Analytical Determination of Pressure on Formwork

A method is presented for determining the distribution of form pressure during the pouring of a vertical slab from a chemically hardening material such as concrete. The pressure distribution against the form surfaces results from the interaction of gravity with the progressive hardening and shrinkage of the material. Essential aspects of the formulation include time-dependent constitutive equations for the solidifying material which incorporate the effects of shrinkage, and a transformation to a moving coordinate system which handles the motion of the pouring surface. Hardening occurs as the consequence of the conversion of the material from an initial liquid-like condition into an elastic solid, where intermediate states during hardening are represented by a mixture of two components having the initial and final properties of the solidifying material. Graphical comparisons of results obtained from the analytical formulation are shown and examined in relation to experimental data and recommended design practice.