Browsing by Author "Neves e Sousa, Albano"
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- Caracterização da propagação de vibração através de estruturas de edifícios de betão armadoPublication . Carreira, A. S.; Neves e Sousa, AlbanoEste artigo descreve os parâmetros que controlam a propagação da vibração através de estruturas de edifícios de betão armado para frequências abaixo de 200 Hz. A influência das propriedades dos materiais e das dimensões dos elementos estruturais foi avaliada com modelos de elementos finitos validados experimentalmente, considerando cinco tipos de funções de transferência de aceleração: i) da fundação para o primeiro piso; ii) entre pisos intermédios; iii) do último piso para a cobertura; iv) entre troços do mesmo piso intermédio; e v) entre troços da cobertura. Os resultados mostram que a transmissão de vibração depende não tanto do número de pisos mas mais de parâmetros como a espessura da laje, no caso da transmissão da vibração num pavimento, ou a esbelteza dos pilares, no caso da propagação de vibração das fundações para o primeiro piso. Observa-se que, apesar da amplitude de vibração ser maior para elementos estruturais mais flexíveis, os elementos mais rígidos transmitem efectivamente mais energia devido a um menor efeito dissipativo. Os resultados também mostram que a atenuação piso-a-piso é aproximadamente constante para todos os pisos excepto a cobertura, onde a atenuação diminui por via da redução do número de caminhos de dissipação de energia.
- Prediction of low frequency sound fields in buildings near railway linesPublication . Neves e Sousa, Albano; Lopes, Isabel; Carreira, A. S.The design of new buildings in the vicinity of railway lines must consider protection against noise and vibrations induced by railway traffic. However, the prediction methods available involve heavy numerical models which have frequency limitations. In this paper a prediction method combining finite elements (FEM) with natural mode analysis is presented for use in reinforced concrete buildings with heavy walls. The method considers 2D FEM models of the railway, ground and buildings to identify the transfer function of vibration from the railway to building foundations. Also 3D models of the buildings are considered to identify the transfer functions of vibration from foundations to walls and floors. Finally, as the impedance of heavy walls and floors is much higher than the acoustic impedance of air, the numerically assessed vibration fields of walls and floors are used to calculate sound fields in rooms by means of natural mode analysis. A set of in situ measurements were made in two different situations in order to calibrate the prediction method and also to identify the factors which most affect vibration and sound transmission.
- Prediction of low frequency vibration and sound propagation through reinforced concrete structuresPublication . Carreira, A. S.; Neves e Sousa, AlbanoPrediction of low frequency sound fields generated in buildings by internal sources as machines or external sources such as road or rail traffic is a difficult task. Assuming that the source is well known, predictions are generally based on the Finite Element Method (FEM), which is used to model building structures and vibration and sound fields, but other hybrid or coupling methods also can be used. In general, these methods are too much time consuming and provide results which are reliable only below 100-150 Hz. Reliability at higher frequencies requires much larger models. It is, thus, important to develop simpler methods to be used with confidence by acousticians and other consultants. In the present paper a method for prediction of vibration propagation to building slabs based on the use of simplified transfer functions between fundamental joints of the structure is presented. The method was developed numerically for traditional multi-storey building with reinforced concrete slabs supported by reinforced concrete beams and columns and also was experimentally validated. The method can be used together with theoretical modal analysis to predict sound fields in dwellings.