Wind loads EN 13480

Here you can post your question about ROHR2.
Antworten
Marcus
Beiträge: 2
Registriert: Di 12. Mär 2019, 20:25

Wind loads EN 13480

Beitrag von Marcus »

Hi,
Issue/Question No 1:
In section 12.3.3 EN13480 is the factor k defined as
k= 1 if the occasional load is acting for more than 10 % in any 24 h operating period, e.g. normal snow, normal wind;
k = 1,15 if the occasional load is acting for less than 10 % in any 24 h operating period;
k = 1,2 if the occasional load is acting for less than 1 % in any 24 h operating period, e.g. dynamic loadings due to valve closing/opening, design basis earthquake;
k = 1,3 for exceptional loads with very low probability e.g. very heavy snow/wind (i.e. = 1,75x normal);
k = 1,8 for safe shut‐down earthquake;

In Rohr2 I can choose between FSH assume represents k
A Normal operating case, FSH=1
B Abnormal operating case FSH=1.15
C Case of emergency, FSH =1.2
D Case of Damage FSH=1.8

If the client specifies the building code EN 1991-1-4 for wind loads, I assume in general these wind loads acts less than 1% (14min in 24h) so k=1.2 may be used, on the other hand k=1.3 maybe is more realistic since wind speeds normally will be around since ASME specify that k can be as much as 1.33xhot allowable. Anyway can you please give some advise or general praxis? If I want to change to k=1 in Rohr2 how is this done?

Issue/Question No 2:
In the load case editor Rohr2 by default uses SRSS-method ( the Root sum squared in the main horizontal axis) for calculating the wind load stress the sustained stress and the wind stress is evaluated against the allowable stress. Is this mandatory by EN code? The wind load acting simultaneously from two directions? (I see that I can split the wind load and check the wind as separate cases, personal I think this is more correct if for instance the building code is used).
Issue/Question No 3:
If I Introduce big non symmetric guide gaps for restraints in the model, say 10mm for one guide side and 15mm for the other side, is this handled automatically by program? i.e is the wind applied in ±directions in horizontal plan if this occur? Or do I need to build my own loadcases?

Discussion:
I understand that I will not get a straight answer, since the program must be flexible enough to cover a lot of different scenarios, for instance allow us to input different wind directions, wind speeds, "wind standards" and also not be to hard to control/understand, simple/understandable user interface.

Regards
Marcus
Benutzeravatar
rohr2support
Beiträge: 455
Registriert: Mi 14. Sep 2011, 08:23

Re: Wind loads EN 13480

Beitrag von rohr2support »

Hi

Question 1 about k-Factors

The load case based settings:
A Normal operating case, FSH=1
B Abnormal operating case FSH=1.15
C Case of emergency, FSH =1.2
D Case of Damage FSH=1.8
are provided as given in the nuclear codes. Unfortunately EN13480-3 has some additional settings so there is no equivalence for k=1.3.
If you want to use k=1.3 you can still set the superpostions for the stress analysis to manual and set K=1.3

Question 2 about wind superpositions

No EN13480-3 does not define how to superpose wind load directions. I guess the question is how the wind was measured. It the wind is the maximum in all horizontal directions, you may not need to combine this value again with other directions.
You can choose the way the superposition is done in the tab of the wind loadcase "load directions".

Question 3 about big gaps

Using supports with big gaps is strongly discouraged for systems which are subject to occasional loads like wind and earthquake. Leaving the pipe some space to accelerate before hitting the limit stop is a good idea if you want to deforme it permanently (like with a hammer) but not if you want to prevent it from breaking.
The suggested approach in ROHR2 is to calculate the occasional loads in a linear manner and disregard supports with gap above a small value (say 2mm - which you specify under "project settings -> Supports -> Ignore bearing with gap > 2mm" ). So your supports with large gap will not help you to hold the pipe in place. If this is sufficient, it means that the supports are not required for wind/earthquake.
You still have the possibility to set the option "Consider non-linear properties" in the load case setting for wind and earthquake. In this case the gap is considered with separate load cases. But this should be used only when you know what you are doing, as you would need to combine wind with all relevant operation conditions (not just one) and you have to ensure that dynamic effect when hitting the limit are not relevant.

Best regards

ROHR2 Support
Antworten