An Indianapolis' bridge over an Interstate Highway did not have the necessary clearance below its span for a proposed new two-lane entrance ramp. Built less than 10 years earlier, the existing structure was a four-span continuous variable depth concrete girder bridge that could still provide many years of service. Rather than replacing the entire bridge, the west span of the bridge was transformed into a cable-stay structure, extending it from 64 to 103 feet while leaving the east half of the bridge intact.
The original concrete slopewall and earth embankment were removed and a new retaining wall was built 40 feet west of the existing outside pier. While the existing span was raised by hydraulic jacks and supported on temporary towers, the bridge bearings were disassembled and the outside pier was removed. Replacing it at the same location, a transverse 6«-foot-wide, post-tensioned girder was constructed to unite the original structure with two new reinforced concrete compression struts. At the midpoint of the compression struts, two 20-foot-high cable-stay towers were erected, one on each side of the bridge. Steel cables extend from the top of these towers to the transverse bridge girder in one direction, and to the concrete deadmen in the other. The transverse girder loads are carried by eight post-tensioned steel bar cables that were used as stays on each side of the bridge.
While the bridge was closed during construction, traffic flow on all lanes of the Interstate below was maintained without a detour. The cost of rehabilitating this bridge with the cable-stay technique totaled $160,000 compared to an estimated $350,000 for a totally new bridge.