Seismic Response of Slender Structures with Foundation Uplifting on Elastic or Inelastic Soil (Pythagoras II) (2005)

The scope of this project was to investigate the rocking response of slender structures. While slender structural systems with a shallow foundation are generally considered as bonded to the ground, during strong seismic shaking uplifting from the supporting soil is often practically unavoidable. Apart from civil engineering structures, uplifting and overturning are some of the most familiar phenomena for free-standing bodies (such as appended equipment, furniture, etc.) during strong earthquakes. In the course of this project, three different systems were examined : (i) a rigid slender block on a rigid base (i.e. undeformable ground), (ii) a rigid block on elastic or inelastic soil, and (iii) a slender SDOF system on elastic or inelastic soil. The problem was analyzed employing a large-displacement formulation. Directivity affected near-fault ground motions were considered, idealized as Ricker wavelets or trigonometric pulses. The conditions under which uplifting leads to large angles of rotation and eventually to overturning were investigated, revealing a profoundly nonlinear rocking behavior. The geometrically nonlinear response was found to be further amplified by unfavorable sequences of long-duration pulses in the excitation.