Seismic Approval for Anchors : do you need it, when and how?

01/31/2019

In today's world, there is a tendency to require seismic approval for anchors for most of the large projects. But what exactly is this certificate? What is its importance? And how should you use it?

First, it is important to emphasize that "seismic approval" to a particular anchor confirms that the manufacturer has paid an approved laboratory to inspect the anchor according to a process set in the European standard ETAG Annex E for earthquake. This does not mean that the anchor is "good" or "bad" during an earthquake, it just means that the manufacturer paid for the test. Of course, a manufacturer usually does not spend money on testing an anchor that is less suitable for an earthquake. However, the certificate itself does not promise in any way that the anchor will function properly (comparing to static or semi-static loads) during an earthquake.

For example, a wedge anchor such as MTP-X M12 holds in cracked concrete 16kN* in characteristic tensile load and the capacity for an earthquake design is 9kN, a decrease of 43% of the loads. In contrast, the SZ M12 / 18* anchor holds the same load in cracked concrete and for an earthquake design. The reason is simple: Wedge anchors are less good for dynamic loads. This means that the standard European certificate for an earthquake only confirms that the anchor has been tested and not that the anchor is good for it.

There are also different degrees of certificate.

In an American standard, all types of applications have different letters and the more the anchor is approved for more letters, the more suitable it is to fit. However, the approvals in an American standard are not accompanied by a clear capacity load for each situation but refer the planner to sections that reduce the anchor load accordingly. Few people use an American standard for planning an earthquake.

The European standard (the basis for anchor design for most design offices in Israel) has two levels: C1 and C2. What is the difference ?

C1 is a certification for nonstructural elements design, C2 for structural elements design.

Clearly, there is not much planning for earthquake for nonstructural elements, and C1 is supposed to be irrelevant in most of the cases. However, in Israel, most planners are not aware of this significant difference and approve mechanical or chemical anchors on the basis of this approval for structural elements.

Moreover, in most of the designs for anchors to an earthquake, the calculation of anchors is done like for standard cracked concrete with static or semi-static loads. The planner only requires afterwards that the anchor got certified with a seismic approval C1 or C2. The planner is wrong twice:

- If we are talking about structural earthquake design, then he must require C2 certificate

- It must take into account the design the capacity of the anchors according to his C2 certification.

If he does not do so, he acts like a director of a engineering office who hire in his office a candidate who had signed up for engineering studies without asking if he has completed his studies. It's neither wise nor right.

Engineer Yves De Lathouwer - Adit Ltd