Formwork Pressures in Tall and Thick Concrete Walls

Investigations are carried out on two concrete wall placements each 20.5 ft high, with thicknesses of 5 ft and 4 ft, respectively, to determine the loads and pressures exerted by the fresh concrete on the forms. Form tie forces are measured at intervals during the concrete placement, by instrumenting form ties with electrical resistance strain gages. Concrete pressures on the forms are determined from these forces by using the respective tie tributary areas. Maximum pressures of 1,062 psf for Wall I and 891 psf for Wall II are measured. The pressure influencing variables such as concrete density, mix design, admixtures, slump, stiffening time of concrete, concrete temperature, pour rate, consolidation method, and formwork dimensions are determined and used in comparing the measured wall pressures. Comparisons are also made between field results and currently recommended and proposed procedures for estimating wall form pressure.