Frame assessment - load in horizontal struts?

[marcg99]

Hi,

I'm assessing a cast iron frame struture, made of vertical columns with horizontal struts.

I am looking through a previous assessment, where only the column loads were calculated - a full analysis with the struts included in a structural model was not performed.

However it was assumed that the struts attached to any 1 column carried 10% on the column load, and were assessed on this 10%.

How realistic is this 10%? I can't find any guidance / code references on the issue, and don't want to go through a complicated re-analysis by adding in the struts and additional loading.

Thanks!

 

[msquared48]

Can you post a sketch of the structure?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[BAretired]

What happens if you assume the struts carry 0% of the column load?

BA

 

[hokie66]

Is the 10% strut load a bracing force? Having a hard time understanding what you mean. As Mike said, a sketch might help.

 

[marcg99]

Ok hopefully attached a diagram...

The column that has been assessed is in black, and has a load, P, from a structure (part existing part new) above. The struts I talk about are in blue - these are assumed to have a load of P/10 (both tension and compression have been checked in the calculations I am reviewing).

There is no full structural model with the struts in to calculate the exact forces - just this P/10 assumpton. It is this I am querying, as I can't find any basis for this (why not 5% or 20% for example) either in the calculations, or in a variety of codes I've looked in - its likely it was just a rule of thumb advised by a more senior engineer originally.

Ultimately if the stuts fail, I will need to take a long buckling length for the column / think about strengthing the existing stuts to ensure they don't fail.

Its may not be not the best approach, but am just trying to verify the approach the previous analysis / calculations have used for now.

Thanks!

 

[hokie66]

That is a bracing force. Modern codes assume this to be 2% to 5%.

 

[marcg99]

Thanks a lot - that helps!

Do you know of a specific code and clause reference? Am in the UK so a eurocode / BS 5400 reference would be handy if possible...