Optimum design of ovehead traveling crane girders

A computer program was prepared (Qbx, ver. 7.0) for the optimum design problem for minimum bridge girder weights of overhead travelling cranes powered by electricity. The welded box-type girders were modelled as a simply supported beam. Stresses and displacements were obtained while the trolley with all the loads on it were moving on the girder in its worst position. A design of crane bridge girders was formulated with inequality constraints as a minimum weight problem. The minimisation of objective function was taken as the minimisation of the girder weight. The stresses, displacement, buckling and sizes were restricted, in such way that will not exceed in safe values defined by the standards. The non-linear programming problem, thus obtained, was solved by means of the practical design optimisation method which is used in designing huge mechanical systems. Input of design variables into the computer program was carried out respectively from a list which was prepared with standard plate combinations and the operation was repeated until feasible solutions were found. Not only that lists were used but also new design variables were obtained by changing the section ratios. In addition, stress, displacement and buckling values were studied for standard box-type girders at different hoisting load and different span. Hoisting load and span were obtained which give minimum stress. The numerical examples were given with illustrations which show the effectiveness of this approach. Key Words : Overhead travelling cranes, girder, bridge, optimum design. VI