What's wrong with footing elevations?

[kgatzke]

Why are footing elevations defined by the top of the footing?  I why am I getting a message telling me the footing was moved to the bottom of the column when I try to change it?  

The convention for the last 200 odd years has defined foundations by their base.  Any old drawing you look at gives you the height at which the footing rests because the first thing that happens after the strings are set is an excavator digs down to predetermined level in undisturbed soil.  That's UNDER the footing!  The footing thickness, the foundation wall or column height, ALL of that springs from that base! 

So what does Autodesk do?  They put the reference level at the top of the footing, and then uses the wall height to drives the footing depth!   If I try to change the depth of footing (after doing some arithmetic to determine what the height needs to be and not the figure from the engineer) Revit moves it back to the base of the wall!  For my convenience, I suppose?

[barthbradley]

I'm not following. Footing are defined by Bottom and Top Elevations. Been that way since my hand-drafting days.  I don't know how it was done 200 year ago though.   

....is this the message you are referring to?  If so, the operative word here is "Attached". 

[ToanDN]

Foundation hosted by walls?  They are driven by the base of the walls which is the top of the footing, as any other hosted components, dependent to their hosts.  If you want independent foundation, use Slab or Wall tool to draw them.

[kgatzke]

@ToanDN

@barthbradley

I understand that the footings are hosted to walls.  That's the problem.  The information I have is the base of the footing, there's a variety of footing thicknesses, and I can't enter the data on the one figure I have!  I have to go out of my way to calculate the base of wall for every footing because I can't just pick a footing, select a family type for the thickess and enter a height for the base.  It's another example of a part of Revit that was stupidly designed by programmers who don't work in our field and I'm sick of it!

[barthbradley]

@kgatzke wrote:

I can't just pick a footing, select a family type for the thickess and enter a height for the base.  

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Sounds like you want footings to behave like walls -- not like a footings.  Well then, why don't you just use walls for footings?  Seems to me that would solve all your problems.  

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@kgatzke wrote:

It's another example of a part of Revit that was stupidly designed by programmers who don't work in our field and I'm sick of it!

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Perhaps, Revit is unaware of how things are built in your part of the world. What country do you work in?  

[kgatzke]

If I use a wall family in place of a footing family will the structural engineer be able to put rebar in it the same way or am I shooting myself in the footing.  

USA, to your second question, where footings have been dimensioned by their base since before Monticello.

[howard.jensen]

I'm pretty sure the foundation for Monticello wasn't built with reinforced concrete.  It was likely stone masonry, so of course the bottom of foundation was specified.  Dig to that depth and start laying up courses of stone bound by lime mortar.  The bottom elevation of a reinforced concrete spread footing is of interest to the excavator but not particularly important otherwise as long as frost protection depth and minimum footing thickness are met.  The top of footing elevation is more important in comparison, since that is the actual datum at which the dimensions begin to warrant some precision.  Bottom of footing elevations can vary significantly, by design or for convenience of the constructor, without significant impact on how the pieces above fit together.  The top of footing elevations need tobe  pretty close to design parameters or there will be issues with the subsequent construction.  Should put the more important elevation on the drawings.

[ToanDN]

Necro thread but whatever...

My structural engineers set the top elevation of foundations and have a foundation schedule showing the various foundation thicknesses. 

If you prefer to set the bottom elevation of the foundation then DO NOT use Wall foundation, instead, use Foundation Slabs and attach the walls to them.  It is really a non-issue.