Did you know
Link to TRM
that
anchor
testing isn&#;t always required in M&E installations?
Are you aware of the
instances where you
would
need to carry out 'pull testing'?
If you usually request &#;pull tests&#; regardless, keep reading. It&#;s great that you are going the extra mile to be super compliant, but sometimes, there&#;s no need to waste your time or money if it&#;s redundant. If you don&#;t usually carry out any testing at all, also keep reading! Because of course, you do need to carry out the necessary testing when it is required. And either way, it provides peace of mind by helping the specifier select the suitable anchor, as well as acting as proof of a compliant installation.
This article is intended to clear everything about pull tests up for you. It will cover:
What is a pull test?
Anchor testing, known colloquially as &#;pull testing&#;, is the process whereby an anchor/fixing is pulled testing of anchors may be done either before or after the installation depending on the type of testing required.
What types of pull tests are available?
There are two types of anchor testing. Sit tight, there&#;s a lot to get through here! The first of which is&#;
Allowable load testing
An allowable load test is carried out where the application involved is not covered by a relevant ETA Guideline, the strength/condition of the base material is unknown with no published data, or the manufacturer has no recommended resistance for the specifier to complete the selection process.
When and how is allowable load testing carried out?
It involves attaching a hydraulic pull tester to an anchor and pulling it to a designated test load, continuing to turn the handle and increasing the load until failure. A further calculation is carried out to work out the new recommended load. The anchor should also be tested five times and the average recorded. It&#;s considered &#;destructive&#; as it is tested to the point of failure.
These should only be carried out on anchors that are approved by the manufacturer for use in the category of base material involved (e.g. solid, hollow, etc.), and before the anchor selection is finalised to ensure suitability and adequate resistance. They also need to be installed specifically for the purpose of the tests only, installed in the base material for the project but away from the anchors that will be used for the project.
There are two principal circumstances when you should conduct an allowable load test:
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When an ETA-approved anchor is available but doesn&#;t meet the qualifications for dimensions and strength. For example, if the project is for an old building and you don&#;t have the design strength data of the concrete, then the ETA cannot apply because it&#;s missing an element that would tell us how the anchor would perform in that substrate. In this case, a test would be carried out by the ETA Guidelines.
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When there is no suitable ETA-approved anchor and another anchor is recommended by the manufacturer but there is no published tensile or design resistance.
Testing the substrate is simple for lightweight materials, but it can be more difficult for blocks of concrete beam sections since there is no clear way of showing the concrete's capacity. It can be difficult to precisely determine the allowable working load if you don't know the substrate's capacity.
This way of testing requires more tests and more skill from the tester (advanced tester) as the loads are higher than its counterpart&#;
Not sure about the design strength of the substrate or nervous about that anchor installation?
Proof testing
The purpose of proof tests is to test the quality of installation and these are the most frequently requested tests (despite not always being required). This is where, if we&#;ve used an ETA-approved anchor and it&#;s fixed into a known substrate, we can apply a test load to the anchor to prove that it&#;s been installed correctly. These are carried out on a sample of working anchors on every safety-critical application.
When and how are proof tests carried out?
The hydraulic pull tester is attached to the anchor and pulled to a specific test load. What it doesn&#;t tell us, though, is if it&#;s been specified correctly, or if it&#;s fit for purpose.
This can be prove more difficult if the anchor is flush-fixed (bolt head anchor or a frame fixing), as it's harder for the tester to connect to this type of anchor.
Proof testing typically happens after the specification and installation stages and is conducted by a &#;general tester&#;. The contractor is responsible for organising it, not the installer.
What does the BS say about anchor testing?
Everything mentioned up to this point is in line with BS. However, it includes other points that are worth mentioning.
For starters, BS states that tests need to be conducted by someone who&#;s not only competent but who also has a vast knowledge of anchors, how they&#;re installed, and how they&#;re likely to fail as this will greatly improve the quality of the tests.
It defines the responsibility of the chosen tester as:
Are you interested in learning more about Bolt Pull Test? Contact us today to secure an expert consultation!
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Where relevant, anchors are installed by the manufacturers&#; instructions, in the correct locations as required by the specifier.
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Results are recorded in a full and comprehensive manner and forwarded to whoever requested the tests.
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He must hold the relevant CFA qualification.
Moreover, the CFA guidance highlights the following points from BS that should be considered.
If you are testing 1 in 40 fixings, you are only allowed a factor of 1.5x the applied load. The actual applied load must not exceed the manufacturer's recommended load. If you test 1 in 25 fixings, the guidelines advise the applied load can be 1.25x the manufacturer&#;s specified load.
To add, the code of practice indicates that once the testing has been done using the correct procedures, and they&#;ve fulfilled the objectives, the results are passed on to the person who requested the tests. This report should include:
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Administration details: date of test, reason for test, name of person requesting test, unique reference test, client's company name, site location, contact name and position.
