Talk:Cantilever bridge

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Contents 1 Identifying cantilevers 2 Longest Spans 3 Descendant brigdes 4 Adding a photo 5 Cantilever versus Continuous Truss

[edit] Identifying cantilevers

The "tappan zee" is not a cantilever bridge —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 [1], 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)

[edit] 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)

[edit] 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)

[edit] 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)

[edit] 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)