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Are heavy vehicles destroying our bridges?
Tidester was wondering wonder whether anyone would like to speculate on whether today's heavier vehicles may be contributing to more rapid deterioration of bridges and highways.
"This article says:
"... the average vehicle today simply weighs a lot more than it did then. In 1981, the average passenger vehicle weighed about 3,200 pounds. Today, thanks mostly to more SUVs and vans, the average vehicle weighs almost 4,100 pounds."
Surely, the engineers who designed the I-35 bridge in Minneapolis didn't anticipate such a load. Each traversal of a bridge by any vehicle has a microscopic effect proportional to its weight but that gets multiplied by 1 to 2 BILLION crossings over 40 years!"
I changed Tides' wording from vehicles to SUVs & trucks to make sure this new discussion got everyone's attention.
"This article says:
"... the average vehicle today simply weighs a lot more than it did then. In 1981, the average passenger vehicle weighed about 3,200 pounds. Today, thanks mostly to more SUVs and vans, the average vehicle weighs almost 4,100 pounds."
Surely, the engineers who designed the I-35 bridge in Minneapolis didn't anticipate such a load. Each traversal of a bridge by any vehicle has a microscopic effect proportional to its weight but that gets multiplied by 1 to 2 BILLION crossings over 40 years!"
I changed Tides' wording from vehicles to SUVs & trucks to make sure this new discussion got everyone's attention.
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But I would doubt that SUVs make much difference, as bridges have always been built to withstand much heavier vehicles (UPS delivery trucks, tractor trailers that were smaller than the ones used today, but still much heavier than an SUV).
Using 1981 as a starting point is not quite fair. The great downsizing was still underway. Most of our infrastructure was not built in the 1980s. If anything, I remember articles in the 1980s worrying that the new downsized cars would not be compatible with the design of our roads and bridges (features designed to route a typical 1960s full-size car back on the road could flip a smaller 1980s car). Most of our infrastructure was built using the 1960s full-size car as the standard.
The bridge that collapsed in Minnesota, for example, was completed in the late 1960s.
In the 1960s, Cadillacs and Lincolns topped out at over 5,000 pounds, and the biggest Buicks, Oldsmobiles and Chryslers weren't far behind. The most popular vehicles were the Chevrolet Biscayne/Bel Air/Impala/Caprice and Ford Galaxie/LTD, which were hardly feather weights.
Heavy vehicles are hardly anything new.
If anything, heavier use by all vehicles is probably contributing to the more rapid deterioration of bridges and highways. Traffic volumes keep going up, up, up.
Being a Pacific Northwesterner originally I have watched the footage of the Tacoma Narrows Bridge's collapse 60-odd years ago. That was engineering error to not take in to account the harrowing winds of the Narrows. My Grandpa lived on the other side of the rebuilt Narrows Bridge in a little community called Gig Harbor. Truly a beautiful place and it's a pretty view down below from the rebuilt bridge as Dad would drive this way to get us to Grandma and Grandpa's house.
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Problems with truss construction usually occurs at the joints where three or more members connect. Usually the connections are a series of plates used to make the connections using rivets (old construction), bolts (Most likely for the Minneapolis bridge) and welding (More modern construction) to connect the plates as they lap on the sides of the main structure members. This would be similar to joining two sheets of paper end to end, using scotch tape on each side to connect them. The paper would be the structure, the tape would be the side connecting plates. The problems with the truss connections is that there can be corrosion in between the plate and member that is not visible from looking at the connection as they inspect. This would require using test equipment of some kind - ultrasound for one. Welds can be inspected with x-rays, but this is expensive. Also micro-cracks can develop in the connecting plates or even in the main structure that can't be seen by the naked eye. These can be generated and enlarged by the passage of traffic.
Looking at the sequence that shows the bridge collapsing, I got the feeling that the bottom cord was the item that failed. The bottom cord is in tension, which means it is being pulled apart. Top cords are in compression - if you try to pick up four books by pressing against the side of the books, instead of supporting from below, you are compressing the books to form a single unit. Compression failures are usually distorted. There was no major distortion until the structure hit the ground. Tensile failures will talk and make noise before they break, but the break is very sudden. With the normal traffic noise I doubt that anyone would have heard are recognized that a failure was about to happen.
