In-situ stress determination used in structural assessment of concrete structures

Large span, post-tensioned bridges are now regularly subjected to spot checks. Bridge assessment requires a knowledge of the design pre-stress and of any losses that may have occurred since stressing. The assessing engineer is often faced with a lack of information, such as no detailed drawings, no confirmation that build was to design, and it is at this stage that on-site in-situ stress determination can be used to progress the investigation. The methods for in-situ stress determination are based upon the measurement of strain distribution due to local stress relief and the relationship of the strain redistribution to the in-situ stress state. The adaptation of the centre hole technique to the in-situ stress determination in reinforcement, stressing tendons and concrete and the necessary site requirements are explained.