Parametric and Two Dimensional Study of seismic behavior of micropile Group in Sandy Soils

ABSTRACT:This paper examines the effects of acceleration amplitude of harmonic seismic load and damping ratio on seismic behavior ofmicropile group. A two dimensionalfinite element model and plain strain in Plaxis software have been used for modeling. Sandy soil is considered elastically and with and without Rayleigh damping. Substructure is modeled with a single freedom degree system composed of concentrated mass and a column. Micropiles are considered in vertical position. Analysis results show that increase in amplitude of input acceleration also causes, approximately at the same proportion, increase in shift, horizontal and vertical acceleration cap. Increase in seismic harmonic load amplitude, also causes increase in the amounts of bending moment, shear and axial force of micropiles. Rayleigh damping ratio causes energy to be depreciated during loading stage and it causes decrease in the amount of force transmission into structure. Damping causes 250% decrease in cap displacement. Rayleigh damping ratio causes slight decrease in vertical acceleration of micropile cap. However, it causes considerable reduction in horizontal acceleration of the cap so that horizontal acceleration of the cap for without damping case is more than fourfold of damping case.