Base Plate Anchor Bolt Loading
Base Plate Anchor Bolt Loading
(OP)
I have an access platform I am adding along a boiler. The design is cantilevered and supported by 6x6x0.25 HSS tube. I did a quick calculation based on max loading to see what tension would be on the anchor bolts (see calc below and model of baseplate). I was looking at using quick bolts and reviewed the hilti specs against the calculated load. My calc shows a tensile load of 5655 pounds along the centerline of the anchor bolts. This load would be shared across two or three anchor bolts. Hilti has a pullout load of 3345 lb in cracked concrete for 5/8" bolts. When I use the spacing factor in Hilti's spec, I get that it would take 7125 pounds (0.71*3345*3) to pull out all three bolts. That of course assumes all bolts share the load equally. Any tips or advice on this?







RE: Base Plate Anchor Bolt Loading
I agree with your approach, its common for concrete anchors like other bolted connections to share load (so long as your interaction affects are taken into account).
However considering you have a cantilever column baseplate resisting an applied moment, I suggest you review column baseplate design. (Blodgett "Design of Welded Structures" Section 3.3-8) You have to look at the fact that your compressive force is a triangular pressure distributions. This affects the force-couple moment arm and tension loads in the bolts. Because you are so close, I'd recommend this exercise to verify you have a sufficient moment arm.
Jeff
Pipe Stress Analysis
Finite Element Analysis
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RE: Base Plate Anchor Bolt Loading
Dik
RE: Base Plate Anchor Bolt Loading
RE: Base Plate Anchor Bolt Loading
Dik
RE: Base Plate Anchor Bolt Loading
RE: Base Plate Anchor Bolt Loading
Failure of one of the three bolts allows failure at design load.
At design load with all three bolts fully engaged: Safety Factor = 7125 lb. / 5655 lb. = 1.26
For safety purposes, say a scaffold is equivalent to an elevated platform. Scaffold Safety Factor = 4 is a widely accepted value.
1.26 SF < 4 SF
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RE: Base Plate Anchor Bolt Loading
Agreed. However, actual design load is 350 pounds plus dead weight of platform (so I already have an FS of 2 in my design load). Additionally, as I previously stated, I revised the geometry of the base plate to get tension bolt load lower. I am almost at 4 (it is like 3.8x).