Effect of foundation flexibility on seismic response of reinforced concrete TV-towers

Abstract

The analysis of tall reinforced concrete TV-towers is commonly simplified by assuming a fixed base and ignoring the effect of soil–structure interaction. However, the foundation flexibility affects the dynamic characteristics of tall structures and influences their dynamic behaviour. To design these towers for dynamic loading, the fundamental natural periods, base bending moment, and base shear force as the most important parameters are needed and must be evaluated properly. In the current study, a finite element formulation for the response analysis of TV-towers subjected to earthquake ground motion accounting for soil–structure interaction is presented. The effects of foundation flexibility on the dynamic behaviour of TV-towers were evaluated for two different types of foundation, shallow footing and deep foundation, and various soil profiles. A typical example for these towers is analysed and the results for a range of soil dynamic parameters are presented. It was found that the foundation flexibility increases the natural periods, alters the natural mode shapes, and decreases the base bending moment. It was also concluded that the effect of soil–structure interaction may have a large effect on the base shear of the tower and should be considered in the analysis, especially for the design of horizontal reinforcement.Key words: soil–structure interaction, TV-towers, natural period, base forces, foundation flexibility.