Elastic axis of special classes of buildings under earthquake excitation

Abstract

In the present paper the existence of a stable vertical axis of twist in single story and isotropic multistory buildings is investigated. For this purpose, a torsional base excitation is applied at the buildings base and the equation of motion is transformed in the frequency domain. By using the diaphragm constraint equations, analytical formulae are developed which provide the location of the twist axis which is called dynamic elastic axis. It is proved that the coordinates of the dynamic elastic axis depend on stiffness, mass, damping and excitation frequency. Numerical examples are presented. All the results produced by using the developed equations are compared with the coordinates of the elastic axis derived by the application of static forces. The divergence of the two methods is discussed in detail.