Un método directo para el diseño de elementos a pandeo en estructuras aporticadas de acero

A direct method for the buckling analysis of steel frame structures

The buckling analysis of steel frame structures is customarily carried out in a two step approach. Firstly, a linear elastic analysis of the structure is performed to obtain the internal forces and moments; and secondly, the buckling analysis and design is done for each individual element. According to the Spanish Steel Code, EA-95, the buckling analysis of each element is primarily based upon the coeffi-cient b, which depends on the buckling mode of that particular element within the structure. In many practical cases this coefficient is obtained by means of approximations and even by mere estimation. This paper presents a direct method for the structural and buckling analysis in a one step method, without having to deal with the p coefficient of each individual element. The key point is to perform a nonlinear analysis of the structure starting from an initial deformation state that includes the initial imperfections of the elements. Such initial deformation state is obtained from the first buckling mode of the structure by a suitable scaling procedure based on an energy approach. The resulting initial deformed shape is introduced along with the external loads in a fully nonlinear structural analysis that yields the resulting element stresses including the buckling effects. The performance of the method is checked against the current procedures (EM-95), by means of a series of numeri-cal examples.