CROSS Safety Report
Site testing of post-installed fasteners in concrete
This report describes a situation where site testing of post-installed fasteners in concrete was undertaken by a contractor as an alternative to adopting the design data from the manufacturer in an attempt to justify an increased design capacity for the fasteners. This led to proposed design capacities which were about 3 to 5 times greater than the safe design capacities determined in accordance with AS5216. Since these fasteners are located in a safety-critical application, the reporter considered whether this may have resulted in an unsafe condition.
Key Learning Outcomes
For civil and structural design engineers:
- Safe design of post-installed fasteners and compliance with NCC2019 and AS5216 is best achieved by specifying a fastener selection for which a current European Technical Approval/Assessment (ETA) is available for the fastener and installation method, and by adopting the design parameters documented in the ETA for the design of the post-installed fastener
- The design resistance of post-installed fasteners should not exceed the values of design capacities published by the manufacturer without approval from that manufacturer
For contractors and construction professionals:
- The purpose of site testing, when undertaken, should generally be to identify any gross errors in the quality of the installation of the anchor
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The reporter encountered an issue where site testing of post-installed fasteners in concrete was undertaken by a contractor as an alternative to design data produced by the manufacturer. This was undertaken to justify increased design capacities for the fasteners which were approximately 3 to 5 times greater than the safe design capacities determined in accordance with AS5216: Design of post-installed and cast-in fastenings in concrete. Since these fasteners are located in a safety critical application the reporter considered whether this may have resulted in an unsafe condition.
A contractor had substituted post-installed chemically anchored threaded rods in place of cast-in holding down bolts specified in the design documentation. When the design capacity of the post-installed anchors was subsequently checked using design data supplied by the manufacturer of the fasteners, the values were found to be inadequate. The design capacities provided by the fastener manufacturer were based on extensive laboratory testing and evidenced by a European Technical Assessment (ETA).
ETA assessment usually involves the testing of a large number of specimens under various conditions over a minimum period of 3 months, some of which are mandatory and some which are optional to qualify the product. For example, the mandatory conditions include testing for sustained load, variable loads, robustness and changed environmental conditions. These are extremely difficult to replicate on-site, and on-site testing cannot produce the same rigorous requirements as laboratory testing.
The reporter notes that site testing, including ULS proof testing, is generally undertaken to identify any gross errors in the quality of the installation of the anchor. However, in order to address the shortfall in design capacity the contractor in this case used the results of the on-site installation tests as the basis for establishing the design capacity of the post-installed anchors. This resulted in calculations for the design capacities of the fastener which exceeded the values of capacity based on the manufacturer’s Technical Data Sheet (TDS) and/or ETA by a factor of between 3 and 5.
Independent opinions were sought from two professional chartered engineers who also expressed the opinion that the site testing could be relied upon as prototype testing to AS1170.0 Appendix B to permit the use of a design capacity 3 to 5 times higher than the design capacity established by the manufacturer’s ETA. However, the reporter notes that these site tests are not equivalent to the suite of tests that are required by the European Assessment Document EAD330499, which includes assessing effects of concrete cracking, epoxy aging, long term loading, etc.
The reporter notes that the Australian Engineered Fasteners and Anchors Council (AEFAC) Technical Note AEFAC-TN05-Site-testing-Vol 3 advises that the characteristic strength obtained from site testing should not exceed capacities determined in the ETA; and that clause B1.4 Determination of structural resistance of materials and forms of construction in the National Construction Code NCC2019, Volume 1, Amendment 1, requires that post-installed and cast-in fastenings comply with AS5216: Design of post-installed and cast-in fastenings in concrete.
Appendix A to AS5216 sets out the mandatory requirements for testing and assessment of fasteners, and requires these to be assessed in accordance with the European Assessment Documents EAD330232 (Mechanical Fasteners for Use in Concrete) and EAD330499 (Bonded Fasteners for Use in Concrete). Clause 1.1.2 Application in AS5216 also notes that "the design parameters and product specifications required for use with this Standard may also be obtained from a current European Technical Approval/Assessment for the relevant fastener". Alternatively, the same suite of tests that would be required by the European Assessment Document EAD330499 can be undertaken by a Registered Testing Authority (RTA) in Australia and assessed by an Assessment Body which should be independent of both the manufacturer of the fastener and the RTA. This involves a large suite of tests and would not normally be undertaken at project level.
