Abstract

The paper refers to stability of compressed prismatic beam columns of circular and filled section, in the range of elasto-plastic deformation. The slendernesses ratio is taken from _H≤≤_r, where _H=√(E/R_H ), E is Young modulus, R_H is the proportional limit and slenderness _r divides elastic and elasto-plastic ranges of deformation. The original experimental test is described and analysis of experimental results is carried out with respect to the proposed by author formulas for determinig both the static and geometric parameters of beam column as well as the energy and the work of external forces relating to critical and supercritical states. The research is complemented by calculation of safety factor, which due to proposed by author analysis is much lower than that proposed by Polish standard PN-76/B-03200, on static analysis and design of steel structures. The presented approach follows the experimental tests on column buckling, namely the column preseved its straight shape only until the loading reach the value of P_E/√3,, where P_E is the Euler value of critical force. At this level of loading the critical compressing occurs and the column axis becames uncompressible. For higher values of the loading the process goes on with the stable bent shape and at the critical state, determined by the force , the stable bent shape occurs concequently. The potential energy at critical state is equal to the maximum value of the energy of elastic deformation. This value depends on the material mechanical properties and the shape of cross-section. For the forces higher than P_E the plastic strains and the material strengthening occurs.