Dynamic behaviour of tall slender structures on flexible foundations subjected to extreme events

The analysis of tall slender structures is commonly simplified by assuming a fixed base and ignoring the effect of soil-structure interaction ( SSI). However, the inevitably flexible foundations affect the dynamic characteristics and dynamic behaviour of tall structures. In this study, an attempt is made to assess the SSI effects on dynamic response of tall slender structures responding in the elastic or inelastic range. The conventional substructure method is employed to develop the practical procedures and concepts with which the effects of SSI for tall structures can be easily and reliably accounted for. The different approaches available for computing impedance functions that are used in substructure-based SSI analyses of flexibly supported structures are reviewed placing special attention on the new Consistent Infinitesimal Finite-Element Cell method.; Response spectrum analysis was applied to quantify the effects of inertial interaction on modal parameters and seismic elastic behaviour of tall slender structures. A comprehensive three-dimensional finite element modeling was formulated and the results were compared with those obtained from one-dimensional stick model analysis. The changes in the fundamental period and the structure response were evaluated for different practical types of foundations and various soil profiles. The results revealed a pronounced influence of the soil profile and the soil modulus of elasticity on the response of a structure. The effect of SSI if yielding occurred in different sections of tall slender structures during intense ground shaking was also investigated. A simplified approach that accounts for inelastic deformations in the superstructure and foundation flexibility was developed. The procedure involves a pushover analysis and is based on the response spectrum analysis. The results showed that SSI produces an increase of the maximum displacements of an inelastic structure when compared with its elastic behaviour. However, the ductility capacity of the individual section was affected by the foundation flexibility, showing a tendency to decrease.; The soil secondary non-linearity is another major aspect of SSI that mostly occurs in the supporting near-field soil during intense ground motions. The method incorporates the CIFEC technique for modeling unbounded and bounded mediums into a three-dimensional time domain analysis capable of evaluating the non-linear response of the soil adjacent to the structure. The results indicated that the soil secondary non-linearity could cause an increase in the lateral total displacements, and depending on the characteristics of the structure and ground motion may have a favourable or detrimental effect on the internal forces induced into the structure, when compared with the linear soil behaviour. (Abstract shortened by UMI.)...