ANALYTICAL DETERMINATION OF THE VIBRATION FREQUENCIES AND BUCKLING LOADS OF SLENDER REINFORCED CONCRETE TOWERS

Abstract

THIS STUDY FOCUSED ON IMPROVING THE DESIGN OF SLENDER STRUCTURES WITH REINFORCED CONCRETE (RC) TELECOMMUNICATION TOWERS AS THE MAIN APPLICATION. ANALYTICAL PROCEDURE BASED ON RAYLEIGH’S METHOD TO COMPUTE THE FIRST NATURAL VIBRATION FREQUENCY AND THE CRITICAL BUCKLING LOAD WAS DEVELOPMENT. ALL THE NONLINEARITIES PRESENT IN THE SYSTEM WERE CONSIDERED, IN ADDITION TO THE SOIL–STRUCTURE INTERACTION AND THE VARIATION OF THE GEOMETRIC PROPERTIES ALONG THE LENGTH OF THE STRUCTURE. THE GEOMETRIC NONLINEARITY AND IMPERFECTIONS OF THE TOWER STRUCTURE WERE COMPUTED AS FUNCTIONS OF THE AXIAL LOAD USING A GEOMETRIC STIFFNESS MATRIX. FURTHER, THE MATERIAL NONLINEARITY WAS ACCOUNTED FOR BY REDUCING THE FLEXURAL STIFFNESS. AS CONCRETE STRUCTURES EXHIBIT VISCOELASTICITY, CREEP WAS CALCULATED USING THE EUROCODE 2 MODEL. THE SOIL–STRUCTURE INTERACTION WAS MODELED AS A SET OF DISTRIBUTED SPRINGS. TO VALIDATE THE PROPOSED METHOD, THE FIRST FREQUENCY AND CRITICAL BUCKLING LOAD WERE COMPARED WITH THOSE YIELDED BY FEM SIMULATIONS. THE FREQUENCY RESULTS WERE IN GOOD AGREEMENT WITH THOSE OF THE FEM SIMULATIONS, INDICATING THAT THE PROPOSED METHOD IS SUFFICIENTLY ACCURATE FOR USE IN ENGINEERING DESIGN APPLICATIONS AND EASY TO IMPLEMENT. ON THE OTHER HAND, THE BUCKLING LOAD RESULTS OBTAINED USING THE PROPOSED METHOD AND FEM DIFFERED SIGNIFICANTLY, MOTIVATING FURTHER INVESTIGATION.