Bolts anchored in concrete 2

[lancealot72]

OK, i am not sure how to approach this problem. I dont have all of the details yet:

I have four 10" bolts anchored in concrete about 8" deep in a 5" square pattern. I will have a 1/2" steel plate with a 15 ft 4 1/2" sch. 40 pole welded to the center of the steel plate. Some minor equipment will be installed on top of this pole.

I am assuming that the bond from the concrete to the steel bolts is the weak link and if enought force is applied that it will rip the bolt from the concrete. I want to find out that max force. Some tip on what calculations to use and how to go about this would be appreciated.

thank you!

 

[lancealot72]

Edit: the bolts are set in the concrete 8" with the threads sticking out 2".

 

[IRstuff]

Have you read the discussions on this site about the concrete bolts used on the Big Dig? There seems to be no guarantee about holding strength.

TTFN

 

[dik]

I would understand that these are regular A307 bolts embedded in concrete by 8"... can you give me a hint about the diameter of the bolt? The AISC has an excellent paper on the design of headed anchor bolts/rods...

Dik

 

[IRstuff]

What exactly are you using the bolts to do? It looks like your set up is on the ground. Are you expecting something to try and pull the assembly out?

TTFN

 

[arto]

ACI 318 "Building Code Requirements for Structural Concrete " App. D has info on calculating bolts in concrete. i.e., Calculating the "Breakout Cone" strength for a given embedment depth of bolt.

 

[lancealot72]

The bolts are 1/2" A307.
The concrete is bascially a big weight to keep the pipe and the equipment mounted from tipping over for any reason. the 4 bolts are set in concrete and a 1/2" steel plate is attached to the bolts and then tightened down with some washers on each side and then the nut.

the steel plate has a 4 1/2" diameter sch 40 steel pole that is 15 ft. long welded to the plate. I just need to make sure, in the event of high winds or if it gets backed into, etc.., that it will not either snap the bolts or rip the bolts out of the concrete, or what kind of force to expect for the bolts or concrete to fail.

dik: 1/2" bolt I will check out the AISc, if you have a quick link, i would be grateful.

Arto: if you can giveme reference to the "breakout cone" strength, i would appreciate it!

IRstuff: Bolts will hold down the plate that has the pole and equiment attached. have not read the discussion on the big dig

basically, how will I verify that this will not tumble in high winds or generate a rough figure of how much lateral force it will take to fail the bolts or the concrete.

I hope this is clear enough for you guys, sorry if it is not!

thanks in advance for all your time!!

 

[dimjim]

I thought 3/4 diameter was the min diameter
used on monopoles. Monopole design url.

http://www.risatech.com/

http://www3/c-conceptsinc/files/Technical_Manual_1.pdf

 

[UcfSE]

To verify your bolts, you would need the wind pressures acting on the pole, and any dynamic concerns. The wind pressures may depend ont he flexibility of the pole to some extent. Afterwards, you would need to check the pole for design forces and then the base plate size and thickness and connection. From there you can resolve the pole and base forces in to forces acting on each bolt. If you have access to the building code you're under you may be able to find allowable forces on bolts directly from the code, job done. Otherwise you will have to either calculate the bolt capacities or use a manufactured product with known, tested strengths. I recommend you do not use hooked bolts (J or L) but instead use a headed bolt or a threaded rod with a nut and washer at the end to create a head.

I'm sure we can try to help you all day long by pointing you in the right direction but we can't actually do the work or run the numbers for you.

 

[dik]

The publications for both Base Plate Design and Headed Anchor Bolts are available free to AISC members. It's matter of searching free publications. I think the AISC link is

http://www.aisc.org.

Take a gander at my user profile for my interests.

Dik

 

[paaz]

lancealot72, the way you can verify if the bolts are going to support your structure is somehow simple. You will need to get the base reactions of the structure you are planning to use, moment and axial loads will do. Once you have this, you need to find out your bolt tension and make sure does not exceed the allowable tension of the bolts.

I am currently trying to develope a spread sheet to help me with the design of base plate connections for communication monopoles and this is how I normally check the bolts that we are planning to use

 

[chicopee]

Here is one case that I worked out for you with the assumption that the base plate is not in contact with the concrete pad but supported by bolts under the plate.

With a 100 mph wind, wind pressure is 25.6 lb/ sq.ft..

Wind and gust(30% extra) creates a 33.28 lb/sq.ft.

Projected surface area of pole is 15'* 4.5/12= .277 sq.ft.

