How to anchors on site in accordance with test BS 8539:2012

Ensuring best fixings practice
www.the-cfa.co.uk
How to test anchors on site in accordance with BS 8539:2012
Code of practice for the selection and installation of post-installed
anchors in concrete and masonry. A guide for testers of fixings.
1
Introduction
BS 8539 is arguably the most significant development in the use of construction fixings since the
advent of European Technical Approvals (ETA)1 in 1997. It includes, for the first time in such a
code, the acknowledgement of the importance of the role of the tester in ensuring that the full
performance of a fixing can be realised. The CFA Guidance Note: Procedure for site testing
construction fixings – 2012 is called up as a Normative reference within the code i.e. it is
effectively part of the code.
This “How to” guide summarises the responsibilities of people charged with the task of testing
fixings on site and provides a degree of commentary on why the Code and Guidance Note are
written the way they are. All stakeholders should acquire a copy of the code2.
1.1
The Code and the Guidance Note
BS 8539 calls up the test regimes for anchors against the different circumstances when testing
may be necessary i.e. it sets out how many tests should be carried out, to what load and how
results should be treated. The Guidance Note summarises those test regimes and details the test
procedures that should be used to carry them out i.e. how to set up test equipment and link it to
the fixing under test, how to apply the load and monitor movement, how to record results etc.
1.2
Terminology
Terminology used in the code is based largely on that used in ETA, in ETAGs (the Guidelines
used to award ETA) and CEN Technical Specifications3 for anchors. This has resulted in the
adoption of some terms and notation not previously used by the CFA or by some manufacturers.
This is particularly significant for the testing of anchors and the reference to test loads etc.
The term “load”, is used only in the general sense having been replaced by the terms “Action”
and “Resistance”. Action being the load to be transferred from the fixture to the base material,
and “Resistance” the capability of the anchor to resist the action. What was previously referred
to as the “Applied Load” or “Unfactored load” is, in BS 8539, referred to as the “Characteristic
action”. The precise meanings of the terms used in testing anchors are all detailed in the code
and repeated in the CFA Guidance Note. The test load to be achieved in all tests which are NOT
to be taken to failure is some multiple of the characteristic action. The factor used to determine
the test load from the characteristic action will depend on the purpose of the test and is defined in
the BS and repeated in the GN.
For a detailed explanation of the differences between the new and old terminology see4.
1.3
Responsibilities
The tester’s responsibilities, as called up in the BS, are limited to ensuring the tests are carried
out to the correct procedures, that, where relevant, anchors are installed in accordance with the
manufacturer’s instructions in the correct locations as required by the specifier and that results
are recorded in a full and comprehensive manner and forwarded to whoever requested the tests.
The tester is NOT responsible for prescribing test loads, for commenting on why anchors fail to
deliver the expected performance or for calculating allowable loads from test results.
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“How to” test anchors on site in accordance with BS 8539.
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Test regimes.
BS 8539 calls up test regimes for two stages of a project (determining allowable resistance when
there is no manufacturer data and proof tests to validate the quality of installation) and for two
statuses of anchors (those with ETA and those without).
2.1
Tests to determine allowable resistance.
Tests may be required at an early stage in a project in order to confirm the suitability of an anchor
in a particular base material and to determine the allowable resistance (allowable load) in that
base material. Such tests are always carried out on anchors which will NOT be used on the job.
These tests should not be needed for anchors with ETA for use in concrete as the necessary
performance data is quoted in the ETA. For anchors with an ETA for use in masonry tests may be
required if the base material of the job does not conform to that defined in the ETA (i.e. it is of the
same category, e.g. solid brickwork, but is either not as large as the masonry units listed in the
ETA or is not at least as strong as the masonry listed).
For anchors with ETA which need these tests the BS necessarily calls up the test regimes
outlined in the relevant ETAG against which the anchor was awarded its ETA. But these regimes
require at least 15 tests to be carried out to failure and this number of tests may be regarded as
excessive, especially with damage to the substrate possible from such tests, so an alternative
approach is allowed by the BS - again testing anchors to failure but allowing more flexibility in the
number of tests with a statistical approach to determining the allowable load which takes into
account the number of anchors tested.
For anchors without ETA again two approaches are allowed in the BS; a simplified method
called “Preliminary tests” using just five tests, or a statistical approach similar to that for anchors
with ETA as mentioned above. These regimes can be summarised as follows:
Anchor status
Anchor has ETA relevant to base
material
Anchor has ETA but base
material does not conform.
No anchor with ETA available and
proposed anchor has no ETA.
2.2
BS 8538
reference
9.2 a)
9.2 b)
Test regime
Test procedure
CFA GN ref’
Tests for allowable load not
needed.
Test to relevant ETAG or
Test to 8538 Annex B.2.2.1.
Test to 8539 Annex B.2.3.1.
(Preliminary tests) OR
Test to 8539 Annex B.2.3.2.
3.1.2.1.
3.1.2.2.
3.1.2.3.
3.1.2.4.
Tests to check the quality of installation – Proof tests.
This aspect is far more straightforward. Tests are required on a sample of anchors on all jobs
except where anchors with ETA have been installed by a competent Installer5 working under
supervision.
