Partitioning of Clamping Strains in a Nineteen Parallel Wire Strand

We report the first direct measurements of clamping strains within individual wires of a 19 parallel wire strand constrained by a clamshell clamp. In these measurements neutron diffraction was used to determine the elastic strains along three orthogonal axes for all of the individual wires across the strand cross section underneath the clamp for various clamping loads. We observed that, while, for all clamping loads, the clamping strains within individual wires were heterogeneously distributed, increasing the clamping force significantly decreased the strain heterogeneity. In contrast, no strain heterogeneity was observed in a rigorous companion finite-element model of the strand unless dimensional variations in the wire diameters were introduced. Our results are in agreement with the hypothesis by Gjelsvik, which states that, within a parallel wire bridge cable, local variations in wire diameter due to manufacturing tolerances can lead to large variations in clamping constraint.