range of widths for steel joists 1

[RacingAZ]

I'm trying to find out the probable chord widths for steel joists (K, LH, & DLH). I understand that these will vary depending on the steel angle sizes (plus the gap between the 2 angles) used for the chords for each steel joist type. Therefore, I'm looking for ballpark ranges for each joist type.

If this info is not available, can someone tell me what the range of angle sizes used for each joist type. Say, for K joists, the angles should vary from 1"x1" to ?. I'm guessing that K-joists angle sizes starts from 1". What about the LH and DLH? thanks!

 

[cntw1953]

Many joists I saw have formed (forged?) web members in stead of standard angles. Have you checked with SJI?

 

[SteelPE]

From what I have seen each manufacturer has their own standard angles that they use. This means that there would be no standard widths for the width of the top chord. However, if I need to know the size of a top chord of a joist I can to one of two things.

1) Call a few manufacturers and get a size of the top chord. Then spec it out on the drawings.

2) Size the chord myself using engineering principals and angle sizes found in the AISC Then set the chord width on the drawings. I believe most manufacturers use angles with Fy =50ksi, but I’m not 100% sure about this. Since joists are bough by their weight this process shouldn’t increase costs that much.

¾” to 1” are standard gap sizes for K series joists (from what I have seen). I’m not sure about LH or DLH joists.

 

[JAE]

I've got an older chart that relates the SJI chord size to the top and bottom chord angles. However, this is pretty old and as SteelPE states, the angle sizes vary so it would only give you a rough order of magnitude. I won't have access to it until Monday afternoon. I'll see if I can scan it in and post it.

 

[efsinc]

1" is the standard chord gap in 1000+ buildings I've been involved with. There may be alternatives, but i haven't seen it.
The chord angles employed have consistently been equal legged angles, leg lengths generally varying in 1/2" increments.
Leg thicknesses vary by the hundredths of inches and vary among manufacturers depending on the economic calculus of their engineering and supply and customer base.
The top chord angles may be larger than the bottom chord angles due to the section requirements of the combined stresses in the top chord ie axial + compression.
The largest angle employed, I have been told is 8x8 (Vulcraft, Quincy), making for a 17" net width chord, and this was for a 100+/- roof joist(if I recall the length correctly) also supporting a very large seismic drag load.

5" net width, utilizing 2x2 top chord angles with a 1" gap is very very common. 6" and 7" is not uncommon and may occur in an otherwise 5" top chord width bay where special point loads are added to a joist, such as from fire sprinkler main loads or HVAC unit loads or other.
Happy New Years!

 

[cntw1953]

RacingAZ:

I don't know what has motivated you to raise this question, but I doubt there is direct answer to it, as the member sizes are results of design by the joist manufacturers under the guidelines set by SJI. The attached paper laying out the general process, and responsible parties for such design. You might gain some idea where to get help you were seeking.

By the way, please ignore my previous response, which was a complete mistake by not understand your question.

 

[JedClampett]

Good luck with this. Many years ago I tried to get member sizes from a joist manufacturer to backcheck some of their undecipherable calculations. All they would tell me was that they would provide pieces that would, when put together, would have the properties in the calculations. They might be bars, angles or whatever. Needless to say, that was the end of my calculation review.

 

[cntw1953]

Yea, I think each design of bar joist is unique, as each manufacture competes to lower dead weight and speed up the assembly process. I have never been able to work out some properties using the formula they provided.

 

[msquared48]

So then, 3 to 6" seems reasonable to me.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[jike]

I have compiled the following info. over the years. Please note there is no standards among manufacturers, but it may get you in the ballpark. Please note that the largest angle depth is limited to the typical seat depth.
I hope this helps!

Approximate Joist Information
compiled from catalogs, manufacturer's data and field data

Joist Web Web Web Web Chord Chord
Depth Panel Panel End End Width Width
Min. Max. Min. Max. Min. Max.
H or K-series (not including joist chords with cold rolled hat sections)
8 14 24 12 34 2.50 3.50
10 14 24 12 34 2.50 4.00
12 17 24 14 34 2.50 4.50
14 17 24 15 34 3.00 4.50
16 18 24 19 34 3.50 5.00
18 20 24 21 34 3.50 6.00
20 22 24 22 34 3.50 6.00
22 24 48 25 50 3.50 6.00
24 24 48 27 54 3.50 6.00
26 24 48 30 56 3.50 6.00
28 24 48 33 60 3.50 6.00
30 24 48 33 66 4.00 6.00

LH-series
18 36 48 14 45 3.50 7.00
20 40 48 16 50 3.50 7.00
24 48 48 20 60 4.00 7.00
28 48 58 24 68 4.00 8.00
32 52 70 28 78 4.50 9.00
36 60 72 32 81 5.00 9.00
40 70 80 36 84 5.00 9.00
44 72 88 40 88 5.00 9.00
48 72 96 44 96 5.00 9.00

DLH-series
52 78 104 48 104 6.00 9.00
56 84 112 52 108 6.00 9.00
60 89 120 56 120 7.00 11.00
64 96 128 60 128 7.00 11.00
68 102 136 64 136 7.00 11.25
72 108 144 68 144 7.00 11.25

Note:
This data has been compiled from information provided by others. There is no guarantee or warranty that this information is accurate.

 

[JAE]

See the attached....this is a table I got from Vulcraft some years ago. Probably not perfectly accurate but does provide a general range of widths.

 

[RacingAZ]

Thanks guys, the info should be helpful. I tried Vulcraft before and the engineer that I talked to was non-committal and wouldn't give out the info. I was told that it is load specific. If you just simply follow the load tables per SJI, there should be a definite chord size for each joist type. I guess fabricators don't want to publish it to keep their competitive advantage in terms of supplying the lightest joist possible.

JAE, how is your table correlates to the joist types? Is the table for K-joists only?

 

[CTSeng]

JAE's chart is from a SJI 50 year digest and is probably the best source for approximate sizes. Got the attached from a colleague some time back. It's for old H-joists and is clearly out of date but provides some insight into how this suppliers setup.

 

[JAE]

Yes - table for K joists only - the chord size is the last number in the joist call-out: 24K10 means you would use the 10 on the chart.