Subject:
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Re: My newest creation, Hell Gate Bridge NY
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Newsgroups:
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lugnet.trains
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Date:
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Sun, 10 Dec 2000 18:23:03 GMT
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Viewed:
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1229 times
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The yellow Technic bridge is a bow truss. It is not an arch. Truss members
are either in tension or compression and truss joints are assumed to be
pinned or hinged. An arch works in compression.
All of the bridges mentioned are cool!
Build On!
John Matthews
Scott A <eh105jb@mx1.pair.com> wrote in message
news:G58xM4.C42@lugnet.com...
> In lugnet.trains, Larry Pieniazek writes:
> > In lugnet.trains, James Trobaugh writes:
> > > Looks like the arch is made from 4.5v curved rails, right Arne? I really
> > > like the look of it, very sturdy and even looking. Nice job.
> > >
> > > I'd have to argue with the "two" arch bridges though, I have a technic • arch
> > > bridge that I made earlier this year.
> > >
> > > http://www.ngltc.org/GRNBRG2000/image6.htm
> > > http://www.ngltc.org/gats2k/image19.htm
> > >
> > > It not a steep arch, but an arch just the same :)
> >
> > Well, no, I'd have to categorise it as a type of through truss.
>
> I was going to leave this, but now that you started...
>
> I agree that is not a arch, and I expect that is was modelled on a truss.
> However, I'd call it a frame as it is pin jointed (trusses, I think are
> not). However, to be a frame all the members have to be in _pure_ tension • or
> compression (ie no bending moments). This is not the case with James's
> bridge. Additionally, the frame is statically indeterminate as it is not
> "perfect". To be a perfect frame:
>
> m=2j-3
>
> m=the number of members
> j=number of joints
>
> If it were a real structure, I'd expect it to have considerable movement.
>
> Basically, the problem is, it is not constructed from triangles. Despite
> that, it is fit for its intended purpose, and it does look very good.
>
> (This is mostly from memory, structural engineering was part of my UG
> degree, (I did peak at my copy of Durka{1} to get terminology) - I am open
> to correction on this. )
>
>
> >
> > Hell Gate and Sydney Harbor Bridge, for example, are suspension arch
> > bridges. Essentially all members below the arch are in tension and the • deck
> > is suspended from the arch. (The arch itself is usually either done as a
> > truss, with some members in tension and some in compression, or as an all
> > compression solid or fabricated structure)
> >
> > Steve's bridge, and the Rainbow Bridge at Niagara Falls, for example, are
> > cantilever arches... Essentially all the members of a cantilever arch are • in
> > compression, with the deck carried above the arch.
> >
> > Trusses are characterised by a mixture of compression and tension • members.
> > Unless all the members below the arc of the top chord are in tension,
> > (including the deck stringers) it's a truss, not an arch. I believe.
> >
> > I posted a link to a site that gave good bridge information in this group
> > some time in the past, but I'm too lazy to dig it up again.
> >
> > A key point here, though, is that the model that started this discussion • is
> > very very nifty.
>
> it is indeed.
>
> Scott A
>
> {1} Durka - almost schoolboy level SE
http://www.amazon.com/exec/obidos/ASIN/0582251990/qid=976273366/sr=1-5/106-5
958974-3391625
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Message has 1 Reply:
 | | Re: My newest creation, Hell Gate Bridge NY
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| (...) See, this is what I get for going into Comp.Eng. instead of Civil. :-) So unless I'm mistaken, (and yes it happens all too often) Arne's, (and James') and all of Ben's are all various examples of bow truss bridges. All the more reason to get (...) (24 years ago, 11-Dec-00, to lugnet.trains)
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Message is in Reply To:
| | Re: My newest creation, Hell Gate Bridge NY
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| (...) I was going to leave this, but now that you started... I agree that is not a arch, and I expect that is was modelled on a truss. However, I'd call it a frame as it is pin jointed (trusses, I think are not). However, to be a frame all the (...) (24 years ago, 8-Dec-00, to lugnet.trains)
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