OWSJ Identification 4

[Deener]

I have been asked to review the capacity of an existing OWSJ. I have been given dimensions and internal member sizes of the joist but no joist designation. Is there a table I can use to look up the joist designation based on the member sizes? i.e 30" deep, 3/4" square bar, 2 x 2 x 3/8" angle. Below is the sketch I received from plant maintenance. Max unfactored point load is around 400 lbs so we're exceeding the 100 lb rule. Joists are on 6' centers. No joist identification tags that I'm aware of.

Thanks in advance

 

[phamENG]

This is the document you need.

I have an older version at home - I'll see if I can find it tonight.

 

[Deener]

Thanks phamEng - I'll download this digital copy. I'm guessing this is about a 30 year old building so hopefully they joist is in there.

 

[JAE]

Well, that publication is not going to tell you what joist size you actually have based on field measured geometry, diagonal and chord sizes.

The usual way to go is to send in what data you have to SJI and they can assist you in nailing down the joist size.

SJI Joist Investigation Form

 

[jayrod12]

Or, since you have all of the measurements you need, you could analyze it the old fashioned way.

 

[JAE]

...except the weld connections always give me worries, jayrod12. A chord or diagonal might check out OK but the weld might have a more limited capacity.

 

[jayrod12]

I don't necessarily disagree with you, however you'd be able to tell right away if it needs any reinforcement of the chord or web members. And then once you know, then you cross the other bridge. Generally speaking I reinforce for the entire new loading in most cases. Very rarely do I only reinforce the deficient capacity since they're usually designed right to the limit to begin with.

Although I was under the impression that they more or less now weld for the full capacity of the web members. we're talking fractions of an inch of weld completed in a shop. It avoids issues that way.

 

[JAE]

I don't think they weld to the full capacity of the members.

Another tool that I've used in the past is this table which is based on old H joists (not the current K joists).
This was from Vulcraft but they stopped giving this out because they didn't want liability associated with designers assuming a certain chord width and finding actual delivered joists varied from this.
But it can perhaps get you close to a size (+/- three sizes perhaps).

 

[JAE]

...aaaaand looking at your chord sizes they are off this chart.

 

[BAretired]

The steel grade is needed in order to determine joist capacity. I wonder how SJI knows the grade of steel used. Perhaps they would want to know the date of fabrication in addition to member sizes.

BA

 

[r13]

Why the diagonals have 2 sizes indicated - 3/4" sq. bars left to the center line, 1"x1"x1/4" on the right? Or my eyes have problem? Also, what is the center line centered on?

 

[JAE]

Why the diagonals have 2 sizes indicated

Some diagonals in compression....some in tension.

 

[BAretired]

Why the diagonals have 2 sizes indicated - 3/4" sq. bars left to the center line, 1"x1"x1/4" on the right? Or my eyes have problem? Also, what is the center line centered on?

Good point retired13. I hadn't noticed those discrepancies. The typical panel length along the bottom chord is usually 4'-0" which would suggest that the overall span of 58' is wrong or else the number of panels is wrong. I doubt that SJI could come up with anything reliable based on the original sketch.


BA

 

[r13]

So this could be a custom made joist, add to the level of difficulties.

 

[JLNJ]

Be careful about field measurements. The people who take them don't understand that the actual member sizes may be rolled down to the 1/32 on an inch.

I would be really surprised if the bottom chord were actually 3/8" thick.

You need some good calipers or ultrasonic measurements to get close, and even then the possible error is very large.

Plus, you don't know the steel strength. In the end, when you don't know the size you are just guessing.

 

[skeletron]

I've run into the same situation before for old roof joists. I was able to track down the supplier (Stelco?), an old sales catalogue, and original structural drawings. Even with all this information, I was only able to ballpark the capacity. Go up in a lift and check out the joist itself, it might save you some sleuthing.

 

[r13]

I guess the center line shown is pointing to load center, not center of the span. Thus, the left side is stiffer than the right side. But why?

 

[BAretired]

I guess the center line shown is pointing to load center, not center of the span. Thus, the left side is stiffer than the right side. But why?

My guess is that the center line is five panels from the right support, as shown. The double arrow on the left is indicating the same five panels on the left, although not all shown.

If that is the case, there are a total of 10 panels, 8@4'-0" and 2@3'-0", one each end. The overall span, if that guess is correct would be 38'-0", not 58'-0" as shown. We cannot rely on this as it is only a guess. I think the OP should confirm the meaning of his sketch.

BA

 

[BAretired]

As for the actual size and location of the web members, it is anyone's guess.

BA

 

[SteelPE]

I go the JAE route and submit these to the SJI for review. I find they may be slightly conservative, but at least I have something to back my number up.

One gigantic issue with steel joist... making sure you measure with a micrometer not with a tape measure! The sizes of the chords can be ever so slightly. I am not sure I would except anyones measurements but my own.... definitely not a contractor unless I know how they took the measurements and how important using a micrometer is.