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Splice repair for fractured truss bridge

DRB bridge night work

Engineers have laid out an eight-week repair plan for the Delaware River Turnpike Bridge in the US, which closed last month after a truss failure.

An engineering task force has been assessing the 2km long bridge and preparing several options for repair. A permanent splice on the I-beam is the preferred option for the structure which normally carries 42,000 vehicles per day.

Delaware River Turnpike Bridge

Delaware River Turnpike Bridge

Source: PA Turnpike

“Right now, that best-case scenario entails repairing the I-beam by constructing a permanent splice to reconnect the fractured section,” said PTC chief engineer Brad Heigel. “But before that can occur, crews must first realign the bisected segment by deploying eight temporary towers and hydraulic jacks to return the span to its original position.”

When the I-beam fractured, the section of bridge supported by two piers dropped by approximately 30mm when the load being carried by the fractured I-beam was suddenly transferred to the adjoining structural components. The bridge needed to be immediately closed as the adjoining structural components weren’t designed to carry the heavier loads.

Piles have now been drilled for the groundwork for the jacking towers. The approximately tall 24m towers will support the entire section of the bridge that has been damaged, so that the splice can be tested and allow engineers to see whether this repair is sufficient or whether further repairs are needed.

DRB jacking tower

DRB jacking tower

Source: PA Turnpike

“The goal of the jacking operation is to return the bridge to its original position and allow us to complete a permanent splice of the fracture. As the jacking operation occurs and load is transferred within the bridge, instrumentation will monitor the actual loads, stresses and displacements which will be compared to estimated outcomes from computer models,” Heigel said. “This monitoring — which involves affixing about 50 sensors to the structure — is the only way we can confirm that the splice is successful before we reopen the bridge.”

This week a programme to install the jacking towers and associated structural reinforcement will start. The jacking will be performed in early March, with the permanent repair splice installed mid-month. That will be followed by load testing.

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