Bearing Capacity of Concrete

Abstract

A review of relevant papers and codes of practice from several countries on the bearing capacity of concrete lead to the conclusion that there was a need for a study of existing data in order to be able to develop a simple yet reasonably accurate general formula to predict failure. Initially 36 cubes were axially loaded through rigid plates and the results were compared with approximately 600 tests by investigators from other countries. In the second series of tests cubes were loaded concentrically through strip, rectangular and knife edge loading pieces with base plates of different thicknesses (4 to40mm). These results were also compared with 85 available tests by other investigators. The distribution of axial stresses in the concrete and bending stresses in the steel base plate were measured using strain gauges fixed to both the concrete and the steel base plate. The third’ series of tests was concerned with loading through universal columns of different sizes, as used in practice. Tests to failure were carried out on both 150 and 250mm cubes through three thicknesses of steel base plate (4, 8 and 12mm). The results from this series of tests could not be compared with any other test results, as none were available. An empirical formula for the bearing capacity of concrete was produced from the first series of tests and then developed for strip, rectangular and square concentric loading pieces applied to a concrete cube through flexible plates. The formula was also used to predict the failure load in the third series of tests with universal columns. The test results from this series were also compared with the design loads recommended by: AISC(29), Draft of Steel Code(30) and BS 449(31). In the fourth series of tests concrete cubes were loaded eccentrically through stiff bearings of various sizes. The empirical formula obtained for concentric loading conditions was extended to predict the failure load for cubes loaded eccentrically through stiff bearings. Finally a linear finite element plane-stress analysis was used to investigate the axial and lateral stress distribution in the- concrete and steel base plate loaded through a knife edge loading piece. The theoretical model was chosen to resemble the tests carried out in this investigation on flexible steel base plate; presented in Chapter 3.