Bridges with Curves?

A lot depends on why a curved bridge is required. Basically, it involves availability of land, and proper horizontal and vertical alignments of the highway bridge approaches and the bridge itself.

In a lot of cases a new bridge is usually constructed next to an existing bridge. Many considerations must be taken into account. Taking of land, usually through the Eminent Domain process, is a huge factor. It is an expensive one. Also, the existing highway and bridge must be maintained during the new construction, as well as maintaining traffic flows not only on the highway and bridge, but also nearby streets and roads.

Another consideration is environmental, especially when it comes to impacts on wetlands and water ways. Another consideration is maintenance of traffic of navigable waterways.....this falls under the jurisdiction of the US Army Corps of Engineers.

Curved bridges utilize land much more efficiently. But they are expensive to construct. Also, very difficult to design, but with modern FEA software it's a snap.

Okay, that should do for now, as a primer.

OK I understand all that but...I've seen a few that are not replacements, have the exact same land requirement straight or curved, do not impact with water traffic...maybe the state/city just had money to burn? Could it be to try and slow traffic due to and intersection just past the bridge?

Like I said before, there are a whole host of considerations. The acquistion of land is very expensive. You must also take into account existing buildings and utilities and the rerouting of utilities that can become disturbed. Also, there are the influences of existing streets and roads.

Then the bridge must be supported be suitable soils or bedrock....or the pier and abutment footings must be supported by piles.

One of the biggest drivers for designing a curved bridge is traffic flow at the approaches and back down the highway, even several miles away......taken into account are intersections, on-ramps, off-ramps, and most importantly the daily and peak design traffic rates.

It doesn't make any sense to introduce a curve in a bridge to slow up traffic speeds. That's the last thing you want to do in regard to vehicular safety. You want to design for smooth traffic flow along the approaches and on the bridge itself, not the other way around.

In some case, a curved bridge makes more economic and alignment sense.

Is there a specific bridge that you've seen that drives your inquiry?

Well that's interesting...I just went back and used Google Maps to take a real look at a couple I had in mind. They are NOT actually curved but the approaches are curved! I also looked for one that I remember as a kid that definitely was curved and it's been replaced by a straight one! There is an interesting one in Macedonia, Greece over the lake of Polifitos, I suspect it has to do with the bottom materials in the lake. I also found some interesting bridge design tools on the web while I was looking...thanks for the knowledge CaptMoosie!

You're very welcome Tom! Now, what bridge design tools did you find? I'm always looking for them. Would you mind sharing the links for them? Thanks!

A few I found interesting and may go back and do a more thorough read.

https://wiki.csiberkeley.com/display/kb/Horizontally+curved+bridges

http://pghbridges.com/basics.htm

http://www.conteches.com/Design-Toolbox/DYO-Project.aspx?gclid=CNGijIikmrQCFexlOgodrXsA1Q

Thanks for the links Tom! Very interesting!!!

Hey CaptMoosie,

Up in your neck of the woods, the Hudson School for Boys offers a bridge design tool geared towards students to pique their interest in the field. Prize money to boot.

http://bridgecontest.usma.edu/

Cheers !!

BSR

Glenfinnan Viaduct in Scotland and the Landwasser Viaduct in Switzerland spring immediately to mind as examples.

In railway construction, the focus is on line speed. Which means that the curves have to be consistent with each other and as large a radius as practicable, even if that means building curved bridges sometimes.

I saw a documentary about the Millau viaduct in France. Although it looks pretty straight in the linked video: they said that they deliberately put curves in it because they were afraid that drivers would be more likely to fall asleep if it was straight.

Most motorways are deliberately curved because of people drifting off, figuratively and literally, on the very straight Autobahn.

There goes your GA.

The same thing is done on the Tappan Zee Bridge in NY (I-87) over the Hudson River

bluebelly, are you from NYS? Just curious....

the melkweb bridge was designed for aesthetics, not practical reasons other that to connect to the downtown area..

I'm not sure I understand how a horizontal curve would prevent expansion/contraction issues?

??? True. That was a major concern in the construction of the Coronado/San Diego Bay Bridge. The center span of the bridge is an independent "box" section. The bridge construction progressed from each landing toward the center span. After completion of the two legs, numerous measurements were taken to determine the precise expansion/contraction characteristics during various temperatures which affected the precise length and tolerances for the construction of the center span.

I'm not privy to the methods used to captivate the center section at each end, but there is a grating on each end of the center section and a various times of the year, the gap is wide enough to see the water some 180~200 feet below, while other times of the year, the water below cannot be seen through the gratings.

I've heard "rumors" that the center section of the bridge was designed and built to float, (possibly syntactic foam filled??) so it could be towed to clear the shipping channel in case of a natural disaster or terrorist attack. That makes perfect sense. We learned a hard lesson at Pearl Harbor.

I traveled the bridge daily for a 15 year period, and during the morning commute to Coronado, the traffic was bumper to bumper, stop and go for the entire length of the bridge. When you were stopped on the center span and could feel the bridges swaying movement, it wasn't a real warm and fuzzy feeling.

Dear Tom

Stone/Concrete and steel,expands while heated ,even by very small amount (for difference of 20 Celsius grades-as an example,see in GOOGLE))

Even for short bridges of tens of meters-you need expansion gaps to compenstae this elongation !! The Romans built their bridges on "bow" (curving) structure-so the expansion will be up (lifting position) - without it, the whole bridge would be destroyed within a short period (due to daily expansion/contraction of several millimetres...)

Now thing of several miles long bridges!!!

I understand the concept of curved "up" i.e. arched bridges, I just don't understand how a horizontal bridge could be built without expansion sections, as you suggested...mybe I'm just confused. Would not be the first time. My first post was just a question about horizontal curved bridges. I've learned a lot since that post!

Usually horizontal curved bridges have roller bearings and expansion/contraction grates where the girders bear on the bridge abutments. Typically, if the bridge isn't too long, roller bearings are utilized the support the girders at intermediate support piers w/o expansion devices...mainly because horizontally oriented curve bridges have to support the gravity loads as well as torsional loads imparted by the gravity loads due to the offset curvature of the girders. The ends of the girders are fixed against lateral translation to the sides, usually by the installation of stiff X-bracing between the ends of the girders and intermediate locations along their spans. this adds a great deal of stiffness and helps reduce the rotation of the girders about their principal axis.

I can see why that's an expensive solution!

Wow great answers. All this time I thought there were curves in bridges because the contractor spilled coffee on the plans.

Nah, I think the coffee was spilled at the steel fabricator's shop! LOL

Ahhhhh Yesssssssssss

Actually, it was the last act of the surveyor that got fired! ;=} ;-}