Determining the Residual Prestressing Force in Unmonitored Full-Scale Prestressed Concrete Members

The accurate determination of the residual prestressing force is essential in the assessment of existing prestressed concrete structures (EPCSs). Since construction practice has not considered the incorporation of measurement devices in the EPCSs for monitoring over time, prestressing losses are usually unknown, and therefore the residual prestressing force. In the case of old prestressed concrete members, additional complexity must be considered in relation to the initial prestress, the materials (prestressing reinforcement and concrete) properties and the short- and long-term prestress losses. From several analyses carried out on EPCSs, it should be pointed out that the residual prestressing force is not always in agreement with the expected value. In this context, this paper compiles a database of experimental tests carried out on old full-scale prestressed concrete members over the years, which were commonly salvaged from decommissioned bridges, and examines the different techniques and methods used to determine the residual prestressing force. Cases with both destructive and non-destructive approaches are included detailing pros and cons together the uncertainties to be considered in the assessment of EPCSs. The summarized information will serve to a better understanding of the testing techniques and may help to protocolize the assessment of case studies with unknown prestressing force.