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?
Solved! Go to Solution.
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.
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.
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
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...
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
Some improvement wish related to it is registered there.
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:
- checking whether FE meshes in panels are frozen
- opening the table of loads and minimizing windows to easily control the active phase in the title bars
- changing self-weight from “Whole structure” to “Part of structure” to avoid this operation later for each phase
- defining 15 phases (part of the video deleted to avoid repeated operations)
- modifying the list of elements to apply self-weight in each phase (part of the video deleted to avoid repeated operations)
- 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
- running analysis - it can be noticed that analysis is repeated for consecutive phases
- 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)
- defining in the collected phase (Ph:0) the combination to cumulate self-weight from all phases in the sequential way
- 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.