Effects of Pore Pressure on Wandering in Structural Natural Frequency

Natural frequency wandering is a phenomenon observed in dynamic structural behavior. Temporary and permanent changes in the determined natural frequencies have been shown to be related to such factors as weather conditions, structural damage or soil-structure interaction. Furthermore, some studies indicate temporary natural frequency wandering during seismic events. This temporary wandering and recovery of the initial pre-event natural frequency has not been specifically explained yet. Some studies indicate soil-structure interaction as a potential reason causing the observed structural behavior. This paper presents a numerical finite element study and aims at investigating the influence of soil-structure interaction on the observed natural frequency wandering induced by seismic actions. The advanced soil constitutive model Severn-Trent is used and an example structure built on saturated granular soil is analyzed. A temporary drop in the natural frequency is shown soon after the earthquake followed by regain to the initial value with time. The results show that generated pore pressure, its dissipation over time, reduced mean effective pressure and nonlinear stress-strain behavior are linked with temporary changes in natural frequencies.