Talk:Cantilever bridge

Identifying cantilevers
The "tappan zee" is not a cantilever bridge &mdash;The preceding unsigned comment was added by 70.236.126.77 (talk • contribs) 18:30, 3 December 2005.


 * It sure looks like one to me. Cacophony 00:54, 18 December 2005 (UTC)


 * Me too. See also, about half way down there is a pic of the cantilever span partly built... it's clearly cantilevered, there is nothing between the two ends reaching for each other except empty air) Modern cantilevers sometimes aren't quite as obvious (c.f. Newburgh-Beacon Bridge both old and new spans are cantilevers too) Also the question could be brought up on the talk:Tappan Zee Bridge page. ++Lar: t/c 18:34, 16 January 2006 (UTC)


 * Cantilevers can be used during construction but that doesn't mean that the finished bridge is a cantilever. For example, there are many types of cantilever construction methods for box girder bridges--balanced, launched, segmental, etc.  But once the bridge is finished, it is a girder bridge and not a cantilever.


 * To me, the best way to know for sure that a bridge (truss or girder) employs a cantilever is for there to be an expansion joint mid-span. But this is not a hard and fast rule.  I just finished removing four cantilever trusses and each had an expansion joint between one cantilever arm and the suspended span.  It is easy to confuse a multi-span continuous truss for a cantilever.


 * I am not sure that the Jeremiah Morrow Bridge shown is a cantilever truss. If you go to this page about an inspection of the Morrow Bridge, it says that the bridge is a five-span Warren truss.  I have been looking for a better source to explain the difference between a continuous truss and a cantilever truss.  When girders are continuous across several spans, I've never heard another engineer call them cantilevers.  Charles 03:36, 12 April 2007 (UTC)

To do this article right, I think we need to start at the basics. Examine the Wiktionary definition of cantilever; I agree with this definition: to have a cantilever, a beam (or truss) must be supported on only one end. I drew the following graphic to show two examples.



The top cantilever is created with a full moment connection at the left end. The bottom cantilever is created when the structural beam (or truss) is extended to more than one span and additional supports are not added (with the understanding that the left-hand support may resist an upward force). A point load at the right-hand end of either cantilever creates a negative moment in the beam.

The lower cantilever then consists of two spans: the left-hand span is a simply-supported span (frequently called the anchor arm of the cantilever) and the right-hand span is a cantilever span supported at only one end (called the cantilever arm).

Extending this principle to cantilever bridges led me to draw this graphic:



This picture consists of two cantilever beams with another beam suspended in the middle. The circles in the beams represent hinges where moment is not transferred. This, of course, is an idealized and simplified drawing of a cantilever bridge. But I consider that a cantilever bridge must have these hinge points where no (or less than full) moment is transferred between parts of a span.

To me, many people see a continuous span truss and immediately say "cantilever." I do not believe that this is true (hence my comments above regarding the Morrow Bridge.  Comments? - SCgatorFan 23:47, 13 June 2007 (UTC)


 * From the photo of the Jeremiah Morrow Bridge, it certainly doesn't look like a cantilever bridge - I've annotated the article to request a citation and assuming one isn't forthcoming, it should be edited to refer only to a continuous truss bridge. -- Kvetner 13:09, 14 June 2007 (UTC)


 * I have edited the Cantilever article to provide a better basis for this article. Check it out and improve where needed. - SCgatorFan 06:39, 15 July 2007 (UTC)

Longest Spans
I'm somewhat confused about the longest span list. Where did the list come from? Is it just us sticking bridges in as we know or did it come from somewhere? If the latter maybe sourcing more specifically is a good idea?

Also is there any merit to a longest total span list? Consider Poughkeepsie Bridge. It has several spans that are in the 500 foot range. Some are not cantilever, it uses a pattern of fixed truss, cantilever, truss, cantilever, etc... Should it be listed in such a list, since it has 3 cantilevers. I'm guessing no merit to such a list but wanted to float the idea. ++Lar: t/c 18:34, 16 January 2006 (UTC)

Descendant brigdes
My english is very poor, sorry. The article says in the table that the descendant of this brigde is "Cantilever spar cable-stayed bridge", but I think that the descendant of this brigde is "Cable-stayed bridge", whith normal spars.--Magnus Colossus 01:02, 21 June 2006 (UTC)

Adding a photo
I have added a photograph of Vejlefjord Bridge because it is a cantilever brigde, but it isn't the tipical truss cantilever brigde. The footnote is very simple beacuse I can't speak a very complex english, and i can't write more text.
 * From the looks of it, I don't think the bridge is a cantilever. Can someone please try to explain why it is a cantilever. Otherwise the photo should be removed.


