Ação dinâmica de vento EPS em torres metálicas treliçadas considerando a interação solo-estrutura

Abstract

The present work carried out a comparative study between static and dynamic analyses in a self-supporting steel lattice tower under action of extended pressure system (EPS) winds while considering soil-structure interaction (SSI). For static analyses, wind actions were considered in accordance with the recommendations of IEC 60826 (2003) on tower supporting members. For dynamic analyses, wind actions were calculated as the sum of the mean wind speed, following the reccomendations of NBR 6123 (1988) for reticulated towers, and the fluctuating time-dependent velocity component in the along-wind. In order to generate longitudinal wind fluctuation signals, the power spectra of Davenport, Harris, and Kaimal were adopted. Thus, this component was simulated numerically using the frequency domain functions, applying the Inverse Fast Fourier Transform (IFFT), after assigning random numbers to the real and imaginary parts that compose the function. In order to evaluate SSI influence on the tower, stiffness coefficients of the vertical and horizontal soil-foundation set were calculated and introduced into the model as nonlinear spring elements. Static analyses were performed using the finite element program ANSYS, while, in dynamic analyses, the equations of motion were solved using the Direct Integration Method (DIM) in FORTRAN. For rigid bases hypothesis, dynamic amplifications in the displacements of the nodes at the top of the tower were obtained around 1.5. These values increased when SSI was considered, reaching displacement up to 102% higher. Furthermore, the axial stress on the support members also increased, in most cases resulting in dynamic amplifications of up to 1.7. When considering SSI, this figure increased by up to 23.6%. Thus, despite the fact that wind actions on tower supporting members along-height were considered fully correlated, the displacements of the nodes at the top, as well as maximum axial stress on tower members, presented significant values.