Total wind load 33.28 * .277= 9.24 lbs.

Moment on base of pole is 9.24*15/2=69.33 ft-lb

Now here is the clincher: since there is no contact between base plate and concrete pad from my original premise, load from the moment is taken by your bolts. One set of bolts will be in compression and the other set in tension.

The set in tension will be designated as 2T and must resist the moment at a leverage arm of 5". the value of T
is equal to 69.33 * 2 * 5= 83.2 lbs for one of the bolts.

It become obvious that the 1/2" plate and 3/4" bolts are oversized by now but will stay with what you got.

For length of embedment of bolts in tension and compression should not be less than 12". From concrete formulae the bolts in tension have this for Ld= (.04or.04)*Dd*Fy/(F'c)^.5. .04 or .05 is bases on size of bolts or rod, Dd is dia. of bolt or rod, Fy is tensile strength of steel, and F'c is compressive strength of concrete.

Since base plate and bolts or threaded rods are well oversized, stay at a 12" of embedment but with bolts or rods make sure that you have a nut or J hook at the ends embedded in the concrete.

 

[dimjim]

thanks to chicopee sharing his approach.
I would be always concerned about some
minor equipment at the top of the pole
as to its effect on the calculation.
Note that the bolts are 1/2 inch diameter
and the plate is also 1/2 inch thick and
not 3/4 diameter bolts. If 3/4 inch bolt,
then the recommended plate thickness should
also be 3/4 inch. What is the effect of
the moment at the concerete base? Looks
like the base plate and bolts are ok.
Isn't more information required as to the
concrete below the base plate?

 

[chicopee]

what is the size of the minor equipment on the pole? How thick is the concrete base if you do not use a footing and is this base or footing subject to frost heaving?

 

[swearingen]

chicopee, 9.24 lbs looked small to me and after checking the math, I think it's more like 187.2lbs equating to 1.4'k moment at the base.

UcfSE has the correct procedure and his recommendation of going with a headed rod or nut embedded in the concrete is the current best practice.

 

[WoodyPE]

I'm a project engineer that anchored two 35 foot tall, four hundred ton draw presses to a reinforced concrete floor. First we made a foot by positioning some 6 inch diameter spiral culvert (about 1 foot long)welded in place to structural rebar. Then we poured the concrete around the rebar and the spiral culvert. Next we positioned the anchor bolts inside the culvert and poured it with structural epoxy.

These draw presses put one humonogous stress load on the floor when they are running. No problems with the anchors though.

If that doesn't work nothing will work.

 

[dimjim]

As to:
I just need to make sure, in the event of high winds or if it gets backed into, etc.., that it will not either snap the bolts or rip the bolts out of the concrete, or what kind of force to expect for the bolts or concrete to fail.

Not certain about the concrete approach as not enough information is given about it.

The bolt formula S = F/A seems appropriate.
A = area = .1419 x 4 bolts = .5636 sq.inches.
This is assuming simple shear at the base of
concrete for the bolts and no moment load.
Nothing is that simple. By rearranging the
above equation, you can get the F (force) required.
S = Stress.

 

[WoodyPE]

Is this like a road sign you are putting up? If so, there should be plenty of information available from civil engineering highway design.

Also, you have the same kind of figuring to do on things like water tanks. You figure the form drag on the object under maximum wind speed assumptions. A flat road sign has plenty of drag.

The taller it is the more bending moment you have. A 4-1/2" square tube that's really long gets rather flimsy. I'd go out and measure a road sign in the range you are thinking about. It should give you a good start.

How large is the "sign" in square feet?

http://www.angelfire.com/planet/gadgetforum/index.html

 

[WoodyPE]

PS, I feel this is probably standard civil engineering design. The farther apart the anchor bolts are spread, and the larger the plate, the more mechanical advantage you will have. I'd use some triangular gusset plates where the pole mounts to the anchor plate, in order to minimize stress concentration. The larger the bolt pattern, the smaller the bolts.

http://www.angelfire.com/planet/gadgetforum/index.html

 

[Scorch]

If you plan on doing a lot of this type of designing I would highly recommend picking up either one of these books.

1. SIGN STRUCTURES AND FOUNDATIONS: A Guide for Estimators and Designers

2. ENGINEERING SIGN STRUCTURES: An Introduction to Analysis and Design

Each of these books have all the info you will need to calculate the concrete strength and bolts/base plates etc...

Both of these books can be found on

http://www.signweb.com

or

http://www.amazon.com

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