In this paper, we present a model for seismic analysis of buildings. In this model, two masses concentrated by each level are taken and applied in the free joints of the structure. Also, a comparison is made with the traditional method to consider a discrete mass by each level, i.e., a mass by each floor of all the buildings, in this all the values are not conservative, as can be seen in the problem considered. The two models take into account the shear deformations. Therefore, the usual practice of considering one mass concentrated by each level is not a recommended solution and it is proposed to consider two masses concentrated by each level, and in addition, it has conditions nearer to the reality.

modal analysis, spectral analysis, eigenvalues, eigenvectors, modal participation factor, spectral acceleration, vector coordinates maximum normal.