Category Archives: Technology

Help! The Hudson River Rail Tunnel is falling to bits.

A few days ago, New York Governor, Andrew Cuomo, accompanied by a film crew, paid a late night visit to the Hudson River Rail Tunnel. His objective was to publicize the sorry state of the tunnel’s physical condition, and to thereby convince the Trump  administration that federal funding is urgently needed to help finance the construction of replacement tunnels. The New York Times called it a Hollywood stunt “ . . . designed solely to win over an audience of [the] one who sits in the Oval Office.” True or not, Mr. Cuomo’s efforts should be applauded. It’s encouraging to see a politician up to his elbows in honest dirt rather than mucking about in the sort politician’s usually wallow in. And apart from that, he does an excellent job of pointing out the tunnels’s defeciencies. Listen to Mr. Cuomo’s exposé on the following YouTube video and decide for yourself:

The tunnel (actually a pair of single-track tunnels), presently operates at or above capacity. About 450 trains pass through the tunnels each weekday (averaging one train every six minutes) carrying about 100,000 New Jersey commuters (plus Amtrack passengers) to Manhattan in the morning and back to NJ in the evening. Whenever the tunnel is shut down, those citizens have no other practical way to get to work because the tunnels and bridges for road and subway traffic are also at capacity.

Map showing route of Hudson River Rail Tunnel from North Bergen, NJ to Penn Station, NYC

Map showing route of Hudson River Rail Tunnel from North Bergen, NJ to Penn Station, NYC

The 14,575 foot tunnel has been in use for 108 years and shows it. The flooding that occurred during hurricane Sandy in 2012, entered the tunnel through the portals at its eastern (Manhattan) end. As Mr. Cuomo points out in his video, the corrosion caused by salt water has intensified the deterioration within the tunnel. In view of his other comments concerning, rotted steel, crumbling cement, exposed rebar, damaged electrical gear, leaking walls, it’s fair to wonder about risk to human life. Are the tunnels in danger of collapse?

The experts say no. Here’s why:

The tunnel was driven through solid rock except were it passes under the river through accumulated silt. That’s where it proved necessary to construct the tunnel using 23 foot diameter, cast iron rings, each weighing 22 tons. The 2.5 foot wide rings were bolted together, one after the other, to form the two tubes running under the river. The seams between the rings were caulked to make the tubes watertight. The tubes were then lined with concrete. The structural integrity of the tunnel depends on the cast iron shells, not on the crumbling concrete that lines them. That said, if the deterioration inside the tunnel continues to worsen, it will eventually become impossible for trains to pass through it.

The next image shows one of the cast iron rings used to construct part of the Hudson River Rail Tunnel. It was one of the exhibits at the 1907 Jamestown Exposition.

Cast Iron Tunnel Ring exhibited at 1907 Jamestown Exposition

New flood gates will keep NYC road tunnels dry next time the city’s streets are under water

New York City was struck by hurricane Sandy six years ago. Since then, while the city has updated its flood-risk maps, it hasn’t taken any concrete steps to prevent storm surges from entering the city. That’s not surprising; the city is rimmed by more than 580 miles of coastline, most of it at risk from storm surge.

Map of NYC flood-zones. Image from NYC Mayor’s Office

NYC flood-zones. Image from Mayor’s Office

Instead, city planners have focused on upgrading critical systems, such as: ‘hardening’ electrical systems; relocating backup generators; flood proofing subway openings; designating more emergency shelters for flood victims. Resilience is a word the city planners like to use these days. In other words, let the seas rise, we’ll deal with the water when it comes.

the most impressive example of this approach so far has been a $64 million project (now complete) to install flood gates on two of the city’s four road tunnels, namely: the 9,117 ft. Hugh L. Carey (Brooklyn-Battery) tunnel under the East River, and the 6,414 ft. Queens-Midtown tunnel, also under the East River. Both suffered serious damage during the Sandy flooding, the Hugh L. Carey tunnel, especially  so. The portals of both tunnels are located within zone-1 (first zone to flood).

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Map showing location of tunnel flood gates

Eight steel flood gates have been installed, two at each tunnel end. The gates were manufactured by Walz & Krenzer, Inc., of Oxford CT. (“Watertight Closures for the Marine industry since 1939”), one of about 50 U.S. companies involved in the flood-control equipment business.

Each gate weighs 44,600 pounds (about 20 tons), and measures 29 ft. wide by 14 ft. high by 22 inches thick.

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MTA Photo

The gate swings on two massive hinges. When parked in its open position, the free end rests on jacks.  Assuming  a two man crew, a machine such as a forklift is needed to help close it. In the event of a storm, the crew will first remove steel cover-plates from  a trough that stretches across the mouth of the portal. Once the gate is closed, the crew will latch it to the face of the portal and to attachments within the trough. Compression seals around the gate’s inner edge will make it watertight.

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MTA photo

The only way to see these gates up close is to drive through the tunnels. You’ll get only a second or two of observation. Considering New York’s frantic traffic, stopping to gaze at the thing is something no prudent driver should attempt.

It’s just as difficult to get a good look at the gates while on foot. Barriers of one sort or another along the streets surrounding tunnel entrances inhibit pedestrians from peering over walls. The Morris Street footbridge will eventually provide a platform from which to observe the Hugh L. Carey flood gates at the tunnel’s Manhattan end, but that bridge is being renovated and will not be available for use this year.

 

Why did the I-35W Highway Bridge in Minneapolis fall down?

Several readers of the post titled ‘Smart Bridge across the Mississippi River’ have asked if the cause of the collapse of the old I-35W bridge has ever been officially determined. The answer is yes.

