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At Rill Architects we run ArchiCAD on Mac OS X. If you work at Rill, this is your stuff. If you don't, but you work in ArchiCAD, you may find something interesting. Anybody else, I don't know.
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Location: 06 Wood & Plastic

A beam, or any other ceiling element, should be shown dashed in the architectural plan, because it's overhead. That same beam needs to be shown solid in the reflected ceiling plan, because then you're upside down looking straight at it. Using a conventional beam element, you would draw it with a dashed line in plan. But you can't show the same element in the RCP, because you can't make the beam draw itself solid. So you trace the beams with lines.

In Archicad 11, we have a model view option which allows objects, but only objects, to be drawn differently in floor plans and ceiling plans. This object is a simple wood beam that responds to this switch, so you don't have to trace it in RCP. There are limitations to using this instead of a beam element, see below. But for a simple beam such as a timber, you definitely should consider this object.

Size: Choose a dimensional lumber size, or choose 'Custom' and set the Depth and Thickness manually.

Slope: The usual roof slopes, or a custom angle. If the beam is sloped, parameters are available to control the Top and Bottom edge angles.

Roll Angle: Turns the beam around the long axis. If the beam is sloped this parameter is not used.

Plan Cover Fill: Just what it says. Turn it on and set the attributes, or don't.

RCP Attributes: The Pen and Linetype that will be used when the ceiling switch is on. When the switch is off, the object's 2D symbol will be drawn with the object's settings. In practice, the object should be set to use a dashed line, while the RCP linetype is solid. The pen doesn't really need to be different in most cases, but the option is there.

Pay no attention to where it says 'Transparent' when the pen is zero, and 'MISSING' when the linetype is zero. Those indicators are automatic and I can't get rid of them. In our case, zero means 'Match the object's settings'.

RCP Cover Fill: Just what it says; this fill will be used when the ceiling switch is on. This can give you some ability to show beams stacking in the ceiling, such as joists running over a timber beam.

Plan Lines: The symbol is a rectangle, with Start, End, Right, and Left lines. Any of these can be turned off, to make the beam meet a wall more cleanly in plan, for example. If the Roll Angle is non-zero, you will also have the option of showing the Roll Corner Line in RCP. This line won't show in the floor plan.

3D Pen: If this pen is non-zero, it will be used in 3D instead of the object's plan pen.

Start and End Miters: Turn these on and you can miter either end of the beam to meet other elements. The angles are graphically editable like any other mitered thing.

We have a special layer for elements we wish to see in plan and RCP, A Ceiling All. Use that layer for this beam.

Limitations

This object is better than a beam element if you're just talking about the RCP. But there are plenty of ways it's not as good. One big disappointment is that you can't cross a pair of them and have them clean up in 2D and 3D. Another, beams can use custom profiles. A weird profile object has to be coded.

So, this object isn't a replacement for all ceiling beams. If it's a cased beam, you'll want to use beam element with a custom profile. If the beams cross, you need beam elements to make them clean up.

And if you're using real beams, you need to trace in the RCP. But, tip: If you have crown inside coffers, you might be able to skip out on the tracing and just let the crown objects (on the F Trim Crown layer) imply the beam shapes.

Another potential frustration is the case of a structural, visible timber beam. Normal structure beams are created with the Wood Beam object, which gracefully labels itself in the framing plans. The layer for these new ceiling beams can't do this, because I don't have a practical way to show the beam in all three plans, but the text in only the framing plan. A promising solution would be to create a label to refer to the beam, which could then show only in structure. Alas, here Archicad has stymied us again, because you can't show a label when the labeled element is hidden. And we can't show the beam itself because it's dashed. And I'm not putting the structure plans in ceiling mode, because I have no idea what the side effects of that would be.

For this case, model the beam using the RCP Beam object, and place another (Wood Beam) object on the +S Struct Note layer, with the Model parameter off.