Pennsylvania Department of Transportation

As a result of the failed pin-hanger connection which caused the collapse of the Mianus River Bridge in Connecticut in 1983, PennDOT immediately inspected all fracture-critical bridges with pin-hanger details. To ensure a greater level of safety, PennDOT contracted Modjeski and Masters to propose cost-effective methods for providing redundancy to state-owned bridges with similar details. One of the bridges was the Girard Point Bridge, located in Philadelphia.

The Girard Point Bridge crosses the Schuylkill River and features a double deck, three-span cantilever through truss with a main span of 700 feet and side spans of 350 feet. There are numerous simple span deck trusses of 200 and 300 feet in length on each approach.

Modjeski and Masters was contracted to design an auxiliary support system at the pin and hanger locations of the truss. There are four locations where the suspended span is connected to the cantilever spans with this detail; two in each truss.

The auxiliary support system consists of four new 6" diameter stainless steel hanger rods which extended from the top chord of the cantilever span to the bottom chord of the suspended span at each of the four pin locations. The support system is approximately 60 feet deep. To accommodate this depth, the rods were spliced. Bearing assemblies and spreader beams were provided where the auxiliary support system bears on the top and bottom chords.

The auxiliary support system is designed to flex as the bridge expands and contracts longitudinally due to temperature and live loading. The rods are also pre-tensioned so that they carry load as the bridge flexes longitudinally due to temperature and live loading.