Wrong Reactions ETABS

Question

Wrong Reactions ETABS

TonnyCIV (Student)

(OP)

6 Jan 21 20:59

Hi everyone!.

I have modeled a simple frames, and when I check the reactions due to self-weight, I am surprised that they are incorrect.
Reactions should be 972kgf, however ETABS gives a result of 939.6 kgf.

BAretired (Structural) · Answer 1 · 2021-01-07 05:41:57

The weight per m is 0.3*0.3*2400 216kgf. The length they are using is 2*939.6/216 = 8.7m. They appear to be deducting 15cm from each column (or from each end of the beam) to account for the fact that your dimensions were centre to centre of member. ~~Your calculation includes the overlap twice, so they are correct.~~

Edit: Oops, I nearly fell into the same trap. I think your figure is correct. The total length of two columns and one beam should be 9m, which makes your calculation correct.

BA

TonnyCIV (Student) · Answer 2 · 2021-01-07 11:55:51

Hi @BAretired!
thanks for taking the time to reply.

You're right, I hadn't seen from your perspective.

So, ETABS already considers a real model, as can be seen in the image, even ETABS applies an automatic rigid link, while SAP2000 does not do the same.

If I consider a beam length of 2.70m, I will get reactions of exactly 939.6 kg. I for a moment thought that there was a bug with the software neutral

My question is how much influence modeling and calculating buildings as it does in SAP2000? It would be dangerous?

BAretired (Structural) · Answer 3 · 2021-01-07 16:56:31

Quote (TonnyCIV)
I for a moment thought that there was a bug with the software

There is a bug with the software! And you found it! Fortunately, in this case, it doesn't make much difference to the result. There may be situations where the result could be affected much more than this, which is why one should always do a sanity check on any results coming out of a computer, particularly when using a new piece of software.

BA

Celt83 (Structural) · Answer 4 · 2021-01-09 13:33:35

Agree with BA this looks like a bug.

If you consider the rigid link then the beam section effectively stops at the column face but there would need to be an extra 15cm of column self weight to account for the extension from the node to the top of the section to complete the frame which accounts for their missing reaction from your hand calc.

The overlap in your SAP sketch is equivalent to the missed open corner so the weight of the missed area is accounted for.

My Personal Open Source Structural Applications:
https://github.com/buddyd16/Structural-Engineering

Open Source Structural GitHub Group:
https://github.com/open-struct-engineer

Come Join Us!

Posting Guidelines

Related Projects

Wrong Reactions ETABS