Applies To
Product(s): AutoPIPE,
Version(s): 2004, XM, & V8i
Environment: N/A
Area: Load Cases
Original Author: Bentley Technical Support Group


Load Combinations 

To review, modify or print new post processing combinations defined for the current model, select Tools> Combinations. The exact list of combinations will depend on the active load cases analyzed and the code
associated with the current system.

There are four distinct TAB GRIDS appearing on the Combination dialog:

  1. Load Cases - All the analyzed static and dynamic load cases are displayed for each analysis set in the grid.

  2. Code Comb. - The "Code Compliance" grid displays the combination set defined for piping code compliance.

  3. Non-Code Comb. - The "Non-Code" grid displays the active load case combination set defined for any purpose other than code compliance

  4. User Allowable - The "User Allowable" grid displays the allowable stresses to be used in the pre-verification and stress summary reports (ASME NB, NC, and ND codes only). 

NOTE: Press the help button on tthe Tools> Combinations dialog to see on line help details for each of the available features.

User load combinations

Once an analysis has been run, use Tools> Combinations to see all code and non-code combinations. AutoPIPE automatically combines the loads required to calculate piping code stresses. The "Other" category contains loads, which need to be combined by the user in order to analyze piping loads on equipment, piping loads on supports, and deflections under various applied loading conditions.

In order to evaluate cold (ambient) load and operating loads on supports and equipment, users may combine individual loads by using creating User-defined Combinations on the respective Code/Non-code comb. tab. For the combination name, choose something meaningful such as GR+T1, GR+T1+W1, etc. Typically, combinations for support and equipment loads are made using the Sum or Absolute Sum combination methods, although users may also use the SRSS combination or Resultant maximum methods to combine loads. On the same screen, select the loads to be combined to make up your operating loads (see Figures below).

 AutoPIPE 6.0 - 8.6

AutoPIPE V8i 9.0 and higher:

Non-Code Combinations Dialog

Code Combinations Dialog


After defining all your operating load combinations (GR+T1, GR+T1+W1, GR+T1+W2, etc.), it may be a good idea to create 2 more combinations for your MIN and MAX to more easily review support loads. Typically, engineers will use the MIN and MAX for their GR and all operating load combinations, ignoring the individual loads for Tl, Wl, W2, El, E2, etc. The MIN and MAX sort through all the selected loads and load combinations, and produce Minimum and Maximum results. The MIN and MAX results for support loads and deflections are a great tool for creating summary reports for the civil/structural engineer responsible for piping support design, saving significant man-hours in the review of worst case loads on supports and equipment.

For reporting purposes, users can minimize output by selecting

AutoPIPE 6.0 - 8.6: Tools> Non-code Combinations> 

AutoPIPE 9.0 and higher: Tools> Combinations> choose Code/Non-code Tab and press New Button.. 

select and de-selecting individual loads or combinations which do not need to be reported. After saving these combinations, the *.CMB file can be copied and renamed to another job, eliminating the need to create user combinations each time.

Please note that users can input a "-1" in the load factor field to analyze wind and seismic loads in the negative direction, e.g. GR+T1-WI, GR+T1-W2. This "-1" feature can be used if gaps or friction do not significantly affect piping loads at a particular support point or equipment connection. This negative direction can be included as part of your user load combinations, enabling users to evaluate results using operating load combinations with wind and seismic analyzed in both the negative and positive directions. AutoPIPE does consider gaps and friction only for the load directions chosen for the original analysis.

Questions and Answers:



See Also

Bentley AutoPIPE

External Links

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

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