Anyone know the history of (US Highway & Interstate) truck weight limits?
And we've tweaked the title a little so we don't pick on Hummers too much - I trust we didn't lose anyone.
What really hurting our bridges, along with our roads, water systems and anything else in the infrastructure is the insane lack of maintenance. You can see the difference when you hit that rare piece of work that actually IS maintained well. The Golden Gate Bridge is one that amazes me. The thing is over 70 years old and looks like they just built it. There is always someone painting it.
Over where I am I'm not sure of the reason but the difference between two of the bridges going for New Jersey to Philadelphia is striking. The Walt Whitman looks fine. The Ben Franklin looks like it is going to rust away. I don't get it.
I suspect that roads and bridges that have to pay their own way do better even though I am loathe to give anyone any ideas about more tolls and the Ben Franklin example would certainly not back this up. I think of things like the Garden State Parkway, George Washington Bridge and the Whitestone Bridge.
Meanwhile, practically new sections of Route 287 are falling apart and I shudder to think about the Tappan Zee - a truly beautiful structure that has been left to rot with a ton of traffic.
They still had ferrys going across the Delaware into the 60s in Wilmington. I remember going across the bridge that is now there when they were still building the second span.
Of the other major bridges - the Betsy Ross Bridge opened for traffic in 1976, the Commodore Barry Bridge in 1974, and the Tacony-Palmyra bridge in 1929.
The 1980 date just happened to be the date used in that particular article. As for the 60s, even though there were some monster cars in terms of weight, the average weight of passenger cars was just over 3,000 pounds. In fact, the average weight of passenger cars has decreased over that period but proportionally far more people are driving SUVs and pickups than the engineers ever imagined.
tidester, host
SUVs and Smart Shopper
Have you ever noticed that ancient structures lasted for hundreds or even thousands of years. Why was that? What is the lifespan of our modern structures? I know in Boston the elevated highway was 40-50 years old and crumbling. It takes 15 years and $20B to replace it. How long are the new tunnels and bridges going to last? I hope not just 40 years!
Maybe we should question whether regular steel and concrete are the best building materials. Replace their use where possible. Once steel is delivered to a building site, and put at the site, you start getting corrosion even before the steel is up. That doesn't bode well for long-life.
But I believe a lot of the construction attitude in this country is that we'll just replace it and that creates a lot of jobs, and chances for corruption to skim from the projects.
I'm afraid we have too much of a throw-away philosophy, that is now a paradigm of policy.
Well, where are our gasoline taxes and tolls going??? To Iraq??? I know here in RI, where we pay some of the largest STATE gas tax in the country, it is SUPPOSED to fund road repairs. Most of it ends up in our general fund, to be spent elsewhere. If the feds and other states do this, it's not fair. This money should be spent on repairs, new infrastructure, and public transportation ONLY!!!!
Precisely so. Big shiny capital projects are much sexier to show off to the folks at home than periodic inspection and maintenance would be. I mean which do you notice more, a big building project of a few guys painting?
Of course a couple of the most impressive bridges are the ones that ARE older and maintained. I already used the Golden Gate as an example. The George Washington is another.
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You must be in my neck of the woods to be talking about the Longview (Lewis & Clark) bridge.
I was surprised to hear that 7 years ago, that bridge was inspected and they didn't do anything since then.
I may have heard it wrong on the radio, but that seemed odd.
Oregon is constantly inspecting the bridges.
They have trucks with special cranes that swing down over the side and the inspectors can view the underside of the bridge and inspect it.
I think that is exactly correct. It makes no difference if it is a car, computer or bridge. I watch the strip malls going up in So. CA. They are pathetic examples of horrible construction. They will be gone in 20 years for sure. Wonder if the pyramids were built like the I35 bridge over the Mississippi river. All we know how to build is for the short term. I wanted to build an adobe home. I see adobe homes in Mexico that are 300-400 years old and still standing. No that is not compatible with current building standards.
Yeah, the city wants a house that falls apart in 20 years so they get more taxes on the rebuild.
The authorities reviewed the safety record of the bridge, which had been designated “structurally deficient” as early as 1990. More than 70,000 bridges across the country are rated structurally deficient like the I-35W bridge, and engineers estimate repairing them all would take at least a generation and cost more than $188 billion.
159,000.
