Anchor Rod with Forged Steel Pin Eye 1

[Szubert80]

Hi,

I need to check allowable tensile/compression load for the Ø2.5" anchor rod with a pin eye made of forged steel (ASTM A235 class C) as shown in the attached file.

The pin eye has been cut off of the original forged steel anchor and welded to 350W round bar shaft. It was tapped to accommodate Ø3/4 threaded rod which joins both parts together and acts as a backing for a groove weld all around.

The ASTM A235 has been superseded by A668 which indicates the equivalent steel grade to be A668 class B.

I`m trying to find out if this steel forging is weldable and can be welded to 350W steel.

The other question I have is whether Ø3/4 threaded rod tensile strength can be combine together with the groove weld to determine the overall capacity of this assembly.

I`m thinking that some of the strength from Ø3/4 threaded rod should be accounted for as it will provide additional resistance to the welded part of the joint.

Please let me know your thoughts.

 

[dhengr]

Szubert80:
Is this a done deal which you are trying to check and justify, or are you designing it, so you can still make some changes? I don’t know the exact grades of the steels, so welding them properly would take some further digging and study. But, there are a couple things about your detail which I do not like. I would make the .75” threaded stud as small as possible to still accomplish its holding capacity during the start of welding and as a backup rod. Then, I would like to be able to ignore it in the total tensile strength calc., except that you still have the tapped or cut threads which cross a tensile stress field, which I don’t like from the stress standpoint. You might be as well off with a slight press fit dowel, only .25” - .5” o.d., so you could start to assume a full pen. girth weld. But then, you still have discontinuities at each end of the dowel hole, and essentially the same tensile load/stress. You don’t have a solid rod any longer, you have a pipe with a 2.5” o.d. and a .75”+ i.d. Secondly, you generally do not want to try to combine bolted or threaded fixings with welded fixings, because the welding is so stiff w.r.t. the threaded parts, that the threaded parts don’t come into play until the weld has yielded significantly or failed, thus allowing enough joint movement for the bolts to come into play. They just do not combine additively for a total cap’y. I think I’d cut a 3/16th or ¼” land on the rod, maybe a ‘J’ groove, and make it a full pen. weld.

What are the four tits on the eye forging intended to do? What are their shapes, in more detail and other orientations, particularly the end view to be welded? Show all the dimensions of the eye forging, before it is cut off, from whatever extends to the right, in your sketch. This weld joint is right at one of the max. force/stress locations on the piece, and I’m having some trouble seeing how you are going to make a nice clean weld transition out onto the eye, from the new rod. These look like potential stress raisers to me. The forging process is generally a good way to make an eye like that, it aligns the grain structure in the steel making up the eye in a favorable orientation for strength and toughness.

 

[gtaw]

I agree with dhengr. A235 is rolled plate, not a forging, so the mechanical properties are unlikely to match A235 Grade C.

The threaded rod isn't permitted to share the load per AWS D1.1, so you've reduced the allowable stress to that permitted for a partial joint penetration groove weld. You've also reduced the cross section by the OD of the threaded rod.

I concur that a CJP groove weld consisting of a double bevel groove is the best bet. Weld one side half way, back gouge the second side to sound metal, weld the second side half way, complete the first side and then the second side. Use low hydrogen electrode.

Modifying anchor rods are always dicey because the access is usually limited. If the concrete isn't cut back far enough, it is difficult to provide proper access and the mass of concrete can contribute to rapid cooling. Preheat is needed.

Best regards - Al

 

[Szubert80]

@dhengr - thank you for your thorough response.
Unfortunately, this anchor rod has been modified as per sketch attached. I got the drawings afterwards to verify the as-built allowable strength so I have no chance to suggest a better solution for that weld detail.
I totally agree with the impact of the threaded rod on the tensile stress field at the joint.
In that case I`m going to ignore any contribution from the threaded rod itself and check the allowable strength based on the weld fusion face area.

What are their shapes, in more detail and other orientations, particularly the end view to be welded? Show all the dimensions of the eye forging, before it is cut off, from whatever extends to the right, in your sketch. This weld joint is right at one of the max. force/stress locations on the piece, and I’m having some trouble seeing how you are going to make a nice clean weld transition out onto the eye, from the new rod.

I don`t have any other section views of this new assembly but I have attached the drawing of the original anchor rod with eye. Please note that the head was cut off the original forged steel anchor and welded to a new 350W round bar.
The effective throat of the weld based on the bevel angle should be appox. 5/8"

@gtaw - I agree with the CJP weld made as you have described would be the most effective way to utilize the strength of the material.

A235 is rolled plate, not a forging, so the mechanical properties are unlikely to match A235 Grade C.

A235 Class C is annealed, normalized, or normalized and tempered, mild steel forgings.
It was superseded with A668 class B. Please correct me if I`m wrong.
[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1595364840/tips/Steel_Specification_x0jq0n.pdf[/url]
Thank you again for your insights.

 

[dhengr]

Szubert80:
Is the thickness of the eye forging 1.75”, I can’t read that dim. The tits that I’m talking about don’t seem to be there on the original drawing. So, the weld should have been be built-up and then ground down and fared smoothly into the eye shape. What inspection and testing was done on the completed weld? Do you have a good handle on the mech. properties of the two pieces, the eye forging and new 2.5” rod, and on the weld metal used, and the weld procedure/process used? What is the size of the pin and its mech. props. which fits in the 2.5” dia. hole in the pin eye. What is this anchor used for, what kind of cyclic loading, what load and stress ranges are you seeing. All of these things should be addressed in your calcs. and report, and they influence the FoS which you should put on your final cap’y. It seems to me that this is much more of a Theory of Elasticity/Strength of Materials problem than something you should try to pluck specific clauses/paras. and formulas from the AISC manuals or codes (or the like in Canada) for a solution and explanation of your thinking. In fact, maybe the best ref. std. is probably ASME BTH-1, Design of Below-the-Hook Lifting Devices. It has a number of different failure mechanisms for a pin pl. which you should look into. A number of good ToE and SoM textbooks have sections on rings, chains, hooks, eye bolts, and the like, and Hertz stresses.

I think I would deduct a little more than a .75” dia. out of the center of the rod and eye piece, because of the stress amplification effect of these features, and still include some stress amplification in your calcs.. And, I would comment in fairly strong terms about the potential stress raiser effect of the threads and the drilled tap hole end as they relate to the tensile stress field which must bend around them at the transition from a solid eye or rod and then around these stress raisers to the annular/pipe shape. At the eye transition area this situation is probably slightly less critical because the flow of the tensile force/stress is away from the annulus shape and out into the two legs of the eye.

The fit btwn. the pin and the pin hole comes into play when you look at the Hertz bearing stress problem which occurs at 12 oc (o’clock) on the pin hole. For this discussion assume the welded joint is at 6 oc on the pin pl. and pin hole. A fairly snug fit btwn. the pin and the hole improves the bearing stress and a looser fit (Dhole vs. Dpin) causes higher bearing stresses and larger deformations at 12 oc. Can you see any deformations in this area from the earlier use? You also have tensile and bending stress in the ring/eye at 12 oc, and you have several different modes of shear failure in that same area. You have the nominal tensile stresses at 3 & 9 oc, plus a bending stress component which are additive. This is not a simple P/A problem if you are going to do it right. This would be a good problem to do a FEA study on, using a fairly fine 3D solid prismatic element mesh on.