Computation of Effective Bending Stiffness of RC Telecommunication Towers

We present some results of the application of optimization techniques to experimental data for the determination of the effective bending stiffness of cross-sections of reinforced concrete (RC) structures. The objective is to determine parameters of unstressed sections for the correct computation of the displacements of these structures and possible applications on structural failure theory. The experimental data from tests with 30 and 40 m long RC telecommunication towers, having circular cross-section with 50 cm diameter for the 30 m structure and 60 cm diameter for the 40 m structure, are used. For cross-sections along the axis of the structure, the effective stiffness equation is derived. To accomplish the structural analysis, the structures are discretized and the differential equation of the elastic line integrated to obtain the rotations and displacements. Optimization problems are defined so that the objective functions are the approximation errors, while the design variables are the coefficients of the effective bending stiffness equations of the cross-sections. Two different formulations are used to compute the effective stiffness. The first one gives one equation for each node section and the other formulation provides only one equation for the whole structure. The effective stiffness is presented in graphs as function of a ratio between the characteristic bending moment and the ultimate moment of the cross-section. The sections where the largest stiffness loss are obtained were the sections that indeed collapsed in real similar structures. Directions for future research are presented.