Bearing Strength of Compressive Struts Confined by Plain Concrete

To study transverse splitting of compresson struts due to spreading of compression, concrete cylinders of varying diameters and of varying heights were loaded over a constant size bearing area. The travel time of an ultrasonic pulse was used to indicate internal cracking, and measured cracking loads were compared to finite element predictions. It was found that when compression struts are confined by plain concrete, the maximum bearing stress to cause transverse splittting depends on the amount of confinement, as well as the aspect ratio of the compression strut. Design recommendations are given for the maximum nodal zone bearing stress to prevent diagonal tension failures in deep memebers with unreinforced compression struts. A simple example is provided to illustrate the suggested nodal stress limits for the design of a pile cap using a strut-and-tie model.