Jafar Najafizadeh, Mohsen Kamalian, Mohammad Kazem Jafari, Naser Khaji,
Volume 12, Issue 3 (7-2014)
Abstract
In this paper, an advanced formulation of the spectral finite element method (SFEM) is presented and applied in order to carry out site response analysis of 2D topographic structures subjected to vertically propagating incident in-plane waves in time-domain. The accuracy, efficiency and applicability of the formulation are demonstrated by solving some wave scattering examples. A numerical parametric study has been carried out to study the seismic response of rectangular alluvial valleys subjected to vertically propagating incident SV waves. It is shown that the amplification pattern of the valley and its frequency characteristics depend strongly on its shape ratio. The natural frequency of the rectangular alluvial valley decreases as the shape ratio of the valley decreases. The maximum amplification ratio along the ground surface occurs at the center of the valley. A simple formula has been proposed for making initial estimation of the natural period of the valley in site effect microzonation studies.
Hamid Alielahi, Mohammad Adampira,
Volume 14, Issue 4 (6-2016)
Abstract
Investigating the seismic amplification of incident waves induced by subsurface cavities and characterizing its patterns for the ground surface are important in seismology, geophysics and earthquake engineering both in theory and practical application. Nowadays, it has been established that the seismic ground response above subsurface structures can be different from the free-field motion during earthquakes. In this regard, this research studied preliminary results of a numerical parametric study on the seismic response of the ground surface above subsurface cavity. Basically, this study is applied to get new idea to move a step forward in site response analysis which can be used in the seismic microzonation of areas located above underground spaces. For analysis purposes, a numerical time-domain analysis is performed by utilizing a robust numerical algorithm working based on the boundary element method. It is observed that the amplification of the ground surface underlain by a shallow elliptical cavity is increased in long periods. Some preliminary simple relationships and tables are presented which could be used while introducing simple preliminary ideas for modification of the standard design spectra in building codes and seismic microzonation studies.
