laced column or braced frame?

[majmaz]

In a structure, distance between two adjacent columns is 4'.
They are connected by horizontal and diagonal elements at
3 points in height. Heights of columns are 9'.
What is the criteria for ratio of Distance/Height to consider columns as a laced column or separated columns with bracing?

 

[BAretired]

I don't know. Why does it matter what you call them?

BA

 

[apsix]

A laced column is analysed as one member, two separate columns obviously aren't.

I couldn't find any separation to length ratio limit (quick look only), but I'm certain that a 4:9 ratio would not qualify.

 

[BAretired]

apsix,

Really? I don't think it matters what you call them or how you analyze them. The result should be the same.

BA

 

[slickdeals]

For gravity, it may not make a difference, but don't you think it is a different situation for lateral loads (braced frame vs. single built-up column)

 

[BAretired]

The steel members don't know what we call them or how we analyze them. They respond to all loads according to their geometry and stiffness.

BA

 

[paddingtongreen]

I agree with BA on this.

I compared the (kl/r) for the overall column and for the individual component columns, usually angles, and then proceed accordingly. I should point out that for a well designed column the (kl/r)s are about equal.

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

 

[apsix]

Our steel code, AS4100, has a whole section for 'Laced and battened compression members'. There are various deemed to comply rules which mean design from first principles is not required for components such as the lacing.

I do agree that you can always ignore the above rules and design each component of frame according to the their individual loading. Component size could probably be reduced with this approach.

 

[vandede427]

assume the lacing only takes shear in lateral loading, not loaded during gravity case.

 

[ToadJones]

Im with BA and Pad.
However, depending on the connection details, one cannot assume that the lacing only takes lateral loads. If heavily loaded there will be column shortening and your lacing will take vertical loads.
I usually analyze bracing and tower like structures under several different release conditions in order to determine the loads that the columns and bracing will take.
I "inactivate" the vertical bracing in these situations in order to ensure that columns take the full gravity load when designing the columns. Then, I reactivate the bracing to ensure that the bracing can take not only the lateral loads but also any gravity loads that may be sneaking there way into the bracing.
Make sense?

 

[apsix]

Just to clarify, this is the definition I'm using for a laced column;
"compression member composed of 2 or more main components which are parallel, intended to act as a single member".

This will not cover structures such as braced frames or lattice towers.