Help with warning logs

[ditso]

Hi. I need help with my model. I am trying to analyze a two-storey house and everytime I solve with just the deadload + selfweight (Load Comb 17) there are these kinds of warnings that pop out:

- Unable to establish span information for member MX. ==> I think this is related to the overhang at the balcony but I'm not quite sure on how to model the overhang. I've already tried actually splitting the physical members.

- Custom rebar layout does not meet min steel (As,min) per Global Parameters ==> I think I did my rebar layouts right. Is this a problem with the actual design of the members?

- Compression Pu exceeds 0.75*Pc (Euler buckling)

- Factored torsional moment Tu exceeds the threshold torsion per ACI 318-11.5.1

I tried looking it up but I can't find anything on the net. I'm not sure whether there's something wrong with my modeling or if it's the actual design. I really need help. Thanks to anyone who would be able to.

P.S. I wasn't the one who did the design. I was just asked to analyze it.
P.P.S I attached a copy of my model for reference. Please ignore the the other load combs I haven't edited them yet.

 

[JoshPlumSE]

The "unable to establish span information" do relate to the cantilever beams. In order to get the distribution of reinforcement correct in concrete beams, RISA tries to determine where the support points are for each member. This is important for concrete when designing for the "moment at the face of support" and the "shear at a distance 'd' from the face of support". The program throws up that flag whenever it had difficulty understanding the support arrangement for a member. In your model, it is almost certainly related to the cantilever areas. I didn't look closely, but I tend to believe you can ignore this message in your model. However, the general recommendation is when you get this message, make sure you take a closer look at the reinforcement that RISA is providing for the member.... especially in the areas where the span information isn't known (i.e. the cantilevers).

The custom rebar layout message is not one that I am getting when I solve the model, so I cannot comment on this too much. My guess is that you are running an old version that could erroneously produce this warning log message. But, that's just a guess.


The Torsional moment warning is actually a good bit better in the newer versions: "M4: Factored torsional moment Tu exceeds the threshold torsion (1.511kN-m) per ACI 318-11 11.5.1". I think that new message explains it a bit better. Essentially, the moment is large enough that per ACI guidelines you cannot just ignore the torsion (which RISA does). Therefore, you (the engineer) need to decide what to do about it.

 

[ditso]

Thank you for the help, JoshPlum.

Okay, I will ignore the warning about span information. Or just uncheck the bad framing warnings.

My version is 11.0. Is this an old one? I sure hope that that rebar layout warning was just as you said. If that is so, should I also ignore this message?

Ohh so there is a problem with the structural design. Is this why the message "Compression Pu exceeds 0.75*Pc (Euler buckling)" also comes out?

Are my end releases correct? Is there anything wrong with the model?

 

[JoshPlumSE]

Unfortunately, I cannot tell for sure why you are getting that custom rebar layout warning log message. Not unless I run that old version 11 that you are running. And, I haven't had time to do that at all. I feel pretty confident in my guess. But, it is just an educated guess. If so, then you can just ignore it. Especially if you have looked at the member reinforcement and it seems reasonable based on your engineering judgment.

I forgot to address the 0.75Pu*Pc message. I was not getting that error message in version 12. That message is generally related to the P-little delta moment amplification equations in ACI... An amplification factor of something like Cm / (1-Pu/0.75*Pc). Can't remember the exact code reference. 10.10-ish.

In the newer versions of RISA, we no longer use these provisions for the newest ACI codes. That's because they allow for a more rational amplification based on a P-Delta analysis. It is possible that this is one of those cases. But, again I cannot know for sure.

 

[ditso]

I downloaded the demo version of 12.0.2 and ran the model there. And just like you said, the warnings weren't there! I checked the envelope member details and saw that my members passed the deadload-only load comb, thank goodness. Thanks to this I was able to run all the other load combs and complete the checking.

Thanks again for your help JoshPlum, I'm really grateful!