Anchorage length of patented wire cables in prestressed bridge girders

This paper briefly describes the methodology, performance and the obtained results of unique experiments performed on original I-73 precast bridge girders. The main objective of the experiments was to determine the actual anchorage length of corroded-through fully grouted prestressing reinforcement (prestressing wires), which is important for determination of the residual load-bearing capacity of prestressed structures. Observation probes leading all the way to the prestressing wires were drilled on selected sections of the girders along the length of the prestressing reinforcement. Optical image acquisition devices were then installed at these probes. Subsequently, controlled breakage of the patented wires (corrosion failure simulation) and observation of the changes that occurred in the prestressing wires after relief of stress were carried out. Evaluation of the experiments was then performed by analyzing the images obtained before and after the prestressing reinforcement failure.

Effects of Wire Drawing and Annealing Conditions on Torsional Ductility of Cold Drawn and Annealed Hyper-Eutectoid Steel Wires

The effects of microstructural features on torsional ductility of cold drawn and annealed hyper-eutectoid steel wires were investigated. The patented wire rods were successively dry drawn to ε = 0.79 (54.7%) ~ 2.38 (90.7%). To examine the effects of hot-dip galvanizing conditions on torsional ductility, steel wires with ε = 1.95 were annealed at 500 °C for 30 s for ~1 h in a salt bath. In cold drawn wires, the number of turns to failure increased steadily, showing the maximum peak, and then decreased with drawing strain. During the post-deformation annealing at 500 °C, torsional ductility of steel wires decreased with annealing time, except for the rapid drop due to the occurrence of delamination for 10 s annealing. The decrease of the number of turns to failure would be attributed to the microstructural evolutions, accompanying the spheroidization and growth of cementite particles and the recovery of ferrite in cold drawn steel wires. From the relationship between microstructural evolution and torsional ductility, it was found that among microstructural features, the shape and orientation of lamellar cementite showed the significant effect on torsional ductility of cold drawn and annealed hyper-eutectoid steel wires.

An Investigation of Small Helical Torsion Springs

The object of the investigation was to provide easily handled data for the design of helical torsion springs from round patented plain carbon spring-steel wire. For this purpose, the validity of the curvature correction to the stress formula was investigated and the effects of variations in low-temperature heat treatment and wire size were explored. It was found that the theoretically derived curvature correction for maximum stress (stress at intrados) was the dominating feature in fully heat-treated springs under all conditions, and for patented wire springs when the maximum stress was tensile. In patented wire springs, however, when the maximum stress was compressive it was found that, although with springs of small index the maximum stress was still the dominant feature, with those of large index yielding was due, not to the maximum compressive stress at the intrados, but to the smaller tensile stress at the extrados, and that a critical ratio existed where yielding occurred simultaneously at both extrados and intrados; a finding that has considerable practical value. It is suggested provisionally that the phenomenon may be due to the combined effect of the low-temperature heat treatment, which relieves textural stresses (present in the wire as the result of the drawing operation and the presence of cementite) and at the same time allows the strain-age-hardening effect to become evident. Design charts are submitted incorporating the results of the above investigation.