Poll Question: % UDL 1

[FoxSE14]

Audience Task: Provide 60% UDL value for a wide flange steel beam, given the following parameters....

Code: AISC, Table 3-6 (provided below), Use LRFD capacities.
Beam Size: W16x31.
Beam Length: 20 Feet.

....What value do you get? Please share.

 

[271828]

"The fabricator we work for is accusing us of over-designing. We are about to accuse the detailer of unsafe design. Just looking for consensus."

Consensus is irrelevant. The discussion shouldn't have progressed to accusations among three entities with no power to decide the answer. BTW, eng-tips posters also have zero power here. Send an RFI to the only one who gets a vote.

 

[dik]

Agent and Fox... you don't want to use the web shear capacity... that's an upper limit and by using the UDL approach, you may be designing for 20% of the web shear capacity... you'll waste a bucket or two of bolts. Fully composite is limited by the web shear.

Dik

 

[Agent666]

No we do I'm afraid. Code minimums for shear connections in this part of the world are 30% of shear capacity (of the bare steel beam). It involves not being lazy and evaluating all the reactions and rationalising them to 10% increments.

We aren't using it lazily like saying all connections should be 80%. If required every connection on a job could have a different percentage. Keep in mind we also design the connections, so the percentage is simply a way to call out typical industry standard connections. These are 100% standard designs, with documented capacities produced by an industry body. If we need something non standard we just design it using the same design model and give it a name/reference to call it out on drawing. We do not have delegated connection design like some other regions.

In the real world you'd rarely see anything over 40%-50% required for a typical composite floor.

 

[dik]

Agent: "Code minimums for shear connections in this part of the world are 30% of shear capacity"

This is a bit overkill... but not excessive overkill... you are likely designing for about 30-50% more than what is done in Canada and likely the US. Are there no exceptions? A rational approach? I just realised... when a new code comes out, one of the first things I check for are the exceptions.

Dik

 

[Agent666]

Your overkill is our normal robust loadpaths....

If you're not subject to seismic loads (which is virtually nothing round here), then I think the limit is dropped to 15%. But everyone just designs for 30% minimum because of the industry standard connections, reality is for a economically designed beam it suits quite well making virtually all of the connections for a given beam size the same, easy for fabricators as they know exactly the configuration and costs.

We also need to ensure simple connections, like the shear tab as they are called in North America have a ductile failure and can accommodate inelastic rotations, plate yields before weld fails or bolts fail in simple terms. This often necessitates a further bolt or two anyway to which the side effect is you get to 30% shear capacity relatively easy. For our max depth hotrolled sections (610UBs) I think it's only 5 (or 6) M20 bolts. The majority of beams less than 360mm deep only require 2 M20 bolts to get to 30% so it's not really too onerous.

The only other exception is if your connection isn't a shear connection carrying shear, then it's subject to other minimums like moment capacity or axial limits.

 

[ldeem]

This is a good catch by the OP, I wonder if the EOR would have caught it if the detailer submitted calcs from their program.

 

[Settingsun]

Agent666, 15% for seismic also? (12.9.2.1.1c)

 

[dik]

From my spreadsheet... Reaction 41.1K. There could be minor variations in the section database data (for 100% UDL, for 60% reactions would be 24.7K).


Jayrod: "0.6*81=48.6 kips. If it were me, I'd round up to 50."

For 60% I get 49.4K... same here 50K sounds OK... 25K each.

Dik

 

[Agent666]

Agent666, 15% for seismic also? (12.9.2.1.1c)

Goes off and reads code... finishes eating hat! Yes you're right. Notwithstanding here in NZ 30% is adopted for simple standard shear connections as the minimum. I always thought it was because of the seismic stuff and could have sworn it said 30%, but its just my old mind playing tricks on me!