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RE: Oversizing Base Plate Holes

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The AISC Steel design guide on Column base plates suggests the use of heavy
plate washers 5/16" to 1/2" thick (page 48).  They also suggest using holes
that are 1/4" larger than those listed in the AISC ASD Manual.

Steve W Bigham, PE
Design/Project Engineer
Braden Manufacturing
Ext. 2256


-----Original Message-----
From: James_F_Fulton(--nospam--at)RohmHaas.Com [mailto:James_F_Fulton(--nospam--at)RohmHaas.Com]
Sent: Wednesday, January 17, 2001 8:53 AM
To: seaint(--nospam--at)seaint.org
Subject: Oversizing Base Plate Holes


I've got a 12000 gal tank, 11'-10" OD,  supported on eight W 14x74 legs,

8 ft. unsupported leg length.  Each leg sits on a 2 ft. high reinforced 
concrete pier, and the leg base plate is anchored by two 1-1/4" anchor
bolts, 
A307 or A36 mat'l. I am concerned about fab and construction tolerances, 
paticularly for this tank leg configuration, and want to oversize the holes 
in the base plate a reasonable amount to help the situation. The suggested 
detail in AISC ASD Manual, on p. 4-130 in Suggested Details, recommends the 
hole be oversized by 1/2" for 1" to 2" anchor bolts. So I end up with 1-3/4"

holes for these 1-1/4" bolts. Heavy Hex nuts are to be specified. My
question 
is the standard washer that will come with these bolts be adequate size 
(thickness and diameter) to span the gap between edge of bolt and edge of 
hole. As a worse case, if the bolt ends up being shoved against the edge of 
the hole, the gap could be as large as 1/2". What is an appropriate washer 
for this condition ? Thanks for any quidance on this.

Jim Fulton