Effect of existing holes under the loading plate on local compressive strength of plain concrete blocks: An experimental and numerical study

The bearing strength of concrete is an important design consideration for structural safety. Base plates for columns are necessary in order to transfer forces to concrete supports. In order to place the post-installed anchorages that hold the base plate to the footing, holes must be bored beneath it. In this study, the first experimental and numerical study is presented to examine the impact of the holes presented under the loading plate, both horizontal and vertical, on the bearing strength of concrete blocks. To simulate the concrete support, a total of eighteen samples of concrete blocks with dimensions of 250 mm by 250 mm and 200 mm in height were produced. A steel plate, 60 mm by 60 mm, was used to apply the column load. It was placed in the center of the upper surface of each concrete block. The compression load was applied on the steel plate after drilling holes. The loading plate and concrete block geometry remained the same for every sample. The variables for holes drilled vertically were hole depth (20, 40, 60, and 100 mm) and hole diameter (6, 10, 12, 16 and 18 mm). The variables for holes drilled horizontally were the hole diameter (12, 16, and 18 mm) and the hole's distance (40, 60, 100, and 150 mm) from the loaded plate. The holes were bored, and the concrete blocks were tested under local concentric compression stresses following a 28-day period of concrete casting. The ultimate bearing strength, bearing stress-slip correlations, and crack patterns of the tested concrete block were documented. The test findings show that the ultimate bearing strength drops by 35 % when the ratio of vertical hole area to bearing plate area varies from 1.4 % to 40 %. While the hole diameter has a bigger effect on increasing the ultimate slip than the hole distance, for horizontally drilled holes, the existence of a transverse hole going through the bottom of the loading plate does not significantly affect the decrease in the bearing resistance of the concrete. Additionally, ABAQUS software was used to create a finite element model (FEM) that was verified against the experimental findings in order to replicate the behavior of the tested concrete blocks. Additional parametric research was also carried out using the FEM. Furthermore, the effectiveness of current design formulae in determining the ultimate bearing strength of concrete blocks is assessed, and new formulas are developed.