Modelling steel joists (trusses)
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I have spent hours trying to find a way to design steel joists (trusses) the kind you can find in any Walmart to hold up the ceiling/roof. There are two opposite facing steel angles on the top and two on the bottom, with either a round steel rod "wave" between the angles on the top chord and the bottom chord assemblies, I cannot find the dimensions of the steel angles (or how to figure their size) same for the rod between the top and bottom. Any ideas? A plugin would be great.
This is probably not the right place to post this, but options are limited to what is offered on the forum. -
Ryan, we first need to find the specs on the pieces. I expect they are out there if we can figure out what to search for. Then drawing them should be a walk in the park. Give me a few minutes and I'll give you an example if you want.
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In the US, there is the Steel Joist Institute. A well known manufacturer is Vulcan. If you can search around, you should be able to find some sizing charts. I think even the American Institute of Steel Construction may have data for sizing of joists. Some lighter steel joists use tandem rods for bottom chords with double L tops.
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I found this: http://www.quincyjoist.com/files/SJI/joist_girder_series.pdf Maybe more engineering data than you want but it would help you figure out how to size the joists for your loads. And Tim's advice seems sound.
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@mitcorb said:
In the US, there is the Steel Joist Institute. A well known manufacturer is Vulcan. If you can search around, you should be able to find some sizing charts. I think even the American Institute of Steel Construction may have data for sizing of joists. Some lighter steel joists use tandem rods for bottom chords with double L tops.
Been all over Vulcrafts site, a lot of data, but not exactly what I was looking for. I have their catalog(s) in pdf.
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Oops, I said Vulcan and I meant Vulcraft. Sorry for that.
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I knew what you meant, Vulcan makes nice ranges though
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Would something like this work?
I'm sure I don't have accurate dimensions but the idea is there. As you can see, I made the web as a full "wavelength" unit and the joist could be made in any unit length desired by adjusting the number of units. You could split that as a half unit to get finer control. Or whatever you need.
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That works quite well, Dave. We know that trusses (joists) can be made is different depths, lengths of span, etc. based on the application. They also come in different styles, but how are they made?
I found a website that offers a little online app that allows you to enter your loads, static and dynamic, truss depth, length, etc. It outputs the suggested truss for your application. I just threw some random numbers in the, it told me that I need a 60" deep truss, for my application and the other specs as well. Kind of fun to play with.
I dropped them a line, we will see what happens. -
@tspco said:
That works quite well, Dave. We know that trusses (joists) can be made is different depths, lengths of span, etc. based on the application. They also come in different styles, but how are they made?
I found a website that offers a little online app that allows you to enter your loads, static and dynamic, truss depth, length, etc. It outputs the suggested truss for your application. I just threw some random numbers in the, it told me that I need a 60" deep truss, for my application and the other specs as well. Kind of fun to play with.
I dropped them a line, we will see what happens.I wouldn't mind a link to that website if you don't mind, may come in quite handy.
In wood trusses we usually use the rule of thumb 1" of depth per foot of span, so a 5' depth sounds like quite a span.
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I'd be interested in that link, too.
I wonder how difficult it would be to make a DC for these joists. The link I pointed to has some information about camber based on span. I think if that needed to be shown, Chris Fullmer's Shape Bender would do the trick nicely.
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Here is the link.
http://www.newmill.com/resources/resources_tools.html -
One half inch to three quarters of an inch for steel joists was the rule of thumb we used for preliminary design.
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In the UK simple timber-members supporting floors/roofs spaced at 16" c/c [400mm] the rule of thumb is for a width of ~2" [50mm] the depth is span_in_feet_as_inches/2 +1; so a joist spanning 14' [4.270m] needs to be 14/2 + 1 = 8" [200mm] - if you use the reg-tables or actually calculate it that is what you'll get !
For most steel-beams we'd take 1/20 span as the initial design depth, so generally a 12" U-beam spans 20' [300mm for 6m].
Obviously these things need calculating properly, but this is useful as an early design indicator - indeed, the standard way of designing a steel-beam in the U K is to 'guess its size', then check that with its live+dead-loads for adequacy in stress/shear/deflection, then if it's under-stressed you 'go down', or over-stressed you 'go up': there are several 'weights/linear m' of most standard steel beams which are nominally the same overall sizes but have differing wall/web/flange thicknesses - since you pay 'by the ton' it can be cheaper to use a deeper beam with thinner cross-sections, as that may well be cheaper than a heavier beam that is smaller - of course is you are stuck for space you may well have to use the more expensive one !
It is difficult to estimate the depth of 'engineered' timber or steel members; however, the manufacturers will usually give tabular indications of spans/loads >> depths etc... A lattice beam may well be deeper than a solid beam for the same span, but of course the lattice version will contain considerably less material, so balanced against its fabrication/connector and additional external envelop costs it can well be cheaper than the solid equivalent - and of course the heavier solid one can have knock on affects on other members/foundations etc, and it is also less suitable for passage pipes and ducts within its depth...
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