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AlexS_2013
Posts: 25
Registered: ‎09-16-2013
Accepted Solution

Load sequencing/construction stages

1290 Views, 9 Replies
10-28-2013 10:17 AM

Hi everyone,

 

I need to consider construction stages in my model of a high-rise building. There are levels with outriggers, so if I don't do that and apply whole dead load at once to a complete model, columns below levels with outriggers turn out to be in tension, what is obviously does not represent the "reality". In order to avoid that, dead load has to be applied as the building goes up, i.e. I need to consider load sequencing.  

 

I tried phases in robot, but I think they are not applicable here. Robot treats each phase as a separate model, and there is no connection between them in terms of loading.

 

Anyone has an idea how to implement staged construction/load sequencing in robot?

Thanks.

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Contributor
alfredmx
Posts: 13
Registered: ‎01-05-2012

Re: Load sequencing/construction stages

10-28-2013 05:43 PM in reply to: AlexS_2013

Hello,

 

I've been able to do a staged analysis taking into account load sequence in Robot using information from individual models (note that bar elements must have the same number in all models). Due to the great amount of data that you need to save for each stage, I ended up writing a program.

 

Regards,

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Product Support
pp2008
Posts: 529
Registered: ‎06-23-2008

Re: Load sequencing/construction stages

10-29-2013 02:39 AM in reply to: AlexS_2013

Load sequence in phases can be considered applying the self-weight load only to the story added in the appropriate phase. Then, after collecting all phases with the most complete phase treated as the base one, it is necessary to define a combination of these self-weight cases from all phases. It is illustrated on the screen capture below.

phases_sw2.png

 

As concerns displaying results for such combination of results from various phases it is necessary to use RSA 2014 with Service Pack 3.

In previous versions Robot was able to display results for such combinations only for elements existing in all phases considered in the combination - so in practice only for the bottom story in the above example :smileysad:

 

Regards,



Pawel Pulak
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Contributor
AlexS_2013
Posts: 25
Registered: ‎09-16-2013

Re: Load sequencing/construction stages

10-29-2013 06:37 AM in reply to: pp2008

Thank you for your response!

To clarify, if after doing all this I want to use total dead load (with load sequencing) in load combinations, what should my approach be? Should I create design combinations for every phase? Or there is another faster way of doing that?  

I'm a bit confused...

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Product Support
pp2008
Posts: 529
Registered: ‎06-23-2008

Re: Load sequencing/construction stages

10-29-2013 10:52 AM in reply to: AlexS_2013

If these combinations "between phases" are related only to some types of loads (usuallly selfweight)  then there are some ways to simlify it, like for instance:

1/ defining design combinations in one phase - usually the most complete one, used as a base phase during collecting. In these combinations selfweight from this phase can be used

2/ after analysis and collecting of phases defining in the collected phase the combination of selfweight cases from various phases as mentioned by me before

3/ in the collected phase modifying the combinations defined in step 1/ in such way that the selfweight case from the base phase will be replaced by the combination defined in step 2/. Such modification can be done on the Edit tab of the table of combinations. 

 

What is important in case of phase structures is that after any modification in any phase it is necessary to repeat analysis and to collect phases again - so steps 2/ and 3/ have to be repeated too:smileysad:

Some improvement wish related to it is registered there.

 

Regards,



Pawel Pulak
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Member
Camh77
Posts: 5
Registered: ‎05-14-2014

Re: Load sequencing/construction stages

05-15-2014 02:47 AM in reply to: pp2008

Hi,

 

Any work example to show how to build this constructional sequence analysis for a high rise building?

 

Thanks

 

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Member
mrkevinht91
Posts: 5
Registered: ‎10-18-2013

Re: Load sequencing/construction stages

05-17-2014 06:39 PM in reply to: Camh77
Is it possible to copy loads to another story ? I have multi stories but add loads manually is not a good idea. I try the function "active story" in robot but it doesnt work.
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Product Support
Rafal.Gaweda
Posts: 5,604
Registered: ‎04-26-2010

Re: Load sequencing/construction stages

05-19-2014 12:53 AM in reply to: mrkevinht91
No you can not copy loads only.
Loads are copied together with copied objects if loads are assigned to them.


Rafal Gaweda
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*Expert Elite*
t.sautier
Posts: 456
Registered: ‎12-14-2012

Re: Load sequencing/construction stages

05-21-2014 03:19 AM in reply to: mrkevinht91

I don't know if is related with construction stage but apart editing the loading table to add element to one loading and therefore copying loads from element a to element b (doesn't work with contour load), you can do this :

 

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Product Support
pp2008
Posts: 529
Registered: ‎06-23-2008

Re: Load sequencing/construction stages

06-13-2014 09:00 AM in reply to: Camh77

There were some requests (both in this forum thread and in private messages) related to showing how to model the construction sequence using phases.

Here is the short video illustrating it for a very simple model.
The model contains both bar elements (beams and columns) and wall panels composing 2D frame with 15 stories. It is done this way for simplicity and speed - analogous approach when extending it in 3D and adding slabs.
This tutorial shows the workflow corresponding to the screen capture in the Message 3 of this thread - the sequential application of self-weight useful especially in high RC buildings, where the differential axial shortening ( DAS ) effects may be significant.
I have also tried to show the efficient way of working with phases in Robot:
a/ remembering about freezing meshes to avoid problems to identify identical element after collecting phases
b/ avoiding work in maximized viewers to see the number of active phase in the title bar of each viewer or table
c/ preparing loads prior to defining phases to later avoid repetition to modify, add or delete them in many phases
...

Here are the main steps of the tutorial:

  1. checking whether FE meshes in panels are frozen
  2. opening the table of loads and minimizing windows to easily control the active phase in the title bars
  3. changing self-weight from “Whole structure” to “Part of structure” to avoid this operation later for each phase
  4. defining 15 phases (part of the video deleted to avoid repeated operations)
  5. modifying the list of elements to apply self-weight in each phase (part of the video deleted to avoid repeated operations)
  6. switching to the most complete phase "ph15 all" and defining the additional load case containing self-weight for whole structure to compare it later with the same load applied sequentially
  7. running analysis - it can be noticed that analysis is repeated for consecutive phases
  8. collecting phases with the most complete phase "ph15 all" as the base one - the collected phase (phase 0) contains results from all other phases (load cases from other phases transferred to it with 1000, 2000, 3000,... offset)
  9. defining in the collected phase (Ph:0) the combination to cumulate self-weight from all phases in the sequential way
  10. some comparisons to show the differences resulting from the sequential application of self-weight in phases (the combination defined in step 9/) and applying it together for whole structure (the load case defined in step 6/) - showing differences in deformed shape and in reactions. Generally these differences increase with the increase of the number of stories.

The example for simplicity does not contain other loads - in the typical situation they would be defined in the most complete phase (here phase "ph15 all")

 

 

 

I have also attached the 2 files corresponding to the beginning and the end of this demo.

Best regards,



Pawel Pulak
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