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• Wall-Slab Intersections

Wall-Slab Intersections

Wall-Slab Intersections are a common type of intersection found in many projects. This article provides several options for modeling these intersections. (A separate article discusses the main possible choices for modeling these Walls and Slabs.)

See How to Model Related Walls and Slabs.

Multistory Wall and Slab

The following illustration shows four possible scenarios.

On both sides, we have multistory Walls with the Slabs cutting into them. In all cases, the bodies of the Slabs were subtracted from the body of the Walls using Solid Element Operations (SEO).

See Solid Element Operations in ArchiCAD Help.

The two upper Slabs cut into the body of the Wall all the way to the outer surface of the Wall.

The two lower Slabs cut into the body of the Wall, but they do not reach to the outer surface of the Wall due to the thickness of the insulation that will be placed there.

The next illustration shows the section of the above Walls.

In the case of the two Slabs on the right, we have modeled the insulation using Beams. In the lower right intersection, the Beam and the Slab do not intersect. In case of the upper one, the Beam and the Slab intersect (since the Slab extends to the outer surface of the Wall). This is not a problem, however, because Beams always cut into Slabs in 3D. Also, since we set the Beam Priority to a higher value than the Wall priority, the Beams cut into the Walls, too. With this method we did not need to employ SEO for the Beams.

In the case of the two Slabs on the left we did not model Beams in 3D (so they must be drawn in Sections/Elevations using 2D elements).

As you can see, the Slabs cut correctly into the Walls. The right-hand slabs use Beams to model insulation, which also results in correct section representation. The left-hand slabs, however, will require additional drawing of Lines and Fills to represent the insulation in Section view.

Note: The Slabs can represent either the Slab structure only or the entire Floor Structure (in which case we would use a composite fill to represent the skins of the structure). In either case, we would have to apply additional lines/fills to create a correct 2D representation. For such a purpose, standard Patch objects may be created and saved, which can then be later reused.

Single Story Wall and Slab

The next illustration shows a scenario in which single story Walls are used instead of multistory Walls.

Each Wall reaches up to the top of the Slab cutting it. The Slabs and Beams used are modeled the same way as in the previous example. As you can see, the results are the same. With this solution, however, Walls can be listed on their correct Story (while in the previous example the entire Multistory Wall is listed on its Home Story). Another way to model this situation is to have the Walls reach up to the bottom of the Slabs above them. In this case there is no need to cut the Slab out of the Wall with SEO. However, the insulation must be modeled if the Slab does not extend all the way to the outer surface of the Wall. The insulation could be modeled using a beam or a little wall, or the wall above could be a complex profiled wall (AC 10 and higher) that has the insulation (and possibly sheathing and more) extending below the wall base.

Slanted Wall and Slab

The main consideration with the intersection of a Slanted Wall and a Slab is that the edge of a Slab is always vertical, so we need to employ some other element types to do the job.

Let us consider the case when the edge of the Slab is located at the inside surface of the Wall.

In this case, we can draw the Slab in such a way that its body intersects the Wall’s body, and then use the Wall as an operator and perform a Subtract Solid Element Operation. The result can be seen in the above illustration.

You may want to model the Slab more accurately. Suppose you want the bottom of the Slab to touch the inside surface of the Wall. Do the following:

1. Go to the Story where the bottom of the Slab is based on the Story’s height value.

2. In the Floor Plan Cut Plane dialog box, set the “Cut Plane height to Current Story” value to equal the height of the bottom of the Slab.

See Floor Plan Cut Plane (Global Setting) in ArchiCAD Help.

3. Make sure that the Floor Plan Display field of the Slanted Wall is set to Projected, Projected with Overhead or Cut only. This way, the 2D representation of the cut section of the Wall will be located at the correct position based on the Floor Plan Cut Plane value.

See Define Element’s Floor Plan Display in ArchiCAD Help.

4. Using the Offset Edge command of the Slab’s Pet Palette, adjust the edge of the Slab to the inner side of the Slanted Wall.

5. Set the value of the Floor Plan Cut Plane back to the value it had before.

With these steps performed, you will still need to subtract the Wall from the Slab, but its edge will show the correct intersection between it and the Wall.

In case you want to model the edge of the Slab slanted, plus you wish to place a slanted insulation, do the following steps:

1. Using the Slanted Wall Tool, create the insulation at the correct height. In Section you can then easily move it into its correct position.

See Create a Slanted or Double-Slanted Wall in ArchiCAD Help

2. Create the Slab. The body of the Slab should extend to anywhere beyond the inner side of the insulation Wall piece. It may be advisable to align it with the outer or inner bottom of the insulation piece. As you can see below, the bodies now intersect.

3. Using SEO, subtract the insulation piece from the Slab. The performed operation should be Subtraction with Upward Extrusion, because if the upper side of the Slab hangs out of the insulation, that extra portion will not be removed if you use a simple Subtract command.

See Solid Element Operations in ArchiCAD Help.

4. Now, again using SEO, subtract the insulation piece and the Slab (both will be operators) from the Wall. With this step, the intersection is now modeled correctly.

You may want to create the intersection in such a way that the Slab cuts into the Wall parallel to its Slanted outer surface, but no insulation piece is shown in the model.

To achieve this:

1. Using the Slanted Wall Tool, create the insulation at the correct height. In Section you can then easily move it into its correct position.

2. Create the Slab. In this case, the Slab should extend to the bottom of the inner side of the insulation.

3. Using SEO, subtract the insulation piece from the Slab using the Subtraction with Upward Extrusion operation.

4. Select the insulation piece and move it to a hidden layer, since we do not want to see it; we just needed it to cut the edge of the Slab to the correct shape.

5. Using SEO, subtract the Slab from the Wall.

Notes: Another option for the Slab is to make it using a Roof with a 0 degree slope. The advantage of this is that the slopes of the edges of the Roof can be easily set to a non-vertical value.

See Set Custom Roof Edge Angle in ArchiCAD Help.

This way you would not need to cut the Slab with the insulation piece. The disadvantage would be that the Slab piece would not be listed in schedules as a Slab, but as a Roof.

The slanted insulation pieces could also be modeled using the Roof Tool. However, for this particular task, the Slanted Wall Tool may prove more appropriate.

Category3dModeling

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