I-35W highway bridge which collapsed November 2008

Old I-35W Highway Bridge. Image from en.wikipedia.org

The National Transportation Safety Board is mandated by Congress to investigate transporation accidents and determine the probable causes. The NTSB issued its report (HAR0803) on the I-35W bridge collapse on November 14, 2008. It’s a detailed, 162-page, engineering study.  Here’s an excerpt from the report’s conclusions (the italics are mine):

[T]he probable cause of the collapse . . . was the inadequate load capacity (bridge was not strong enough), due to a design error by Sverdrup & Parcel and Associates (the bridge designers) of the gusset plates at the U10 nodes (specific places within the bridge structure described in the report), which failed under a combination of (1) substantial increases in the weight of the bridge which resulted from previous bridge modifications, and (2) the traffic and concentrated construction loads on the bridge on the day of the collapse.

What exactly are gusset plates?

The collapsed bridge belonged to a class of bridge called truss bridges. These are bridges assembled from straight pieces of steel — girders, beams, angles, etc. — that are connected together in the form of triangles, and whose ends are tied together by gusset plates. The NTSB report defines a gusset plate as “A metal plate used to unite multiple structural members of a truss.

Gusset plates on Old I-35W highway bridge in Minniapolis, MN

One of the bridge’s ‘nodes’ where structural members were joined together by gusset plates. Image from NTSB report.

The I-35W bridge had a total of 112 nodes. The gusset plates at each node were 1/2 inch thick steel. According to the NTSB report (page 128), they should have been 1 inch thick. That was the design error. Catastrophic failure of one or more gusset plates in the central region of the bridge initiated the sudden collapse.

As noted in the report’s conclusions, there were two contributing factors:

(1) The bridge was initially constructed with 1.5 inches of concrete as the deck surface. To combat corrosion of the underlying steel, the layer of concrete was eventually increased to an average of 8.7 inches by the time the bridge collapsed. The weight of the additional concrete increased the dead load on the bridge by 13.4 percent (page 23).

(2) On the day of the collapse, deck renovations were underway. The additional weight of construction equipment as well as piles of sand and gravel for making cement were concentrated on one side of the bridge.

 

Smart Bridge across the Mississippi River

The new, ten-lane I-35W St. Anthony Falls Bridge carries the highway across the Mississippi River, just east of  downtown Minneapolis, Minnesota. The bridge is modern, it’s state-of-the-art, and it’s billed as ‘smart’, and if you have time to do only one thing during your visit to the city, take a look at the bridge.

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Source: National Atlas of the US; US Dept. of Interior

If you’re not familiar with the area and you drive across the bridge, you probably won’t notice the bridge or the river. The bridge has no super structure above the deck and there’s little to differentiate the bridge deck from the highway. The transition from highway to bridge and back to highway is seamless. And whether you’re your heading north or south, you’ll be on a five lane highway and unlikely to get even a glimps of the river. To get a decent look at the structure, you must get off the highway, park your car, and walk.

Take any off-ramp leading to downtown Minneapolis. Your objective will be the West River Parkway. Several downtown cross streets connect to it. Once on the parkway, turn right and follow it to the riverside park called Bohemian Flats. There’s a pay-lot for cars within the park.

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Map shows I-35W Bridge in relation to West River Parkway and riverside parking lot.

The old eight-lane I-35W bridge collapsed suddenly on August 1, 2007 at 6:05 p.m. CDT, taking cars and trucks with it. Thirteen people were killed, many more injured.

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The 35W bridge in Minneapolis seen the day after it collapsed. Image by Mory Gash/AP

Nancy Daubenberger, bridge engineer for the state at the time (now Assistant Commissioner for Engineering Services), speaking on NPR’s ‘All Things Considered’ August 1, 2017, ten years after the collapse, said this: “The shock that came over me, that such a large bridge like that could collapse . . . it was devastating and tragic and shocking; a very, very sad situation.”

Considering the importance of the I-35W river crossing to the state economy, a new bridge was designed and built in jig time. It opened September 2008, a little more than one year after the collapse of the old bridge.

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Old I-35W Bridge. Undated image from en.wikipedia.org

To see the new bridge up close, follow the footpath beside the West River Parkway, first under the No. 9 bridge (a former railway bridge, now a bike path), then under the four-lane, 10th Ave. bridge which crosses the river within 50 yards of the new St. Anthony Falls bridge. Follow the footpath a bit further and you’ll be standing directly under the I-35W and behind the bridge’s four south piers. This is where you can see that the bridge is in fact two bridges, side by side but separated by a few feet of empty space.

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Under the I-35W St. Anthony Falls Bridge looking north. Image by innovata/Wikimedia Commons/ CC-BY-SA

Apart from its graceful lines and modernistic look, what makes this bridge a state-of-the-art ‘smart bridge’? Here’s an excerpt from The Catalyist, a publication of the Center for Transportation Studies, University of Minnesota.

During its construction, the [St. Anthony Falls] bridge was instrumented with more than 500 sensors that monitor strain, load distribution, vibrations, temperature, potential corrosion, and the overall movement of the bridge. Other sensors were installed to monitor the bridge’s security and control automatic anti-icing and lighting systems.

Although we can’t see any of these devices, we can imagine them constantly at work, transmitting information to the engineers responsible for the bridge’s wellbeing.

St. Anthony Falls Bridge at night

St. Anthony Falls Bridge at night. Image: Center for Transportation Studies, U of MN

For side views of the New bridge, continue following the waterfront footpath to the Stone Arch Bridge, half a mile upstream. Built in 1883 as a railroad bridge and still standing firm after 135 years, the Stone Arch Bridge is now used only by pedestrians. The new I-35W bridge is designed to last 100 years.