How to analyze a FDN with ribbed beams in one direction and grade beams in another direction with STAAD Foundation advanced?

Question

Hello everyone, 
 I'm trying to analyze a FDN (combined footings with ribbed beams in longitudinal direction and jointed with grade beams to another combined FDN. 
 Is there a way to analyze this kind of complex FDNs with STAAD FDN adavanced or any equivalent solution or modeling?

Seth Guthrie · Answer

SFA can handle simple combined footings with a ribbed beam, but not with beams in both directions. This is the kind of design that Ram Concept excels at. Otherwise, using some kind of equivalent sections is the best you can do.

Sye · Answer

It is correct that the combined footing job type does not allow one to define grade beams connecting the various footings. 
 However in STAAD Foundation Advanced ( SFA ) there are ways to handle this type of modeling. 
 To begin with, if your intention behind modeling the grade beams is to get additional resistance to sliding against lateral loads, what you can do is, account for the additional sliding resistance by adjusting the factor of safety against sliding from within the combined footing module. That way you are not modeling the grade beams but the sliding checks would not show as failed in your calculation sheet due to the lower factor of safety input. 
 Alternately if you are looking for an analysis of the whole system with the ribbed footings connected by grade beams, you may define the foundation job type as mat. This would allow you to model the individual combined footings using mats and you can then use physical beams to model the ribbed beams and the grade beams ( use the Physical Beam table within Mat Foundation job to model these beams ). The combined system can then be analyzed using a full fledged FE analysis in SFA.

Sye · Answer

When the footings are modeled using separate boundaries, results for one boundary will be visible at a time but you should still be able to analyze/design each boundary and also view the results for each boundary. If you are having difficulty with the same, please upload the model and I will take a look. 
 
Regarding large analysis time for mat analysis, as you know, SFA defines support springs as compression only and hence the analysis is an iterative type analysis which may take some time. However 5 hours of analysis time seems absurdly high. Here are some of the things that you can do to cut down on analysis time 
 
1.	Ensure that the model is on a local drive and NOT on a network drive. I have seen this being the problem more often than not. 
2.	Ensure that you are including ONLY those combination cases as part of your job that requires an analysis. Avoid including basic primary load cases like wind or seismic acting by themselves as these can lead to huge number of iterations leading to large analysis times. 
3.	Avoid using a mesh size that is very fine. The software’s meshing algorithm is equipped to generating finer mesh at regions where needed and so try using a target mesh size may be double or three times what you are currently using. 
 
If the above does not help, please upload the SFA file and I will take a look