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July 29, 2015

Bolted End Plate Moment Connections

DG16Version 5.0 of RISAConnection greatly expands the number of bolted end plate moment connections available in RISAConnection.

Previously, this had been limited to the moment connections described in AISC design guide 4 which was intended specifically for the higher demand connections associated with seismic and wind design. The available connections have now been expanded to cover most of the connections in AISC design guide 16 including flush end plate connections and end plates which are extended only the tension side.

New Extended End Plate Connections:

The MRE 1/2 connections stand for “Multiple Row Extended (1 row above flange, 2 rows below flange)”.  The 8 bolt unstiffened connection looks the same as the MRE 1/2 connection when viewed from the side.  But, a front view shows how this allows for additional bolts in the top row.

MRE12                                                                       8 Bolt Unstiffened                                                MRE 1/2

The solution for the MRE1/2 connection is taken directly from AISC design guide 16. It can easily be shown that the 8 bolt unstiffened connection has the same yield lines as the MRE 1/2 connection. However, the prying force calculation for this connection wouldn’t necessarily be the same.  Therefore, this connection is only checked for the thick plate procedure and is assumed to fail for thicknesses that would necessitate consideration of bolt prying.

Flush End Plate Connections:

There are two flush end plate bolt configurations, one with one row of tension bolts and one with two rows.  The two row connection offers option for placing a plate stiffener between or below the tension bolts as shown in the image below.

Flush             Two Bolt                        Four bolt                     Stiffener Inside Bolts              Stiffener Outside Bolts

These connections are based on the procedures described in AISC Design Guide 16.  Unfortunately, the Design Guide 16 procedures are somewhat incomplete in that they don’t explicitly check column flange yielding in their examples.  Since this remains a valid limit state (per Design Guide 4), the procedure used in DG4 is also used for the DG16 connections.

When drawing possible column flange yield lines, it quickly becomes apparent that their geometry is almost identical to the yield lines already derived in the design guides for plate yielding. Therefore, the basic equations for plate yielding are also be used for column flange bending with some important (but minor) changes.  The changes mostly relate to replacing the width and thickness of the plate with the column flange width and thickness instead.  But, they also include using the value of s rather than Pf,I.

Note:

  • A γr value of 1.25 is always assumed for flush end plate connections. The design guide recommends the use of this value whenever they are used for rigid frame construction.
  • The γr value is applied to the design of the plate, and for column flange bending. But, not for the design of the bolts or column web.
  • There is a discrepancy between the definitions of h0, h1, h2, in the two AISC design guides for bolted end plate connections. Design Guide 4 is the more recently published document and reflects a more refined procedure. Therefore, the DG4 definition is the basis for all bolted end plate yield lines used in RISAConnection, even if the particular end plate connections only appear in Design Guide 16.
  • Web yielding and crippling equations for flush connections are not given in any of the design guides. Therefore, they are assumed to be halfway between the equations given for direct weld connections and traditional bolted end plate connections.  This is equivalent to assume that the load spread for the extended end plate connections (which are assume spread out in both directions from the flange) do not spread out on the flush side of the end plate.
  • For asymmetric connections, it is possible for the “compression side” to control the design. This would normally only occur when there is some moment reversal, which may indicate that a asymmetric connection is a poor choice.  Even so, if a moment reversal is detected, the program will check for “compression” side failure as well.  When this controls, the limit states will add some text explaining that the compression side controls as shown in the image below.


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This entry was posted by RISA News on Wednesday, July 29th, 2015 at 8:00 am and is filed under Technical Solutions. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.

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