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Large RISA Models

Large RISA Models

Large RISA Models

I have seen advertising for RISA3D and the huge structural models that are being analyzed. What kind of computer systems is being used to run those large of models? My models are not all too large in comparison. My Computer is @2.5Ghz & 5.9 GB of RAM(It is also 64bit) and my models still take a while to run through all the load combinations & If I were to run a batch I get an error. The only way I can get my model to run is by reducing the # of sections and # of internal sections being solved (2&5 respectively). I noticed that the # of Sections by default is 5 and Internal by default is 100. What is the magic behind these numbers? Does anyone have comments on how I get my models to run by reducing the sections?

RE: Large RISA Models

There are a few things associated with todays building codes that are really increasing solution times.  

1) The large number of load combinations required for a solution.  
A possible solution to this problem: Personally, when I have 100+ load combinations I will always run an "envelope" solution to determin which LC's are generally controlling the design of my structure. Usually this results in may 10 or 15 LC's which mght control. From that point on, I will run a batch solution using only these controlling LC's.  

2) The stiffness adjustment requirements of the Direct Analysis Method.  If you have to solve each load combination to determine the level of axial load and then adjust your stiffness matrix, then that really hurts you.  You end up solving every load combination twice.  Even worse, you're decomposing the stiffness matrix for every single load combination.  

A possible solution to this problem: During the early stages of design (when your member sizes may be changing and such), turn off the stiffness adjustment of the Direct Analysis Method. This can be done on the Codes tab of the Global Parameters.

At least those are the things that immediately come to mind.  There are certainly other ways to increase speed or reduce memory usage as well.   

RE: Large RISA Models

How do you turn off the stiffness adjustment? I went in global/codes tab but did not see that option? If you go to the global parameters/solution tab what values do you often use for the # of section & # of internal sections? I use 2 & 5.

RE: Large RISA Models

The turning off of the stiffness adjustment is a check box directly underneath the HR steel code selection.  But, that check box only appears if you are using the AISC 13th edition steel code.   

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