الفهرس 
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Abstract
Due to high cost of experimental tests for finding out the ultimate toad and corresponding failure mechanism of steel plates and connections, a theoretical simulation model is presented. The yield line method has been used successfully for estimating the ultimate load and the corresponding failure mechanism .Two approaches were used , firstly the failure mechanism is assumed with unknown parameters , secondly the plate is divided into a number of division by potential yield lines and nodes liach node is given a virtual displacement, this leads to an independent mechanism. A number of independent mechanisms equal to the nodes given a virtual displacement are obtained . For the two approaches the ultimate load is determined by equating the internal work done by yield lines and the external work done by the applied load. The solution is determined by minimizing the energy equation .The first approach leads to unconstrained nonlinear objective optimization problem which varies from simple to complex one depending on the problem to be analyzed , while the second approach leads to a linear objective optimization problem and a large number of linear constraint equations A modified genetic algorithm technique was developed to solve such optimization problems ,this modification enables genetic algorithms to find the solution more faster in the search space compared to the traditional ones. The modified genetic algorithm is presented in details, calibrated and tested using a sizing ten-bar truss problem.
To verify the above approaches steel plates subjected to out of plane loading , overlap and gap k-joint connections were tested giving successful results compared to those given in the literature either theoretical or experimental. Applications were made to demonstrate the accuracy and efficiency for the above procedure. The ultimate load and the corresponding failure mechanism for a plate connected to a box column section and a T-connection under tension /compression load were determined. Also, a modified failure mechanism for an I-section subjected to knife loading was determined. This modification takes into consideration the reduction in the plastic moment capacity due to axial load in the web yield lines. Good agreement has been found between the present solution and the results from experimental tests .