A prestress testing method for the steel strands inside in-service structures based on the electrical resistance

To test the prestress of internal prestress steel strands, the relationship between the resistance and the prestress was analyzed. The equivalent electrical models of the testing systems were established. The results of the prestress testing experiments showed that there was a nearly linear relationship between the resistance and the prestress. Steel strands with similar physical properties had similar resistance-stress relationships that were not influenced by the prestress variation. Connecting both ends of the steel strand to the testing circuit, the prestress of the inside steel strands could be measured outside the structures. Both in the structural construction phase and the operation phase, the prestress testing errors were about 10%. When testing long steel strands, the proposed method may have higher sensitivity and smaller errors.