Bearing strength of lightweight concrete

This paper presents an experimental investigation into the bearing strength of lightweight concrete cylinders. Cylinders of both lightweight and normalweight concrete with compressive cylinder strengths of approximately 5000 and 8000 psi (34.5 and 55.2 MPa) were tested. These cylinders were loaded with bearing plates of varying sizes. The ultimate loads and failure modes were rioted. It was found that the equation for bearing strength presented in ACI 318 can over-predict strength for lightweight and high-strength normalweight concrete at ratios of supporting area to bearing area (A(2)/A(1)) less than approximately 7. Two possible corrections are presented, one involves applying a lightweight concrete factor a to the existing equation, and the other is a new equation based on a Mohr failure criterion for the concrete in the test prisms. Both provide safer predictions of the bearing strength of lightweight concrete than does the current ACI equation.