Lake Champlain Bridge closed

[MichaelJ]

but ice has another mechanism--frost cracking (water freezes in cracks and expands with great force). And if salt was used on the bridge, it could have damaged both concrete and steel.

Yes, although cracking from water intrusion is going to happen regardless of the presence or absence of reinforcement. The advantage of reinforced concrete is that a center crack won't matter as much, as the (presumed) hoops will hold it a footing or pier together. That's the idea: the concrete is very strong in compression but needs to be "held together" to have that strength.

However, generally what happens is that water intrusion finds the steel and rusts it, and like ice, the volume of rust is greater than the volume of steel, and so it spalls off the outer layer of concrete, and then since it's no longer embedded, the steel doesn't develop any strength with the concrete.

Salt getting into the steel is nasty, you end up with a cathodic (anodic?) reaction that will rot the steel right out from inside of the concrete. However, I would be very surprised if they were putting down salt on this bridge, that's very environmentally unsound. The bridge likely has scuppers that send runoff right into the lake.

Note that prestressing is used for precast concrete beams, and post-tensioning for either precast or cast-in-place beams, but you would not prestress a pier, footing, or piles.

 

[Tom Rankin]

It should be noted that the current design consultant indicated that structures of this type, typically have a 75 year life span. This bridge is 80yo.

So this is a 5 year win!

Then again, what were they thinking 5-10 years ago?

 

[mookie]

its all about the zebra muscles.
http://www.vpr.net/flash/audio_player/audio_player.php?id=29609

 

[DougPaul]

Salt getting into the steel is nasty, you end up with a cathodic (anodic?) reaction that will rot the steel right out from inside of the concrete.

Not quite. For a cathode-anode reaction you need two dissimilar metals in electrical contact (ie a shorted battery). The anode is eaten away and the cathode is protected from corrosion.

Rust is iron oxide--wet steel will rust and steel in salt water will rust faster. Once rust is present, it becomes a catalyst which increases the speed of the reaction (rusting).

However, I would be very surprised if they were putting down salt on this bridge, that's very environmentally unsound.

Don't know--it is possible that they considered public safety more important than the damage to the lake. (It is a big lake--perhaps they figured it would dilute the salt.) They may also have done it at one time and have stopped. And the storm drains from the roads near the lake probably ultimately drain into the lake, too...

The bridge likely has scuppers that send runoff right into the lake.

Also with oil etc from the cars, which could be worse than the salt...

Doug

 

[MichaelJ]

It's been 11 years since I designed a bridge, my memories aren't perfect. A little followup shows I was remembering cathodic protection (see below).

Regardless, we structural engineers *hate* salt. It does nasty things to steel, but even worse it will dissolve the lime right out of the concrete. When that happens you're in big trouble. Depending on the design of the bridge, there are probably expansion joints, and those are likely directly over the piers and/or abutments. Despite best efforts, road runoff will find its way through those joints (or no efforts at all in the case of finger joints) and land directly on top of the concrete, probably corroding the bearings along the way. If ever you drive under a highway bridge and you see the concrete piers have their outer layer spalled (cracked off) and you perhaps can see the gridwork of steel within, that's likely what has happened.

As to dissimilar metals, we aim for steel-to-steel but once those architects start mounting lighting and railings on the bridge, anything can happen. There are actually ways to electrically charge a bridge to produce the reverse effect and protect the steel from corrosion and oxidation. Very cool stuff, but again, it's been a decade since I thought about it.

 

[DougPaul]

As to dissimilar metals, we aim for steel-to-steel but once those architects start mounting lighting and railings on the bridge, anything can happen. There are actually ways to electrically charge a bridge to produce the reverse effect and protect the steel from corrosion and oxidation. Very cool stuff, but again, it's been a decade since I thought about it.

Zinc anodes are commonly used to protect other metals (cathodic protection), for instance in your hot water heater*. You can also drive cathodic protection from an electric voltage (power source) rather than from a dissimilar metal. (Of course, you still need an anode, but it can be made of a material that will not corrode away.)

* If you want to maximize the life of your heater, check the anode occasionally and replace it if it has corroded away.

BTW, soft/cast iron lasts a lot longer than steel in the outdoors. (I believe some old cast iron bridges exist in Europe (UK?).) Pitons also used to be made of soft iron, which outlasts modern chrome-moly steel. But soft/cast iron isn't as strong as steel...

Doug

 

[smitty77]

I wonder why the limited insight at the time...

Still, I'm inclined to blame the frozen (stuck fast, not cold) bearings rocking the piers back and forth more than the ice.

First, it sounds like someone didn't fully appreciate the forces generated by frozen water.

