الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Over the past years, many researches were developed to cover advanced analysis methods that can taking into account the material and geometric nonlinearities. The nonlinear analysis of steel frames can be obtained using finite element method. The finite element method can be employed for the nonlinear analysis using a line (beam-column) or using solid or shell elements. Modeling structure members using line elements saves time and calculations required for modeling using solid or shell elements. Line element is widely used in nonlinear analysis and depend on two approaches, plastic hinge and plasticity spread.
This work presents a simplified model to capture the nonlinear behavior of steel frames depending on the spread of plasticity method. New formulae were developed for the determination of the plastic strengths of steel I-sections subjected to uniaxial bending about major or minor axis combined with an axial compression force. Moreover, new formulae were developed to describe the plastic yield surfaces of steel I-sections under biaxial bending moments combined with an axial force. The proposed formulae were obtained by performing large data regression analysis on exact I-section strength results. Also, the proposed formulae were presented as simple formulae valid for standard I-sections (IPE – IPN – HE – HL – HD – UB – JOISTS – UC – UBP – W-shaped – HP) and as general formulae valid for general built-up steel I-section with conditions depend on dimensions ratios. The proposed formulae were compared with the exact analytical solution and with previous analysis methods. These comparisons show that the proposed formulae correlated very well with the exact analytical solution. New modified simple formulae were derived to predict the yield surface of I-section these formulae are more practical and easier for design purposes and lead to very good results compared to EC3 and exact solution.
In the present work, new empirical formulae were derived to predict the tangent modulus of steel I-shaped cross sections considering the effect of the residual stresses recommended by the European Convention for Construction Steelwork (ECCS). The secant stiffness which depends on the tangent modulus is used for evaluation of internal forces. A finite element program based on stiffness matrix method is developed to predict nonlinear behavior of space steel frames using the derived formulae. The proposed model results compare well with those given by the fiber model. Some numerical examples were solved to verify the accuracy and computing efficiency of the proposed model. The analysis results show that the new proposed model is accurate and is able to minimize the solution time.