In situ stresses in bridge beams. Part I: concrete stresses

An advanced investigation of the core-drilling method (CDM) for direct application in bridge assessment is conducted. In the CDM a small hole is drilled into concrete and the displacements that occur as a result of load redistribution around the hole are measured and related to in situ stress. Knowledge of the stress profile within the concrete of a girder would allow determination of the magnitude and location of force in its prestressing steel. This paper discusses evaluations of concrete stresses with the CDM using drilled holes 100, 75 and 50 mm in diameter, because existing work used the size 150 mm, which is impractical in field evaluations of many bridge girders. The present paper verifies that the method can be used with relatively small holes to determine stresses in concrete slabs; the technique has also been used to investigate the stresses in a prestressed girder and its prestressing steel, showing that the in situ prestressing force could be determined (see the companion paper). The tests herein show that the CDM with small holes gives stress predictions with an average error of 1·01 MPa, 16·7% of the applied stress. The accuracy is relatively independent of the hole size (for the sizes considered), and thus future investigations in structures can consider using these smaller hole sizes.