ACI 318 Anchor Reinforcement 6

[Struct-007]

In Section 17.3.2.1 of ACI 318-14, the calculation of concrete breakout strength is not required if anchor reinforcement is provided in accordance with sections 17.4.2.9 and 17.5.2.9.

In concrete pedestals supporting light poles; If the vertical bars are sufficiently developed, then can we consider them as anchor reinforcement?

 

[AskTooMuch]

Yes, get a copy of Anchor Bolt for Petrochemical Facilites. It explains more in detail how to use pedestal rebars for anchor bolt tension and shear using strut and tie.

 

[driftLimiter]

I agree the API method for pedestals is very nice for this application. Essentially you have a shear failure cone from the anchor bolts and you need to the verts developed above and below that to transfer the tension.

 

[Struct-007]

Thank you very much for suggesting this useful reference.

I have a follow-up question; Do you suggest a reference illustrating the design of "multiple anchors connected to a single steel plate at the embedded end of the anchors"?

 

[driftLimiter]

If you mean that all the anchors are going to have a common washer, for concrete breakout checks just use the area of the washer as your bearing area and the perimeter of it to determine the breakout surface.

 

[Rabbit12]

http://www.construccionenacero.com/...o_para_anclajes_en_pedestales_de_concreto.pdf

See the above PDF. Goes through both tension and shear anchor reinforcing.

 

[Struct-007]

Thank you guys, much appreciated!

 

[dik]

I try to avoid washer/plate anchors for fear of introducing a plane of weakness. I would not consider using a single solid plate washer. When I was going to university about 60 years back, I worked at Dominion Bridge in the galvanizing shop for a couple of summers (it was the highest paying job I could find). We galvanised several items that were a circular shaft with a spiral plate welded to them. They were anchorages for Manitoba Hydro to attach tension ties to for some of their tower work. The objects had the sprial plate welded to them to prevent a plane of weakness.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[jk2017]

The objects had the sprial plate welded to them to prevent a plane of weakness

Do you have a sketch of these? Struggling to picture them in my head.

Regarding using washer plates on each anchor (i.e. not one large plate like OP sketched), would that really create a plane of weakness assuming the washers aren't very close to one another nor particularly large (in plan)? I see this such a detail used pretty frequently, including for blast and seismic applications.

 

[driftLimiter]

@jk2017 If the bolts each have individual plate washers with a decent clearance between them you shouldn't get that effect. But I also agree with @dik the single plate is not only extraneous but also potentially a point of weakness.

 

[BridgeSmith]

But I also agree with @dik the single plate is not only extraneous but also potentially a point of weakness.

We use ring plates to anchor the bottom of the anchor rods for high mast light towers, and have for several decades. Of course, we embed it deep enough for a full 'lap' between the anchor rods and the vertical rebar in the outer cage, so we're not really relying on the concrete. It's also a 3" wide ring in a 4' diameter drilled shaft, so it's not a significant discontinuity, area-wise.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[Agent666]

I'd prefer the single plate, for the sole purpose of it removes one more stupid thing the contractor can get wrong. It holds all the bolts in the correct orientation relative to one another, that is a win in my book. I'm sick of seeing butchered base plates and being asked after the fact to justify it. If the contractor just has to consider getting the location and orientation as a whole in the right position, it is arguably better in my experience than having to do the same with 4-8 individual bolts and ending up with god knows what. I disagree that is it a significant point of weakness but I guess it's all relative the application and loading, provide all the shear capacity in reinforcement in the plinth if there is a concern, and stop relying on the tension capacity of concrete?

https://engineervsheep.com

 

[WinelandV]

Agent666,

What, you don't like getting photos of field notes from your contractor that look like this?

 

[dold]

What, you don't like getting photos of field notes from your contractor that look like this?

No doubt those sketches were part of a RFI that reads: "URGENT!: anchor bolts for braced frames misplaced. need epoxy fix ASAP! Crane waiting on site burning through budget."