Model shows inaccurately large deflection?

[JCS613]

Hi,

I've modeled a 1 story building according to the plans and given steel shapes,
It appears there is one problem area which has high deflection.
I've attached a screen shot showing the worst deflection, about 3.2"

After changing the beam section many times we've reduced it further but my boss and I believe something is wrong with the analysis thus resulting in too large of a deflection.

We applied a 175 psf dead load and 200 psf live load.

What I did was draw a floor around the entire perimeter of the plan, and then applied the load to that.

We tried both individual dead/live loads, and just one load of 375 psf.

We're designing in ASD so we do not want any load combinations to be applied, and I do not know if any are being applied or not?

My boss has calculated the deflection due to the reactions on that beam using the A-beam app and the numbers do not match ETABS.

Any advice suggestions?

I will upload the etabs file but unfortunatly I did this project in the evaluation version.

Thanks,

 

[JCS613]

I've attached the .zip folder with the ETABS files

 

[structSU10]

The deflected shape looks reasonable to me. How are you calculating the deflection by hand? That 3.2" is not just due to the W21x57 but also the deflection of the W21x93, which is likely significant. When I run a quick check (I don't have access to ETABS but got a rough idea of your framing) I get around the deflection you state with this framing. 375 psf is a large load, and your bay looks to be 30'x40' - I would expect much heavier members.

 

[JCS613]

Thanks for your response, that bay is actually 29' x 29'

I now understand you're saying the 3.2" is net displacement from 0 that that particular joint has moved.

How would I use ETABS to give me just the displacement of one particular beam due to the loading, NOT including the displacement of the other beam's it is anchored to?

As in , if I'm using the ETABS deflection #'s to design this building and to check L/360 maximum deflection under total load of the beam...

I take 29' x 12 / 360 = 0.967"

Where do I find the number corresponding to the maximum deflection under total load of this one particular beam (in ETABS) to compare to my 0.967" to see if I meet the design requirement?

Thanks,

 

[JCS613]

BUMP

anyone have an answer for how to find actual deflection of a beam , not displacement of a node?

Thanks.

 

[Agent666]

Work it out by hand. How hard would that be, sometimes people's reliance on a computer to work out the simplest of questions astonishes me...

Now if you right click on the beam while showing the moment or shear there is also a deflection also shown from memory, you can select "relative to ends" or something like that. I don't have etabs in front of me at the moment to verify exact steps, but it's hidden away in one of those dialog boxes.