Applies To Product(s): AutoPIPE, Version(s): 2004, XM, & V8i Environment: N/A Area: Analysis Subarea: Original Author: Bentley Technical Support Group Whenever a static analysis load set includes Gaps/Friction/Soil it is calculated using a non-linear analysis. As a non-linear analysis, individual load cases (i.e. Gr, T1, P1, E1, W1, etc..) are applied one at a time in a sequence. This specific sequence does affect the calculated combination results (see AutoPIPE online help for more details). For example, by default, occasional load cases like Earthquake or Wind are analyzed after Pressure cases, that are applied after Thermal loads, that are applied after the initial load case Gravity. Wind hitting the operating position of the piping may calculate different support loads than earthquake or wind loads calculated just after GR (wind hitting the ambient position of piping). When perfoming a nonlinear analysis, select Loads Static Analysis Sets and check boxes in the "Non-Linear" columm or enable Gaps/Friction/Soil inside of an analysis set . To define all non-linear options, modify the analysis set, and check the option "Gaps/Friction/Soil", Click OK and the next screen appears, see online help for details on this dialog screen. For more complicated load sequence, uncheck the "Use Default Sequence" box to modify the Load sequence and press OK button as shown below: Attention: 1. Please see the following AutoPIPE help section: Help Contents Search Tab enter " Understanding Load Sequencing " (include the quotes), press List Topics button, double click on the selected topic from the list provided to see more information select the hyper link for "Understanding Load Sequencing". 2. Open the PDF file directly from the AutoPIPE folder, search for "Load_Sequencing.pdf" or "Non_Linear_Load_Sequencing.pdf" on your computer. 3. Additional documents found on the WIKI sites: a. Non-linear_Guide_explained b. Discussion of AutoPIPE Advanced Non-Linear Analysis Engine c. Understanding Non-Linear Load Sequencing d. Treatment of Support Friction in Pipe Stress Analysis e. Nonlinear Effects in Piping System Analysis f. Improved Iteration Strategy for Nonlinear Structures g. Defining Nonlinear Wind Load Case Additional Information: The Non-linear method is a sequence of applied load cases as defined on the initial states dialog (shown above). For example, a guide support with 0.2" gap left / right, non-code combination GT1E1, is analyzed by: 1. First applying the Gravity weight load case to the system and calculating the deformation based on modeled restraints. 2. Then the thermal expansion load case (T1) is applied to the deformed model, and again a new deformation is calculated. 3. Finally, as indicated above, occasional load case E1 is applied to the deformed model, and the final deformation is calculated. When looking at the output report In the output report only look at the operating conditions (i.e. GT1E1, GT1W1, etc..) and not the individual load cases (i.e. Gr, T1, E1). The individual load case(s): A. may have displacements that are larger than a gap on a support allows or B. support may have a load in a direction of a gap. However, when the individual load cases are added in a valid combination, the results of non-linear load sequencing are correct. Review of 3 General methods used by Stress Analysis computer programs: In 2009, ASME published that there are generally 3 methods used by most computer programs for stress analysis, 2 of which "General Straightforward Approach" and "Algebraic Subtraction Approach" (used by Caesar II) were found to produce inaccurate results. Only "Operating Condition Approach" used by programs like AutoPIPE, FE Pipe, Ansys, Abacus, Simplex II. that meets the code philosophy and requirements. Example: Example: Summary: When support conditions change, superposition leads to inconsistent and less accurate results. Using AutoPIPE's method of loading sequences is much closer to reality and is used by the best known programs such as ANSYS finite element, FE -PIPE, ABAQUS, etc. Reference: The non-linear technical paper refered above: https://www.asme.org/products/books/pipe-stress-engineering See Also Bentley AutoPIPE External Links Bentley Technical Support KnowledgeBase Bentley LEARN Server Comments or Corrections? Bentley's Technical Support Group requests that you please submit any comments you have on this Wiki article to the "Comments" area below. THANK YOU! Gaps/Friction/Soil
↧