Using Risa to Determine Structure Loads along top of Foundation

[ollie24]

So I am creating a Mathcad 15.0 template to design a concrete foundation for a small 16ft x 36ft building. Designing the foundation is just fine. What I am trying to incorporate in the template is allowing the user to use Risa (not Risa foundation) to apply the load cases and combinations to the Risa model (typical roof live and dead loads, snow and wind, wall dead load, floor live and dead load). The foundation is a continuous concrete foundation wall below grade with a footing. The floor is a concrete slab with 2 spread footings. There are 28 anchor bolts total around the foundation perimeter. If part of the design process includes creating a Risa model, can the user (me for now) end up with a distributed load along the top of the foundation wall (and then incorporate that load into the Mathcad template)? Or should I place pins at the locations of the anchor bolts and simply come up with reactions at each pin? What do you recommend? I don't want to simply get reactions at all those pins, but that is all I have been able to work out so far. Thanks in advance!

 

[JoshPlumSE]

Not sure I understand the question. Maybe the question isn't clear, or (and this wouldn't be the first time) I'm just not properly envisioning what you're trying to do.

What are you entering in RISA and what is that model trying to analyze? Then what results are you trying to get out of RISA?

 

[ollie24]

Hello! So the template allows the user to input wall dead loads, floor dead load, roof live and dead, wind, snow, and so on in Mathcad (all they have to do is follow instructions and input numbers). I am trying to allow the user to also create a model of the simple 1-story building in Risa just to apply the loads and load combinations (and to have a good visual of the building). Then, based on the results of the model, the user can go back to the template and design the foundation perimeter. Building the calculation for the design of the foundation (continuous concrete wall with footing), reinforcement in the wall and footing along the perimeter, and the anchor bolts is not an issue. But I am trying to figure out what results I should get from Risa that the user can use as loads along the top of concrete. Ha I am sorry if it doesn't make sense. Is Risa only able to produce reactions at the structure supports since Risa is not RisaFoundation? I haven't used RisaFoundation, but from looking at it, I think it just designs the foundation like my template is doing. My approach for designing the foundation is considering 1 foot of length to determine footing width and so on.

 

[ollie24]

Would it be possible to get a service load (dead and live) in kip/ft along the base of the simple building structure in Risa from all the applied loads? Is Risa able to do that?

 

[JoshPlumSE]

If you're looking for "reaction" results from a RISA model, then there are two types of results you can get.
Type 1:
Joint reactions at an individual node. This would be a single load (or moment) with respect to the global directions at that joint.

Type 2:
Wall Panel Reactions for a wall. These are given in TOTAL reaction with respect to the center of the base of the wall. So, you would get a vertical reaction (relative to the global axes, not the wall's axis) in kips. And, moments (also with respect to the global axes).

However, you will also get a wall force results spreadsheet that is probably closer to what you want. You will get an axial force in the wall and an in-plane moment for the wall. You could convert thos into a distributed load, of course. But, that's not how the program would report it.

 

[ollie24]

Okay, so looking at the plate forces spreadsheet (I have plates instead of walls just temporarily). So when the top of the spreadsheet says "(per ft)", is it saying for each 1 ft of length, here are the 3 moments and 3 reactions (in x, y, and z) basically at a single point of the segment? And then the loads at that one point can be distributed along the 1ft segment?

Yeah, I could work with the reactions at a single node (Type 1), but I am trying to get a load along a 1ft segment on top of the concrete foundation.

 

[JoshPlumSE]

The plate force results spread sheet is the result for a single, individual plate. Not the result for an overall model or a wall. You would need a mesh of plates to have an accurate overall analysis.

Assuming you have meshed your model appropriately, then plate force results spreadsheet will show you the force or moment (per foot) at the natural center of each plate. You could use the Fx of Fy value (depending on plate orientation) as the approximate axial force per foot in that plate. That should be reasonably accurate (assuming you have a good model / good mesh). Of course, if there is variation in the value between adjacent plates it means the axial force is varying.