Characterisation of design spectra for vertical ground motion

Design recommendation on vertical ground motion offers dual challenges, namely the spectral shape and conditional peak-ground-acceleration. One way of recommending the vertical spectra is through V/H spectrum that can be multiplied with design horizontal spectrum. Seismic code recommendations do not explicitly account for the possible effects of magnitude (except EC8 Part-1) and epicentral distance. This paper is aimed to assess the possible effects of magnitude, epicentral distance and average shear wave velocity (representing the soil sites) on resulting V/H spectra. About 6,000 strong motion events are considered for this purpose. Resulting V/H and vertical spectra conditioned to the horizontal spectra are compared with the seismic code recommendations and prior-art. Also explored is the feasibility of possible recommendations on V/H spectra contingent on magnitude, epicentral distance and average shear wave velocity. Finally, the framework is assessed with respect to a strong motion event which was not included in the developmental database.