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?

Floor Slabs - Deck Profile Setting

Revit Structure has had the ability to show a deck profile as part of a slab definition for quite a while. When Autodesk decided to include more structural tools in the Subscription Advantage Pack, released back in the Fall of 2009, Revit Architecture inherited this feature.

It is added as Function of a floor's layer.

You can choose from profile families that are loaded into your project.

The floor is able to include this because it is also possible to define the span direction of the metal deck. Revit Structure provided a tag to do this and it comes along now too. It is necessary to define the floor slab as "Structural" as shown in the image.

Here's what the decking looks like when the view is assigned to Detail Level: Medium or Fine. When you use Coarse you just get the simpler two line representation.

Shaft Opening and Foundation Slabs - Just Not Fair

If you are familiar with the tool found on the Modelling menu > Opening > Shaft Opening you have probably become as fond of it as I have. If you are not, it is a specific tool that will cut any floor, ceiling and/or roof it comes into contact with. Just sketch the shape the opening should have, define it's top and bottom constraint as well as any offset you need and Finish the Sketch.

You now have one element that creates a nicely coordinated shaft for the entire vertical height required. If the shape changes you must create another shaft opening for that, still less work than editing floor, ceiling and roof sketches all afternoon.

As a bonus you can also define Symbolic Linework while in sketch mode. This can be the proverbial "X" in your HVAC chase or the Yin/Yang symbol in a circular pipe chase. It can even be the sketch of an elevator.

To make it even better they just need to let us import a detail component and place it while in sketch mode so we don't have to draw the elevator but once or just use a nested dwg in the detail component...but I digress...the unfair bit.

There are Floor and Slab elements and they are the essentially the same but there is also a Foundation Slab and it is different, at least when it comes to the Opening Shaft. On floors and slabs it works, on Foundation Slabs they don't and that's just not fair! Even these need holes cut in them for elevator shaft pits, sump pits etc.

The solution is to use the other option on the same set of tools, Modelling menu > Opening > Opening by Face.

Here are couple images of shaft openings used less conventionally. First is the finished slab that shows using them (shaft openings) to create true holes in a slab so that the floor slab reports actual volume without using Join Geometry between columns and floors. Also showing how the slab edge plan was altered.


This image depicts the shaft openings overlaid on the floors. A bit easier managing a slab edge alteration instead of editing multiple floor sketches by just using one shaft opening.


If you are in a shaft binge mode you can review this earlier POST.

Added THIS POST to the HOK CAD Solutions blog.