Economy of higher-strength steels in overhead travelling cranes with double-box girders

Abstract

Abstract In the case of a simple box beam subjected to uniaxial bending, the cross-sectional area optimized with regard to stress constraint is inversely proportional to the square root of the yield stress. Therefore, increasing the yield stress from 230 to 355 and 450 N/mm 2 may result in mass savings of 19% and 28%, respectively. In the case of double-box main girders of OT cranes the mass savings can be determined only by numerical computations comparing the optimized cross sections. In the optimization procedure the four dimensions of a box-section are found which minimize the area of the cross section and satisfy the design constraints. Constraints on static and fatigue stress, on local buckling of flange and web plates, as well as on static deflection, are considered. Numerical computations show that the mass savings depend on the crane classification and on the constraints relating to the fatigue stress as well as to static deflection.