AISC Standard vs. Oversized Holes - Bearing Connections
AISC Standard vs. Oversized Holes - Bearing Connections
(OP)
I've often had confusion over an issue, and could likely contact AISC directly, but would be interested to get input from the experience of those on this forum. This regards steel bolt hole size. I've had many projects where the contractor needs to fasten a steel plate to an existing concrete surface with expansion or adhesive anchors, and they constantly request "somewhat large" hole sizes so they can use the steel plate as a template and drill into the concrete without binding on the steel.
I am familiar with AISC Table J3.3's hole size provisions. My confusion lies in two adjacent statements. The first says standard or short-slotted holes shall be provided unless long-slotted or oversized holes are approved by EOR. In the very next paragraph the spec says oversized holes are permitted in slip-critical but not bearing type connections. In my view these paragraphs seem to contradict, as the first paragraph seems to give the EOR the judgment call for oversize, or is it only giving EOR the judgment call for slip-critical only? (i.e. strict prohibition on oversize for bearing-type?)
I've also read Section 3.3 of RCSC and its commentaries. The verbiage seems mostly consistent with the AISC spec but is more expansive. The result is that I'm still unclear on how much is left to the EOR's judgment and approval without violating AISC/RCSC.
I am familiar with AISC Table J3.3's hole size provisions. My confusion lies in two adjacent statements. The first says standard or short-slotted holes shall be provided unless long-slotted or oversized holes are approved by EOR. In the very next paragraph the spec says oversized holes are permitted in slip-critical but not bearing type connections. In my view these paragraphs seem to contradict, as the first paragraph seems to give the EOR the judgment call for oversize, or is it only giving EOR the judgment call for slip-critical only? (i.e. strict prohibition on oversize for bearing-type?)
I've also read Section 3.3 of RCSC and its commentaries. The verbiage seems mostly consistent with the AISC spec but is more expansive. The result is that I'm still unclear on how much is left to the EOR's judgment and approval without violating AISC/RCSC.






RE: AISC Standard vs. Oversized Holes - Bearing Connections
A better way to do it is provide oversized holes and then weld a plate washer of sufficient thickness and material strength to provide a bearing surface once the bolts are located (doubly provides the washer needed to bridge the oversized holes).
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
https://www.facebook.com/AmericanConcrete/
RE: AISC Standard vs. Oversized Holes - Bearing Connections
You should make this a standard in your office. There's just no other REASONABLE way to do it. I can't imagine trying to preload expansion and epoxy anchors enough for a slip critical connection.
RE: AISC Standard vs. Oversized Holes - Bearing Connections
RE: AISC Standard vs. Oversized Holes - Bearing Connections
When the EOR goes outside the specification, they should have some reasoning and justification. If the bolt group has significant force in shear, it can be hard to justify oversized holes without weld washers (or similar).
RE: AISC Standard vs. Oversized Holes - Bearing Connections
RE: AISC Standard vs. Oversized Holes - Bearing Connections
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
https://www.facebook.com/AmericanConcrete/
RE: AISC Standard vs. Oversized Holes - Bearing Connections
RE: AISC Standard vs. Oversized Holes - Bearing Connections
Oversized holes are often needed to accommodate tolerances.
Welding the washer is one option....but everybody that knows the cost for site welding in USA knows that this can get expensive
It should be up to the engineer to proof the connection and not up to the code ...but often the ERO wants the code to be followed
RE: AISC Standard vs. Oversized Holes - Bearing Connections
WannabeSE, I understand the thought to come up with some justification, but here is a common scenario: a mechanical/electrical equipment with pre-set holes in its base. Let's say the shear and tension loads due to wind/seismic are pretty low (in the hundreds, not the thousands), and the preset holes are 5/8"-diameter. The natural anchor choice is post-installed 1/2"-diameter. Almost all the time the steel anchor failure mode is not close to capacity with the concrete breakout or pullout invariably governing. But according to J3.3, 5/8"-diameter hole would be oversized for 1/2"-diameter anchor. Does this mean the anchor choice is not allowed per AISC without the use of welded washers to provide fixity? Every general contractor will gripe non-stop to the owner until we, as EOR, are deemed too conservative, rigid, and ultimately not worth using. Of course, our job is to provide structural-sound designs, not make contractors happy.
RE: AISC Standard vs. Oversized Holes - Bearing Connections