Seismic Protection of Monuments and Historical Buildings By a Sustainable Reduction System of the Seismic Input Motion

Abstract eng:
The basic idea of the described research work, lies on the exploitation of the incoherency and the out of phase physical phenomenon among the in-coming seismic waves that excite the structures through their foundation. This beneficial function is valid only if the foundation is quite large, stiff and strong along all directions. The ground motion mitigation system consists of a grillage of reinforced concrete beams that are constructed in direct structural contact with its foundation body. The dimensions of the plan of the orthogonal grillage should be longer that the half seismic surface wave’s length in order to achieve a substantial reduction. A parametric analysis was carried out considering the foundation as a two dimensional elastic beam and the velocity of the propagation of the ground motion as basic parameters. Two strong ground motions have been used, each one with quite different characteristics compared to the other one. Finally, a combination of 32 cases was examined, and the resulted motions at the center of gravity of the beams as well as the corresponding response spectra were calculated. The ratios of the resulted response spectra over the free field spectral values at various natural periods and for 5% critical damping are calculated, and it was proved that the reduction may reach the 50% of the free field values. The application of the methodology is presented in various case studies of monumental structures such as churches and residential buildings. These results are checked following the FEMA 440 methodology. It was proved that the difference between the two approaches is within engineering acceptable limits given the large amount of parameters involved in the problem.

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