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Transitioning Loads and Capacities between ASCE7 and EN 1990 / ETA

Transitioning Loads and Capacities between ASCE7 and EN 1990 / ETA

Transitioning Loads and Capacities between ASCE7 and EN 1990 / ETA

I am more familiar with ASCE7 and want to use a product which has testing done by EOTA which references EN 1990, 1991, etc. In general I'm wondering what I would need to do in order to go between the two standards.

In my specific case have an ETA (European Technical Assessment) report for an anchor that attaches to a ceramic panel. It outlines combinations for loads parallel (i.e. dead load) and perpendicular to the panel (i.e. wind load).
The factors are:
gamma_G = 1.35 for dead loads (permanent action)
gamma_Q = 1.5 for wind loads (leading variable action)

The test results for shear and tension use the 5% fractile and confidence level of 75%.
They recommend a safety factor, gamma_M = 1.8. So the value obtained within the 5% fractal would be divided by 1.8

EN 1991-1-4 derives their basic wind speed using a 50 year return period, 10 meters above the ground in open country terrain with low vegetation, and the average speed over 10 minutes.

These are all similar to ASCE7-05 except for the average speed duration. ASCE7 uses a 3-second gust.

So I'm thinking I can either convert my loads to EN and use all their standards or convert their resistance factors to ASCE7 (which I'd rather do).

Convert Loads to EN and use EN Docs:
Change wind speed from 3-sec gust to 10 minute average. Use all EN 1990 docs from here on out.

Change ETA resistance factors to ASCE7:
Not exactly sure. For starters, the 1.35 and 1.5 appear to be similar to DL=1.2 and WL=1.6 LRFD factors.
So if I define my loads using ASCE7 and use ASCE7 load factors, then use the ETA test result and reduce them by 1.8 it seems like that would give me a conservative result. However, I'm not sure what I would need to do to actually convert everything.


RE: Transitioning Loads and Capacities between ASCE7 and EN 1990 / ETA


Am I way out there with this?


RE: Transitioning Loads and Capacities between ASCE7 and EN 1990 / ETA

OK so I"m familiar with ASCE but not EN or ETA reports, etc...

Sounds like you are trying to get to an apples to apples comparison but I think that is going to be pretty tough. You indicated that the test results recommended a factor of safety of 1.8 be applied to the ultimate load results from the test. I assume this factor of safety was calculated using a formula based on statistics. I'm going to assume you are trying to apply this testing to a US based project.

OK so if the test report publishes the ultimate load applied at tested failure or the ultimate pressure at tested failure. Than my advice is to use ASCE 7-10 or whatever version is applicable in your area of the country and calculate the wind pressures according to that. But instead of using LRFD load combinations just use service load ASD combinations. Than take the test report's average ultimate load at failure and divide by a factor of safety. In the US for most roofing or cladding applications the factor of safety I see applied to test results are between 2.0 and 3.0. If you are designing the fastener I'd suggest using a 3.0 factor of safety. If you are designing an assembly (sheating and fasteners tested together) than a safety factor of 2.0 might be appropriate.

The real question will be whether or not your jurisdiction will accept the testing methodology and its results to begin with. If they do, and you can determine the load applied at failure than you might be able to avoid converting and simply apply US standards to the test result.

John Southard, M.S., P.E.

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