Seismic Approval for Anchors : do you need it, when and how?
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
website : https://adit.org.il
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