Armature Anchor Assembly 1

• Aug 12, 2020

• #2

SlideRuleEra

Structural

Jun 2, 2003

5,528

...using an anchor bolt assembly composed of four threaded rods bolted to a steel plate and the whole thing embedded into the concrete.

Click to expand...

No, I have not heard the term used to describe an anchor bolt assembly, but it make sense. There is such a thing as a "squirrel cage" (AC) induction electric motor. The armature (rotor) of this motor is basically a pair of plates at each end of the motor's shaft with solid rods connecting the plates. Cut in half and stood on end, the motor's armature would look exactly like the anchor bolt assembly you have described.

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• Aug 12, 2020

• #3

STrctPono

Structural

Jan 9, 2020

703

Unless this is something more advanced than I think, we specify anchor bolt assemblies that are bolted together at the bottom with a steel plate. We typically use these for overhead sign structure bridges on the freeway. The assembly looks something like this. Maybe yours is different.

 

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• Aug 12, 2020

• #4

SlideRuleEra

Structural

Jun 2, 2003

5,528

STrctPono - The photo is similar to armature anchor bolts, but not the same. All of the anchor bolts would need to have been anchored by one plate. In the photo, 3 individual plates are visible, each with a small group of anchor bolts.

We used many single-plate anchor bolts groups (armature) for equipment in generating stations. Allows for precision locating of the bolts (relative to each other) that equipment manufacturers require.

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• Aug 12, 2020

• #5

r13

Civil/Environmental

Oct 26, 2019

5,988

I guess the name "armature anchor" came from the idea of ship seabed anchor.

 

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• Aug 12, 2020

• #6

STrctPono

Structural

Jan 9, 2020

703

SlideRuleEra,

Thanks for clarifying that. For me, the "armature" or my "half-breed armature" serves two primary functions: 1.) Adds additional confidence for the design Engineer in the breakout capacity of the anchor group and 2.) Ensures proper bolt placement/alignment during installation. I also find that the top plywood template is just as important (if not more important) for getting proper bolt placement.

Either way, sounds like this Engineer merely came up with a fancy name for this bolt group, nothing more.

 

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• Aug 13, 2020

• #7

HTURKAK

Structural

Jul 22, 2017

2,903

Apparently this Engineer familiar with Russian language and called this bolt group ' armature ' and nothing more .

Just write ( арматура) and search , this term is used for (reinforcement, fixture, fitting..)

 

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• Aug 13, 2020

• #8

SlideRuleEra

Structural

Jun 2, 2003

5,528

I neglected to mention that the single-plate armature approach has two advantages:

1) Proper spacing of all anchor bolts in a group is initially established. (Which I did mention.)

2) Together with an above-surface template, the embedded bottom plate insures that all anchor bolts in the group remain parallel with each other during concrete placement. (Which I forgot to say.) Important when a thick sole plate for equipment has to be put in place over all anchor bolt simultaneously.

Goes unsaid (but required by specs) that the Contractor is responsible that the anchor bolt group remains plumb during placement, the group is properly located, and anchor bolt projection above concrete is correct.

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• Aug 13, 2020

• #9

phamENG

Structural

Feb 6, 2015

7,277

Potential downside to this arrangement is consolidation of concrete around the plate. Plate gets too big, and you increase your chances of voids at the anchors. Proper concrete mix and placing procedures and proper plate design will take care of that in most cases, especially on you heavy civil projects. A medium sized building where you have one really complex connection to the foundation - this is likely to confound many contractors...

 

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• Aug 13, 2020

• #10

SlideRuleEra

Structural

Jun 2, 2003

5,528

phamENG is exactly right. A hybrid approach instead of a single plate, like the combination of anchor bolt groups shown in STrctPono's photo, is a good compromise for many applications.

Precise and detailed location is so important that we would have three independent surveying teams set and verify all critical groupings, such as the for the turbine-generator. One team of surveyors from the construction Contractor. Two other teams working independently, from different companies, we (Owner) retained to confirm the Contractor's work. Still, some "problems" every now and then.

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• Aug 13, 2020

• #11

dauwerda

Structural

Sep 2, 2015

1,035

Here is a pretty typical anchor cage used for large monopoles in the utility industry. The bottom template is typically welded to the anchor rods as often as it is bolted. I have never heard it referred to as an armature - just anchor cage or anchor assembly.
The second definition for armature given in the dictionary is, "a metal framework on which a sculpture is molded with clay or similar material." I can see the connection but I would say it is an atypical word to find on a structural drawing.

 

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• Aug 13, 2020

• #12

KootK

Structural

Oct 16, 2001

18,112

Drifting in to the arcane technical, I've always wondered if the plates don't actually reduce the anchorage capacity. Obviously, relative to individual washers, you interrupt more of what used to be the assumed concrete tension stress interface and replace it with a plane of weakness. Constructability issues aside, and proper nut & washer design assumed, I'd rather not have the plates in the finished product.

 

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• Aug 13, 2020

• #13

KootK

Structural

Oct 16, 2001

18,112

@dauwerda: Great pic. What's the logic in the partial paint galvanizing of the bolts at the bottom?

 

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• Aug 13, 2020

1
• #14

dauwerda

Structural

Sep 2, 2015

1,035

That is actually the top of the cage that is galvanized. Typically only the portion of the anchor that is ultimately exposed to the weather needs to be galvanized (usually spec'd as the projection + 12" or something similar). Obviously , the top template is removed after installation so it does not need to be galvanized. As I mentioned, often the bottom template is welded to the anchors so using fully galvanized anchors makes that weld a bit more of an issue (grinding away galvanizing, etc.). Sometimes you will see spec's that call for fully galvanized cages but this is typically only when they anticipate the cages not being installed right away, these are also typically threaded and nutted at the bottom to hold the lower template rather than being welded.

 

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