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Just as the tightening of guitar strings changes the lateral stiffness and natural frequency, axial tension load in piping and structural frame elements increases lateral stiffness of those elements, whereas compressive loads soften lateral stiffness. Legacy pipe stress programs totally ignore these real world P-delta effects on element stiffness. P-delta also accounts for loading about the deflected position of the piping which is ignored by legacy pipe stress programs.
Another important consideration ignored by legacy pipe stress programs is the sequence or order of the applied loads. Whenever friction, gaps, or soil is modeled, the order of the applied loads can and will make a difference in design calculations. To take one example, proper analysis of a winter shutdown load case scenario should not start from ambient temperature, the shutdown should realistically start from the operational state where the piping is already in a stressed and deflected position, and then transition from there to winter shutdown temperature/pressure with removal of fluid contents load, if applicable. Legacy pipe stress programs cannot properly model that load case scenario.
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 pipe supports and anchors. 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 practical tool to properly consider combined pipe/structure interaction. Modeling structural frames in a legacy pipe stress program is time-consuming and very limited. 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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There are other important analysis considerations that CSiPlant offers such as nonlinear load sequencing which combines loads incrementally (important when friction or soil is modeled) including load sequencing of multiple thermal loads, nonlinear time history dynamic analysis which can account for gaps, friction, and one-way supports in the dynamic analysis, a unique nonlinear damper element, unique soil modeling features including soil distributed imposed displacements, nonlinear load sequencing (important when friction or soil is modeled) including load sequencing of multiple thermal loads, and the time saving ability to work with user defined libraries of pipe supports and expansion joints which can be reused to name a few other CSiPlant advantages.