## Robot Structural Analysis

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# Continuous Footing Design - Initial Setup Confusing

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I am having difficulty trying to design some simple continuous footings. The video on continuous footings on this site: http://www.robotoffice.com/rsa/ is awesome, however, the initial part is confusing. The inidividual applies an "Elastic Ground Bar" to some objects. What were those objects? It lookes like those objects turn into a "T" shaped footing. How would I model a "T" shaped continuous footing? Does the initial bar have to be that shape before I apply the "Elastic Ground Bar" to it, or is it changed once the continuous footing is designed?

If I wanted to model a rectangular grade beam that sits under a simple retangular frame, how would I do this? What about modeling a continuous "T" footing under a wall? Do I need to model a bar under the wall first?

Great forum. Best resource by far!

Solved! Go to Solution.

# Re: Continuous Footing Design - Initial Setup Confusing

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You should define either a rectangular or 'reversed' T shape RC beam under a wall.

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

**Artur Kosakowski**

# Re: Continuous Footing Design - Initial Setup Confusing

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What am I doing wrong? Attached is a sample model that has continuous footings under a simple box shaped structure. It has both columns and walls that bear on the continuous footings. I get a no support warning when I verify the model. The model won't solve as it won't converge. Really confused right now. Any chance you could look at the sample model and tell me where I screwed up? I wanted to test both point loads on continuous footings as well as both vertical and lateral loads coming from wall panels.

# Re: Continuous Footing Design - Initial Setup Confusing

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1. There are no horizontal restrains (supports) which cause the instability warnings. Solution: define either some horizontal nodal supports or modify elastic soil definition adding some Ky (Uy) elasticity.

2. As you rotated the supporting beams by 180 deg the definition of unidirectional elastic soil should be Uz- rather than Uz+ (definition is in the local coordinate system of a bar). In such case there will be no convergence for wind load cases but this is obvious as there is no vertical load to stabilize the structure. All combinations converge.

*If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.*

**Artur Kosakowski**