Gerber System on RISAFloor 1

[Parosh]

Hi all,

I've modeled and designed Gerber systems through RISA 3D, but this is the first time that I'm attempting to model it through RISA Floor, but I can't seem to figure it out, if it's even possible.

In short, I have a beam that's spanning between two cantilevered beams. I can't seem to figure out how to draw a beam between two beam ends as the program does not give me an option to snap to the beam ends, and when I try to draw a beam at the joint where the cantilevered beam ends, I get a message saying that node is unsupported.

Has anyone done anything similar? Is this possible?

Thanks!

 

[JoshPlumSE]

I've never worked on a "Gerber" system before.

I take it that you have beams that cantilever over columns and these end points of these cantilevers support your edge beams. Is that correct? My guess is that it's the drawing of the cantileves that's messing you up.

If, so RISAFloor should allow that. The one caveat is that RISAFloor does some odd things with cantilevers. First you draw in the backspan of the cantilever, then you use a "cantilever" tool to extend out a cantilever from the back span.

I think it was done this way because RISAFLoor relies heaviliy on the interface to detect any framming issues or instabilities.

 

[Parosh]

Josh,

A "Gerber" system (I believe this may be a Canadian term) is a method used on a multiple span system where you can take advantage of the bending moment diagrams to "drop-in" a section that is typically shallower and lighter than the rest of the beam system. Essentially, the drop in beam is simply supported by the cantilevered ends of the cantilevered beams. I've attached a picture for reference.

I drew my cantilevers using the way you explained by drawing my backspan and using the cantilever tool to extend them out. My problem arises when I try to draw the drop in beam between both those cantilevered ends. The program gives me errors about unsupported nodes. I was questioning if I was simply not drawing them properly, or if the program was even capable of connecting members to cantilevered ends.

- Parosh

 

[JoshPlumSE]

Oh, I've seen lots of systems like that. Usually with Glu-Lams and such.

Regardless, this should be allowed fine in RISAFloor. You just have to make sure that you defined the cantilevers correctly... Or else the program isn't going to understand that the tip of the cantilever is a "support point" for other framing.

 

[dik]

Beats Gerber all the time... 0.0858ql^2, I seem to recall...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Parosh]

Josh,

Thanks for the reply. I'll have to revisit the model when I get back on the project to make sure I have my cantilevers modeled properly.


Dik,

This system you drew... eliminate the drop beam and extend one cantilever to the next? Does this have a name? What's the advantages of this way compared to the Gerber? I suppose I could model myself and find out, but if you could give some insight that would be great. Also what are you referencing with the 0.0858ql^2?

Keep in mind I'm still an EIT, and these systems are still very fresh to me, hah.

 

[dik]

Plastic design for a UDL... the connection has to have a shear/moment connection. Lighter section and fewer parts... nearly always less costly. Limited to a class 1 section. Alternate loading only affects the splice moment... End plate connections are quite economical. If 4 span, the interior beams are even lighter.

http://www.assakkaf.com/Courses/ENCE355/Lectures/Part2/Chapter8d.pdf

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Parosh]

In my case, it's a 3 span system and the client wants a shallower beam in the middle for more head room, so I believe the Gerber is the best way to achieve the shallowest section in the middle span. Let me know if I'm mistaken.

 

[dik]

correct...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Parosh]

Just updating and I recently jumped back on this project - I managed to model the Gerber system discussed above on RISAFloor. I needed to use the "draw to a colinear location" feature as opposed to inputting a specific distance to allow those cantilevered ends to support a beam between.