Experimental analysis of residual stress-strain in prestressed concrete by saw-cut testing under laboratory conditions

The assessment of residual prestress in existing prestressed concrete members is a crucial issue, particularly as members approach advanced service ages. In this study, the saw-cut test (SCT) instrumented with mechanical strain gauges is applied as a minimally invasive technique with potential for field application for assessing residual prestress. A total of 33 post-tensioned beams were tested under laboratory conditions, representing a wide range of time-dependent stress states generated by combining six prestressing ages and seven testing ages from 3 to 240 days. The SCT was performed through progressive cuts spaced 120 mm apart, in two saw-cut zones per beam, allowing detailed measurement of internal displacements and subsequent strain changes within the resulting isolated concrete block. Results show a repeatable and approximately symmetric strain-release response; younger beams exhibit larger deformations, while older ones show reduced release due to increased concrete stiffness. Normalized strain-release profiles revealed consistent behavior, with no systematic dependence on prestressing or testing age observed within the investigated dataset. A condition close to full decompression was consistently reached at approximately 35 mm for the investigated rectangular specimens, 120-mm cut spacing, tendon arrangement, and laboratory boundary conditions. The comparison between the SCT response at a cut depth of 35 mm and the response associated with complete prestress removal showed close correspondence, supporting the consistency of the identified decompression condition. These results support the repeatability and consistency of the SCT for assessing residual prestress under the investigated laboratory conditions. To assess its broader practical applicability, future work should extend the investigation to full-scale members, considering the influence of field and in-service conditions.