×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Anchor pull testing... am I crazy or is this wrong?

Anchor pull testing... am I crazy or is this wrong?

Anchor pull testing... am I crazy or is this wrong?

(OP)
I'm working on a project for which a client has:

1- asked me to design a structure supported with rock anchors in tension
2- asked me to define an anchor test load equal to the ULS load effect on the anchors
3- provided an anchor pull testing procedure for which the final load increment is 1.33 x ULS load effect

Am I crazy, or does that not de facto mean that my actual ULS design load (if I wish to pass the load test) should be 1.33 x ULS loads provided?

In other words, if designed for given ULS and tested to 1.33 ULS, isn't it bound to fail?

RE: Anchor pull testing... am I crazy or is this wrong?

Your structure should be designed for the appropriate loads, which will result in an ultimate level (ULS) reaction at the anchors.

The client then wants the anchors themselves to be sized for and tested to 1.33x the expected ULS reaction.

This is common in the realm of soil and rock anchors, especially in cases where not every anchor is tested (at least partially due to inherent variability in anchor performance since the substrate is not as well controlled as typical engineering materials, sometimes to aid the process of prestressing anchors when that is desired to prevent load reversals).

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

RE: Anchor pull testing... am I crazy or is this wrong?

Or is a case of designing for the uls load (not 1.33x) but eating into your capacity margin during a controlled test that doesn't present danger to the public?

What is the capacity reduction factor used in the anchor design?

RE: Anchor pull testing... am I crazy or is this wrong?

(OP)
Thanks Lo. We're actually testing every rock anchor, but the approach you laid out makes sense.
I'll confirm that the intent is to oversize the rock anchors themselves.

RE: Anchor pull testing... am I crazy or is this wrong?

Quote (steveh49)

What is the capacity reduction factor used in the anchor design?

Usually very large.

Here's an example from Hilti- granted this is a concrete anchor not a rock anchor- but I would expect the calculations to be similar with, further appropriate reductions due to variation in the base material.

https://www.hilti.com/medias/sys_master/documents/...

RE: Anchor pull testing... am I crazy or is this wrong?

I do think typical values have a larger reduction since they are not going to be tested. If you are testing everyone why do you need a FS of 5?

I think this is similar to visual graded timber has a larger reduction than machine stress rated.... same wood (ignoring knots and quality) but the testing reduces the standard deviation and allows a smaller reduction.

RE: Anchor pull testing... am I crazy or is this wrong?

(OP)
RE geotech SF, I'm not sure yet as we're in the preliminary stages. I haven't received instruction from the geotech as far as the design parameters.

I just spotted that odd looking client requirement, especially since all anchors require testing.

RE: Anchor pull testing... am I crazy or is this wrong?

To me, it never made sense to specify a maximum test load. I am always curious to see the failure or breaking load. That really gives you an idea of how much of a "fudge factor" you have. And its cool to break stuff.

RE: Anchor pull testing... am I crazy or is this wrong?

You don't really want to put a stressing crew at risk by failing an anchor in the field. Even with the proper safety precautions (never, ever, ever stand in line with the jack)-- it's still a lot of energy wanting to go somewhere, and several of the potential failure modes can be non-ductile.

In a lab, sure. But a lab environment won't give you much useful information on field performance.

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

RE: Anchor pull testing... am I crazy or is this wrong?

It has been way more than a decade since I designed, installed and tested rock anchors, so take this with a grain of salt.

There may be a misunderstanding with nomenclature between you and your client re the "1.33 x ULS".

PTI's Recommendation for Prestressed Rock and Soil Anchors has a bunch of info on design and testing. My experience was with the 2nd Edition - I think the latest is the 5th Edition. [Link]

It discusses Proof and Performance Testing, and for both test types the test loads increment to 1.33 x P, where P is the design load of the anchor (P = anticipated final max. effective load in the tendon, allowing for time-dependent losses).

The max test load will not exceed 80% of minimum UTS of strand/bar - you do not wish to yield or fracture the tendon.

Also, when you undertake Proof and Performance testing it is an UNconfined test, so it does NOT test the rock mass pull-out - only the rock/grout interface, the grout/tendon interface and the tendon section.

RE: Anchor pull testing... am I crazy or is this wrong?

I am with Ingenuity on this one, i dont know the US codes but I always understood testing of anchors, piles etc to be your design load x (some factor). You are correct in saying that you should not be testing past your ULS load.

An example from our pile test spec below which is in essence the design load times 1.5.

For static pile load tests, test piles shall be loaded to the DVL (Design Verification Load) + 50% using the extended proof load test procedure in SHW Clause 1609.34 (where DVL in this case is qual to the SWL (Specified Working Load) as shown in Table 7.

RE: Anchor pull testing... am I crazy or is this wrong?

Correct, you should not try to (and theoretically would not be able to!) test past the UTS (Ultimate Tensile Strength) of the anchor.

I think MotorCity accidentally put us on a tangent.

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

RE: Anchor pull testing... am I crazy or is this wrong?

Ground anchors are usually tested to no more than 1.33 x the UNFACTORED SERVICE LOAD of the anchor. You can't test an anchor beyond its ultimate structural or geotechnical capacity. The maximum anchor test load should be no more than 80% of the guaranteed ultimate strength (GUTS) of the high strength tendon (GR150 for threaded bars or GR270 for strands) or not more that 80% of the yield strength of a GR 60, 75, or 80 threaded bar. GUTS and yield strength are not the same or equal. Per PTI, the maximum allowable working load of a tendon is 60% of the GUTS or yield strength depending on steel grade. DOT's and railroads will lower the allowable work load percentage because, apparently, their projects are "much more important" than private projects. Strangely, DOT's usually want the anchored walls designed using LRFD which gives factored anchor design loads. However, the anchor testing is usually specified to be to 120% or 133% of the unfactored anchor load. Therefore, you need to design the anchored wall twice - once using LRFD, once again using ASD to get the unfactored anchor DL for testing and any required wall deflections. IMHO, LRFD for anchored walls is just busy work!

Added comment: Every ground anchor, soil or rock, should be tested. The days of testing only a few anchors to a much higher percentage of the DL ended back in the early 1970's.

www.PeirceEngineering.com

RE: Anchor pull testing... am I crazy or is this wrong?

(OP)
Ingenuity, PEinc, I completely agree which is why I felt this was funny.

If anything, the test load should be 1.33 x SLS, not ULS loads.

RE: Anchor pull testing... am I crazy or is this wrong?

atrizzy, for the record, please define SLS and ULS. I don't want to assume what you mean. I've been designing and installing ground anchors since 1975 and have never seen SLS or ULS.

www.PeirceEngineering.com

RE: Anchor pull testing... am I crazy or is this wrong?

ULS = Ultimate Limit State
SLS = Service Limit State

It is like the metric system - Everyone but the USA use it smile

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close