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PennDOT to Fill Plug Welds After Bridge Incident

Wednesday, January 10, 2018

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Nearly a year after a cracked beam closed a major bridge between the Pennsylvania and New Jersey turnpikes, the Pennsylvania Department of Transportation is looking to eliminate potential weak spots on other bridges in order to prevent a similar incident.

Fort Duquesne Bridge
daveynin, CC BY-SA 2.0, via Wikimedia Commons

PennDOT is making repairs to 13 bridges across the commonwealth, including Pittsburgh's Fort Duquesne Bridge (pictured), in an effort to replace plug welds with bolts that will provide improved structural integrity.

The Pittsburgh Post-Gazette reported Sunday (Jan. 7) that PennDOT is making repairs to 13 bridges across the commonwealth in an effort to replace plug welds with bolts that will provide improved structural integrity. Plug welds—welded fills of misdrilled holes in the steel—were common practice when many bridges were built in the early and mid-20th century, but are thought to have contributed to the catastrophic failure last January on the Delaware River Turnpike Bridge.

Turnpike Bridge Crisis

That bridge, which carries 42,000 vehicles daily, was closed to traffic Jan. 20, 2017, when workers inspecting a coating job discovered a truss that was broken completely in half. Repairs to the beam took nearly seven weeks; the bridge reopened March 9.

Cracked bridge truss
Pennsylvania Turnpike Commission

A crack was discovered in a truss on the Delaware River Turnpike Bridge last January, leading to a seven-week closure of the busy highway bridge.

Pennsylvania Turnpike Commission officials said that the failure may have been caused by a weak spot created by plug welds at the time the bridge was built. Cold weather and overweight truck traffic may have exacerbated the problem, according to the state.

The Delaware River Turnpike Bridge opened in 1956.

Truss Bridge Review

The Post-Gazette reports that PennDOT, in the wake of that crisis, decided to review bridges across the state that might have similar welds, and identified 13 bridges that are candidates for preventive fixes. A contractor will be hired this year to drill out plug welds and replace them with nuts and bolts to lend additional stability.

The Turnpike Commission also reportedly reviewed its bridges last year after the incident, identifying only two other truss bridges under its maintenance and making minor preventive fixes to those bridges.

PennDOT’s Bridge Safety Inspection Manual, last updated in 2010, addresses plug welds as “member defects,” noting that steel members that were treated with plug welds should be given a hands-on inspection. “Of particular concern are tension members on truss bridges,” the manual notes; breaks in the paint and rust stains around the area of a plug weld can signal structural trouble.

   

Tagged categories: Bridges; Rehabilitation/Repair; Steel

Comment from william campbell, (1/10/2018, 7:43 AM)

The right way to inspect the plug welds is to straight beam them with UT inspection to determine if they are solid metal all the way through with no voids. Plug welds correctly done do not represent weak spots unless they are not solid. Breaks in the paint and rust stains only represent a breach in the coating unless a crack in the steel is actually apparent. Mag particle testing in a suspect area would reveal incipient crack indications in the beginning stages. Just my opinion, I have been a CWI for over 20 years with NDT certifications and current NACE III, academic background in welding metallurgy, and 10 yrs actual welding experience including US military certifications to DOD and Navy Bureau of Ships standards. The fact that these welds have been in service for over 60 years would indicate some degree of serviceability and it is a recognized procedure by the American Welding Society.


Comment from Kevin Keith, (1/10/2018, 8:49 AM)

UT testing is the right way to check the welds, but the real problem is finding them. These were done in the field and they never were documented on as-built drawings. A good blast and paint job will make them almost invisible. Bridge inspectors, iron workers, and even bridge painters have to be look for them and document locations so they can be tested. As a resident engineer for painting projects, I always have the structure inspected by either myself or a bridge inspector after blasting to look out for problems like plug welds, section loss, tack welds, etc.


Comment from Robert Bullard, (1/10/2018, 11:12 AM)

I have found insufficiently alloyed steel in some structural shapes imported to the US in the 30 or so post-WWII years, with this issue being revealed by weld failure, not in the weld itself but in the base steel material. For ambient exposure steel (e. g., bridges) the basic 2D simplicity of the initial designs of yesteryear did not include many secondary, but potentially significant 'service stresses' such as torsion, thermal cycling, delta P and/or errant geometry/local buckling. The use of modern as-built laser measurements and analytical structural suites applied to as-built structures may be worthwhile in directing attention to locations of acute or chronic overloading sites that may not be evident by visual inspections.


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