Evolution of Bridge design 2

[davidinindy]

I work as a mechanical designer on machines and vehicles, so don't frequent this forum much.
I'm also coming from a non-engineering viewpoint on this subject.
In recent years, I've noticed the trend of replacing older bridges built with character and architectural attractiveness, with purely functional, unnatractive, plain concrete walled bridges with walls so high, that you can't even see what you're crossing unless you're in an 18 wheeler. I miss being able to see the great views of rivers, railroad yards, etc.
To me, this detracts from much of what a road trip is all about... taking in the scenic beauty of the states you're driving thru. For example, when you cross the Wabash river on I-74 in Indiana, all you see (if you're in a typical family car) is concrete wall. In the middle of Indianapolis, I remember crossing a bridge on the north side of town, and looking down and actually catching a view of some deer swimming across the river. That bridge has now been replaced with on of these concrete bridges.
I've driven to Florida almost every year for many years, and have noticed many of the bridges that used to be a nice scenic break, are now replaced, and we ussually can't see the lake or river we're crossing.
I think it would be worth the states efforts, and money to make bridges compliment the scenery.
Is the reason for this transition purely safety related? or is it more economical?
What are you bridge professionals views on this topic?

David

 

[HgTX]

It's both money and safety. The higher walls are for safety. The lack of darling trusses, stone arches is monetary. The lack of dainty little rails is due to both factors.

Texas for a while anyway was earmarking funds for aesthetics. I don't know if they're still doing that, but it's definitely something that one has to pay extra for, and these aren't exactly flush times for that kind of thing.

Depending on the kind of traffic, there are varieties of open bridge rail that gives better visibility, but the more open designs aren't cut out for heavy truck impact.

Hg

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[crossframe]

To expand on HgTx's points:

Money: Many of those bridges were built as part of WPA projects designed to employ people and pull the US out of the Depression. This was an era when materials were expensive and labor was cheap. Now it's the other way around. DOT's also have an obligation to spend money wisely. Even DOT's that actually care about aesthetics (TXDOT is one) can't do all they like, but still try to incorporate some details in design.

Safety: I'm sure this can also be read as liability. Litigation (or even the threat of litigation) can often stifle engineering creativity.

 

[Qshake]

On that point of aesethics mentioned by crossframe, the most aestheic thing you're likely to see nowadays, the super structures notwithstanding, are decorative formliners which are very cheap compared to other treatments.

While many DOTs are very sensitive to aesethics (taxpayers and user fees often demand) most are still looking for the holy grail of function coupled with pleasent, cheap features.

Signature bridges are quite the opposite, but then who has money to spend on these mammoths today? Or for that matter, the appropriate place. In my opinion many of the cable stays in Florida are built in the right place but look at that Charles River BRidge in Boston.....man does it look out of place!




Regards,
Qshake

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[SoeSoe]

Does anyone think it has to do with the increase of standards and codes. Bridge rails get aesthetically displeasing by the year. Concrete box girders are one too many.

It's a shame a lot of money is spent, but nothing different is allowed.

 

[HgTX]

Even more money would be spent if something different were allowed.

It's exactly the standardization of "one too many" concrete girders that allows for economy. You want pretty custom jobs, you'll have to pay for them both in design time and in loss of economy of scale in fabrication, and no one's going to bother with that extra expense except for the rare signature project. Maybe all the people dissatisfied with today's highway aesthetics can start pooling their resources for a special Aesthetics Endowment.

Changes to bridge rail codes occur in response to changes in reality--increased truck traffic along the highways, increased use of pickup trucks & SUVs vs. passenger cars, etc. They have to be sturdier and taller. That doesn't look pretty. Que bummer.

The last Wow!aesthetic bridge rail I ran across was a fabrication and inspection nightmare.

Hg

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[SoeSoe]

These sound like excuses for a broken a system:
1) Most bridges that were designed for H15 carry todays trucks, including permit loads.
2) Many old bridge rails have functioned for 75 years, and have functioned under today's pedestrians and vehicles.
3) The funding system does not promote maintenance and rehabilitation of existing bridges, the worse shape the bridge is in the more money is funded. The funding requires strict adherence to an ever increasing pile of legislation, codes, standards, and specifications. Hence, the lack of design and the loss of those that were.

In my opinion, this situation is similar to the previous generation of engineer's disregard of the environment. However, I could be wrong--which is something I wish I heard people say more of.

I couldn't imagine trying to put something through that was nonstandard, it just isn't allowed.

 

[Dinosaur]

Bridge parapets and railings are a substantial liability issue. In addition, because most DOTs have prepared standard details, engineers will not be compensated for developing alternative railings that will most likely not survive the review process. My company would not accept the legal liability of developing a rail design and they would not accept the financial risk of developing a rail design when we would not be paid for the work.

