Anchor Bolts

[jcrickey]

I have designed a 65 ton bearing press and now must attach it to a foundation. As a mechanical my knowledge of concrete is limited. I have searched some literature an have some formulas, but I do not know if these are the best for my situation. The load is in the horizontal direction this causes a tension force about 25ksi in one of my anchor bolts (FEA model). The formula I used for a j-bolt suggested 27.77" for a factor of safety of 3 with 3000psi concrete. I dont have this kind of depth available. Any suggestions on formulas or anchor types other than j-bolts? I would like to keep the foundation to 24" is this reasonable.

 

[UcfSE]

What kind of forces are these anchor bolts exposed to? For tension I would not recommend J-bolts. They have a tendency to straighten out at the hook and pull out of the concrete. Typically I use F1554 anchor rods, grade 36 (36ksi yield). You can get these rods in grades 55 and 105 also. At the embedded end we put a washer and one or two nuts tack welded to the rod to form a "head". As far as the breakout strength of the concrete, you might be able to get away with a small depth, but you only have so much concrete to work with. You either have to increase the size of the pullout "cone" - by using more bolts over a wider area or by increasing embedment - or you have to increase the concrete strength itself, or both.

Depending also on your application and need, a manufactured anchor, such as an epoxy-grouted anchor, may work also. Check out Hilti, Ramset, and Powers for their epoxy anchors. If your loads are dynamic or under a great deal of vibration, these may or may not be suitable for you.

 

[jcrickey]

Is there a formula used in determining the strength of the pull out "cone"? Also once this is determined is there a specification on minimum bolt spacing. My current design has bolts as close as 5", this was done to lower the stress in one of the anchors from 38ksi to 21ksi. I can have a depth of 24"-36" if needed. My knowledge of concrete strength is limited to the values in the back of my strength of materials handbook (1ksi-10ksi).

 

[archeng59]

I've used AISC Design Guide 1, the chapter on Design of Anchor Bolts in Tension, in the past with straight anchors as described by UcfSE. ACI 318 Appendix D may be applicable.

 

[jcrickey]

Our library is limited to the AISC Manual of Steel Construction, as all 18 of us ae Mechanical Design Engineers (rail car construction). The AISC Manual refers to ACI 318 in the 1 paragraph section on anchor rods and bolts. I have no access to the ACI literature so any help locating the formulas else where would help.

 

[UcfSE]

You may have to get your boss to buy you guys the ACI 318-02 or 05 reference. Hilti has some brief explanation of the new method referenced by the ACI 318 appendix D in their catalog section 4.3.1 as it pertains to their specific bolts, but it is not complete enough for you to really use without the source reference. It's just enough information to get you in trouble. If you have an IBC 2000 you'll find the method in section 1913. To help with your search, the method is also referred to as the "Concrete Capacity Design Method" or CCD method, I believe.

If you cannot get access to design equations, a manufacturer may be your only route, without hiring someone else to design your connections.

 

[jimzpe]

this same post in the Structural Engineering Other Topics section gives some "other", potentially major information on this topic.

 

[MikeDB]

A rule of thumb that I have used for years is an embedment depth of 25 bolt diameters with a minimum of 6" edge distance with the anchor bolt pattern located within horizontal reinforcing hoops.

Appendix D of ACI 318 provides more specific guidelines for various anchor bolt/ base plate configurations.

The use of J bolts is not recommended for high strength bolts and many do not use them at all any more.