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Bent Plates in RAM Connection

Jason McCool

I noticed that a skewed shear tab wouldn't work for a particular beam to beam connection, but a bent plate with the same bolts and eccentricity did. Looking at the results with View Formulas enabled, I see that the equivalent bolt factor C = the number of bolts for the bent plate (no reduction for eccentricity) while the shear tab takes the normal reduction in C based on bolt layout. This seems a little suspicious that we don't have to take any reduction for the bent plate like we do the shear tab. Anybody (at Bentley or another user) aware of where that is specifically allowed? Otherwise, I would err on the side of caution and assume they're both reduced. This is a bent plate welded to the support and bolted to the supported beam, compared to the normal shear tab, both with a=3", SSLT holes, t=3/8", 2-3/4" A325, AISC-LRFD-2010 code in version 10.0.0.129.

Thanks,

Jason

  • 0 in reply to Jason McCool
    That's what it looks like to me, but it begs the question why the e=3" treated specially since 3.5" eccentricity has far less capacity. Still checking into that part.



  • 0 in reply to Seth Guthrie
    Yeah, in my sample file the bent plate connection with a=3" is at 44% strength ratio, but then jumps to 72% at a=3.01", so obviously some disconnect between using the calculated bolt C factor and assuming it equal to bolt quantity there. I don't recall any significance to a=3" other than that the shear tab table values (Table 10-10 in the 14th ed) are noted as based on a=3" in both current and previous edition. The 9th ed in its "Design Procedure" section on shear tabs (p. 4-52) directs the user to assume 3" eccentricity in the C tables for the bolts (Table XI), which results in the C-factor using a=3.01". I don't think they ever gave much guidance specific to bent plates, but the single angle table, which might be comparable to single bent plates sometimes, also assumes a=3", but still comes up with C factors < bolt quantity. So it doesn't seem to match with any of the similar conditions I see.
  • 0 in reply to Jason McCool

    For bent plates design and for the bolt shear capacity on the beam side, RAM Connection neglects the beam bolt eccentricity when these conditions are met:

    • Bolt columns = 1
    • Bolt distance to support <= 3

    So if those conditions are met then e = 0 and then C = Number of bolts. In other cases, e = bolt distance to support (in the case of bolt columns =1).

    This approach is the same used for single angle connections as described in the AISC Manual v13 p.10-123 and AISC Manual v14 p.10-133:

    The only reference for bent plates design gives us the idea to design it as single angles, AISC Manual v13 p10-150 and AISC Manual v14 p10-160:



  • 0 in reply to Seth Guthrie
    OK, I think I would agree with all of that. I only have one question. Further down on p10-160, they say "In all-bolted construction, both the shop and field bolts should be designed for shear and the eccentric moment." That makes it sound like having the bent plate bolted on both legs would count eccentricity at both sets of bolts without qualification, though maybe not on the actual plate strength, just bolt strength. I realize all-bolted is a little different condition than my initial post, but just wanting to reconcile that statement with the first statement from 10-133 and Figure 10-14, which I agree, seems reasonable to apply to both angles and bent plates.
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