الفهرس 
CHAPTER 1: INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Cold formed members with hollow steel sections are extensively used in industrial and many other non-industrial constructions worldwide, which include portal frames in a large scale that are consisted of open and closed sections. It may be considered relatively a new concept in Egypt. Cold-formed steel frames are an assembly of structural members that has proven over time to meet a wide range of structural and aesthetic requirements. For most common cold, formed opened sections such as channel and Z-section have behavior such as distortional buckling and this study will not be interested with these sections. This study interests with Cold-formed tubes sections. Cold-formed tubes are available in many forms such as rectangular hollow sections (RHS), square hollow sections (SHS), circular hollow sections (CHS), and oval hollow sections (OHS). Cold formed hollow sections have the advantages of ease of mass production, prefabrication, uniform quality, lightweight designs, economy in transportation and handling, and quick and simple erection or installation. Cold-formed hollow sections have many properties, such as high torsional stability, which results in less bracing that could be exploited beneficially in design.
This study was carried out using non-linear finite element analysis of 3D steel models. Firstly, the validation study was conducted by ABAQUS® finite element software for four experimental tests. At first, verification was done for frame with RCFHS by Avery [24]. While, the other three verifications were done for unstiffened, stiffened and welded sleeve knee joints for portal frame with RCFHS by Wilkinson and Hancock [29]. The comparison of the results between both the experimental tests and FEA method gave a good agreement. The FE method proves sufficient accuracy to predict the behavior and to investigate the load-displacement curves, ultimate strength and the failure modes.
Secondly, the verification study helped to conduct a parametric study and develop three-dimensional steel frames by using ABAQUS® program. A total 144 Finite element models of steel frames with major axis bending were carried out in ABAQUS® software. All steel frames by using finite element models consisted of beams and columns, which have the same cross section and thicknesses. Models were modelled with two cross sections, RCFHS 200×100 and RCFHS 150×50. Parametric study was carried out to study numerically the behavior of steel frames using RCFHS and influence of using different thicknesses of cross section, frame spans, frame heights, size of cross section, initial imperfections and residual stresses.
Based on parametric study, increasing thickness of cross section could be efficient in resisting loads and give higher ultimate load while the value of ultimate load with increasing the frame height has the greatest effect on decreasing the ultimate load capacity of the frame than increasing the frame span. Also, the effect of the dimensions of the cross-section at the ultimate load capacity of the frame influence both the axial load and bending moment capacities and the global buckling of the frames can occur faster in frames with smaller dimensions.