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:
Tab #1: Load Cases
The Load Case tab is used to review the load cases that were included in each analysis set.
Tab #2: Code Comb
The Code Combinations tab displays the combination sets defined for piping code compliance, which will be used to check code stress results. Some default combinations are will already be created, based on the active load cases and the code associated with the current system . Any default code combination may be modified, deleted or reset and any new user combination created and modified in the same grid. User-defined sets can also be defined.
Tab #3: Non-Code Comb
The Non-code Combinations tab displays the active load case combination set defined for any purpose other than code compliance (e.g. displacement and support results). Any default non-code combination may be modified, deleted or reset and any new user combination created and modified in the same grid. User-defined sets can also be defined.
Tab #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 the 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.
For more information see the following WIKI page: Is this a Valid combination using AutoPIPE?