Decades-old mistake may have caused bridge beam to fail

The Philadelphia Inquirer ^ | January 23, 2017 | Jason Laughlin

[Tolerance Sucks Rocks]

An apparent construction error six decades ago could have caused the fracture discovered Friday in a steel beam that forced the closure of the Delaware River Bridge, an engineering expert who viewed pictures of the cracked truss said Sunday.

An image of the cracked truss - a supporting piece - on the bridge that runs between Bucks County in Pennsylvania and Burlington County in New Jersey shows signs of holes that had been mistakenly drilled into the steel beam and then filled with plug welds, a typical solution in the 1950s when the bridge was built, said Karl Frank, professor emeritus of engineering at the University of Texas at Austin. His areas of study include fractures and fatigues in metal structures and welded and bolted joints, according to the university website.

The image is on the website of the Pennsylvania Turnpike Commission, and Frank viewed it there.

"What we do nowadays, we don't do that," he said. "If you have a misdrilled hole, you would just put a bolt in and tighten it up. The problem is they welded it up."

The plug welds created a weak point, Frank said, and the stress of traffic crossing the bridge continuously since it opened in 1956 could have led to a sudden crack, splitting the beam at the welds.

A spokesman for the commission, which operates the 1.2-mile-long bridge jointly with the New Jersey Turnpike Authority, did not dispute Frank's conclusion, but said turnpike engineers had too little information to confirm anything about the crack's cause.

"Don't want to make premature assumptions without science," said Carl DeFebo Jr., the spokesman.

[norwaypinesavage]

You’re in the right zone. HAZWOPER training is unnecessary.

[sig226]

You wished a Philadelphia reprieve
But the bridge is broke
Now youse can’t leave

Burlington Shave

[MurrietaMadman]

Burlington Shave
I had a few
On that two lane bridge
I rue

[null and void]

I was alluding to HAZ - the Heat Affected Zone, the area near a weld where the heat draws the temper and weakens the steel.

[Ruy Dias de Bivar]

We used plug welds for mistakenly punched holes on electrical transmission towers clear through the 1970s. they were considered safe.

[norwaypinesavage]

Note that I said "you're in the right zone"

[null and void]

Ah! Totally missed that!

[Tolerance Sucks Rocks]

Do you guys use bolts for these holes now?

[Ruy Dias de Bivar]

The way we did it was to take the angle iron, clamp a thick piece of copper on the underside, then fill the hole with 7024 DC welding rod. When done right the copper won’t stick but will hold the weld in till it solidifies. Then turn the angle iron over and do the other side, then grind down flat.

But then, that was forty years ago.