This is the seventh of my Anchor Watch articles, if you have missed any of the previous six you can access then on https://www.masonryfixings.ie/articles
A question we at Masonry Fixings are often asked is 'should anchors be tested on site and if so, how many should be tested'? This topic is covered in the HSA COP for the design and installation of anchors and BS8539 where it states that site testing of correctly installed ETA approved anchors, used within the scope of the ETA, is not required.
Unfortunately, we still see requests for site testing which simply state that site testing is required. This can be a loaded question that requires a lot more information to ensure any testing carried out is accurate and meaningful.
Here are some of the issues that need to be considered by anybody requesting or performing tests.
Type of test required
Traditionally there are two types of testing:
- Testing to determine the allowable resistance: This testing may be necessary when fixing into a substrate for which there is no available published data to confirm the anchor capacity. If involves installing and testing sacrificial anchors to failure or a predetermined load. The results are then evaluated and subjected to partial safety factors to determine the allowable resistance.
- Testing to check the quality of installation. Modern fastening technology became increasingly popular in civil and structural engineering in the early 80’s. At that time there was little regulation or guidance on their performance and installation. There was also a training and expertise gap with the installers that often led to poor installation. This all led to a demand for site testing.
Over the past number of years, we have seen the development of the construction products regulation, European Assessment Documents (EAD), European Technical Assessments (ETA), and CE marking of fixing systems in concrete and masonry.
This now means that we have very dependable published data for anchor performance issued by independent bodies and verified by CE marking. These systems don’t require further testing when used within the scope of the ETA.
Tests to determine allowable resistance is still very important but only when we intend to fix in any substrate for which there is no published data.
The issue of ‘testing the quality of installation’ is also becoming less of a concern as installer training is closing the training and expertise gap. Testing can be mitigated if the anchor installation is supervised and carried out by competent installers.
Installer training can be found on in the video above, or here. The Construction Fixings Association are also in talks with us to provide certifiable anchor training courses to anchor installers in Ireland.
A high percentage of anchors used on site are known as torque-controlled expansion anchors. If these achieve the prescribed torque during installation, then the anchor will function correctly. The use of a torque verifier will also allow the installer to provide documented proof that the installation torque was applied to every anchor.
Additional tips
- Most anchors will have been designed for use in cracked concrete, most site tests will not emulate this so don’t necessarily prove suitability;
- Tests cannot be easily performed on working anchors that have hexagon or countersunk heads;
- Most anchor reports will verify that concrete capacity is decisive for an anchor group. Testing single anchors where the concrete is confined by the anchorage and restricts the development of concrete failure will not verify the design resistance;
- Anchors that are correctly torqued will be subjected to a prestressing axial force that will exceed the 1.5 x characteristic action test load required in BS 8539;
- Anchors that are torqued generate local stress in the concrete that relaxes in a short time, re-torquing will re-stress the concrete and this will relax a second time. This should not be misconstrued as evidence that the anchor was not torqued in the first place;
- Applying a tension test to anchors that are subjected to a characteristic shear action is meaningless as there is no correlation between tension failure and shear failure when we consider the concrete capacity method;
- Drill bits with PGM mark should only be used when installing anchors.
Please refer questions to technical@masonryfixings.ie
Author: Bryan Carroll, technical director, Masonry Fixings