AISC Design Guide 4 and 13. Possible contradiction?

[ul92]

AISC GD 4 is based on yielding line calculations of the column and beam flanges which is understandable. However, AISC DG 13 recommends to prevent yielding of column flanges under tensile flange forces which can not be found in the DG 4. Why is that and which design guide must be referenced for calculation of column capacity at extended end plate connection?

DG 4

DG 13

 

[DrZoidberWoop]

Our office uses DG13 Eq 2.2-8 as a general/supplementary check for moment connections to a column flange because it's consistent with AISC Section J10-1. We don't use Eq 2.2-9 as far as I can tell. Probably because the research is dated and the experiments used to derive it only included A36 steel (This note was included in the 2003 version of DG13. I'm not sure what the latest version says). Otherwise, we use the procedure from DG4/Seismic Design Manual pg 9.2-29 for extended end plate moment connection design. AISC can be tedious at times and slow to update material.

 

[ul92]

Wrt AISC 360-16, it recommends to refer to AISC DG 13 which is confusing!

 

[DrZoidberWoop]

I'd contend that checking both DG4 Eq 3.21 and DG13 Eq. 2.2-8 is fine as long as the end plate and flange thicknesses are selected using DG4 Eq 3.20. Speaking from a fabricator's perspective, DG13 Eq 2.2-9 is the kind of requirement we talk with the EOR about discarding.

 

[ul92]

Thanks!

In my example, I'm not designing for earthquake area so the Mnp in DG 4 Eq 3.20 can be taken equal to the required moment as long as the required moment is not less than 60% of the available flexural strength of the beam.

 

[DrZoidberWoop]

I'm replying on the fly right now, but if I remember correctly, the Mnp is a variable for selecting a "no prying" end plate thickness, based on bolt-group development/tension. The 60% recommendation is for designing the beam flange to end plate welds, ala the flange force. Two different variables.

 

[JoshPlumSE]

I had a similar question for AISC some time ago, when I was working on the end plat moment connection development for RISAConnection. The response was that Design Guide 4 2nd edition was based on the newest research and publications and should be used when there is a conflict between the two.

 

[ul92]

Yes, it's correct that the Mnp defined in DG 4 is based on thick plate - small dia. bolts which leads to ''no prying''. However, 60% recommendation is also for design of end plate connection incl. welds as per AISC 14th Manual.

The connection that I am checking has thick end plate but the column flange is thinner. While the end plate develops the full moment capacity of the bolt group, the column flange can't even when a pair of transverse stiffeners are introduced between the column flanges. Therefore, I have to calculate the reduced connection capacity. The latter task is out-of-scope of DG 4 where DG 16 has to be referenced which unfortunately doesn't address the column strength. In this case, AISC prying force calculations (ref. AISC 14th Manual 9-10) may be used to calculate the prying force developing on the bolts assuming that one side is flat (end plate). Only then, DG 16 can be used to determine moment capacity of the bolt connection considering prying. This part addresses the bolt rupture. Column flange yielding can be calculated based on the column flange thickness.

Considering that the failure can happen either because of bolt rupture and/or yielding of the column flange, the lesser capacity will govern the design.

 

[JoshPlumSE]

It's definitely true that some yield lines are missing. I remember that for certain column flange yielding for certain bolt arrangements. There is a PhD thesis upon which these design guides are based that has the missing column flange yield lines.

Sumner, I believe. I believe this is the link below.

https://vtechworks.lib.vt.edu/bitstream/handle/10919/28078/etd_Sumner.pdf?sequence=1&isAllowed=y

 

[volunteera]

Thanks. Will go through it.

It's really pity that DG 16 does not include column checks