Uma avaliação experimental e numérica do efeito da rigidez geométrica na resposta dinâmica de estruturas esbeltas sujeitas à excitação de vento. / An experimental and numerical evaluation of the geometric stiffness effect on the dynamic response of slender structures under wind excitation.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

Due to a politically and economically pragmatic decision, Brazil has chosen to intensely develop its cellular phone system, in order to bypass a stage of development. Once the decision has been taken, implementation was set in an explosive pace in the 1990s decade by installing tens of thousands of stations. As the electronic systems are usually more expensive than the civil constructions, very little has been invested on the involved structural engineering, resulting in designs and constructions done with doubtful methodologies and in the heritage of great amounts of structural problems. Impounded by esthetical and environmental considerations, the indiscriminate installation of towers occurs. Thus, there is a new demand for the structural engineering in the analysis of the utilization of existing installation sites for bearing new loads. In this manner, what it can usually be observed are structures composed of just one cantilever pole of misleading simple analysis. What it is quite often ignored is the extraordinary slenderness of these elements, which should suggest to the designer the immediately necessity to consider the intrinsic existing geometric nonlinearity. Moreover, the wind is the most important and dominant load, of dynamic and random nature, misadvising either static or deterministic dynamic analysis, usually recommended by Codes and Standards. In doing so, the objective of this thesis is to evaluate the influence of the geometric stiffness on the dynamic response of slender structures subjected to wind excitation. As a first step, a simplified analytical model was developed, with dynamic characteristics established by a Rayleigh type technique, which enhances the intrinsic existing geometric nonlinearity due to the slenderness of the elements. As a second step, for validating the theoretically obtained results, a series of dynamic tests was carried out in laboratory, using models of cantilever bars, and a real structure was monitored in the field. The proposed analytical model was also checked by other analytical and numerical methods, such as the Eulers solution for the critical buckling load and the Finite Element Method. The influence of the geometric stiffness in the structure response to wind loads was also evaluated by comparative calculations among the different models recommended by the Brazilian Wind Code. It was verified that, depending on the existing loads, the consideration of geometric stiffness can have significant reductive effect on the capacity of the telecommunication poles have exposition area to wind for installation of antennas.

ASSUNTO(S)

análise experimental de estruturas rayleigh s method análise numérica wind action on the structures geometric stiffness numerical analysis dinâmica das estruturas structural dynamics experimental analysis of structures ação do vento nas estruturas

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