Knee Brace Hand Calc 1

[BadgerPE]

Hey all,

I am trying to solve a knee brace problem by hand but have run into some difficulties (Friday afternoon perhaps?). I am trying to match results in RISA for a cold-formed knee brace frame. Loading on it is fairly small (about 1 k lateral with minimal gravity loading). This is the first time I have tried to do a knee brace calc and I can't get it to work out. I tried method of sections but that doesn't take into account the stiffness of the members in bending so my results were not close.

Does anyone have any examples of methods to use or examples to follow? My boss was out today so I have been on my own with this since talking with my boss yesterday and would like to come up with a hand solution (even an approximation) over the weekend to match my RISA results.

Thanks much!

 

[Ron]

From a global standpoint, the knee braced connection creates a rigid frame analogy. Resolving that is sometimes difficult (well, actually it's always difficult...particularly when trying to equate to FEA output!)

Seemingly an elementary answer...do a FBD of the knee brace and superimpose the FEA results on that...you should get close.

 

[JLNJ]

I believe that the force in the brace is just the base shear times the height divided by the normal distance from the joint to the kneebrace.

 

[BadgerPE]

Ron,

Thanks for the response. I am a little confused what you mean by superimposing the FEA results on the knee brace though. Could you perhaps shed a little more light on your response? Thanks!

 

[paddingtongreen]

If the brace was short, only occupied a small amount of the column, I used to consider it a fixed joint and then divide the fixed end moment by the vertical component length of the brace to find the horizontal component of the force in the brace.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[Splitrings]

This is an indeterminate structure that can be analyzed by one of many methods; moment distribution, stiffness method, etc. You'll need to turn off shear deformations in your FEA program. Then you should be able closely match your results