Anchor Bolt Design 8

[dbags]

Can anyone help me find a good reference(s)/example(s) regarding the design of anchor bolts for a sign support? The base plate is circular, the column is circular and the anchor bolts are in a circular pattern. I have many references with square/rectangular base plates and bolt patterns. Also, a good reference for anchor bolt embedment would be appreciated. The references I currently use are as follows:
AISC: Column Base Plates
Blodgett: Design of Welded Structures
PCI: PCI Design Handbook

 

[Lutfi]

Anchor bolt length can simply be calculated based on the bonding between concrete the AB surface area. I have an old copy from an article that was published in Plan Engineering Magazine and will post a URL if appropriate.

Good Luck

 

[diamondjim]

A circular pattern that is divisable by
4 is just a special case of the rectangular
method. If there were 8 or 12 bolts, use
2 times and 3 times your 4 bolt result for
the 4 bolt rectangular or square result.
You would have to calculate the lengths
based on the base circle diameter to determing
your square or rectangle.

 

[MikeDB]

I don't think that the previous post is correct, as the bolts closest to the nuetral axis don't carry as much load. The problem addressed is quite common in the transmission line and communication tower business. Most suppliers/fabricators have their own methods, but most use the moment area principals to determing the moment of inerta for the bolt pattern about the neutral axis
(I' = I + Ad^2).

I think ACI 318 Appendix D might be a good reference.

I seem to recall a bond strength for determining embedment depth in the pre 1971 ACI 318, but have not seen it for years and don't recall the formula. Not sure that it would even be a recognized method today.

 

[cwdancer]

the bolt or bolts only need to be as strong as the steel it is attached too.

 

[aybee]

Pressure vessel design Handbook will show you how this is calculated

 

[e4e5qf3]

I need some help finding correct anchor sizing information for seismic zone 4. I'll be installating some mechanical equipment.
I've found some calcs in ASHREA and the CBC (California Building Code) but its difficult to get a handle on where to start. There seems to be some conflicting information.


thanks
jay

 

[jheidt2543]

See ACI 318-02 Code, Appendix D for anchor bolt design and put your thinking cap on, because it is not a spectator sport!

 

[kahlilj]

i need to know how to determine the correct length for anchor bolts that will be used to hold down a tank. Lutfi, can you post the URL that you referred to? and/or if anyone knows the formula which can be used to determine bolts lengths please share.

 

[unclesyd]

Look at this website:

http://www.engineering-software.com/me/

 

[structuresguy]

ACI 318 (1999 & newer)and IBC2000 both have sections on anchorage to concrete from which you can calculate the required anchor rod embedment depth.

I assume you have a moment type conenction, so that the rods are not equally loaded. In this case, figure out your worst case rod, and design for that embedment depth for all rods. Now if you have overlapping failure cones, you will have to reduce the capacity based on the reduction in projected surface area. So you might have to iterate a few times to get the correct answer. If you need to prestress the rods or have a significant ductility requirement, make sure you have enough rod length unbonded to provide for the required ductility. This may mean either extra long embedment depth, or connecting the rods to the columns some distance above the base plate.

For analyzing the stress at each rod, assume a neutral axis thru the middle of your round column, preferrably thru two of the rods. Now, assume a linear strain distribution. Using this, you can calculate the strain at each rod in tension based on its distance to the neutral axis. Once you have the strain, you can figure out the stress, and rod area required. This would be similar to a deep concrete beam with multiple layers of reinforcing steel. I actually had to do this analysis during a concrete exam back in university for a round beam with bars spaced around the perimeter. Kinda took us all by surprise, but the same method holds as for rectangular beams.

 

[curvbridger]

Sign structures subject to gusting winds (especially from traffic loading) have experienced fairly frequent fatigue failures. For best installation practice refer to Michigan DOT website at

http://www.mdot.state.mi.us/specbook/

Refer to Section 810.03N

In my opinion, supporting sign bases on nuts and anchor bolts is preferable to counting on grout under the base plate, which is often of questionable quality.

 

[haynewp]

I thought I saw in the LRFD connections manual that you should not use the anchor bolt (if smooth) for bond development. The anchor uplift resistance should either be calculated by using the hook or head at the end of the bolt only.

 

[CSEllc]

I didn't notice anyone mention AISC Design Guide #1, Column Base Plates. The guide was written by John DeWolf, of the Univ. of Connecticut and Dave Ricker, retired Vice Pres of Berlin Steel.

The guide not only covers base plate design but also anchor bolt design. The guide has examples problems in both ASD and LFRD.

If you have a copy of the guide, check the AISC website since there is an errata sheet.

 

[locksman]

Does AISC Design Guide #1 address circular base plates? I have the same situation as dbags. I have design of welded structures by Blodgett but still wondering on how to deal with a circular pattern. How can I obtain this design guide and how much will it cost?

 

[MikeDB]

locksman,
The AISC Design Guide is available from aisc.org for $60, but it is about 15 years old and does not address the new OSHA requirements or round base plates or circular bolt patterns. ASCE has a design "standard" for steel transmission poles in committee that will have a good example in it, but I don't know if it is in the present design "guide". It will be some time before the standard goes to press.

 

[locksman]

I have been able to determine my stress per bolt on the bolts for a HML but I am using A36 rods (not A325 or A449). On page 6-83 in LRFD second edition it references Table J3.2 which does not include A36 bolts. My Fy=55 ksi and Fu=81.5 ksi as provided by the manufacturer. Can I still use these specs given in Section J3 part 6 for checking my tension and shear?

I was using from ASD:
Ft=0.5Fu
Fv=0.3Fu

But this is for Allowable Shear rupture. Can anyone clarify this for me. I don't think I am to use LRFD J5-2 Design strength of Connecting elements in Tension since this is not that type of connection (e.g. plate, gusset)

 

[MatthewKelly]

I am looking for a good example of a anchor bolt design for some large process equipment and motors (up to 1000kw)

Would "Lufti" post a copy from an article that was published in Plan Engineering Magazine and will post a URL if appropriate.

 

[Hookem]

As a conservative rule of thumb, use 17 x nominal diameter for minimum embedment and 7 x nominal diameter for centerline to edge distance. One can spend a lot of time and effort to calculate to the nth degree, but time is money. This will cover most installations.

 

[MikeDB]

Hookem,
The danger of "rule of thumbs" is that everyones thumb is a different size. I have seen 20 and 25 x nominal diameter for minimum embedment. ASCE's steel pole committee is discussing wether it should be 25 or 30 times nominal bolt diameter. By comparison, the 17 seems to be unconservative. For low strength bolts on large spacings, it may work, but not for high strength bolts on small spacings. Lots of variables at play -- bolt strength, bolt spacing, bolt edge distance, concrete strength, and transverse reinforcement.