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Anchor/application details: name of manufacturer, anchor type, size and finish, proposed application of anchor, design resistance and manufacturer's recommended resistance in the base material concerned (for proof tests)
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Test objectives, test location, base material, installation details, test equipment details, test results, method statement, gauge calibration certificate.
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Specific procedures for applying test loads, monitoring movement, etc.
This is all in accordance with the CFA Guidance Note Procedure for site testing construction fixings.
Lastly, the standard also highlights when testing isn&#;t required, which brings us to our next point&#;
When is and when isn&#;t testing necessary?
As mentioned, while in certain situations testing is required, a lot of the time requests are made for unnecessary testing to be carried out. I&#;m all for the enthusiasm and overachievement (especially when it comes to safety and compliance!), but you could really save yourself time, effort, and money by double-checking the requirements before going through with a test.
We&#;ve already established that ETA-approved anchors should always be used whenever applicable and available. In the case that one is used and installed into a known substrate by a trained installer with competent supervision, the BS states that testing actually isn&#;t required. That&#;s because for an anchor to be ETA-approved in the first place, it needs to undergo rigorous testing (it costs &#;1m!) that proves its performance.
There are exceptions, though. Even with an ETA-approved anchor, on-site testing proving its suitability for the specific application may be required if, for example, it&#;s been approved for use in the category of the masonry used in the project, but doesn&#;t match the strength and/or dimensions of the approval. And of course, if the supervision isn&#;t satisfactory or operatives are not adequately trained, it defeats the purpose of using an ETA-approved anchor &#; in which case, testing can be conducted.
The standard states the two key areas where anchor testing is recommended:
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To determine the allowable resistance when there is no manufacturer data and proof tests to validate the quality of the installation
To understand the performance characteristics of both ETA-approved and non-ETA-approved anchors
Conclusion
Anchors are one of those things that are often neglected and seen as a commodity product, so people often underestimate their importance, as well as the importance of testing their performance. In reality, this is vital to ensure a safe and successful installation. But it might not always be your responsibility to undergo the testing. Sometimes the work has already been done for your &#; other times, your project, in particular, will prompt a request for testing.
In any case, I hope this article has provided you with enough insight to feel more comfortable with the concept of anchor testing, familiarised you with when you&#;d be required to conduct it, and the processes behind the two types. Happy testing!
Background
The quality of a crimp joint depends on the mechanical strength of the joint as well as its electrical conductivity. If results from pull force tests are within an allowed range, it assures that the proper crimp force has been applied during the crimping process.
This is crucial as enough force must be applied to break down the layer of non-conductive oxides that may build up on the stripped conductor and the plating on the inside of the terminal. This is necessary to provide a good metal-to-metal contact. If this does not occur, electrical resistance can increase.
Overcrimping a crimp termination will reduce the circular area of the conductor and thereby increase electrical resistance.
Crimp joint testing (commonly known as "pull testing") ensures the integrity of the final product but, more importantly, it ensures the effectiveness of the crimping tool itself since it can be calibrated according to test results. Calibration is best carried out in response to Statistical Process Control (SPC) analysis which can be gathered from data obtained by pull testers.
Standards and methods
There are many standards to adhere to and each manufacturer or user might have different requirements to fulfil. But one thing in common is that international and industry standards all prescribe procedures for testing the tensile strength of wire terminals in a repeatable manner.
It is essential that there is no jerking or sudden application of force. This is the reason why standards state that there should be a 'constant rate of pull' and most define a pull rate at which tests should be performed. The only practical way to achieve repeatability for pull force tests is to set a speed by using a motorised pull tester such as the WTST range of testers.
Although standards define a minimum acceptance-value for the pull force according to the wire diameter and AWG conductor size, it is of greater importance to the manufacturer and user to know that joints can definitely sustain higher loads. So an increasing axial force is applied to the connection until either the terminal and wire separate or the wire breaks.
Pull and Break
Directly pulling the wire joint until destruction at a constant rate (typically 25 to 50 mm/min) is the most commonly adopted test method and is known as 'Pull and Break'. It is performed by using a motorised pull tester in which the peak force to separate the terminal from the wire is measured. This value is then compared to the table of minimum pull forces outlined in the standard in order to determine a pass or fail of the connection.
Other test methods call for more in-depth procedures:
When carrying out a pull test most companies do not remove the insulation sleeve around the crimp. However, the IPC/WHMA, UL, USCAR and VW standards specifically require that the insulation support is rendered mechanically ineffective by opening it up. Certain other standards (e.g. VW) provide a higher pull force value if the insulation support is left in place around the crimp.
Contact us to discuss your requirements of Friction Bolt. Our experienced sales team can help you identify the options that best suit your needs.
- Pull and Return
A non-destructive test whereby the terminal is pulled to a specified force and then the force is removed.
- Pull and Hold
A non-destructive test whereby the terminal is pulled to a specified force and held for a specified period of time. The force is then decreased to zero.
- Pull, Hold and Break
A destructive test whereby the terminal is pulled to a specified force and held for a specified period of time. It is then pulled further until either the terminal and wire separate or the wire breaks.
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