Collecting phases
With regard to using phased correctly, what exactly does "collecting phases" actually do? For example, say I have a simple beam as an initial phase. At some point in the future the beam will have additional loading applied along with a new middle support added. What is the proper way to set up the completed phase and each individual phase.http://docs.autodesk.com/RSA/2013/ENU/filesROBOT/GUID-B63EE66D-4406-4838-B238-507A1AAD05FE.htm
What about load combinations? Should these be setup under each phase or under the completed phase?After collecting phases you can create combinations with cases from different phases.Then to get results, how does phase collection work? When would I want to chose a different phase from the drop down box?this is the window where you can switch between phases.I've been through the help file and made many test models, but I can't seam to understand exactly how it should be setup.
http://forums.autodesk.com/t5/Autodesk-Robot-Structural/Using-Phases/td-p/3501632
Rafal Gaweda
I have already shortly explained it in this forum post:
Different phases In Robot correspond to different calculation models - with possibly different support conditions, different loads, some elements existing or not and even different properties of analogous elements.
Collecting phases superposes the results from these different models (phases) into one model (so called collected phase) - the geometry, support conditions, properties are taken from base phase specified in collection window:
Load cases and combinations from the base phase are left in the collected phase with the original numbering while load cases and combinations from other phases are transferred to the collected phase with the offsets of 1000, 2000,... for consecutive phases.
The recommended approach when defining phases is to define the most geometrically complete model (all elements, nodes existing, panel FE meshes generated and frozen, etc), run analysis for it and then to define phases for appropriate selections of bars, nodes and panels.
This way later it should be no problem for Robot to identify corresponding elements after collecting phases.
I have attached very simple example of beam with and without internal support which was defined using phases: phase 1 "Without internal support" and phase 2 "With internal support".
After running analysis and collecting phases with phase phase 2 "With internal support" as the base phase the envelope of bending moment diagrams MY can be displayed for collected phase and considering results from both phases:
The geometry and support conditions correspond to the base phase but on the envelope diagram of MY moment the results corresponding to simply supported beam (case 1001) can be indentified too.
What about load combinations? Should these be setup under each phase or under the completed phase?
As concerns combinations if there is no need to define combinations of cases from different phases then it is recommended to define combinations inside each phase. After collecting phases all of them will be transferred to the collected phase in the same way as simple load cases.
If combinations of cases from different phases have to be defined then it is necessary to define them at the end in the collected phase. The disadvantage of it is such that after modification in any phase it will be necessary to re-run analysis and to collect phases again so combinations defined in previously collected phase will be lost.
When would I want to choose a different phase from the drop down box?
This window is used most often to select active phase to make some modifications in it or to view results for it - usually before collecting phases.
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Regards,
Pawel Pulak
Technical Account Specialist
If I define a number of load cases + loads in a specific phase, will it not be possible to edit these loads in loads/load table as usual?
No, it is possible to edit loads in specific phase when such phase is activates. It is easier to see which phase is active in appropriate view or table if this view or table is not maximized - it is displayed in the title bar of it:
Also, if I want to add a UDL to the floor plate in all phases, will it be required to do it individually in each phase?
No, it is not necessary. See this help topic:
http://docs.autodesk.com/RSA/2012/ENU/filesROBOT/GUID-541E37E3-5DEB-4524-9CCD-2921162E87C-420.htm
"Beside each of the defined phases are the number and a toggle for bar/element transfer to other phases. The defined bars/elements in the currently selected phase will also be included in the phase for which the transfer has been switched on. If off, the bars/elements defined for the currently selected phase will not be included in the given phase."
This check-box works not only for bar/element transfer to other phases. It works also for creation of load cases or definition of loads in load cases. But when using this setting pay attention to switching it off when not necessary - it is very easy to forget about it and to make unnecessary changes in the model
Furthermore, if a certain number of phases are defined is it possible to add and/or move columns in just one of these phases? I'm trying to do it and I keep getting a warning message saying "No active selection for this operation. Do you want to perform these operations for the whole structure".
