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?
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?
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).
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The name is a long story -- just call me Lo.
RE: Anchor pull testing... am I crazy or is this wrong?
What is the capacity reduction factor used in the anchor design?
RE: Anchor pull testing... am I crazy or is this wrong?
I'll confirm that the intent is to oversize the rock anchors themselves.
RE: Anchor pull testing... am I crazy or is this wrong?
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 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?
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?
RE: Anchor pull testing... am I crazy or is this wrong?
In a lab, sure. But a lab environment won't give you much useful information on field performance.
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The name is a long story -- just call me Lo.
RE: Anchor pull testing... am I crazy or is this wrong?
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?
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?
I think MotorCity accidentally put us on a tangent.
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The name is a long story -- just call me Lo.
RE: Anchor pull testing... am I crazy or is this wrong?
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?
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?
www.PeirceEngineering.com
RE: Anchor pull testing... am I crazy or is this wrong?
SLS = Service Limit State
It is like the metric system - Everyone but the USA use it
RE: Anchor pull testing... am I crazy or is this wrong?
www.PeirceEngineering.com