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Steel Joist

Steel Joist

Steel Joist

(OP)
In an existing building there is a floor supported by 20K4 @ 2'-6" span 29' steel joist and metal deck type s. The owner propose to move to that floor 6 legal lateral files (5 drawers). The files will be located perpendiculars to steel joists. I figure out that the files fully loaded weight will be 375 pounds in 20 inches of width (width of lateral files). I divide the 375 pound over the span of the steel joist and give me an additional 13 pounds per linear foot of dead load. I have the following loads estimated

Dead load = 7.6 pounds steel joist weight + 93.75 pounds steel deck and concrete + 50 pounds utilities (partitions, ac, sprinklers, etc.) + 13 pounds files = 164 pounds per ln ft

Live load = 125 lbs/ln ft office use (50 lbs/ft2 x 2.5' tributary area)

WU = 1.2 x 164 = 196.8 lbs/ln ft +
1.6 x 125 lbs/ln ft = 200 lbs/ln ft
= 396.8 lbs/ ln ft < 439 lbs/ln ft LRFD THEN OK

Can anyone check my numbers and give me any suggestions on the calculations procedure.

Any help will be appreciated.

RE: Steel Joist

I'd be more concerned about the application of essentially a point load rather than the bending capacity of the joist as a whole. You need to worry about localized bending of the top flange where these will sit and depending on where in the span, the strength of your bearing seat.

I still think it's likely manageable since it works out to about a 600 lb point load but top chord localized bending capacity would be my biggest concern.

RE: Steel Joist

(OP)

Thanks jayrod12
Because the file will be installed diagonal on the floor the location of the load varies at the differents steel joists separated at 2'-6". It varies form mid span to 1/10 of the span length from the support.

How can I investigate the localized bending of the top flange?

RE: Steel Joist

Treat it like a beam that spans between panel points.

RE: Steel Joist

Your analysis implies there is only one lateral file cabinet per joist. Is that the case? I use the SJI procedure of determining the shear and moment diagrams for the actual loading conditions and then determine an equivalent uniform load that would produce the same maximum shear and bending moment. Then I investigate local effects due to the concentrated load. You might also look at the equivalent uniform load on the area (footprint) of the lateral file and compare that to your floor live load.



RE: Steel Joist

(OP)
Because the files will be located in a diagonal direction passing over 6 joists (approx), for that reason the loading condition indicate one file per joist with a variable location between mid to 1/10 of the joist span.

RE: Steel Joist

Sound like you have about 3 1/2" of concrete. That should distribute the load out enough to not worry about localized effects (IMHO).

RE: Steel Joist

^^ Good point XR250, you're probably right in that regard. I read right past the concrete and deck part.

RE: Steel Joist

First, the files are a live load, not a dead load.

Second, I don't like how you spread the concentrated load along the entire length of the joist--as has been stated above, it is a concentrated load, not a uniform load.

DaveAtkins

RE: Steel Joist

(OP)
Thanks for all comments.

RE: Steel Joist

Quote (Hokie93)

I use the SJI procedure of determining the shear and moment diagrams for the actual loading conditions and then determine an equivalent uniform load that would produce the same maximum shear and bending moment.

I second this. Draw your loading diagram with the uniform+concentrated load and check the cases with the file cabinet load near mid-span and near the end. I would ignore the live load that occurs where the cabinet is placed because the cabinet is the live load.

For this situation I wouldn't be concerned with localized loads. The cabinet is pretty wide (probably spans close to the full panel width) and you have concrete to further distribute load.

RE: Steel Joist

Quote (Hokie93)

I use the SJI procedure of determining the shear and moment diagrams for the actual loading conditions and then determine an equivalent uniform load that would produce the same maximum shear and bending moment.

I recommend going one step further. Draw the shear diagram for the actual loading superimposed on the allowable shear envelope for the joist. The center portion of the joist can resist 15% of the allowable end reaction. Check for any location where the actual shear diagram goes outside the allowable envelope.

DaveAtkins

RE: Steel Joist

I do not have them in front of me, but I think the K joist specification requires that joists resist 25% of the maximum end reaction at midspan (as opposed to the 15% mentioned above). Check out publications by James Fisher for the graphical method that DaveAtkins describes above.

RE: Steel Joist

(OP)


Anyone have a link of the publication by James Fisher for the graphical method.

RE: Steel Joist

Some freebies:

Link
Link

I consider this to be the Cadillac document and well worth the $30US: Link

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Steel Joist

Here is another document that may be of use. There is alot of free information out there provided by joist suppliers, you can find quite a bit through google, but as KootK mentions, the SJI Technical Digest is the most thorough.

http://www.vulcraft.com/decks/deck-catalog/designi...

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