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THE POSSIBILITIES AND LIMITATIONS

OF ANCHOR SITE TESTING

Don’t guess. Test. But interpret it correctly.

If you have the following questions, you will find the answers in this document.

• “Why is on-site testing of anchors useful and under which conditions?”

• “We did proof loading on the jobsite with Hilti and with other products. The results

are the same, why should I use Hilti?”

ABSTRACT

On-site testing is one important element of the inspection of anchoring or post-

installed rebar activities where:

• additional assurance of installation quality is deemed necessary (non-destructive

proof-loading)

or where:

• resistance values for the design are missing for a similar but not identical base

material as given in the relevant approval document of a specific anchor type

(destructive pull-out test or non-destructive proof-load test).

Fig.1 Hilti test execution and evaluation framework based on base material and anchor

type, purpose and type of on-site test.

Summary of content (12 pages)

PAGE 1
THE POSSIBILITIES AND LIMITATIONS OF ANCHOR SITE TESTING Don’t guess. Test. But interpret it correctly. If you have the following questions, you will find the answers in this document. • “Why is on-site testing of anchors useful and under which conditions?” • “We did proof loading on the jobsite with Hilti and with other products.
PAGE 2
However, if the interpretation of on-site testing results is not done correctly, this assessment could compromise the stability of the structure, put human life at risk and/or lead to considerable economic consequences. The statements above are explained and justified on the following pages.
PAGE 3
loading equipment may have load reactions far away from the anchor to determine the base material strength. Note that Hilti provides a complete on-site testing service with the latest equipment, including a detailed test report an evaluation report. Destructive loading is also done by applying tension loads. The load level is selected sufficiently high to result in damage (e.g. in the form of yielding or base material failure).
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As shown in Fig. 2, the relevant testing and evaluation methods are: (a) British Standard 8539 Annex Ann. B.2.3.1 and B.2.3.2, Code of practice for the selection and installation of post-installed anchors in concrete and masonry, tests to determine the resistance and site testing regimes (b) British Standard 8539 9.
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Fig.
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LET’S GO ON-SITE AND DISCUSS A FEW SCENARIOS Scenario A (a1) Anchors approved for masonry installed in a non-standard masonry brick (a2) Anchor or a post-installed rebar approved for concrete to be installed in concrete where the concrete strength class is not known. Is that the right scenario for Hilti on-site testing? The answer is a clear “yes” Why? No technical data for the design of the anchor is available or the technical data for the specific fastening solution is incomplete.
PAGE 7
Jobsite experience: The mechanical properties of a base material, especially masonry, are not always what you would expect. Some weaker-looking bricks will deliver the tension values you expect, while others that you’d expect to manage higher tension loads, fall short. In one specific case, Hilti assisted a team on-site who estimated that the capacity of an anchor installed in a brick wall would be at least the minimum of our allowable load. He estimated right, but the design still has to be changed.
PAGE 8
Scenario B (b1) Approved anchor or rebar system is to be installed in known and approved base material. The designer included proof load requirements on the general notes sheet of the structural drawing set. Is that the right scenario for Hilti on-site testing? The answer is a clear “yes” Why? A scenario where on-site testing is included (proof load) in their structural drawing serves as one piece of the big picture of quality assurance.
PAGE 9
Scenario C First of all, this is the wrong scenario for on-site testing even if it happens quite often (c1) Anchor or post-installed rebar performance of different products are compared on the jobsite via on-site testing by means of comparing the measured load values of the individual products. Is that the right scenario for Hilti on-site testing? The answer is a clear “No”.
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anchor and during service life. In summary, we can say a product sensitive to these circumstances may have comparable test loads during on-site testing compared to a non-sensitive product. However, if all circumstances would be tested (involving hundreds of tests, as carried out during the approval process) the differences could be significant or it could even happen that such a product would never get an approval.
PAGE 11
Fig. 4a shows the results of three different products by means of plotting the measured displacement as a function of the numbers of crack openings. While two systems would fulfill the requirements concerning the maximum displacement the other would not fulfill the requirements due to the fact that measured displacement is larger than the limiting displacement of 3 mm resulting in pullout failure during its lifetime.
PAGE 12
This behavior of the anchors can never be checked by on-site testing. However, this is included in the basic characteristic bond strength values provided in the relevant approval document. In the words of an experienced engineer: “Testing is easy if you know what you're doing. It doesn't have to take a lot of time if you use Hilti’s on-site testing service. And it can give you peace of mind knowing you are not guessing.