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The performance of distributed base isolation using smooth geotextile for seismic protection of masonry buildings was studied. The concept of frictional base isolation is applied to masonry buildings by separating the superstructure from the foundation at plinth level by a sliding friction interface in the form of a nonwoven geotextile–smooth (machine ground) marble. The dynamic friction properties of the masonry–geotextile interface were investigated. The shaking table test was performed on a one-half scale, single storey brick masonry model on a sliding interface for bi-axial earthquake ground motion compatible with the 5% damping design spectrum of the Indian standard code for earthquake-resistant design corresponding to the level of maximum considered earthquake in the most severe seismic zone. It was observed that the use of geotextiles as frictional base isolation was quite effective in mitigating earthquake-induced vibrations. A 65% reduction in absolute response acceleration at the roof level was obtained in comparison with the response of the fixed base structure at the cost of 25 mm peak sliding displacement, which was well within the plinth projection of 75 mm.

A feasibility study of friction base isolation system for seismic protection has been performed. Four different sliding interfaces, namely, green marble/High Density Poly Ethylene (HDPE), green marble/green marble, green marble/geosynthetic, and green marble/ rubber layers have been studied through experimental and analytical investigations. The experimental investigations show that the coefficient of friction values of these interfaces lies in the desirable range for seismic protection, i.e., 0.05 to 0.15. The analytical investigation reveals that most of these sliding interfaces are effective in reducing spectral accelerations up to 50% and the sliding displacement is restricted within plinth projection of 75 mm (3 in). Green marble and geosynthetic are found to be better alternatives for use in friction isolation system with equal effectiveness of energy dissipation and limiting the earthquake energy transmission to super structure during strong earthquake leading to a low cost, durable solution for earthquake protection of masonry buildings.

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A new approach has been presented to characterise phase spectra for simulating realistic nonstationary characteristics in synthetic accelerograms. The phase characteristics of the recorded earthquake accelerograms have been studied for this purpose and it has been found that the phase curve/unwrapped phases exhibit a monotonic downward trend which allows the problem of phase characterisation to be cast as a constrained nonlinear programming problem. The phase spectrum is first characterised by matching mean and variance of the generated distribution of relative phases with those obtained from recorded motions. As a practical application, it is shown how phase spectra can be characterised for an ensemble of synthetic accelerograms so as to maximise the severity of sample realisations.