Measured And Predicted Seismic Response Of Two Similar Buildings, One With Rigid Foundation And The Other With A Base Control System.

Abstract

Based on the study of two similar buildings equipped with seismic instrumentation, finite
element models are developed and calibrated using seismic signals of input and response, recorded on
the two buildings in August 2006. One building was constructed on a traditional rigid foundation and
the other was isolated with a Base Control System (BCS). These numerical models are used to carry
out an exhaustive comparison of the buildings’ dynamic behavior and to evaluate the isolation system
performance. The isolated building’s behavior is weakly nonlinear, because the dynamic properties of
isolators depend on displacements and frequencies. The stiffness and the damping coefficient of the
isolators are considered as constants, these approximations allow the use of commercial finite element
software to study the dynamic response due to the seismic excitation. The dynamic equations are
numerically integrated in time domain, considering the non proportional damping caused by viscous
dampers as a nonlinear load term. Acceleration at different buildings’ levels, base displacements, axial
forces and bending moments on different columns, base shear and dissipated energy are compared for
the two considered cases, BCS and the fixed base building model. The results show an effective
reduction of accelerations and seismic loads in the isolated building to less than one third of the values
corresponding to the rigid base building. The strategy of including some vertical flexibility and
vertical damping in the isolators and admitting some small rocking motion of the building is also
validated; considering that in the present case the vertical movements contribute to dissipate 20 % of
the seismic energy.