Evaluation of efficiency of ALSC floating-sliding base-isolation system based on shake table test and floor response spectra

The ALSC base isolation system was investigated by testing a church model to the scale 1/3.5 on the two-component shaking table at the IZIIS' Laboratory, Skopje, Macedonia. The investigation was performed within the frames of the European FP6 project PROHITECH, related to seismic protection of historical buildings by innovative and reversible mixed technology systems. This system was originally developed in 2001 and applied on a model of a steel reservoir. The church model was tested twice: with an active base-isolation system and fixed to the base. The effectiveness of the base-isolation system was investigated by the transfer function/floor response spectra technique. Special software for calculation of the transfer functions and floor response spectra based on experimental data, referred as SPECTRA, was developed by the authors of this paper. The main objective of the investigations presented in this paper was evaluation of the effectiveness of the ALSC floating sliding base-isolation system by using the Response Spectra approach. Comparison of the Floor Response Spectra was done for two cases a fixed base model and a base-isolated model. The base response spectrum was calculated from the input time history of the Montenegro earthquake compressed 3.5 times (geometry scale of the model). The Transfer Functions and the Floor response Spectra at a particular level were calculated from the Cross Power Spectra (CPS) and the Auto-Power Spectra. The obtained results showed that the effect of the base-isolation system was considerable, with a low transmissibility of energy from shake table to the model.