Base Plate Design - New Welded Plate Washers

Tekla Structural Designer
Tekla Structural Designer

Base Plate Design - New Welded Plate Washers

Following customer requests, the scope of US base plate design is extended to include welded plate washers. The primary design advantage of these is to equalize the shear load to all anchor rods (as explained in AISC Design Guide 1 (Section 3.5.3)). In previous releases the recommended cautious approach of using only two of the anchor rods to transfer shear was adopted (and continues in this release when the new option is not enabled). This enhancement was first introduced in release 2023 Service Pack 2.

A new base plate property setting to use welded plate washers is added as shown in the picture below, which is disabled by default. This can be used (and applies to all rods) in the following circumstances; when the Horizontal Shear Transfer option is set to one of those involving shear on rods and when there are only 2 rows of rods.
With this new option enabled, you can review and amend plate washer initial sizes (square side length, thickness, and hole diameter) and steel grade (A36-36) as shown below.

Some key aspects of this new feature are as follows:

  • The plate washer side length and hole diameter are set to sensible initial values dependent on the rod size at the time the plate washer setting is enabled - these do not update automatically following changes to the rod size.

  • There is no validation of whether the square side length will fit in the available space (you can review this in the graphical model view and detail drawing).

  • There is no design of the weld to the plate washers and hence no inputs of weld properties for the plate washers. (In the base plate report and detail drawing the weld detail for the washers is shown as “tbc” i.e. “to be confirmed” by the engineer.)
  • When welded plate washers are used, a new calculation is shown in design details which verifies the plate washer thickness (to AISC 360 J3.10) as shown in the picture below.

  • It should be noted in particular that rod tension develops due to rod bending, within the thickness of the plate washer and base plate, under the effect of lateral shear, regardless of whether the column net axial load is tension or compression. (Refer to AISC Design Guide 1, Section 3.5.3 and design example 4.11) The rod tension calculation is shown in the design details within pre-existing calculations for rods in tension and rods in tension + shear (to AISC 360 J3.6).

  • With all anchor rods mobilized for shear transfer when welded plate washers are used, the calculations for concrete anchorage strength take into account the distance between the two rows of rods in the base plate when determining the possible distribution of shear forces (refer to ACI 318-19 for example, Figure R17.7.2.1b).

  • The plate washers are included in the Material Listing Report in the same Plates table as the base plates.

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