The higher design capacities based on site testing of ULS if adopted would, in the reporter's opinion, result in the use of unsafe design capacities not compliant with the minimum safety requirements of NCC2019.
When a site pull-out test of an anchor is undertaken it is easy to understand how these test results might be accepted as representing an accurate assessment of the anchor capacity accounting for the specific project site conditions. However, these site tests are generally undertaken in uncracked concrete for loads of short duration without aging and environmental effects, and are unlikely to represent the true design conditions.
The reporter notes that although the provisions for prototype testing in AS1170.0 mention that these effects must be taken into account using separate factors, there appears to be less awareness of the extent to which these affect the design capacity of post-installed fasteners.
The reporter also notes that the requirement for post-installed fasteners to comply with AS5216 is relatively new (that is circa 2019), and there appears to be little awareness of the testing and qualifications of anchors required to satisfy AS5216 to ensure the safety and reliability of post-installed fasteners.
In summary the reporter notes:
Appendix A of AS5216 as referenced by the NCC2019 is a normative (i.e. mandatory) requirement which requires that the testing of post-installed fasteners for suitability and admissible service conditions be performed in accordance with EAD330449;
guidelines in AS1170.0 and AS4100 for the use of test data for design are not satisfactory evidence of compliance with AS5216 (and NCC2019). These guidelines advise that there are several qualifications for the use of test data obtained in accordance with these referenced standards which require variables or conditions not covered by test procedures to AS1170.0 and AS4100 to be taken into account separately. These additional effects are explicitly included in the EAD330499 approach required by AS5216 (and NCC2019) and include:
loading scenarios (such as dynamic, sustained and combined loading);
substrate conditions (such as cracked and uncracked concrete);
durability and effects of aging;
age and duration of loading;
environmental conditions; and
in accordance with the advice from the Australian Engineered Fasteners and Anchors Council (AEFAC) it is recommended that characteristic strengths obtained from site testing should not exceed capacities determined in the ETA.
The reporter further recommends that the design resistance of an anchor should not exceed the values of design capacities published by the manufacturer without approval from that manufacturer.
In conclusion, the reporter considers that the simplest way to ensure safe design of post-installed fasteners and compliance with NCC2019 and AS5216 is to specify a fastener selection for which a current European Technical Approval/Assessment (ETA) is available for the fastener and installation method, and to adopt the design parameters documented in the ETA for the design of the post-installed fastener.
Expert Panel Comments
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An Expert Panel comment on the reports we receive. They use their experience to help you understand what can be learned from the reports. If you would like to know more, please visit the CROSS-AUS Expert Panel page.
The Panel fully endorses the reporter’s comments along with the recommendations contained in the report.
Concrete cracks under all types of loading including restrained concrete shrinkage, thermal loads, foundation settlement, dynamic loads, and extreme live loading. Testing anchors after installation is a poor indicator of their capacity at the time when the anchor may be subjected to critical loading. It is considered that the primary purpose of the pull-out test [as envisaged by AS5216] is to verify that there have been no gross errors in the physical installation of the anchor, not as an abrogation of the responsibility to design the anchor.
Anchor design in accordance with design values provided by the manufacturer makes assumptions on several variables (e.g. concrete strength), and assumes unreinforced conditions. If the anchor is found to require additional capacity, it may be possible to refine the accuracy of the variables whilst maintaining the integrity of the standard design process
With respect to the advice on prototype testing in AS1170.0, this requires that separate account should be taken for those variables or conditions that are not covered by the test procedures (items which are in fact covered by the EAD330499 testing regime). Further, Appendix B3 of AS1170.0 states that the prototype test method is not applicable to the establishment of general design data.
In addition, particular attention needs to be paid to the acceptability of chemical anchors in fire conditions, and in such a situation as indicated by the reporter (i.e. change from cast-in to post-fixed anchors), an application to the building certifier for material change in system may be warranted.
It is the considered opinion of the Panel that any decision to circumvent compliance with AS5216 (as described in this case by the reporter) may create unacceptable and avoidable risk, which, in the very worst-case scenario, may lead to injuries and/or fatalities.
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