I have a built-up structural truss (model rendering here) for which I need to find performance properties. It’s 20 feet end-to-end and 16 inches tall; it appears to be some sort of industry-standard configuration, so I’m hoping that I can find it listed in a handbook somewhere.
Can anyone point me to an online reference where I can look up properties for such things?
Looks like a common floor truss. Or a truss for a flat roof. The properties would depend on the material used to make it, along with a lot of other things. I used to work for a company that modeled trusses for the building industry, but I am no longer of any help with regard to trusses.
There are probably software packages available to model everything, but they are probably only available to those in the industry.
Yeah, geometry alone can’t tell you what the max load is for instance. You’d need the properties of the material and the configuration and geometry of each element at minimum. You could do some basic calculations like if load A is applied at point X while the structure is supported from both ends then you could figure the load on each end support and probably the rest of the elements. It might get tricky but really all you’d need is a calculator and a good statics and dynamics book.
Almost definitely a flat roof truss for single storey commercial. Have you examined it for manufacturer’s markings?
I have done no commercial framing so am unfamiliar with the product. There are plenty of mass manufactured residential structural components, and with those you can get PDFs with everything you need to now from their website. Multi-bay single storey commercial is so common and standardized I would not be surprised if there are similar mass produced products used.
That being said, most trusses are going to be custom engineered and fabricated. Characteristics of the truss design are basic 1st year engineering Statics and Dynamics. The rest is up to the material, and I have no idea how common or variable the different varieties of steel used are. Where’s our resident Civil engineer or Boiler Maker?
That looks like a pre-fabricated open-web steel joist. Steel joists are generally a proprietary design - the structural engineer uses a design manual provided by the manufacturer and picks out the proper size of joist depending on the uniform dead and live loads. There are a few main steel joist manufacturers - I think I threw out my old catalogs since I’m not a practicing structural engineer anymore, but one manufacturer is Vulcraft.
I would recommend finding out the manufacturer and trying to contact them for further information. “Performance properties” is pretty vague - are you trying to find out uniform dead and live load capacities? How large a point load you can hang from the bottom chord? Uplift capacity? Deflection properties?
So I suppose the short answer is no, there is no online handbook. But you may be able to find out what you need by contacting the manufacturer.
Safe load limits is what I’m after, i.e. maximum allowable distributed/concentrated loads.
I finally found it: this is a “K series open-web joist, parallel-chord, underslung.” This has come up for discussion because of a concern about whether it may be overloaded. We’re going to have a PE take a lookat the details as soon as we can, but assuming it’s made of A36 steel, a simple bending moment analysis that looks only at the structural angle elements that make up the top/bottom flanges suggests we’re probably safe for now.
You need to look at the entire structure, unless you are designing a structure. There are many structural programs out there that can help you, but it looks like you need an engineer to look at it. I seriously wouldnt use our advice here for safety reasons, if you are in construction.
Notice the bolded word: entire. The truss may be the right strength for your needs…but the truss doesnt exist by itself. It sits on supports and it is attached with bolts, etc…All of which have to work together (the proverbial weakest link, etc…)
Since you said you’re going to have a PE look at it ASAP I’ll hold off on the 20 lashes with a wet noodle, but you need to be very very careful. The top and bottom chords are only a small part of the structure - you still have the connections, lateral support, diagonal members, bearing support, etc., to analyze to figure out the joist’s capacity.
Joists of this type are also very sensitive to the location of point loads, so if there are any point loads that were not included in the original design, especially ones not at a truss joint, they could be a big concern.
Sounds like the sort of thing used for flat roof . Eg a carport. Old codes…
Therefore, Is there any point to doing analysis ? Will the building inspector pass it in the new configuration ? He may simply reject it out of hand if you are promoting it to be more important structurally speaking… eg changing it to hold up a floor. whereas it was only holding a roof or ceiling
In the present case, yes, it’s being used to support an elevated open-mesh grate floor. Our problem is that the grating is poorly supported in some spots (in one place it’s cantilevered 18 inches past the edge of one of the trusses), and we have a 5500-pound load that’s supported at its four corners instead of around its entire perimeter. This is a circumstance that has gone strangely unnoticed for about a decade.
My intent was to determine whether the truss would still be overloaded even if we took measures to better distribute that load across the grating (and to better support that cantilevered grating), but it’s all academic now: access to the area (and to the room below it) has been cut off until the PE can check it out.
Well, that’s a good idea. I’m afraid the “academic” part of the problem is all we can really help you with here, because giving you direction that might harm someone gets into legal and moral complications.
To answer your question, if it is a K Series Truss 16” depth, there are only 7 of them
This, at least per the joists book I have, and that one is at least 8 years old and from Columbia The designs are quite standardized by the Joist Institute. Online you can find all types of manuals used by the engineers and the properties from all the joists companies.
However as already said the point loads, bridging, and other issues greatly affect structural properties.
I understand completely, and I definitely was not looking for opinions in this thread, professional or otherwise; that would be akin to asking a doctor for medical advice. Just wanted a factual question answered, i.e. where’s a handbook that would list properties for the truss.
davida03801, thanks for narrowing the possibilities; from that list of seven, based on the details of what I’ve got, I’m pretty sure I can pin down which one I’m dealing with.