Forced vibration of an eight-story reinforced concrete building

The determination of the dynamic characteristics of an eight-story reinforced concrete building was undertaken. Lateral stability of the structure was provided by shear walls in one direction and by a space frame in the other direction, an unsymmetrical location of rigid elements providing a natural coupling of lateral and torsional vibration.

A pair of synchronized vibration generators were used to generate the desired steady state vibrations. Measurements were made of one translational mode in the direction parallel to the shear walls, two translational modes in the direction parallel to the space frame, and two torsional modes.

A definite nonlinearity in the response of the space frame was observed. Values of damping were 3.5 per cent of critical damping in each direction. The value of dynamic modulus of elasticity that gave the best analytical results compared favorably with standard laboratory determined values for dynamic modulus of elasticity. A simple method for obtaining approximations to the natural frequencies and mode shapes of multistory space frames is discussed.