Measurement of Localized Deformations in High-Strength Steel Cables

Measurements of deformations in monostrand steel cables experiencing axial and transverse deformations is challenging due to their complex geometry and difficulties with the placement of strain gauges in the vicinity of the anchorage. Nevertheless, quantitative information on local strains is often required to evaluate the fatigue resistance of steel monostrands. This paper focuses on the application of a digital image acquisition and analysis technique to determine deformations and resulting strains in the vicinity of the strand anchorage. In a previous study, the applicability of the image analysis technique was demonstrated on pretensioned high-strength steel monostrand specimens, which indicated good agreement between the wire strains measured using image analysis and those measured by conventional strain gauges. The current study focuses on the comparison of deformations within the strand induced by static inclination of the bearing plate (as stipulated in the PTI and fib evaluation guidelines) and the strains due to actual transverse displacements of the strand. Results of this parametric experimental study show that axial fatigue tests with inclined bearing plates to induce local bending deformations are not realistically simulating the behavior of the monostrands at the anchorage. The local strain ranges induced by the above-described test setup are considerably different from those caused by transverse displacements of the strand. Furthermore, the strain information obtained with the image analysis technique is used in the identification of potential fatigue failure modes in monostrand cables.

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