The sample rate may be:
1 in 40 with a proof test load of 1.5 x the characteristic action,
OR
1 in 20 with a proof test load of 1.25 x the characteristic action,
and at least three.
The latter test regime (1 in 20) matches the test regime of the Scaffolding6 industry. Guidance is
also given as to what action to take in the case of failures during proof testing.
2.3 Arranging for tests to be carried out.
When a test is required it is important that the company asked to carry out the test has all the
information they need to quote for the work and to carry out the tests. To help with the provision
of this information the CFA publishes a form CFA Form 8539/04 Anchor Test Request which may
be downloaded from the CFA website at www.the-cfa.co.uk section Guidance Notes and
Downloads – CFA 8539 Forms.
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“How to” test anchors on site in accordance with BS 8539.
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Test equipment
The following types of equipment are needed and are explained in more detail in the CFA GN.
Equipment for
Commentary
Linking the tester with the
fixing
Depends on fixing type and test objective, may be
threaded coupler for projecting studs, adaptor to fit
under bolt heads or nuts, clevis for eyes or ringbolts,
pulling frame for bolts or nuts, special adaptors for
e.g. rebar, remedial wall ties etc.
May be a test meter or hollow hydraulic ram
Usually via a pressure gauge directly calibrated in
kN but may be by digital gauge.
The distance of reaction loads from the fixing
centreline is given. Various different bridges are
available to meet these recommendations and load
capacities.
Generally first movement (required to be recorded in
all tests) may be determined by simple procedures
and rarely requires detailed recording by e.g. dial
gauge. If movement is to be recorded in detail the
dial gauge needs to be remotely mounted (NOT on
the bridge) so as to avoid being affected by the test.
Applying the load
Showing the load
Supporting the test meter
or ram so as to direct
reaction loads away from
the fixing under test
Monitoring movement if
needed
4
6.1
6.1
6.3
6.4
Carrying out tests – More detailed test procedures are set out in the CFA Guidance
note: Procedure for site testing construction fixings – 2012, section 4.
1
2
3
4
5
6
7
CFA
See GN
section
6.2
Confirm the test objective: e.g. to determine allowable load, and to which regime,
or Proof Tests.
Confirm the required test load and number of tests. Check that the basis of the test
load is the characteristic action (applied load or unfactored load). If the basis of the
test load is the design action (or factored load) divide this by 1.4 to give the
characteristic action from which the test load can be determined.
Check that the anchors to be tested are as specified, the locations are as
requested (See GN section 5) and, if installed by others check, as far as possible,
that anchors were installed to the manufacturer’s instructions.
Assemble the test rig to meet the test objective including reaction spacings.
Apply the test load slowly and progressively noting first movement (and recording
the load) until the required test load – or failure load – is reached.
If monitoring movement apply the load in increments allowing both load and
displacement to basically stabilise at each increment before recording
displacement and load (See GN section 4.1 on the subject of load relaxation).
If failure has occurred note the load at which it occurred, any displacement if
possible, and the mode of failure (see GN section 4.1).
“How to” test anchors on site in accordance with BS 8539.
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Recording results – drawing conclusions and making recommendations.
Results should be recorded as per the BS and CFA GN where the requirements are listed
in section 8.1. Enough detail is required so as to demonstrate that the test objectives have
been met and to ensure that any questions that may be asked by the person requesting
the tests can be answered. Test reports should contain merely the results of tests. Unless
the person carrying out tests is particularly knowledgeable and experienced in the whole
subject of anchor technology no conclusions should be drawn as to why anchors may
have failed or what remedial action should be taken in that event. Testing companies who
feel in a position to draw conclusions or make recommendations should ensure they have
appropriate levels of professional indemnity insurance.
6
Working out allowable loads
Methods for calculating allowable loads are detailed in both the BS and CFA GN and will
not be dealt with here. They are not the responsibility of the tester but of the engineer
calling for the tests. Despite this a format for the reporting of results for this tests is
provided for CFA Approved Testers which includes sections for the calculation of
allowable resistance.
7
Approved Tester companies - Competent Testers
The CFA offers Associate Membership to companies as “Approved Testers” as long as
they satisfy the CFA qualification requirements. Membership entitles companies to training
at the CFA Academy for their staff to become certified as Competent Testers. Training
covers basic anchor technology as well as CFA procedures for site testing to comply with
BS 8539. Method statements and report formats are provided.
1
For more information on ETAs see CFA Guidance Note: ETAs and design methods for anchors used in
construction. www.the-cfa.co.uk go to section Guidance Notes and downloads.
2
For copies of British Standards relating to construction fixings, at a discount of 20%, contact the CFA via
our website www.the-cfa.co.uk.
3
Design methods for anchors with ETA may be contained in CEN Technical Specifications in the series
CEN TS 1992-4 Parts 1 – 5. (Otherwise they are as the relevant ETAG.)
4
CFA Guidance Note: Anchor terminology and notation
5
For competent installer training contact the CFA secretariat via the website.
6
See CFA/NASC Guidance Note TG4:11 – Anchorage systems for scaffolding.
CFA
“How to” test anchors on site in accordance with BS 8539.
(Issue 2. May 2014)
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