BIM & BEAM

Slab Edge Hidden Lines Display

Back in February/March 2008, during our Revit Structure 2008 Beta testing period, there was a discussion among our Beta testers (from different countries) about the slab edge hidden line display. In fact, the standard or culture of displaying slab edge hidden lines on plan could be different from country to country.

For example, many USA companies have a standard to show the inside (or bearing) line to be displayed for slab edges.

However, some other countries users have also told us that their standard is to display both/all lines which is:

 

I would like to share a technique with you in Revit Structure 2009 of which one of our QA expert Joe Charpentier has explained in the Beta discussion forum an option, to be invoked via the Revit.ini file, that can change the display of hidden lines. Quote:

"By default, the inside (or bearing) line will be displayed for slab edges.

In the official release of Revit Structure 2009, we are providing an option, to be invoked via the Revit.ini file (typically located at C:\Program Files\Revit Structure 2009\Program), that can change the display of hidden lines.  This is similar in behavior to the "Show hidden lines" options for beam families.

Add the following section heading and variable names to the Revit.ini file, if it doesn't exist already:

[Graphics]
HiddenSlabEdge=All

Possible values for HiddenSlabEdge variable:
"All"  - Show all lines from a slab edge
"Itself"  - New default behavior, the "Bearing" or lower edges
"Other" - The edge intersecting with the slab, (Beta 1 and 2 Behavior)
"None" - Show no hidden lines for Slab edges (r2008 behavior)

Note that this is not set for the project, but for the session of Revit.  That is, if you open a file with a certain variable setting, that will not prevent the project from being displayed differently if opened in a different install with a different setting."

Thanks

Wai

Is it possible to import accurately an "almost orthogonal" DWG/DXF Line into Revit?

Some users have reported that when they tried to import/link a dwg/dxf file representing the property boundary (where one of the boundary is accurately measured with 90 degrees, 0 minutes and 30 something seconds; or there is a deviation of 3/8” over the length of the site) provided by the property surveyor, Revit will treat and round up those angles as exactly 90 degrees.

They would like to know how they might set up their models to account for this level of accuracy, or explain the thinking behind this rounding up by Revit.

Here is the technical explanation.

Revit requires almost-vertical and almost-parallel lines (where "almost" is defined as 0.02 degree off or something like that) to be made exactly vertical or horizontal in order for our Geometry engine to work properly. This code applies to the imported lines as well. That’s why when importing a DWG/DXF with “almost orthogonal” or “very sharp angle” line, Revit will somehow “straighten” it for the Geometry engine purposes.

For now, here is a workaround that for users to input exactly the 90 degrees, 0 minutes and 30 something seconds:

1-     Import the DWG/DXF in Revit (yes, I know that some of “almost orthogonal” line will become “straightened”)

2-     Go to Site > Property Line > Create property lines by sketching

3-     In sketch mode, use Pick Lines tool and select all the imported DXF lines.

4-     Finish sketch

5-     Click on the Revit generated Property Line and then on the option bar Edit Table

6-     Now you can do the adjustment by inputting/adding back the 30 something seconds into the original “almost orthogonal” line. (See below jpgs)

Structural framing underneath a warped slab

Some users have asked me what is the best and quick way to place a beam or beam system to a warped slab (Figure 1)?

(Figure 1)

Currently, a slab cannot host a beam or beam system. However, if users have already added the columns, they can then attach the columns to the underside of the slab (Figure 2).

(Figure 2)

Then in the Plan or {3D} view, users can use the regular Beam tool with "3D Snapping" option checked in order to layout quickly the perimeter girder beams (Figure 3).

(Figure 3)

Finally in the Plan view, user can add the Beam System with "3D" option checked in order to populate the joists to achieve the desired goal (Figure 4).

   

(Figure 4)

Adjusting beam elevation based on slab thickness

When using the Beam tool to layout the framing on plan, by default the current Level has already been selected by Revit as the Work Plane. Therefore, if user draws the beams, they will be referenced to the Level itself only (Figure 1).

(Figure 1)

Also, user has to manually adjust the beams Properties Start Level Offset and End Level Offset so that the position of beams will match the thickness of Slab. By consequent, if the thickness of Slab changes, the beams will not follow or auto-adjust with the Slab (Figure 2).