 * This bridge is probably a cantilever - it is similar in appearance to a bridge under construction in Northern California That bridge is being constructed by first placing footings, then erecting columns, and then building in balanced fashion out from the columns using cast-in-place tubular sections, forming a balanced cantelever at each column, which are extended until they meet. - Leonard G. 01:26, 23 July 2006 (UTC)


 * I've amended the image caption to make it clearer - it's a balanced cantilever bridge, i.e. cantilevered during construction only, although not once completed. I think it would help the article a lot to split out bridges which are cantilevered only during construction into a separate article. I'll see if I can find some time. -- Kvetner 08:43, 12 April 2007 (UTC)

Cantilever versus Continuous Truss
I found a listing published by the National Steel Bridge Alliance that has lists for both Cantilever and Continuous Truss bridges. Check it out: NSBA Longest Spans. - SCgatorFan 04:32, 21 July 2007 (UTC)

cantilever bridges
cantilever bridges are very cool —Preceding unsigned comment added by 216.73.69.193 (talk) 16:07, 10 March 2009 (UTC)

waz up? hi. —Preceding unsigned comment added by 64.33.149.151 (talk) 14:00, 30 September 2009 (UTC)

Get rid of the photo of the men holding up their arms
I see no reason why the men are holdidng the outer two sticks. It seems wasted effort holding their arms out like that, when the only sticks that need to be held by them are the inner sticks. The bricks are not supporting the inner sticks in any way, the men are. What upper cord is the description talking about? I see no no cord in the drawing of the bridge. There are decorative steel beams illustrated, which look like they are adding unneeded weight to the bridge. It looks the steel mill was ripping off whoever paid for the bridge.--75.36.47.40 (talk) 08:16, 20 January 2013 (UTC)


 * chord, not cord. It means "structural element" (and specifically, their arms in tension), not "string". The illustration is admittedly widely reproduced and rarely understood. The main point of it is to show how the central load is balanced in a "balanced cantilever" like this by the tension through the cantilevers (the men at the sides) who would otherwise topple inwards. It also shows how a load is held "up" by another load acting "down".
 * The photo should stay. It's a very well-known historical photo, it's related to a famous bridge, it has some scope for explaining balanced cantilevers and even the guy in the middle has an interesting story. Andy Dingley (talk) 18:24, 20 January 2013 (UTC)
 * I like the photo also. Oaklandguy (talk) 02:12, 31 July 2015 (UTC)

Credit for the 1st cantilever bridge
It appears that Captain Elisha Huntley Mack was the first person to invent or discover the cantilever bridge, rather than Heinrich Gerber. It was during the time frame he built the 1st dam at Turners Falls in 1793, long before the first patent listed in this article. I read he died while in Washington D.C. planning to apply for a patent and I can't help but wonder what the patent was for. Refrences:
 * History of Greenfield: Shire Town of Franklin County, Massachusetts, Volume 1 By Francis McGee Thompson, Lucy Jane Cutler Kellogg
 * History of Montague: A Typical Puritan Town By Edward Pearson Pressey, Robert Parker Clapp, Mrs. Lyman O. Gunn--AquarianEssence (talk) 21:48, 22 March 2015 (UTC)


 * The sources are problematic because they are local histories rather than histories of bridges per se. Local histories tend to ignore things outside their scope, so all the sources are good for is citing instances (and pointedly, using fewer words here than in the source), rather than asserting something was done first. A paragraph in a source like that amounts to a sentence here. TEDickey (talk) 22:37, 22 March 2015 (UTC)


 * By the way, your use of tags interferes with other editor's comments TEDickey (talk) 22:39, 22 March 2015 (UTC)


 * This is my first contribution and I apologize for my ignorance. I removed the ref tags but I used them because I see below, "cite your sources" with ref tags. I also apologize for not responding earlier. I didn't get notice of a reply. I see your point but I'm wondering how this information could be found within a history of bridges unless the compiler read these local town histories. I've searched and don't find this kind of source. I am not sure what all would be considered a valid source for this. If there were an article published in the local newspaper describing this bridge, would that be considered a valid source? It was certainly newsworthy. AquarianEssence (talk) 20:08, 6 April 2015 (UTC)


 * Local newspapers have the same problem: they are local, written for local interests. That tends to undermine any discussion of what was first.  A published article or book (by a knowledgeable historian) of the overall topic which discusses the structures would help. TEDickey (talk) 22:46, 8 April 2015 (UTC)

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Photos
An editor made an edit with an edit summary saying: ''Examples: rm half the gallery. We need better photos, and side-on to show cantilevers. Some of these are nice images, but they're not encyclopedically illustrative.''

I disagree. In my opinion, the article need images that show this bridge type from different angles. If the article is only going to show cantilever bridges from one viewpoint, there might as well just be one photo in the entire article. Toddy1 (talk) 19:05, 1 April 2020 (UTC)

continuous across multiple supports
what exactly does "continuous across multiple supports" mean? It wouldn't be a bridge if it wasn't continuous would it? (I'm guessing it refers to the structure supporting bending at the supports and someone has gone too far trying to avoid technical language? ) Gjxj (talk) 17:10, 6 July 2020 (UTC)

Ambassador Bridge
In the article on the Ambassador Bridge, no mention is made of the design life of the bridge. I heard that the bridge has exceeded this age. 2600:1700:6A10:84B0:8584:78A2:AC5A:D477 (talk) 22:32, 9 February 2022 (UTC)