a fabrication constraint that the diameter should be minimum 2 m to make it possible the welding and painting inside of the shell.
József Farkas, Károly Jármai

Backmatter

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