RISA TOWER Question 1

[msquared48]

Josh:

I heard that RISA sold this program to another company, but I have a question. I am trying to model a 16" diameter monopole with a 24" diameter shroud on the top, all the antennas being inside the shroud.

It does not appear that RISA allows for the shroud condition. The only way I see is to fool the program with a 24" diameter pipe extension at the top to model the shroud, but that is not the true structure.

Inside of the shroud are the antennas, and a 4" diameter pipe column used to support the shroud and antennas.

Am I missing something?

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[JoshPlumSE]

Our lead developer (Peter Chojnacki) decided he wanted to be his own boss. So, we put our heads together and came up with an agreement where he would purchase the program from us over the course of a few years. The agreement is going pretty well as far as I can tell. Hopefully, Peter feels the same way.

So, it's basically the same program (but updated). It's written by the same guy. It still interacts with the RISA products. It's got the same license protection. For the users, not much has changed.

For your situation, Peter might have a better suggestion. You'd have to check with him (support@towernx.com) to be sure.

I'm pretty sure that this question has come up before. And, I think your suggestion sounds pretty much like what we suggested before. The one difference being that we also had them export the model over to RISA-3D. That way, the loading for the model was entirely defined through the Tower program (with the correct wind area). However, once the model was exported to RISA-3D, we were able to change the properties of the upper pole to match what they were really supposed to be.

 

[msquared48]

OK. Thanks Josh. I'll get ahold of him.

Tower is new to me. How do you import to 3D from Tower?

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[msquared48]

Josh:

1. I took the manual home and read up on my last question this weekend, however, that prompts another question:

At work, I have one computer and both programs on the same computer. In that I have a sentinel for each program that must be inserted into the ONE slot in the computer for only one program to work at a time, how do I make the transfer?

2. From the manual, I see wind, ice, and gravity loads, but no seismic whatsoever. In general, has it been found that the modal frequenciy differences between a "typical" pole structure and "typical" seismic events that dissimilar that they can be ignored? I am very, very skeptical about that! Looks like I need to import the structure into RISA 3D to do a seismic (dynamic) analysis.

If you prefer, I can forward these two comments to Peter, and I do have a lot more questions for Peter, but these two questions do include elements of both programs.



Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[JoshPlumSE]

Mike -

1) You should probably get a USB hub. When reading a *.rt3 file (the one exported by tnxTower / RISATower), the RISA-3D program requires both Tower and 3D authorization. So, you have to have both keys plugged in.

2) Two responses:
a) I believe Peter was planning on adding some more seismic to tnxTower for one of the upcoming releases (maybe even the current v6.0). So, you might want to contact him directly.

b) If you like you can send an e-mail to me at the regular RISA support account. I'm putting together a new training manual on dynamics + seismic for RISA-3D. In that manual, I walk through the three TIA Rev G methods for accounting for seismic (Equivalent lateral force, equivalent modal analysis, and true modal analysis / response spectra). Seismic ends up being very unlikely to control the design of these types of very flexible structures.

I believe Peter may use these examples for his training class as well. So, if he's already sent you something it is probably very similar to what I have.

 

[msquared48]

Josh:

I receoived this answer to one of my questions from Peter yesterday:

Hi Michael,



Thank you for your inquiry. The arrangement you are describing may be modeled as a stepped monopole (24” + 4”), antennas with areas set to 0.0, and the shroud entered as a continuous appurtenance (Discrete Loads page) with the Offset set to None. The properties of the shroud should reflect its DL and the 24” diameter. There is no need to export the model to RISA-3D to analyze/design this configuration.



Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[JoshPlumSE]

I forgot about continous appurtenances, but that makes sense. I haven't used tnxTower very much in the last 18 months or so. And, Peter was always more knowledgable about Tower industry practices. I was just dabbling in that field.

If you want to get those Seismic write-ups, just let me know. Probably through regular e-mail channels. Right now they're just draft documents and not necessarily fit for public consumption.

 

[msquared48]

I would appreciate getting those seismic writeups Josh. Thanks.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com