'X' Bracing/out of plane bracing Analysis
'X' Bracing/out of plane bracing Analysis
(OP)
To all,
I am curious how most engineers handle the analysis of 'X' bracing with regard to lateral support out of plane.
I noticed the "Tension Only" thread as well, so I thought it might be a good time to start a discussion on vertical bracing. I typically use RAMAdvanse, but have used other 3D analysis such as STADD and RISA. When building a model I typically do NOT add a node at the intersection of the 'X', otherwise I would have to manually input the effective length of the brace, as I do not consider the members braced out of plan. Now of course Tension Only members will avoid this all together; however, your reactions will be higher having only half the members doing the work (half being relative to a symmetrical structure).
I have also read articles, where a certain amount of out of plane lateral support can be provided to the compression member by the tension member, based on the connection and the continuity of the bracing.
Again, I was wondering how others view this and their approach to design.
Thanks
I am curious how most engineers handle the analysis of 'X' bracing with regard to lateral support out of plane.
I noticed the "Tension Only" thread as well, so I thought it might be a good time to start a discussion on vertical bracing. I typically use RAMAdvanse, but have used other 3D analysis such as STADD and RISA. When building a model I typically do NOT add a node at the intersection of the 'X', otherwise I would have to manually input the effective length of the brace, as I do not consider the members braced out of plan. Now of course Tension Only members will avoid this all together; however, your reactions will be higher having only half the members doing the work (half being relative to a symmetrical structure).
I have also read articles, where a certain amount of out of plane lateral support can be provided to the compression member by the tension member, based on the connection and the continuity of the bracing.
Again, I was wondering how others view this and their approach to design.
Thanks






RE: 'X' Bracing/out of plane bracing Analysis
A colleague of mine believes the tension diagonal does brace the compression diagonal.
So I guess I'm not helping much, am I?
DaveAtkins
RE: 'X' Bracing/out of plane bracing Analysis
RE: 'X' Bracing/out of plane bracing Analysis
RE: 'X' Bracing/out of plane bracing Analysis
RE: 'X' Bracing/out of plane bracing Analysis
Even if you use a rod in an X brace, a typical analysis program will not "know" that it is a flimsy rod that doesn't do anything in compression and will, within the solution matrix, solve the model assuming the compression rod takes axial stress just like a tension rod....and your results will not be realistic.
In answer to your main question, we usually model as tension only braces - for rods and angles and such. For heavier sections, where we do want to take compression, we use the intersection as a brace point in the code strength derivation.
RE: 'X' Bracing/out of plane bracing Analysis
DaveAtkins
RE: 'X' Bracing/out of plane bracing Analysis
WillisV,
Thanks for the article very interesting read.
RE: 'X' Bracing/out of plane bracing Analysis
A more exact solution is
KL=L1+L2(2m-1)
m=sqrt(0.523-0.428(T/C))>=0.5
T=force in tension bracing
C=force in compression bracing
I would like to use K=1 if no special reason. A little conservative but simple