Questions regarding pure wind and seismic loads in CAESAR II

If the pipe model contains nonlinear constraints (such as clearance between obstacles, sliding friction surfaces, or the pipe becoming detached under certain operating conditions), it is conceptually not possible for the \"L4\" and \"L5\" states you mentioned to occur. Some companies use in practical projects a method that involves removing all nonlinear factors from the pipeline model to obtain a load. Conceptually, this load corresponds to what could be referred to as “L4” and “L5”. However, it remains to be determined whether this load can actually be used in such projects; for example, it is necessary to consider how much this load differs from the original load

The last edit to this post was made by hejoys on 2016-4-25 at 10:21. A brief explanation of \"non-linear constraints\": for example, if the gap between the stops on the support is 5 mm, and under a certain load – say 10 kN – the pipe moves 3 mm; in this case, since the pipe does not come into contact with the stops, the load effect on the pipe support is 0. When this load continued to increase to 20 kN, the pipe shifted by 6 mm; at this point the pipe had come into contact with the stop block. The load effect on the pipe support was assumed to be a bending moment of 50 kN·m (assuming that the pipe support is a typical member subjected solely to bending forces). It can be seen that although the load increases linearly over time (10 kN -> 20 kN), the load effect on the support does not increase linearly either (from 0 moment to 50 kN·m of moment).

I don’t understand what you’re saying, because I’m just starting out and learning*

Thank you very much for your explanation; I wasn’t at the company recently, which is why the reply was delayed. I would like to ask you a few more questions. First, regarding what you mentioned earlier – that conceptually L4 and L5 conditions, as they occur in my operational scenario, are not allowed – I would like to know what exactly is meant by that concept. Second, if I set all the clearances of the thrust and guide frames to 0, meaning there are no clearances at all, can I then use the L4 and L5 conditions that I have defined earlier? Thank you again for your answer.

A concept refers to operating conditions calculated by a model with nonlinear constraints; when linear subtraction or addition is performed, the results become distorted. The gap is just one element among the nonlinear constraints; others include sliding friction, tube emptying, and other factors. When all these nonlinear elements are removed from the model, it becomes a purely linear model. The conditions calculated by this model can be subjected to linear subtraction or addition. However, this model itself remains distorted because it eliminates gaps, eliminates sliding friction, and eliminates voids……

Thank you very much for your answer! I just thought of another question: for the L4 and L5 operating conditions here, if I use combinations such as L4+SUS or L5+SUS as accidental loading conditions due to wind or earthquakes, should that work? Also, when looking at the stress conditions due to wind and earthquakes, should I consider only L4 and L5, or should I look at the stresses under the combined condition of L4+SUS and L5+SUS? Because I encountered a colleague today who was a bit confused when discussing this issue, and I hope to get your answer! Thank you so much!

If by L4+SUS you mean L4+W+P1+F1, the problem remains the same: linear subtraction within L4 is conceptually invalid for nonlinear constraints. To view the stress conditions due to wind and earthquakes, one should look at L2 and L3. If a separate load value is indeed required for the pipe rack design, I have thought of two approaches: 1. Check whether the support reactions of this model, after removing the nonlinear constraints, differ significantly from those of the original model; if the difference is not significant, then loads can be applied separately at L4 and L5, as you suggested. 2. If the support reactions of the two models differ significantly (for example, the reactions of the nonlinear model are much larger than those of the linear model), you should inform the pipe rack designer that the nonlinear constraints in this pipeline model play a controlling role, preventing the determination of separate load values. Using the method above, compare the models of various projects more closely to see if any patterns can be identified. If the reaction forces for the models of each project differ little, it means that projects of a similar nature can generally have loads applied to them using L4 and L5 separately.

This aspect is too complex; it should be simplified appropriately depending on the specific circumstances, or analyzed on a case-by-case basis