Plate washers on base plates 1

We use plate washers frequently. They cover up the oversized holes, and sometimes we actually weld them to the top of the base plate in braced frames so that there is a direct load path for the shear to be taken through the anchor rods (i.e. the baseplate does not have to displace some distance due to the oversized holes for the anchor rods before the shear becomes resisted).

I have used plate washers before for a variety of reasons, oversized or slotted holes, bolts with the wrong thread length, misalignment,... Done properly I do not think it is a problem.

I like welding the washer plate to the base plate, both for load transfer and corrosion protection. I also like to put a normal round washer on top. I am no expert, but as far as I understand it, the function of the washer is to aid tightening and ensure a correct load transfer, those functions are still required even after putting a plate washer.

Section 2305.3.11 of the 2006 IBC requires 3"x 3" x 0.229" (min) steel plate washers on anchor bolts for shearwalls between the sill plate & the nut for structures in Seismic Design category D, E, or F.

5 plies of 5/8" washer above the base plate?

Agree with JKStruct: I also use them at braced frame locations to provide a load path for the horizontal load between the base plate and the anchor bolts without the base place having to displace first.

(5) - 5/8" thick washers is quite excessive IMHO. Did they set the anchor bolts to high? and they can't get the nut down becasue they ran out of threads?

AISC also recommends using plate washers at any and all baseplates where anchor rods may be subject to tension (e.g. moment frames with high bending moments or braced frames in uplift etc) and oversized holes are used. This is to keep a typical size washer from pulling through the oversized hole in tension.

The AISC 13th ed. manual provides maximum hole size dimensions and corresponding washer dimensions and thicknesses in Table 14-2. Typically 1/3 times the diameter of the anchor rod is used for the baseplate thickness - so for a 1 1/2" anchor rod a 1/2" thick washer should be used.

err...for the washer thickness.

Nothing wrong with using plate washers for the right reasons, but as others have pointed out, the contractor may have done it to cover up something, such as big torched holes and anchor bolts set too high. Need to check to see if you still have have adequate embedment.