That's the approximate number of bridges that are either "deficient" or "obsolete," according to the American Society of Civil Engineers.
159,000.
That's more than one in four.
Approximately 73,000 of them are "structurally deficient" - like the bridge in Minneapolis - while 80,000 others are "functionally obsolete." That means they're carrying more traffic than they were designed to carry.
Not scary enough? Then try this quote on for size: "I think we're going to see bridges collapse, and we do on a regular basis," said Kent Harries of the University of Pittsburgh's School of Engineering.
London bridges falling down
It reminds me of a question posed to old Mayor Daley. Why did your son in law get the contract? Mayor Daley popped right back with "What Kind of Man Does not Look out for His Own Kin".
So we have a lot of bridges built with substandard materials and maybe unskilled labor.
I don't know about that up here in the northeast. Most, if not all jobs are union, so they are skilled. Now I know that on the Big Dig in Boston, there was talk of using a lower grade or watered down concrete for the tunnel tubes (now they leak) and questions about the method used to fasten the concrete ceiling tiles and the final inspection of them prior to opening it (one fell on a car killing a young lady).
Fugit inreparabile tempus.
The future is going to be a mess.
I think the NHTSA will have to add a new safety test. Bridge collapse worthiness.
Many bridges have been reinforced for earthquakes, but this is for side-side sway and road joints from separating or sliding off the pylons.
Some bridges are being rebuilt as they are widened, but there are some (several on the 710 freeway, a __major__ carrier of truck traffic) that are deficient.
Then again, a recent visit to Portland, Oregon revealed an astonishing number of badly maintained bridges on the I-5 and elsewhere.
Or, perhaps, SCUBA gear in every vehicle?
I've been wondering about all these people we have been watching giving interviews on TV. They tell us they were in free fall during the collapse - like 40 to 60 feet free fall - and yet they are able to talk about it? How much of a role did their vehicle type play in their survival?
At least. The population of California has just about doubled in 40 years.
The bottom line with maintenance of the infrastructure is the fact that it is not glamorous. Politicians want to say they are going to spend money to promote important projects like football stadiums.
Bridges, not to worry!
Putting aside my wise crack you know the calculation was that you can buy more votes with overpriced corn than with bridge maintenance.
Meanwhile, with the authorities over here, most of the bridges are very nicely maintained but the Ben Franklin looks bad and there really isn't an excuse for it. The Tacony-Palmyra and Burlington-Bristol have no excuse. These things are gold mines.
The PANYNJ seems to do pretty well with their crossings. The GW bridge looks as impressive as ever and holds as much traffic as you can throw at it. The Lincoln Tunnel is pretty amazing. I mean one tube goes back to the thirties and the third tube opened in 1957. I'd be hard pressed to tell you which tube is which. The only thing wrong with the Holland tunnel is that one end is in Jersey City. I don't suppose they can do much about that.
If those residents were to pay their freight on ferrys, not touching the fuel tax, the questionable bridges could be made safer sooner. Earthquake is the fearsome hazard. Sports fans enjoy Safeco and Qwest fields for their kid's games and they were financed with tax $'s.
I could never understand why good people in the Inland Empire should pay fuel taxes to subsidize the Puget Sound ferries. :sick:
They are indeed designed to handle large static loads but I am not so sure that the cumulative effects of microstresses were adequately considered back in the 60s.
Sure they could, make it a one way OUT of NJ.
What's the best part of being from NJ? Being FROM NJ!!! :P :P :P
Down the shore though. Can't complain.....too much....
We do have a wicked bridge that goes from our town to the barrier island next door. It's coming up on 50 years old. Is scheduled more major refurbishing but at least two years away. We'll see if the new inspections change that.
What is funny is my wife has always hated going over big bridges. Maybe she knows something we don't. The odds are that we will not have another incident like this for many years.
For the 1960 model year, weights for the full-size Chevrolet ranged from 3,485 pounds (Biscayne two-door sedan with the six) to 3,960 pounds (Nomad wagon with V-8).
By 1969, weights for the full-size Chevrolet were up to 3,530 for the comparable Biscayne, and 4,300 for the Kingswood Estate. By 1976, every full-size Chevrolet was well over 4,000 pounds, with some at 5,000 pounds. Almost every Chevelle/Malibu weighed at least 4,000 pounds, and this was supposed to be the midsized car.
