RISA DEMO 2D

[ajk1]

Why is it that when I "solve" RISA DEMO 2D it produces zeros for results? The truss diagram is correctly displayed and the applied loads are correctly displayed.

How do I tell it the load combinations? It is a truss with only one joint load.

Is it possible that the problem is that it does not pick up the wood properties properly from the wood sizes that I input? Should I input the area and E of each truss member manually?

 

[EngineeringEric]

You need load combinations, load cases... RISA isn't a program you can wing. you need to learn how it work, i would suggest talking to co workers or going through tutorials.

 

[BUGGAR]

Risa knows if you have paid for it or not.

 

[ajk1]

I figured it out and got it to give me answers! The answers look right. The problem was that I had a second load case with zero load. When I deleted that, it worked fine. I suppose like any program, it takes a lot of practice to master it. Maybe printing out the 145 page user's manual and reading it would help too. It would have been nice it it had superimposed the member forces on the diagram, but I guess that it does not do that. Maybe no program does that.

 

[jayrod12]

You can get risa to display the loads on the diagram. Directly above the diagram there is a drop down box that contains some text about loading (i.e. LC 1: 1.25D +1.5L, or something similar) on either side of the dropdown box are the buttons to turn your loading on and off. The one on the left of the dropdown turns the visibility on or off, the one on the right cycles between load combinations (LC 1, LC 2, etc) and basic load cases (DL, LL, etc).

If you want it to show the reactions you have to click on the blue monitor looking thing on the far left, the options are in that screen to show each reactions including magnitude.

I probably didn't describe that as clearly as the user's manual but it's the best I could do.

 

[ajk1]

In another model that I have made on RISA, it tells me that it cannot solve until I specify the load combinations. This was the same issue I had on my first model, but I got over it, but I don't know how. I have only one load so I don't know why it wants the load combinations, but if I go to the load combinations spread sheet, it won't allow me to enter anything. What am I doing wrong?

 

[JLNJ]

I'm looking at the DEMO version of RISA 3D and it will let me enter Load Comb data, even if I don't have any loads assigned.

Despite BUGGAR's cynicism, I find RISA's demo modules quite generous. We have a network license (or licenses) here and when I don't have one I can still do much of what I am interested in DEMO mode.

 

[bookowski]

Even with only one load case you need to create a load combo, i.e. that load case x 1. Some programs also run your basic load cases for you, Risa doesn't - only combos. There are some tutorials/videos on the Risa website, check those out.

 

[ajk1]

I figured out how to enter load combinations. Have to click on an innocuous looking box that lets me in to enter load factor. The it solved it ok. I am using the DEMO version too.

I still however do not see how to get RISA to superimpose the calculated member forces onto the diagram. I do not see the reference items that jayrod said to click on, but maybe it cannot be done in the Demo version, or am I missing somehting? Any comment?

 

[EngineeringEric]

Load combinations are more than you are thinking. you are using a very powerful program to analyze something. It is made to handle an entire building so sometimes it will require a bunch of front end work to do something as trivial as size a single beam (or a single truss). This is why you need Load combinations, Basic Load Combinations, member sizes, fixity per member, and everything. If you are wrong on some items your model is garbage. The program will work fine but poor input gives poor output. I once worked on a problem for a long time before i realized i put in all my DL as a global X not global Y. as you can imagine this was only discovered when looking at reactions in the D+L case... although that case never governed in this model so it went un-noted for too long.

 

[ajk1]

I realized more than 50 years ago the garbage in equals garbage out. That is why I always do some form of manual check to verify the output. In the case of the current model, I was able to solve it by making use of both symmetry and statics and get exactly the same answer as RISA.

 

[EngineeringEric]

Well that is good it is working then now! It scares me sometimes when people just open RISA for the first time and assume the output is better than logic... Sorry if i came off short, didn't mean to!

For the forces, using the following screen shot from the internet:
-to see reactions and so forth us the button, second row from top (not counting file,edit....) left most. it is blue with a teal M in the screen
-The other options for loads in members and so forth are at the end of that same row, the second. RISA 3d has more options to show loads and forces than the screen shot seems to depict. 3d depicts all the forces, moments, shears, axial and so forth, i would have thought 2D did the same but i seem to be corrected.

 

[ajk1]

Yes Eric, you are absolutely right. Thanks.

 

[Splitrings]

In the upper left corner, just below the "Start New Model Button", is a button that looks like a M with a border. Hit that button, click the "Members" tab, then under the "Member Results" section select axial and check the "Magnitudes" box. You can only show one force at a time.