Beam System Question

[Paul Andersen]

First off I'd like to say that I don't know how I got along before without this tool, it has been a tremendous time saver throughout the course of a given project. I'm currently framing a very large campus that is in SD's. I'm framing using the beam system tool exclusively for the musical grid lines that will surely occur through CD's. My question is this. We've chosen to layout the bulk of the campus utilizing maximum spacing as our layout rule and 7'-0" for the spacing. Everything is laying out exactly as expected with the exception of a 10'-0" bay. Rather than getting 2 spaces at 5'-0" I'm getting 3 spaces at 3'-4" (essentially 2 beams instead of 1). Has anyone else run into this? Has anyone found any other curious behavior or pitfalls with this tool? As always thanks in advance for your input.

[Tom Weir]

Hi Paul,

I tried it and got the same results you did. at 6'-11" the bay shows only one beam member. But at 7'-0" it begins to show two beams.

For simple one beam bays the beam system might not be worth it. One thing you could do is:
1. Add a member at the center of the bay
2. dimension the member and set the EQ symbol.
3. Erase the dimension but do not unconstrain.
4. The beam will stay centered in the bay if you change dimensions of the bay due to the dimensional constrain.

Downside: If the bay changes too drastically you might need another beam.


Tom Weir
Los Angeles

[Paul Andersen]

Thanks for the prompt reply Tom. Had this bay started out as 10'-0" and a single beam spacing I probably would have been inclined to take the approach you have outlined and is how I used to do most of my framing when we were testing in RB prior to RS and the beam system tool. I actually found this as the bay shrunk from 21'-0" and was a little surprised to see it keep the additional beam. Ideally, I would like to use a beam system for every bay including single beam bays especially when the model is started in the very early SD phases of a project. It would also be nice if the grid spacing shrunk below the maximum spacing that no beam would be displayed at all. It seems that every job these days has a curved beam or some area where it isn't prudent to use a beam system but for the most part I prefer to use it whenever possible. Thanks again for confirming this behaviour.

[Tom Weir]

Hi Paul,
I have been less than diligent about using the beam system function than you, but am also impressed with its possibilities. I think next job I will try it for the whole nine yards and see how it goes. I think early on I found it a little unreliable, as you did, and have shied away now a little too much.

Have a great day....

Tom Weir
Los Angeles

[tsbykatherine60220]

...Ideally, I would like to use a beam system for every bay including single beam bays.....
The only work arounds that I can think of are to either:

Change the beam systems with bays less than or equal to 2x your maximum spacing to Fixed Distance - Center Justified.
Unpin the members from the beam system, delete one and move the other. If the grid changes the 2 affected members will not go back to normal but there will be additional members added and it's pretty obvious what you've done at that point :banghead:

Any API guru's out there? Is there a way to add a reactor to beam system's width (perpendicular to the beam direction) to automatically behave this way?

I think this one should definitely be on the wish list, it's not the 1st time I've seen this and it would be nice to have it monitor itself in this fashion.

[Paul Andersen]

Thanks for the suggestion Rick. I did opt to go the unpin, delete one and move the other route. The benefit of this method is that the layout rule and spacing that I want applied to the beam system can remain and if the bay changes size drastically in the future I can simply edit the beam system and hit the reset structural beam system button in the sketch options. I do see this as incorrect functionality however and have filed a support request.

[tsbykatherine60220]

simply edit the beam system and hit the reset structural beam system button in the sketch options
hadn't seen that part of it yet! good to know.....

rpm

[KMGuillotte]

I have encountered the same situation and have mentioned this to Nick M and Marie O. From what I'm hearing the issue has been addressed (or will be) in RS3 when it comes out later his year.

For the current work-around, I too have chosen to use a beam system equally spaced w/ a set # of beams (in my case I did use 2). If the bay changes, well...my skills of manually changing items in autocad haven't gone to waste! ;-)

[Paul Andersen]

Thanks for the good news about a possible fix for this in RS3. Not to beat this to death but the maximum spacing layout rule seems to have other issues. I just checked another bay that looked correct at first glance. Turns out that using the same 7'-0" maximum spacing in a 16'-2" bay also produces an extra beam: 4 spaces at 4'-0 1/2" instead of 3 spaces at 5'-4" and some change (5'-4 171/256" to be exact).

Per the help section - Maximum Spacing: This value allows you to specify the maximum distance between beams. The quantity of beams required for the beam system is calculated automatically and centered within the beam system.

It seems that the calculation is taking the first cleanly divisible number beams less then your maximum spacing which often times requires the addition of an extra beam. After chasing through my project most of the bays are incorrectly spaced which would have resulted in 50 extra beams being called out on plan for the lobby alone. While I'm glad that the error is adding steel rather than subtracting it I think I'll be going back to doing this manually until RS3.

[david_peterson]

While I'm glad that the error is adding steel rather than subtracting it I think I'll be going back to doing this manually until RS3.I'm still wondering how it can be called maximum spacing prior to having the system run through an analytical program? It just seems backwards.