The comparable Fords showed the same growth pattern.
Most of our infrastruture was built for 1960s full-size cars, and the weight of those cars was steadily increasing when those bridges and roads were built. I would think that this would have been taken into account when those roads and bridges were designed.
A couple years back, I had to have a bunch of dumptruck loads of gravel for a driveway and garage I was putting in. Each load of gravel was 14 cubic yards, and one cubic yard was 3,000 pounds. So that's 21 tons right there just for the load! I'd guess that Mack dumptruck weighed about 8 or 9 tons itself, so figure the fully loaed truck would come in around 30 tons. And that's on a fairly compact footprint, i contrast to something like a bus or a tractor trailer.
So after having to deal with a 30 ton mass, I don't think a private vehicle is going to make much difference, whether it's a Metro or an Excursion.
Now if the road surface or some part of the bridge is starting to fail, a larger car/truck/SUV might do more damage than a lighter one, but I imagine that it's still just old age/lack of maintenance that's doing most of the harm, along with original construction that may have just been done quick and dirty.
By 1969, weights for the full-size Chevrolet were up to 3,530 for the comparable Biscayne,
I'm kinda surprised that a base '69 Biscayne isn't even heavier than that, when you consider how much they bulked up from 1960 to 1969. But then, wasn't the '60 still using the old "Blue Flame" inline-6? If so, that was a heavy engine, and just switching from it to the more modern 230/250 CID inline-6 probably saved at least 200 pounds.
I'm pretty sure the '57 models were very close in weight to the '56 models, but not sure if they were lighter. I think the base weight of my '57 Firedome hardtop coupe is something like 3910 pounds, but I'd imagine the '56 was very close. I wonder if the 3-speed torqueflite transmission was much heavier than the 2-speed Powerflite?
I think modern cars also have much more substantial bracing up underneath, where it matters. So while all that flimsy plastic and beer-can thick sheetmetal may scatter to the four winds in an accident, the remaining hulk will still protect the occupants better than an older car with thick sheetmetal, but inadequate sub-structure.
But bridge designers would have expected vehicles to get heavier, as that was the trend at the time (1960s).
Of course, some bridge designers didn't need to worry about that. The bridge linking the Macungie Car Corral area to the rest of Macungie Park only has to be strong enough to withstand a certain 1974 Cadillac Calais hardtop that returns once a year...
Andre hit on a couple of things that are exactly the problem. One is low maintenance You can't just let most of these things go without maintaining them. They will fail guaranteed.
The other point is low bid contracts. Someone got the bright idea that the lowest bid is the best deal. Do you take your car to the cheapest mechanic? Have the cheapest contractor build your house? Use the cheapest plumber? I have dealt in these things and we invariably get the worst service for the cheapest price. This is all well and good when we are talking cleaning contracts but I can't tell you how many mistake ridden buildings we have because of this.
Besides, someone earlier hit the nail right, poorer structural integrity may have to be blamed for the collapse stemming from "Quick Build" techniques that is more prevalent now than ever (not sure how things were, back in the 60s though).
The 15 residents of the unreachable area are happy using an old railroad flatcar so the FD asked them to make their bridge safe for their engines. The residents balked.
Their lack of cooperation was met with researching the County Records to see who paid the annual tax bill. That revealed the mortgagee. The mortagee, upon being informed of the situation, divulged the name and policy number of the insurance company. The different insurance companies were advised of the problem and they wrote to each of the 15 residents advising them to install a safe bridge or get other insurance. Other insurance is not economically available. The 15 are being stubborn. :sick:
Trucking in the country has simply gone nuts. We American's with our comparative wealth have lost even the slightest sensitivity to how much stuff we consume. Hundreds of years from now when society looks back (if we survive that long) the stories of waste are going to be completely shocking to our grand kids.
The trucking industry still gets large subsidies from government. Make the trucking industry pay for the bridge and highway maintenance. Car drivers are definitely not the problem folks.
The truth is that local, state and federal officials simply steal the tax money from the "trust funds" established specifically for construction and maintenance of roads and bridges. They vote themselves an ever-growing share of our taxes to spend on pet projects. Then when something bad happens, they try to blame us for not paying them enough money.
Don't fall for this self-perpetuating scam.