(Figure 2)

Currently, Revit Structure doesn't have a direct feature to "attach" beams to slab. However, there is a solution to quickly draw beams that will associate with the Slab instead of the Level which is to use the 3D Snapping option when drawing the beams on plan (Figure 3). This option allows Revit to select automatically the underside face of the Slab geometry as Work Plane and places the beams underneath it. As a result, if the thickness of Slab changes, the beams will follow and auto-adjust with the Slab (Figure 4)

(Figure 3)

(Figure 4)

P.S. I know that some customers use the method of drawing the Ref. Plane by assigning it as the Work Plane, then aligning and locking it to the bottom of Slab. This method would work fine as long as the Slab is horizontally flat, but if user decides to make it sloped then the constraint will break and the beams will no longer follow the Slab.

Custom shape of stair stringer

One of my structural users specializing in industrial building type has sent me an email saying that he needs to model some exterior stairs with C-Channel stringers. However, he realizes that currently Revit Structure provides rectangular simple shape of stringer only (Figure 1).

(Figure 1)

Currently, Revit Structure doesn't have the ability to create custom shape of stringers. However, there are several workarounds to achieve that and the one that I would like to show you is an alternative use of Railing tool. Here are the steps:

- First, you need to turn off the Stair Stringer by setting the Right Stringer and Left Stringer parameter value to None (Figure 2).

(Figure 2)

- You can then turn on the visibility of Railing category that was turned off by default in Visibility/Graphics (Figure 3).

(Figure 3)

- You can now select the Railing geometry and go to the Properties in order to modify the Rail Structure type parameter. In the Edit Rails dialog box, you can assign your custom profile ex. C-Channel Profile and then adjust the Height and Offset so that it will be at same location as the stringers (Figure 4).

(Figure 4)

- In order to trim the bottom or top of the "fake" stringers, you can select and edit each Railing sketch by splitting the sketch line and assign the slope to "Flat" (Figure 5).

(Figure 5)

How to identify the Beam Start and End

Many structural users have expressed that it seems quite cumbersome in Revit Structure to quickly identify the Beam Start and End (Figure 1).

(Figure 1)

Currently, one way to identify the Beam Start and End is to go to the Properties of a selected beam and try to adjust the Moment Connection Start (or End) parameter value in order to see which end the moment symbol will show up. This trial and error process seems very inefficient and cumbersome (Figure 2).

(Figure 2)

Some Revit users have discovered another solution to help identifying quickly the Beam Start and End. The solution is to open and edit the existing beam .rfa family by adding a "Control" Horizontal symbol (single arrow) on plan. Assuming the arrow end represents the Beam Start and the arrow head represents the Beam End (Figure 3).

(Figure 3)

After modifying the .rfa, you can reload it into the project and overwrite the existing family. Now, if you select the beam on plan, you will see the blue horizontal control arrow showing up which can be used to identify very quickly the Beam Start and End (Figure 4).

(Figure 4)

P.S. Technically speaking the Control command allows users to place arrows in order to rotate and mirror the geometry of the family. However, due to the current software limitation on any 2 Pick Structural Framing .rfa family, although you can place the blue horizontal arrow, but it really cannot rotate and mirror the beam.

Wai

Vertical Attachment

I was recently asked by a few people how to constrain the top of a column to the bottom of beam.

Actually, columns could be attached not only to beams but also to roofs and floors. Also it is not only the top of columns that can be attached to floors, roofs and beams, but also the bottom of columns. So we are talking about 6 situations. For each of the 6 situations, we have 9 configurations so we have a total of 54 cases

For this post I am going to present only the 9 configurations related to top of columns attached to bottom of beams.

In the following, target can be a floor, a roof or a beam and I will be using beams for the illustrations.

In order to better understand the different available options, I use a slopped beam:

 

In order to attach a column to another member, you need to select the column and in the option bar you get the attach/detach options:

 

Select Attach and you get the following options:

 

The tables below describes all the combinations for the 3 Attachment Styles and the 3 Attachment Justifications.

Justification Style	Minimum Intersection
Cut Column
Cut Target
Do not cut
Justification Style	Intersect Column Midline
Cut Column
Cut Target
Do not cut
Justification Style	Maximum Intersection
Cut Column
Cut Target
Do not cut

In order to detach the column, you need to select it again and use either [Detach All] if top and bottom are attached or just [Detach] and select the target

To restore the original geometry, change the [Top Offset] property to zero in the column dialog box:

Nicolas