[Paul Andersen]

I'm still wondering how it can be called maximum spacing prior to having the system run through an analytical program? It just seems backwards.
We primarily use the beam system tool as a quick and easy method for framing the structure. Since we start this early on in SD's when the grid is still in constant flux either subtly or drastically the beam system is very handy for keeping the framing spacing intact with little or no effort after it's initial placement. To date we've only used the fixed number layout method since it was the most stable option. If maximum spacing worked the way we expected it would be our primary choice since it would not only respace the beams as necessary when bay sizes changed but would also add and subtract beams as well.

Prior to analysis in the SD phase of a project our engineers discuss a framing layout strategy with our technicians and the technicians begin developing the RS model using this initial layout strategy and the preliminary grid from the architect (beam and column sizes are irrelevant at this point). Since we have not currently taken full advantage of any one analytical link yet the RS model is either passed to the analytical software for member sizing or the engineer provides member sizing based on the separate analytical model they have built. If beams need to be respaced for whatever reason (initial incorrect assumption of spacing, system depth for clear height not met, etc) the technician is informed of the new spacing which can quickly be adjusted by tweaking the beam systems and then resent to the analytical software for member sizing updates.

I'm not sure that I follow how this is backwards. Perhaps it's the inability of the engineer to be able to tweak the spacing in the analytical software and have that adjust the RS model? This is just a subtle workflow shift to RS that either the engineer or technician can handle in RS. I'm not aware of any analytical software that actually produces the spacing for you or readjusts spacing automatically where it would be a necessity for RS to update this information from the analytical model. So at this point it's just a matter of where you tweak the model which is generally always in RS. As the links become more robust perhaps more tweaking in the analytical software will be allowed.

[kmarsh]

David,

You keep referring to "running the beam system through an analysis program" to determine spacing. This is never done. The fact is that we engineers GUESS at the proper beam spacing and then analyze it. We use some rules of thumb and alot of luck. No analysis program that I've used (in 7 years of designing mostly steel joist structures with hundreds of, said, beam systems = joists), picks a beam system spacing for you. I've used RAM extensively as well as RISA 3d. When we model beam systems in Ram or Risa, we pick a spacing and then determine if it works well when we design the members that comprise it. Most of the time, we are picking the spacing based on what works with the layout, NOT necessarily what is most economical. In fact, there are several combinations of spacing and beam that would fit the bill for economy and to get the process started, we just pick one or the other and calculate the other one. The calculation of which member to use is by far the quicker calc and so we typically start with spacing known.

What Revit provides in a beam system tool is vastly superior to our previous mode of operation in that you can lock the beam system extents to the gridlines (or bounding beams) and when we have to change the location of the grids, the beam system AUTO-respaces the beams. This saves DAYS of work and makes it very quick to send back to the analysis program to gain (or loose) some economy on the beam systems for the new spacing (but probably increasing safety one way or the other).

The setting of "maximum spacing" is NOT an analysis determination, it is a LAYOUT rule. This may be where you're getting hung up. There is no such thing (as far as I know) as an analysis program that optimizes beam systems for maximum spacing AND member size. You HAVE to set one end of the dog-run or you can't solve the problem. You either pick member size to use (then you can determine a maximum possible spacing to use) OR you pick a spacing and determine what member size can fit the bill.

Hopefully this clears up this beam system question for you, I've noted several posts where you've mentioned this as some kind of Achilles heel of Revit when, in fact I believe, it is the TRUE power of Revit and just one of the reasons why it beats ACAD + RAM/RISA hands down for me.

On a related note, having modeled in both Ram and Risa, and having found their packages to be great for engineering design and, at the time, even enjoyed their modeling packages, now that I've found Revit, I would prefer to not model in Ram/Risa but rather do model manipulations in Revit for it's powerful modeling, layout, alignment, beam system tools. I think that if you have the engineers try doing model manipulations in Revit as opposed to in the analysis package, you might find that they too, will enjoy the power and flexibility of Revit for analysis model creation and manipulation.

For your own proof of concept, have the engineers show you the process involved in changing the spacing of a beam system in Ram or Risa (or probably etabs too), then show them the same conceptual operation with an existing beam system in Revit. (select beam system, right click>properties, change number of beams). Then show them that if you move the gridline that all the beam systems respace themselves. for those of us who do tons of joists, these are invaluable features.

[David Sammons]

It seems that the beam spacing problem with the 'Layout Rule' parameter set to 'Maximum Spacing' still persists in RS3. Is this the case or has anyone been able to use "Maximum Spacing' without a workaround?

[Paul Andersen]

You are correct David, the Maximum Spacing Layout Rule still does not work correctly in RST3. The factory is aware of this. I've sent 2 separate support requests on this issue. One for RST2 when I first ran into it and again for RST3. Currently I've been using Fixed Number until this is resolved.