Vertical Seismic Load Effect on Building Response

An analytical procedure is presented for the calculation of the statistical properties of the response of a linear elastic tall building under earthquake excitations. The emphasis is placed on the effect of the vertical ground motion. The restoring force in each story of the structural model is assumed to arise from the bending deformation of the columns whose rigidities are subject to a general reduction due to gravitational forces and to a random variation due to vertical ground accelerations. To illustrate the application of the procedure, numerical results are presented for a 6-story building. Within the limit of linear elastic deformation, the vertical ground acceleration is shown to be capable of causing an increase in certain response variables in the order of 10% for this moderately tall building. The percentage is expected to be larger for a taller building and much larger when the deformations exceed the elastic limit.