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CivilComp Proceedings
ISSN 17593433 CCP: 81
PROCEEDINGS OF THE TENTH INTERNATIONAL CONFERENCE ON CIVIL, STRUCTURAL AND ENVIRONMENTAL ENGINEERING COMPUTING Edited by: B.H.V. Topping
Paper 171
Computation of Effective Bending Stiffness of RC Telecommunication Towers based on Experimental Data M.A. Silva+*, J.S. Arora$ and R.M.L.R.F. Brasil+
+Department of Structural and Foundations Engineering, Polytechnic School, University of São Paulo, PEF/EPUSP, Brazil
M.A. Silva, J.S. Arora, R.M.L.R.F. Brasil, "Computation of Effective Bending Stiffness of RC Telecommunication Towers based on Experimental Data", in B.H.V. Topping, (Editor), "Proceedings of the Tenth International Conference on Civil, Structural and Environmental Engineering Computing", CivilComp Press, Stirlingshire, UK, Paper 171, 2005. doi:10.4203/ccp.81.171
Keywords: effective bending stiffness, experimental results, large displacements, reinforced concrete, structural optimization.
Summary
We present some results of the application of optimization techniques (Chahande
and Arora [9] and Arora [5]) to experimental data for the determination of the
effective bending stiffness of crosssections of reinforced concrete (RC) structures,
according to Silva and Brasil [10,11] and Brasil and Silva [7,8].
The objective is to determine parameters of unstressed sections for the correct computation of the displacements of those structures and possible applications on structural failure theory. The experimental data from tests with 30 and 40 m long RC telecommunication towers, having circular crosssection with 50 cm diameter for the 30 m long structure and 60 cm diameter for the 40 m long structure, are used. Inspired in Branson's equation (Branson [6], ACI [4], ABNT [3]), for crosssections along the axis of the structure, the effective stiffness equation is derived in function of the bending moment level (the ratio between the characteristic bending moment and the ultimate moment of the crosssection). 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 crosssections. 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 the bending moment level. The sections where the largest stiffness losses are obtained were the sections that indeed collapsed in real similar structures. We discuss the effect of the concrete elasticity modulus (ABNT [2,3]) on the obtained results, and possible applications to nonlinear dynamic analysis of RC structures subjected to wind loading (ABNT [1]) and to structure collapse. Directions for future research are also presented. References
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