Evaluation of Prestress Force on Bonded Tendons Using Practical Formula

Abstract

This work introduces a non-destructive experimental technique to evaluate the existing prestress level on bonded tendons embedded in a post-tensioned concrete structure. By measuring the longitudinal stress wave velocity on the strands, the applied stress level can be evaluated using an experimental formula. The experimental relation between the applied stress levels and the stress wave velocity is derived from various impact-echo test results for a set of prestressed concrete beam specimens with different tensile stress levels. The experimental results reveal that the longitudinal stress wave velocity of the bonded strands increases nonlinearly as the applied tensile stress level increases. To investigate the field applicability and feasibility of the approach, longitudinal impact-echo tests are conducted for two prestressed bonded tendons embedded in a nuclear reactor containment building. This reveals that the proposed approach is feasible and applicable for the unique identification of the existing prestress levels on the individual strands embedded in a real post-tensioned concrete structure.