As for aesthetics, the people in charge (almost exclusively government employees) by-and-large use only initial cost for decision making with regard to design. There are some exceptions such as Tennessee, but not many. These people are not rewarded for improvements in the area of aesthetics and therefore concentrate on the items they are evaluated on, which include project cost and construction schedule.

If you can get the legislature (remember we are talking about government employees executing the program) to change the DOT priorities (and what legislature is going to ask for more expensive bridges, that take longer to construct and expose the state to substantial liability) you see the engineering community move in that direction.

Not going to happen.

 

[davidinindy]

I think that, while safety and economics are important, maintaining your states identity, and scenery is also important. Yes, there are some "landmark" bridges, but I'm just talking about your normal, everyday bridge. Surely they can be made safe, while maintaining the view of the rivers.
Were there that many SUVs driving over the railings?

David

 

[HgTX]

Keep in mind that there are certain members of the taxpaying travelling public who will call the DOT if a particularly aesthetic bridge is built and bitch and moan about their tax dollars being wasted on such frivolity.

And I don't know how many more times those of us who understand this concept can explain this, but CREATIVE DESIGN COSTS MONEY. State resources are FINITE. Take your pick--repave that potholed road, or make your overpasses cuter?

SUVs over the rail? I don't know, Dave. How many SUVs over the guard rail do you think would be appropriate before we start sacrificing aesthetics for safety. Give us a number, wouldya?

Concrete AASHTO beams are used when they're the cheapest way to go. End of story. I personally think they're ugly as sin. That's fine; that's more money the state can spend on things like raises for me.

Bridge rail is at its cheapest when it's a single material (which rules out those shorter concrete ones with the metal rail on top). It's also easier and faster to form when it's solid rather than with lots of nooks and crannies.

Like I said, all y'all who are discontented with the looks of things around you and who value aesthetics over economics, go ahead and take up a collection.

SoeSoe, you're so damn sure the codes are unnecessarily and worthless? By all means, go ahead and pore through them. Pick out the parts that are wrong, or that you have data to show are unnecessary. Take it up with AASHTO; I've had success getting various code bodies to change their documents and I bet you could too.

I will say that you are right in that the funding system doesn't promote maintenance & rehabilitation. If you let your bridge go far enough, they'll buy you a new one instead of paying for the repair, so why repair it?

'Course, a lot of the existing bridges that would be maintained & rehabbed are pretty ugly themselves.

Hg

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[davidinindy]

HgTX
"SUVs over the rail? I don't know, Dave. How many SUVs over the guard rail do you think would be appropriate before we start sacrificing aesthetics for safety. Give us a number, wouldya?"
It was rhetorical.
That's like saying cars don't sacrifice some safety for asthetics.
I'm not trying to argue with anyone. I merely wondered what the experts had to say about this subject.
As far as desiging for safety, there are a couple of new ramp systems here in Indy that are extremely high in the air, and seem to have lower walls than some smaller bridges. They remind me of my childhood slotcar track layouts.

David

 

[Qshake]

SoeSoe,

Please note that non-standard is a great deal different that sub-standard.

Just because one DOT/agency doesn't use something should not necessarily preclude that product's value.

Regards,
Qshake

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[BradPL]

The reason that you're seeing higher, thicker (and subjectively more unattractive) barrier rails has to do with NCHRP 350. This report dictates the different Test Levels (TL's) which are required for barriers based on ADT, traffic and roadway characteristics, and design speeds. For example, structures on NHS (National Highway System) facilities are required to have a barrier with a TL-3 rating minimum. That dictates a minimum height of 27 inches however not too many DOT's have standard rails that are too far shy of 36 inches.

There are pleasing rails available for all the Test Levels (well, maybe not the TL-6). See the 2005 Bridge Rail Guide at the following link:

http://www.fhwa.dot.gov/bridge/bridgerail/index.cfm

Aesthetically pleasing structures can be achieved without adding enormous amounts of cost. But you have to remember that beauty is in the eye of the beholder. A bridge architect may "beautify" a bridge by adding spires and corbels and other such features while others find the functionality of the pure structure visually pleasing. If the bridge will be located in a prominent place, typically public hearings are held and money is budgeted for aesthetic treatments. We have used form liners to simulate stone abutments that were later stained by an artist that look very authentic. We have also used form liners to simulate that pigeon hole rail that was on the structure we replaced.

If aesthetics are important to the community, they can and will be budgeted for. But safety must remain paramount in all cases.

 

[davidinindy]

BradPL.
Thanks for that link. It made for some good comparisons. You can see the price/foot. Definately puts things in perspective.
Here's your star.

David