And I buy your hypothesis on the bearings. Especially when initial repairs were required only 15 years into its service life, and have been a going concern ever since. And as Craig mentioned there seems to be no physical connection of the piers to the cap aside form the concrete itself. The report noted the cofferdams were dewatered and the pier stems were concreted "dry", so this is likely the only method of connection.

I am also a little perturbed at the bucket placement method, especially into a wet hole. I do know tremie work becomes a real bear if the concrete slump isn't above 6 or 7" (and I've seen as high as 10"), and I don't think they had the plasticizer technology back then to allow concrete to be made so "wet" and still retain it's compressive strength. My guess is they batched it very stiff and hoped it would be more or less homogeneous in it's final form. Judging by the range of compressive strength values I'd say this is not the case.

 

[Craig]

Author of the “Lake Champlain Bridge Safety Assessment Report (Draft)” pg 14-16

The use of unreinforced concrete piers for major truss bridges was an unusual
practice by the late 1920’s, with many bridges of similar size and span
incorporating a minimum amount of reinforcement. Two such examples that
were contemporary with the construction of the Lake Champlain Bridge, the
Pulaski Skyway in New Jersey and the Cape Girardeau Bridge in Missouri, both continuous truss bridges with similar spans over water, have piers constructed of reinforced concrete.
The American Association of State Highway Officials (AASHO, a precursor to
the present day AASHTO) provisions were not adopted until the early 1930’s,
however, development of the specifications began in 1921 and they were widely distributed by 1931. Therefore, they are representative of design practices at the time of the design of the Lake Champlain Bridge and are consistent with other relevant handbooks on concrete construction that pre-date the formal adoption of AASHO provisions.

Reinforcement would also have been beneficial in reducing the amount of
damage the pier has experienced at the water level. Although it is impossible
to predict how much the reinforcement would have prevented the deterioration of the concrete, it is certain that, had reinforcement been provided, the bridge would still likely be open to traffic.

Numerous repair contracts have been issued for the piers
and bearings starting as early as 1945. This in and of itself is critical in
understanding the existing condition of the piers. It is highly unusual for
concrete and bearing repairs to take place on a bridge that is only 15 years old, as the Lake Champlain Bridge was in 1945.

Ouch, this guy is killing the original engineer.

 

[smitty77]

Ouch, this guy is killing the original engineer.

Kind of. Considering he was employing "best practices" of the time and the bridge technically outlived it's anticipated service life, albeit with much repair work along the way, I would say he did a satisfactory job on the design, but no more than that. One would think a "good' engineer is a forward thinker and takes every effort to identify and incorporate emerging technologies in his design (in this case the inclusion of rebar), but as someone who does this for a living with highway pavement I know that state agencies are often very reluctant to be "experimenting" and deviating away from industry accepted practices.

Case in point: There now exists a way (actually several ways) to make and place hot-mix asphalt at temperatures 33% lower, 300F down to 200F, while keeping the same quality and performance characteristics. Let's just say the specifying agencies are not exactly fighting for space on the bandwagon right now. Progress is being made, but it's slow.

 

[RoySwkr]

Ouch, this guy is killing the original engineer.

Well, it's probably too late to sue him

Presumably the designer thought that with piers of such massive size, the psi strength of the concrete wasn't important. It sounds to me like the ice problem is more with abrasion at the ice location than with structural failure, many bridges have steel icebreaker noses in rivers and something could have been done here. If anybody has access to a structural design program, I'd be interested in knowing exactly how much stress the solid bearings put into the tension face of the pier - was it enough to overcome the downward load?

While they may not have used straight salt on the bridge, a certain amount of salt is mixed into most highway sand to keep it from freezing. And any car driving over the bridge could drip salt it picked up elsewhere. However the scuppers usually don't drain onto the piers.

 

[Craig]

Ouch, this guy is killing the original engineer.

Kind of........

My comment was mostly based upon the below unsubstantiated commentary that I found highly unusual for a factual structural analysis report designed for public consumption.

Reinforcement would also have been beneficial in reducing the amount of
damage the pier has experienced at the water level. Although it is impossible
to predict how much the reinforcement would have prevented the deterioration of the concrete, it is certain that, had reinforcement been provided, the bridge would still likely be open to traffic.

Additional Information

In 1923, the Vermont General Assembly appointed a Commission to study the feasibility of bridges across Lake Champlain. The Commission concluded that New York should be involved in bridge planning. In 1925, the VT Commission was reorganized by the VT General Assembly and NY appointed a commission to work with Vermont. The Joint Bridge Commission of NY and VT recommended in their final report the creation of a Bridge Commission by compact between the states and immediate construction of a bridge between Crown Point, NY and Chimney Point, VT. The compact creating the Lake Champlain Bridge Commission was signed on May 11, 1927. The Commission, which consisted of three members from VT and three members from NY, was given the powers to construct, maintain, and operate a bridge. The Lake Champlain Bridge (or Crown Point Bridge) opened with elaborate ceremonies on August 26, 1929. An amendment to the NY/VT compact in 1935 allowed the building of a second bridge. The Rouses Point Bridge, which was funded by a grant from the Federal Emergency Administration of Public Works, was completed in 1937. Both bridges were designed by the engineering firm Fay, Spofford & Thorndike, which served as consultants to the Bridge Commission throughout the life of the Commission.

