Dominant Elements in Concrete Joins

This information is "ripped" from the WikiHelp topic...

Whenever elements that use concrete for their material interact with each other one element retains its geometry while the geometry of the other element sharing the join is cut to create the appearance of a single form. For example structural floors and walls possess dominant geometry characteristics and always maintain their geometry when sharing a join with other elements. Because of this, they will not automatically join with one another. These other concrete elements behave as follows.

These join behavior rules cannot be changed and it is not possible to disable the automatic joining of geometry. It is possible to manually change this condition using the UnJoin Geometry tool.

While were at it these are the valid combinations for concrete elements to join, in other words they may automatically join with one another.

• beam to beam
• beam to column
• isolated foundation to isolated foundation
• isolated foundation to wall foundation
• structural floor to beam
• structural floor to column
• structural floor to slab edge
• wall to beam
• wall to column

Remember that joined geometry may have an impact on project performance.

Concrete Volume between Slab and Beams

A message via Linked In arrived the other evening asking about the volume of concrete when slabs and beams are involved. The hopeful question hinged on the slab reducing its volume by however much the beam overlapped the slab. The answer is a qualified "yes" because it is aware when Join Geometry is used but in the opposite direction, beam reduces volume not the slab.

Here's a floor slab that is 20'-0" x 20'-0" x 6" thick and a 12" Wide x 24" Deep x 20'-0" long concrete beam reporting a volume of 200 CF and 40 CF respectively, before using Join Geometry (slab properties shown).

Here's the properties of the beam before Join Geometry as well, reporting a volume of 40 CF.

Here's the properties of the beam after Join Geometry, now reporting a volume of 30 CF.

I didn't bother capturing an image of the floor slab, its volume didn't change, still 200 CF. I hope you'll take my word for it. The point of the exercise is to determine how much concrete is really needed, at least in my mind. The floor slab volume is intact (for this particular condition at least) but any beams that are joined with the slab will reduce their volume appropriately.

That means a two schedules, one for slabs and one for beams, should provide a reasonably close total if you look at both schedules together. It might be cool if the slab could inherit the beam volume and report a total that included the beams or the reverse subtract the beams from the slab.

In the field the beam and floor, minus any topping slab, are often poured together so the reinforcing ties it all together. Curiously, the way Revit deals with beam sizes and types is generally in conflict with how engineers think of the beam size as it relates to the slab. It's never simple or easy is it?