A UNIFIED APPROACH TO THE TIMOSHENKO GEOMETRIC STIFFNESS MATRIX CONSIDERING HIGHER-ORDER TERMS IN THE STRAIN TENSOR

Abstract

NONLINEAR ANALYSES USING AN UPDATED LAGRANGIAN FORMULATION CONSIDERING EULER-BERNOULLI BEAM THEORY HAVE BEEN DEVELOPED WITH CONSISTENCY IN THE LITERATURE, WITH DIFFERENT GEOMETRIC MATRICES DEPENDING ON THE NONLINEAR DISPLACEMENT PARTS CONSIDERED IN THE STRAIN TENSOR. WHEN PERFORMING THIS TYPE OF ANALYSIS USING TIMOSHENKO BEAMS THEORY, IN GENERAL, THE STIFFNESS AND THE GEOMETRIC MATRICES PRESENT ADDITIONAL DEGREES OF FREEDOM. THIS WORK PRESENTS A UNIFIED APPROACH FOR THE DEVELOPMENT OF A GEOMETRIC MATRIX EMPLOYING TIMOSHENKO BEAM THEORY AND CONSIDERING HIGHER-ORDER TERMS IN STRAIN TENSOR. THIS MATRIX IS OBTAINED USING SHAPE FUNCTIONS CALCULATED DIRECTLY FROM THE SOLUTION OF THE DIFFERENTIAL EQUATION OF THE PROBLEM. THE MATRIX IS IMPLEMENTED IN FTOOL SOFTWARE AND ITS RESULTS ARE COMPARED AGAINST SEVERAL MATRICES FOUND IN THE LITERATURE, CONSIDERING OR NOT HIGHER-ORDER TERMS IN STRAIN TENSOR, AS WELL USING EULER-BERNOULLI OR TIMOSHENKO BEAM THEORIES. EXAMPLES SHOW THAT THE USE OF TIMOSHENKO BEAM THEORY HAS A STRONG INFLUENCE ESPECIALLY WHEN THE STRUCTURE PRESENTS A SMALL SLENDERNESS (SHORT MEMBERS). FOR HIGH AXIAL LOAD VALUES, THE CONSIDERATION OF HIGHER-ORDER TERMS IN STRAIN TENSOR RESULTS IN LARGER DISPLACEMENTS AS EXPECTED.