How do I designate steel joists on drawings? 2

[Revv]

Hey guys so basically I'm trying to call out 16k Joists so that covers the depth and the type. I see other numbers after it on some callouts and not sure what those are referencing, I have 10 joist spaces if that's all it is would it be 16k10 Joists? Thank you!

 

[le99]

No. You shall use the joist designation on the load table, from which the joist was selected.

Per SJI, "The K-Series, LH-Series and DLH-Series standard joist designations shall be:
established by their nominal depth, followed by the letters K, LH or DLH as
appropriate, and then by the Section Number designation assigned. The Section
Number designations shall range from 01 to 25."

Designation for standard K-series: 10K1 to 30 K12 (depth from 10" to 30")

 

[phamENG]

The number after is the chord designation. Look at the load tables - you'll see 16k2 through 16k9. Each one with a higher capacity and higher weight of steel.

You have a couple of choices in steel joist design: you can design it, or you can leave it to the manufacturer. If you design it, you select a standard joist from the load table and call it out (16K4 JOISTS at 4'0" o/c). If you leave it to the supplier, you say "16" DEEP OWSJ BY MANUFACTURER, Maximum Spacing = X, Refer to Sheet YYY For Loading" or something like that.

 

[Celt83]

review the guide provided by Vulcraft here: Link

I'm making a thing:

http://www.thestructuraltoolbox.com

(It's no Kootware and it will probably break but it's alive!)

 

[KootK]

The "10" in 16k10 specifies the weight category of the particular, 16" joist specified. A 16K10 is a heavier, higher capacity thing than a 16K8 for example. The second number is not indicative of the number of joist spaces.

 

[dold]

I've been using the following nomenclature: 16K (240/120). That would be joists at 6ft o.c. with 20psf DL and 20 LLr. My understanding is that the joist manufacturer still designs the joists whether you spec the full designation or just give them the loads. The number at the end isn't a guaranteed chord size, but more of a "capacity group" if you will. A 16K4 that's 25ft long might have a different chord section than a 16K4 that's 24'-9" long, for example. So essentially this cuts a step out for both parties. Apparently it is a regional thing too.

But, OP, you should definitely get a copy of any of the manufacturers joist and deck catalogs and read up on joists a bit more before specifying them. But I'm assuming you have a copy of this since you say you're seeing other numbers..? Pretty much everything you need to know is in the book you're looking at. Do you have someone in your office who can give you some guidance and review your work? How did you arrive at the 16" depth?

 

[Revv]

@dold so I am using a vulcraft catalog along with a design tool. On the design tool it does seem to indicate I should spec it how you're saying you spec it and does NOT give me the number at the end. Obviously in the catalog is does and I'm just trying to understand why there is the disparity and make sure I'm understanding things. I think your response and others have filled in the blanks for me though.

 

[dik]

Are you speccing from a catalogue or is the spec generic?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[SandwichEngine]

I used to work for a company that owned a joist company so I'll add some of what I know.

You can use the load tables to call out the exact joists you want, you can let the joist manufacturer design whichever standard joists that work, or they can design custom joists that work for your loading/deflection/whatever specifications.

The least expensive is to let them design custom because they'll squeeze every drop of excess steel out. The downside is that they are all super slow and you'll be waiting for months to get their drawings. If you can wait, that's the least expensive.

Also, if you do it this way, they'll take forever to give you a cost estimate because they have to do a quick and dirty design.

However most people can't wait so they call out standard sizes from the SJI code. This also helps with pricing and planning because you can easily compare prices from different joist manufactures and get an apples to apples comparison on drawings, delivery and cost.

 

[dik]

I generally spec a max depth based on an L/18 and drop it to the nearest inch and a max spacing. For example, with a 40' span I would have 26" (I'd probably use 24 since in these environs they are still considered as short span) max joists @ 6'-8" o/c, or whatever. With our snow loads L/18 gives about the most economical roof joist. I'd let the OWSJ suppliers determine what joists they needed.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[Brad805]

We call out depth, and indicate the exact spacings we want them. The joist supplier sorts out the mass. In my role as a designer for a precast company I despise the lack of dimensions we see these days. We are always waiting for the steel shops, and it is solely because of non-committal BS. In October one set of dwgs included a +- for the joist spacing.