The message is probably caused by selecting column without end nodes and trying to move it. But moving bars should be avoided - especially if it results in intersecting with another bar in different place than in some other phase. In such case it is recommended to use copy and delete "the original" in appropriate phase. In opposite case it may be impossible to identify corresponding element after collecting phases. I have shown such example in the screen capture below. Numbers of calculation elements are displayed in light blue. It can be seen that after Move command two calculations elements 6 7 are replaced by single calculation element 7 while element 6 is degenerated to point. It can result in incorrect collection of phases for the segment of beam between nodes 7 and 4.
Additional remark related to model generation and calculation elements for phase structures: after the first run of Phase Collection model generation is switched off for the phase model - unchecked "Model generation" and not available "Structure Model" tab in Analysis Type window shown in the screen capture below. So starting from this point any modifications of existing phases or definitions of new ones, which require model generation (like intersecting of elements) are not possible. In such case it is necessary to delete all phases and start creation from the beginning.
Is it required to do the following:
1. Set the phase that needs to be modified to the base phase.
2. Activate the collected structure (base phase as above).
3. Select the members that needs to be moved/modified.
4. Activate the phase that needs to be modified.
5. Move the members in the phase corresponding to point 4 (as marked in point 3).
Modifications should be made only in the appropriate active phase. Or if you want to make them simulataneously in some other phases you should mark "transfer" check-box for them (see my explanations above). There is no need to activate collected phase. The only modifications made sometimes in collected phase are not related to the model itself but to results - like definition of combination of cases from different phases (if it is necessary).
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If this post answer your question please click "Accept as Solution". It will help everyone to find answer more quickly!
Regards,
Pawel Pulak
Technical Account Specialist
Yes, it can be done using phases.
In some cases it can be also done without phases: defining bracings as tension only - providing they all switch off for gravity loads and simplifications resulting from linearization of non-linear model for modal and response spectra analyisi is acceptable.
Regards,
Pawel Pulak
Technical Account Specialist
I suppose that if we are working with elastic (linear) analysis, then only with phases we are able to do such kind of approach aren’t we?
Yes, except of 2 separate models (2 RTD files).
Is there any kind of problem when we try to combine load cases caused by vertical loads (dead and live loads) that belong in a phase (part of a structure, i.e the part without braces) with seismic load cases referring to the whole structure?
No, there should be no problem with it. But some disadvantages can be observed:
a/ if necessary to define some combinations containing cases from different phases (combinations "between phases") then it has to be done after collecting phases. In such case any repetition of analysis will result in necessity to re-run collecting of phases, so it will be necessary to re-define combinations "between phases"
b/ for elements not existing in all phases (like bracings in your model) results for combinations "between phases" will be not available (N/A in tables) because for some components of these combinations they will be not available - no availability in NOT treated as zero.
Modal analysis should normally take place in the whole structure, isn’t it?
Yes, modal analysis should be made for complete structure.
In the 2nd case that you described when we use tension bars, the compression state at members that consists the bracing system wouldn’t ever appear. I personally would prefer the brace members to be active in both tension and compression (actually it is more usual that these members fail due to compression-buckling rather than tension). But anyway I would like you to explain the option “inactive bars” (I haven’t used it yet): if some members are inactive, so they don’t contribute at all in the bearing system, then why to define them..? (maybe they can be ignored-inactive only for a selected load case?)
“Inactive bars” are for temporary switching off some elements when calculating various variants of structure.
Regards,
Pawel Pulak
Technical Account Specialist
According to remarks of Tuctas from P.S.:
Yes, you are right - both using 2 separate rtd files and using "inactive" members you have no possibility to merge the results from different variants inside Robot. So you have to do post-processing "by hand" outside of Robot.
Only using phases it can be done inside Robot.
Regards,
Pawel Pulak
Technical Account Specialist
Some update concerning point b/ of the message 9:
@pp2008 wrote:
b/ for elements not existing in all phases (like bracings in your model) results for combinations "between phases" will be not available (N/A in tables) because for some components of these combinations they will be not available - no availability in NOT treated as zero.
This limit was removed in Service Pack 3 for ARSA 2014. Can be downloaded using live update or the link below:
http://usa.autodesk.com/adsk/servlet/ps/dl/item?siteID=123112&id=22436870&linkID=13140816
Regards,
Pawel Pulak
Technical Account Specialist
