How to interpret Amendment 3 of NZS 3101 for post-installed anchors
The recent Amendment 3 of the New Zealand Concrete Standard 3101 requires post-installed steel anchors to be designed in accordance with the European document EOTA TR045 and for the anchors to pass the prequalification testing stipulated in ETAG 001 Annex E. This new prescription is only one sentence, but it has important implications for how post-installed anchors are assessed and designed. Despite the importance of this clause (17.5.5), the wording is not entirely clear, and many practicing engineers are asking questions regarding not only how to interpret that single sentence but also how the full design should be done.
Below is a list of what Professor Jason Ingham (as chair of Chapter 17) and myself think are the most pressing questions (questions 1 to 3) and what we think are the two most important missing points in the European documents (questions 4 and 5). We would appreciate any constructive feedback that could be provided. These suggestions will be compiled and compared, and a number of recommendations will be made depending on them. These recommendations will be published in a future SESOC journal and provisional results will be presented at the NZSEE/PCEE conference next April in Auckland, together with a brief summary of how the previously used ACI documents and the newly European documents compare.
1.- Amendment 3 of the NZS 3101 Standard references ETAG 001 Annex E for testing and EOTA TR 045 for design, but these documents only specify seismic testing and design. Non-seismic testing and design is also necessary and ETAG 001 should be referenced (main body for testing and Annex C for design).
2.- ETAG/TR045 require Category C1 or C2 depending on the seismicity of the region in Europe and the Importance Class of the building as per Table 1.1 of ETAG 001 Annex E.
New Zealand practice considers the seismicity of the region in a different manner to that of the Eurocode. Two options are available, i) Use site acceleration data, such as the ground acceleration map from GNS and consider C1 for PGA<0.1g and C2 for PGA>0.1g, or ii) use the hazard factor Z from NZS 1170.5 (Figures 3.3 and 3.4 of NZS 1170.5), using C1 when Z≤0.13 and C2 when Z>0.13. In both cases Auckland and Northland are the only regions where C1 can be used. The Importance Class is similar to the Importance Level from NZS 1170, so can be adopted directly.
3.- The tension-shear loading combination can be tested in ETAG. Should this testing be mandatory instead of using Equation 17-5 from the NZS 3101 Standard?
N*/(phi Nn) + V*/(phi Vn) <1.2
4.- The tensile and shear testing requirements are quite different, with tensile testing comprising four tests (low- and high-strength concrete that can be cracked or uncracked) and shear testing comprising only two tests (low-strength cracked and uncracked concrete). The same number of tests should be performed for both loading cases.
5.- Special substrates such as steel-concrete composite slabs and hollowcore floors are not considered. Recent research at UoA found that anchors installed in the lower flute of composite slabs can be up to 40% weaker than when installed in the upper flute, and anchors installed in the hollow region of hollowcore floors can be half as strong as those installed in the web region.
The Eurocode EN 1992-4: 2018 was published in October 2018. According to the note in the introduction of EOTA TR 045:
..Once EN 1992-4 has been published no ETA should be issued with reference to this Technical Report…
Therefore, EN 1992-4 should now be used (however, I’m not sure whether different rules to those presented in TR 045 are given within this Eurocode).
AS 5216: 2018 Design of post-installed and cast-in fastenings in concrete has recently been published (which claims to be based on EN 1992-4). Because there was insufficient interest from New Zealand, this document was developed as an Australian Standard. As a consequence of this, there are unfortunately no seismic provisions in AS 5216.
Any updates on post installed anchors for the NZ practitioner?
Have had to come to terms with these European standards on a recent project and decided to install two additional anchors and undertake load tests to have some confidence with the design and install. Questions include;
1. Does the EOTA TR 045 still apply given it has been superseded by the EN 1992-4? Has MBIE given any guidance n this?
2. The restrictions on fitment hole size severely penalize the shear capacities of anchors. Presume there’s been some testing to verify this 50% reduction? The 2mm oversize limit is not practical when you’re trying to line up 10 post installed anchors with 10 holes, as we were on a recent silo installation!
3. NZ designers are presented with a real mishmash of requirements. NZS derived loads to design cast in anchors to ACI based requirements, and post installed anchors to EU or BS codes. Leads to confusion and lack of clarity, and makes professional vulnerable to anchor / adhesive companies who provide apparently great products and software but accept little responsibility. Is it time to revisit this?