If You have high steel structures or towers exposed to wind, how shall the displacements of the steel structure and vessels be handled. Some rules in germany allow the evaluation of this stresses against the figures of thermal expansion. This seams senceful at first sight, because the stresses out of displacement are self limiting as the stresses for thermal expansion. Nevertheless, if the steel structure is modelled as beam in the model, standard practice is the evaluation of the pipe stress as occasional load. What is the right procedure acc. to B 31.3?

Windloads bring in structures "Force from out".
And this have a primäry charakter.

The stress analysis of your piping system addresses two types of failure - collapse and fatigue.

In general, wind loads are force-based and not self-limited. These loads, applied to your piping system, are evaluated as collapse loads and must remain below material yield. As stated by Ohliger, these are primary stresses.

But you offer an interesting twist by loading the building. If the deflection of the building due to wind is unaffected by the piping, that is, if the piping stiffness does not change the building deflection, then I would accept the possibility that these wind loads could be considered as a secondary (fatigue-based and stress-limited) load. I know some piping codes allow three times yield for a one-time settlement. And other codes include seismic support motion as a secondary load. In these cases, however, there is limited cycling. If you want to consider the wind as a fatigue load, you would also consider the number of cycles. Now you have a numbers game, where you are counting cycles for different displacement sets (high wind, low wind, etc.) and taking a cummulative damage approach. CAESAR II can do this but I think it impractical.

B31.3 para. 302.3.5(d) hints at this - "When the computed stress range varies, whether from thermal expansion or other conditions...". I believe we are talking about one of these "other conditions" here.

Servus,

Ordinarily these wind anchor motions (WAM) are not considered. This in practice usually works out because although there may be many WAM cycles that are small and many more that are large their cumulative damage affect on the pipe is quite small. This is due to the fact that the piping geometry usually has adequate flexibility to keep the stresses of these imposed WAM displacements quite small.

However if you have a geometry and a pipe support/restraint system that is not adequately flexible for the WAM you can run into trouble!

So what stress level is too much????? Use the cumulative fatiuge calculation out of the B31.3 code 302.3.5 (1d) to see where your calculated stress puts you.

In 30 yrs + of this work I've only seen this become problematic a few times.

Auf Wiedersehn und...