The selection of a dynamic model of a RC chimney based on in situ research

Abstract

This paper refers to the dynamic in situ investigation of a RC chimney and the choice of an appropriate numerical model in order to evaluate it. The first part of the study deals with the evaluation of the dynamic characteristics of a typical RC industrial chimney which belongs to a heating plant. In the investigation, different sources of excitation were used in order to better assess the structure’s free vibrations. In this investigation, wind gusts and rhythmic, human-induced swaying were used as sources of excitation in order to better assess the structure’s free vibrations. The following three pieces of measuring apparatus were used in order to record the structure’s movement: electro-dynamical strain gauges; piezoelectric accelerometers; a Doppler laser vibrometer. Power-spectral density (PSD), cross-spectral density (CSD) and fast Fourier transform (FFT) algorithms were applied to determine the natural frequencies of the structure. The second part of the study involves the determination of the calculated dynamic characteristics of the selected RC chimney. A FEM model was built and important structural factors were used in its determination. Ground properties under the foundation of the structure were applied and variations in concrete characteristics due to carbonation and decay were factored in as were geometrical imperfections of the structure. By using natural vibration excitation sources, the lowest frequency of free vibration of the structure was determined. The third part of the paper focuses on the evaluation of the accuracy of the applied models resulting in the identification of the most valuable FEM model of the chimney. Different element types and varying levels of material modelling precision were used. The results of experimental studies were used as a basis for the verification and rating of the proposed models. The most accurate model was chosen – this was defined on the basis of it being the most capable of being successfully applied in further calculations of the dynamic response of the structure.