Span in construction of concrete precast products: Bearing beams and reinforced slabs

Abstract

The recent introduction in Spain of the Building Technical Code (CTE) means that CE labelling is now mandatory on construction products that will be permanently incorporated in buildings. One of the requirements with which manufacturers of precast slabs must comply in order to obtain the CE mark of conformity on their products is the satisfactory completion of tests that guarantee the resistance/strength qualities that are shown on the certificate of conformity. Load-bearing beams and reinforced concrete precast slabs imply greater quality control at the manufacturing plant, shorter construction periods and improved safety at the construction site. They may also be used as resistant plank moulds during execution. The purpose of this study is to determine the span in construction (the distance between false-work) for the bearing beams and RC slabs during the construction phase. It is intended to optimize the number of false-work structures to be calculated to withstand their own weight, the weight of the poured concrete and an additional under construction load of 1KN/m2. The criteria used to calculate the span in construction were the ultimate bending strength, the ultimate shear strength and the flexural rigidity. The tests are in compliance with Standard UNE-EN 13747:2006 whereby the distance between props or temporary bearings of the span in construction is specified. The testing method used was four-point bending. The test consisted of supporting the bearing beam or slab on two end supports and applying two equidistant equal loads to the span. The results for extreme bending strength are very similar and a fraction higher than the theoretical results that might have been expected. The fineness ratio corresponds to the curve of the upper bars observed in the flexural load tests. The results of the extreme shear strength are about twice as high as the expected theoretical values; values which may be readjusted with a lower slenderness ratio. Copyright © 2011 AHS.