Lifting eye anchor pull-test

[Temporaryworks]

Hi,

I would like some advice about the calculation of a suitable kN value to specify for pull-testing of post-fixed lifting eyes. Some context:

- I am British temporary works engineer who has recently started practicing in Australia
- A 0.5t reinforced concrete Mural is to be lifted by an excavator standing on concrete and then placed on to a pallet for transportation elsewhere by a forklift.
- It will be lifted using 2no post-fixed resin anchors a 2-leg chain using a 20t excavator.
- There will obviously be shear and tension in the anchor during the lift against which I have designed the anchors for and have factored up the load by 1.65 for dynamic effects of using an excavator.
- The client have a calibrated pull-test kit (the type scaffolders use). As it will only test tension and not shear, I have had to specify a pull-test value that will be suitable to confirm the integrity of the installation.

I have settled on the unfactored axial chain load * 1.65 dynamic factor * 1.25 test load and specified this as a pull-test load. Is this an appropriate way to calculate the test load and what do you usually do?

Additionally, I have designed the anchor for a second load case which is the tensile test load as described above to ensure that the integrity of the anchor installation will not be damaged during the test.

I put this into the demo section as it is a demolition contractor doing the work and they are not likely to apply finesse to the installation and lift procedure. Therefore I wanted some demolition engineers take on this situation.

Thanks in advance.

 

[Lomarandil]

I'm not familiar with your pull test kit, but can't you pull at an angle (same as your excavator will) to check anchor tension & shear?

I think your 1.65 load factor is appropriate. Demo operators may be used to ripping through jobs quickly, but they're also often very skilled when needed. If needed (and possible), observe the operation and chat with the operator beforehand about how nice the mural is.



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The name is a long story -- just call me Lo.

 

[dhengr]

Temporaryworks:
Many lifting eyes are only rated for a straight pull and very little shear (zero shear). A footnote will say something like only 5̊ max. off the axis of the bolt, or some such, for a sling angle. Some have a larger cast shoulder under the eye, in contact with object being lifted, which allows some angle to the lifting slings. But, this causes tension, shear, bending and prying in the bolt, all of which must be accounted for. You may also have the situation where the conc. failure wedge/cone around the anchor bolt (lifting eye bolt) will be the failure mechanism, and you should check that. This will be particularly true if the conc. panel is very thin where the lifting eyes are applied. You might be better off to install the two lifting eyes, x feet apart, and then use a spreader beam of the same length above the lifting eyes, and then whatever slings or chains up to the hook or bucket.

I agree with Lomarandil, many equipment operators pride themselves on being able to finesse things when they have to. So, some discussion with them is in order for this job. They can do it with a backhoe. You haven’t been very explanatory about what this conc. mural panel really is, width, height, thickness, C.G. (much relief?), any weak lines/planes in the panel, etc. .5t (1100-1200 lbs.) isn’t really heavy. You might be better off to excavate at the four corners of the mural, so you can insert four 90̊ angle iron corner support weldments, like partial/short corners of a picture frame, 18" long on a side and grouted to fit your excavated corner on the mural. Then weld/bolt these corners together with some longer lifting frame pieces and lift off of this whole lifting frame. Of course, you have to grab the back of the mural too, to hold it in the lifting frame. This frame might also protect things during the forklift transit.

 

[Temporaryworks]

Lomarandil, the test kit they would typically bring to site would this -

http://www.hydrajaws.co.uk/Products/Model-2000.

It does not have a function to pull parallel to the chain. That would be ideal though. This type of kit is typical for testing of these sorts of anchors.

dhengr, the lifting eye I have specified is rated for loads at any angle. I have design the post-fixed resin studding anchor that receives the eye properly, taking in to account combined shear and tensile effects, edge distance etc. and all to AS3600 and the manufacturers tech literature. So no worries there either.

I am not sure about finesse, I think it is best to assume they will be less than gentle,hence the 1.65 dynamic factor before even applying the ULS factor for anchor design and 1.25 multiplier for test load. I agree with both of you though that if you know the driver and can talk the lift through with them then this can increase confidence, but I don't have any contact with the drivers or Foreman unfortunately.

The item to be lifted is a 2.1x1x0.1m thick reinforced concrete wall with a mural painted on the face of it. The wall is tied in to a building from which it will be saw-cut and separated before lifting. I have specified a sequence to ensure stability during this process. The mural is not of great value or particularly expensive, but the client wants to retain it before the building is demolished. Think of the mural as a fin wall sticking out the side of the building.

