Braced frame deflection calculation 1

[Naggud]

Hi all,

I'm looking to calculate the relative stiffness of a number of braced steel frames on a 3 storey building using the unitl load method.

I've come up with the bones of the derivation (I think it's correct!) but I'm finding that the defleciton that I'm getting for the frame differs from that of my anayslis in ROBOT (Robot gives deflection of 0.45 at top of frame, I get 0.42).

I've attached my derivation attempt and the calculated deflection. I would be very thankful if some of you could have a quick look and see if the derivation makes sense to you/if anything jumps out as being wrong.

Thank you

 

[DETstru]

I didn't check you calculation and I don't use ROBOT but I wouldn't fret over a <10% difference in hand calc vs. software result.

 

[Celt83]

could be that ROBOT is considering shear deformations and your hand calc is not. Not familiar with ROBOT but I would look in their calculation options to see if you can toggle off the shear deformations for the sake of comparison.

 

[RPMG]

Robot may be performing a second order analysis. There shouldn't be any shear.

Usually hand calculations only consider the brace stiffness for lateral drift. I think the equation is: K = (AE/L)*(cos O)^2.

 

[MotorCity]

I did not look at your numbers, but I would say that if you hand calculated the deflection of braced frames on a 3 story building by hand and your results were within 0.03 (inches??), you deserve a pat on the back. I'd call it good.
(Either this is a homework problem or you have a huge budget for your project)

 

[Naggud]

@motorcity nope, doing it on my own time for a project, I did a push over using a fictional unit load (I'll have higher deflection in reality). I enjoy trying to get these things out. I'm in the early years of my career and think it's important to have a good understanding of where results are coming from!
Thanks for your responses guys.

 

[patswfc]

Is the E value of the steel in Robot the same as in your calc?

 

[rb1957]

am I right in reading your deflection calc, in level 3 as saying the load in the vertical member 5-6 has a lateral deflection ?

should the deflection be factored by h3/L to create a lateral component ?

Is the lateral deflection correct for the diagonal ? *(d3/L) or *(L/d3) ?

another day in paradise, or is paradise one day closer ?