A state-of-the-art review of vertical ground motion (VGM) characteristics, effects and provisions

Previous earthquake events have shown that the vertical component of strong ground motion has been proved to damage or totally destroy the structures. But in seismic resistant design of structures, effects of horizontal ground motions are mainly considered and effects of vertical ground motions (VGMs) are ignored. However, the field evidence of damaged structures indicates that the VGM was more significant particularly for near-fault earthquakes. Therefore, the addition of vertical component in seismic design has been recognized in the literature. In seismic resistant design of structures, horizontal ground motions are extensively studied and used for designing of structures. However, VGMs are not considered of more importance as horizontal one. But with the past near-fault earthquakes and their damage evidence effects have increased the awareness of VGMs. In this paper, the critical reviews of the literature associated with VGM are explained and reviewed. The important characteristics like vertical response spectra, near-fault influence, frequency influence and time lag between peak vertical and peak horizontal ground motion, vertical response period influence and local site conditions are explained. The provisions in latest national and international standards and the field evidence of damaging effects caused by VGM are also explained. Considering all the above parameters associated with VGM, the past studies on different types of structures are reviewed. Finally, a methodology for identification of critical parameters and future scope on VGM is proposed. This study leads to some important conclusions that VGM needs to be included in analysis and design.