What are your views on my calculation of pull-test value? In a perfect world we would test parallel to the chains but this is not practical on this site. Shear testing of anchors is not simple either. Therefore I am stuck with specifying a pull-test value, how would you calculate this value? Or do you think it is pointless undertaking this test?

Thanks both of you for taking the time to answer.

 

[Temporaryworks]

dhengr, I like the idea for the steel frame, that will come in handy for another lift I have on my to-do list.

 

[Lomarandil]

Can you provide a sketch of the orientation of the anchors, lugs and murals? I think I understand your arrangement, but want to be sure.

If it is what I think it is.... I'm really not sure that the pull test does much for you. You can determine whether the resin bond is good or not, but that's the least likely of your failure mechanisms, in my opinion.

I don't suppose a jig to allow the tester to pull at an angle would be a possibility? (You wouldn't be able to pull directly on the anchor, of course... would have to figure out how to link the tester to an eyebolt connected to the lifting lug or something).

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The name is a long story -- just call me Lo.

 

[Temporaryworks]

Lo,

Apologies for the delay in my response. I have attached a sketch to this response illustrating the lifting set-up.

Yes it was my thought that the test will only be of value if the resin anchor installation was poor and the test picks this up. It will not directly test the capability of the concrete to withstand the loads that will be imposed upon lifting. Perhaps this is enough; if the anchor is designed correctly and the pull-test identifies that the installation is decent and that the lifting eye is OK then this may be sufficient.

I like the idea of a jig but the reality is that my clients would not go for it unless it was a special circumstance. Perhaps if you had many to test and the risk was high it would be worth fabricating such a jig.

This Qn/lift may seem trivial but I design anchors for heavier and riskier lifts and wanted to be able to apply a sensible approach going forward.

Attachement:

http://files.engineering.com/getfil...a7b9-128025c70922&file=Lift_sketch_for_Lo.jpg

 

[Lomarandil]

OK, that's what I figured.

I honestly wouldn't bother with the pull test (or do it for show to ease any nerves the owner has). A successful pull test may correlate to a successful anchor installation, but it doesn't prove it.

In this case, I think a jig would really only be a few timber blocks cut at the appropriate angle (maybe a strap to the opposite side of the mural). But, as you said, that doesn't help much when we think about bigger lifts.

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The name is a long story -- just call me Lo.

 

[Temporaryworks]

Lo,

Just a final Qn - in what situations would you specify a pull-test for new anchors as a must?

 

[Lomarandil]

Off the top of my head:
Whenever the suspended load has to pass over sensitive areas (utilities, environmentally protected, etc).
Whenever the suspended load is itself of considerable value (monetary or schedule).
In response to a history of anchor failure (by contractor or on that project).
Perhaps in response to reports of poor installation practices or environmental conditions.

Depending on contractor experience and how many anchors we're talking about, I wouldn't necessarily require tests on every anchor for all of these triggers. In some cases, I could be content with testing some random subset.

----
The name is a long story -- just call me Lo.

 

[Ingenuity]

...I will add a few somewhat relevant anecdotes:

I have installed thousands of resin anchors (threaded rods, rebar, etc) over the last 30 years, and field load tested many of those installed (hydraulic load testing, sometimes to destruction). Adhesive anchor installation is tough to do correctly - and unfortunately a task typically given to the least experienced, construction laborer.

Back a few months ago I did the ACI Adhesive Anchors Installer certification course [Link]. There were 11 candidates and only 5 passed the full course. It is a one-and-a-half day course - classroom theory, demonstrations, practice sessions, followed by a written exam and performance exams of vertical down anchors, and overhead. Most of those who did not pass, failed the overhead anchor installation 'simulation'.

I asked our examiner if the failure rate of our course was similar to other areas in the US - typically 50% pass/fail rate across most jurisdictions. That is a high failure rate.

With regards to load testing: Although field load testing of anchors is not especially common, when it is specified/required it is usually a simple tension load test of the adhesive anchors for 'bond' failure, however, we have occasionally undertaken testing to also check concrete pull-out using a stiff steel cross-frame that 'bridges' the probable failure/rupture surface with a center-hole hydraulic ram - such a test is checking bond (adhesive-to-steel, and adhesive-to-concrete, steel tensile failure and concrete pull-out.

On a project we did about 20 years ago was tensile load testing to #8 overhead rebar dowels - we installed the 50 ton ram, hydraulic hoses and the wedge grips - turnaround and the whole test setup (including #8 rebar) fell to the ground - it was an international air port terminal, and following that very unsuccessful test, a minimum of 10% of all remaining anchors were load tested, with a proportionate increase in the frequency of testing based upon the number of failed tests.

 

[Temporaryworks]

Thanks Ingenuity