We organize the joists for several customers. Due to the delivery timelines with OWSJ we have fast tracked three projects in the last few days. I send the request to our salesman, and he sends back a quote in a few days for the client to sign. I do not have the problems SE mentions, but I have worked with this guy going on 10years now.

 

[JLNJ]

Sounds like you need help from an in-person mentor rather than strangers on the internet regarding the design of joists.

Said another way, if you don't understand joist designations, then maybe you shouldn't be responsible for the design.

 

[jimstructures]

KootK,

I would be careful of referring to the second number in the "joist designation" as the weight category. Maybe the capacity category or PhamENG's chord designation. The weight per foor is on another line in the table and does not have a close relationship with the second number of the "joist designation. i.e. 16K10 vs 16K12


Jim H

I have not tripped over the definition of joist designation even though I made a cursory search for the definition.

 

[KootK]

I would be careful of referring to the second number in the "joist designation" as the weight category. Maybe the capacity category or PhamENG's chord designation. The weight per foor is on another line in the table and does not have a close relationship with the second number of the "joist designation. i.e. 16K10 vs 16K12

I get what you're saying but it sounds like hair splitting to me. That's precisely why I said "weight category" rather than just "weight". The higher numbered joists from any one supplier will tend to be made of beefier stuff and will tend to weigh more. I don't see the nonlinear nature of that relationship requiring any great duty of care. That said, I do like the greater precision of dold's "capacity group" and will try to remember to use that in the future.

 

[Lomarandil]

JNLJ, that's a little harsh. This is segment-specific and regionally varying information.

I consider myself a fairly experienced engineer, but have never specified an OWSJ. Being able to ask questions like this helps engineers broaden experience without enabling unethical or shoddy design.

----
just call me Lo.

 

[jimstructures]

KootK,

I agree, it is hair splitting but I think it is significant hair splitting. There is almost no relationship between the second number in the Joist Designation and the weight per foot of the joist, except that as the weight per foot goes up so does the second number.

It is too easy to try to conflate the joist designation with the steel shape designation and confuse the second number with the weight per foot of the joist.

Jim H

 

[KootK]

I agree, it is hair splitting but I think it is significant hair splitting.

Significant hair splitting?? I call oxymoron.

There is almost no relationship between the second number in the Joist Designation and the weight per foot of the joist, except that as the weight per foot goes up so does the second number.

The weight per foot generally going up as the second number goes up is, truly, the only relationship that I was laying claim to.

The main reason that I feel this to be an issue of little concern is that, from an EOR perspective, it's very rare that one explicitly considers the weight of an individual joist within a particular series. Rather, one simply assumes a blanket PSF covering a broad range of joists within a particular series. I've only ever considered the exact weight of particular joists in Hail Mary, retrofit applications.

It is too easy to try to conflate the joist designation with the steel shape designation and confuse the second number with the weight per foot of the joist.

The weight of the joists is usually right there in the tables, near the joist designations. I feel as though one would have to have a pretty weak understanding of the products and the process to screw that up. On some level I feel it appropriate to restrict our serious consideration to folks who are at least marginally familiar with the task before them.

 

[dold]

For what it's worth regarding the 'second number' (capacity group, if you will) - I've spent a considerable amount of time looking into this in the past when I was doing a ton of retrofits. I've scoured the internet for old references, design manuals, manufacturers literature, documents from SRE's website, on and on. There's no direct correlation between the 'second number' and any specific chord profile/section (with a few exceptions from specific manufacturers decades ago). For modern/newly fabricated OWSJ it will always depend on the specific spans and a variety of other factors, and they are designed squeak out every ounce of material. That's why you'll always see "approximate weight" as opposed to an exact weight. Furthermore, the shapes that joist manufacturers use for fabricating OWSJ are non-standard or in-house special rolled angles that are designated in increments as small as 1/64ths or 1/32nds of inches, typically specified in decimal inches. I.e., a specific joist might have a bottom chord of LL1.375x1.375x0.102, and a top chord of LL1.5x1.5x0.129, for example. Here's a clip from some joist calcs.

 

[JLNJ]

.077? Yikes.

That's under-rolling a 5/64ths angle. I'm designing with a crayon and they are cutting with a micrometer.