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It doesn't take a pipe stress or structural expert to see that pipe/structure interaction can often have a profound impact on design calculations as compared to piping-only models with rigid supports. Not only consideration of support structure flexibility which is important, but also consideration of imposed displacements at pipe support locations caused by structural frame displacements. Pipe racks are often designed to accommodate lateral deflections of Height/100 or Height/200 under wind or seismic load. That means 2", 3" or more imposed displacements at some pipe support locations. Sometimes even small imposed displacements can be quite impactful for design calculations. There is also a coupled analysis effect to consider, particularly with rack structures supporting large diameter piping in which the cross sectional area of some pipes can be larger than the supporting columns.
Proper consideration of pipe/structure interaction has typically been ignored or greatly oversimplified because before CSiPlant there was not a reliable, feasible tool to properly consider combined pipe/structure interaction. A typical pipe rack structural analysis model has a LOT of assigned loads which account for weight load of heavy equipment, live loads, cable tray loads, fireproofing, and other entities with significant weight and mass. Those assigned loads need to be properly accounted for if you want to have a realistic analysis of piping combined with the structure.
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