Influence of the placement rate on the fresh concrete lateral pressure in the design of formworks

Abstract

ResumoThe fresh concrete lateral pressure generates a load that has great influence in the design of the formworks of columns, walls and lateral faces of the beams.Its prediction must be performed in such a way in order to approach precisely well over the rate values supported by the formworks, avoiding, therefore, the oversizing or undersizing of these temporary structures which represent up to 12% of the total cost of the construction. The calculation of the lateral pressure that fresh concrete exerts on the formworks involves several variables; one of them is the placement rate. The main objective of this work was to study the influence of the placement rate, in situ, on the lateral pressure of fresh concrete calculated from theoretical models presented by norms and international references. For this purpose, measurements of the placement rate were conducted on columns of five building work places at Goiânia city, Goiás, Brazil and it was calculated the maximum pressure supported by their respective formworks from the dimensions and spans between the supports of the components that constituted them. The obtained results indicate that the placement rate in the field observations reach 249 m/h, exceeding the values limited by the theoretical methods of calculation, and that the lateral pressure estimation produced from the placement rate measured in situ exceed the maximum values supported by the formworks up to 604 times. Thus, it was concluded that it is necessary to adjust equations to estimate the lateral pressure of fresh concrete at high rate of concrete placement, according to the current practices in the construction market.Keywords: lateral pressure, formworks, columns, placement rate.A pressão lateral do concreto fresco gera uma carga que possui grande influência no dimensionamento das fôrmas de pilares, paredes e faces laterais das vigas. Sua previsão deve ser realizada de modo que se aproxime bem dos valores suportados pelas fôrmas, evitando-se, assim, o superdimensionamento ou subdimensionamento dessas estruturas provisórias que representam até 12% do custo total da obra. O cálculo da pressão lateral que o concreto fresco exerce sobre as fôrmas envolve diversas variáveis, sendo uma delas a velocidade de concretagem. O principal objetivo deste trabalho foi estudar a influência da velocidade de concretagem sobre a pressão lateral do concreto fresco calculada a partir de modelos teóricos apresentados por normas e referências internacionais. Para isso, foram realizadas medições da velocidade de concretagem em pilares de cinco obras de Goiânia e calculadas as pressões máximas suportadas por suas respectivas fôrmas, a partir das dimensões e dos vãos entre os apoios dos elementos que as constituíam. Os resultados obtidos apontam que as velocidades de concretagem em campo chegam a 248,57 m/h, superando os valores limitados pelos métodos teóricos de cálculo, e que as estimativas da pressão realizadas a partir das velocidades medidas in loco ultrapassam os valores máximos suportados pelas fôrmas em ...