Formwork pressure induced by highly flowable concretes – design approach and transfer into practice

Abstract

An analytical model for the calculation of the pressure of concrete on vertical formwork has been developed on the basis of experimental tests on highly flowable concretes in the fresh state (see companion paper “Material investigations and large‐scale tests”). The model takes into account the time‐dependent material parameters of the fresh concrete, the specific properties of the highly flowable vibrated concretes and self‐compacting concretes (SCC) as well as operational aspects. A proposal for the design of formwork was developed based on the experimental tests and the semi‐probabilistic safety concept. It was found that the design load is often lower than the hydrostatic concrete pressure – even for highly flowable concretes. On construction sites, the pressure can be best controlled by limiting the casting rate. Insufficient experience of personnel in the handling of highly flowable concretes increases the uncertainties with respect to the design values and the safety risk.Further investigations into construction management‐related aspects regarding the use of highly flowable concretes cover the risk assessment during concreting, design of the processes on the construction site and the development of the basis for a documentation system.

Experimentelle Untersuchungen und numerische Verifizierung zum Frischbetondruck bei geneigten Schalungssystemen

“…Aus Versuchsergebnissen [13,14] mit einer sogenannten Kombinierten Versuchseinrichtung (KVA) [15] an Betonen der Konsistenzklasse F5 und F6 wurden Funktionen des Seitendruckbeiwerts als Mittelwerte in Abhängigkeit von der Zeit λ i,MW (t/t E,eff ) für eine nachgiebige Schalung abgeleitet (vgl. Gln.…”

Characterization of the Interface Between Fresh Concrete and Formwork

“…After mixing, the concrete was placed in the sample holders. The normal pressure was increased incrementally until the final setting state (Proske 2007;Graubner et al 2012).…”

“…Some of these phenomena are directly related to the friction between the materials in contact. The friction at the concrete/formwork interface can be considered a favourable factor that reduces lateral pressure exerted on the formwork, but it can also be unfavourable to the quality of the concrete surfaces (Proske et al 2010;Graubner et al 2012;Libessart 2006;Kwon et al 2011). Some studies have reported on the effect of friction on formwork pressure.…”

Field validation of models for predicting lateral form pressure exerted by SCC

“…In the last decade, a number of models for predicting lateral pressure of SCC have been developed worldwide [4][5][6][7][8][9][10][11][12][13][14]. Some of them are phenomenological and others are developed by empirical testing in the laboratory.…”

“…would lead to increased formwork system costs or risks of form deformation or eventual collapse. However, the literature has repeatedly shown that lateral pressure is considerably lower than the hydrostatic pressure when casting SCC [3][4][5][6][7][8][9].…”