LRPH device optimization for axial and shear stresses

The paper concerns an in-depth study of a special connection for steel structures and the formulation of the related optimal design problem. The connection is called Limited Resistance Rigid Perfectly Plastic Hinge (LRPH) and it represents an innovative device devoted to join steel beam elements of frame structures. The device consists in a sequence of steel cross sections constituted by two parallel flanges with suitably different thickness connected by as many webs with constant and equal thickness. The fundamental innovation of the device is the possibility of designing special connections with elastic stiffness and limit strength independent of each other. Such a special characteristic makes the proposed device definitely unique within the steel structure constructions. The LRPH limit strength is evaluated with respect to axial force, bending moment and shear force, coherently to the international standards. The optimal design problem is formulated minimizing the ratio between outer and inner flange thickness, taking into account constraints related to the imposed reduced resistance, to the required elastic stiffness and to further suitably defined technological requirements. In the application stage, the optimal design is reached by means of a standard non-linear solver for continuous variable problems.