Replies

Clark857

Not to hyjack the thread, but it’s interesting that you consider all these to be “trusses.” Are there bridges in the world that you *would* call “Cantilever bridges?”

i.e. at http://en.wikipedia.org/wiki/Cantilever_bridge it lists the longest cantilever bridge spans in the world, but you refer to these as trusses. These all have compression members on the bottom, tension on the top (except in the suspended truss span). Compare to the examples at http://en.wikipedia.org/wiki/Truss_bridge where every bridge has the tension members on the bottom and the compression members on the top.

Not to belabor an issue, but can you steer me to a lexicon used by bridge engineers where these are defined as “continuous through trusses” rather than cantilevers? It’s always been something I’ve been curious about, how different groups use different terminology for the same bridge.

Or, what is a typical “basic text” used by bridge engineers that I could go dig up at the university library?

Thanks,
Kwuntongchai

Don’t know that I can refer you to an exhaustive engineering lexicon. I have heard of engineering dictionaries, but I don’t have one. My references come from a combination of textbooks and field experience. The most general form of all the bridges discussed here thus far are trusses. If you read the first paragraph of the wikipedia entry cited, it says a cantilever can be made of trusses or steel or concrete beams. The truss cantilevering doesn’t preclude it from being a truss. The Firth of Forth Bridge pictured is a truss bridge. It employs cantilever sections over the piers to reach out and support the much shallower suspended or “drop-in” spans at mid-span. I disagree with the articles contention that the Jeremiah Morrow and Newark Bay Bridges are cantilevers. A cantilever requires a hinged section. It it not obvious those bridges have hinges.

The Newark Bay Bridge is an example of a Truss Arch. Think of it this way. Simple trusses don’t continue over their supports. Each span of a simple truss is independent. Continuous trusses are dependent on their adjacent spans, hence the height at the piers. Truss spans employing a cantilever (i.e. locating the hinge somewhere other than the pier) could be considered a hybrid of simple and continuous trusses. Sorry I didn't answer sooner. Your question wasn't shown as a new post to me.