Looks like the Rouses Point Bridge only lasted 40 years.

By the mid 1970's Rouses Point Bridge was badly deteriorated and plans were made to replace the bridge.

It's unclear who designed the new 1987 Rouses Point Bridge but it looks like Fay, Spofford & Thorndike did a Study for “Replacement of the Rouses Point Bridge” in 1976

The new Rouses Point Bridge opened in 1987. On December 11, 1987 the Bridge Commission was abolished, both the bridges became toll free and all functions of the Lake Champlain Bridge Commission were transferred to the VT Agency of Transportation (AOT) and The NY Department of Transportation (DOT).

It's interesting that Fay, Spoddord & Thorndike wasn't invited back for the engineering and feasibility study for the new Lake Champlain Bridge.

It's also interesting that the present design consultant, ***HNTB seems so critical of Fay, Spoddord & Thorndike.

Politics? Business rivalry?

* “Lake Champlain Bridge Safety Assessment Report (Draft)”
** Lake Champlain Bridge Commission
*** Lake Champlain Bridge Project ORG Chart

 

[MichaelJ]

IIRC, FST & HNTB had a major joint venture contract on the CA/T. Perhaps they didn't get along very well?

One important thing to remember - from a structural engineering standpoint, this bridge is technically a success. It did not fail catastrophically, it did not cause any loss of life.

As for the horizontal forces applied to the tops of the piers from the frozen bearings, keep in mind that in unreinforced concrete, there's no shear resistance, and so it's less about whether the moment could cause a tension in the outer face, but more about whether it's going to simply break apart the pier from the interior.

 

[The Hikers]

Can only say I'm glad we made it across four times this year. At those times they had survey crews asking questions related to destination, etc.

 

[Rivet]

As for the horizontal forces applied to the tops of the piers from the frozen bearings, keep in mind that in unreinforced concrete, there's no shear resistance, and so it's less about whether the moment could cause a tension in the outer face, but more about whether it's going to simply break apart the pier from the interior.

Umm, no. Unreinforced concrete has quite a bit of shear resistance. See ACI 318 Ch. 22 for plain concrete.

Vn=(4/3) * sqrt(f'c) * b * h

Even today, many concrete components (footings and slabs) are designed with flexural reinforcement but without shear reinforcement. Just increase the depth to inrease the shear resistance to meet the demand.

 

[MichaelJ]

AASHTO sure specified plenty of shear reinforcement back when I was designing bridges. Not just in the beams and deck, but in the pier or abutment tops as well. Not down in the bottoms, no (except the feet of spread footings), but up top, to resist the longitudinal forces.

 

[RoySwkr]

AASHTO sure specified plenty of shear reinforcement back when I was designing bridges. Not just in the beams and deck, but in the pier or abutment tops as well. Not down in the bottoms, no (except the feet of spread footings), but up top, to resist the longitudinal forces.

And this sure caused a lot of grief on the construction end, and didn't always get done. Imagine an abutment with sloping rear face which widens at top to hold girders, with rebar designed as % of concrete width. Contractor tells resident that its cheaper to form as vertical face, he will pay for extra concrete. If resident is familiar with _design_ part of AASHTO spec (which he probably isn't), he tells contractor that more concrete requires more rebars, contractor says that's silly with more concrete you need less rebar for strength.

But I agree that diagonal shear crack in pier sounds like the sort of catastrophic failure they're worried about, the whole span could collapse in one fat hurry.

 

[jniehof]

Contractor tells resident that its cheaper to form as vertical face, he will pay for extra concrete. If resident is familiar with _design_ part of AASHTO spec (which he probably isn't), he tells contractor that more concrete requires more rebars, contractor says that's silly with more concrete you need less rebar for strength.

And before you know it, you have the Kansas City Hyatt.

For those that like this sort of thing:
Any "Engineering Disasters" episode of Modern Marvels (History)
"Why Buildings Fall Down", Salvadori and Levy.

 

[Craig]

Oh no, not the Hyatt.

Before this turns into a battle royal between engineers and contractors, best to bring it back into the hiking realm.

 

[The Hikers]

Oh no, not the Hyatt.

Before this turns into a battle royal between engineers and contractors, best to bring it back into the hiking realm.

Yes, strange how things evolve.....

 

[rup]

Is this the bridge at Crown Point??