Bracing 1

[L17Aurora]

Can you tell me when you would consider using bracing on say a platform supported on 4 legs. (no horizontal loads)
If the legs are short I suppose they are not needed and even if they were long and wouldn't buckle (according to cals) you wouldn't need braces ??
Is there a rule for fitting them
Thanks
Mick

 

[kslee1000]

beton1:

You are correct, agree with you.

 

[BAretired]

A platform supported on four columns, each hinged top and bottom, is a mechanism. It will collapse with or without horizontal load.

Best regards,

BA

 

[Lion06]

I'm not getting personal, I just think there is a major disconnect somewhere.

Like BA said, a platform with four posts, each hinged top and bottom, is unstable - i.e. it doesn't work on paper. This is what I was getting at.

What kslee was proposing was to provide a diagonal brace to help with lateral motions, but that the platform was fine if it were short and stocky enough. I was respectfully disagreeing and trying to state why. The reason is that without the brace the structure is unstable unless you can consider the columns to be cantilevered. If you can consider them cantilevered then design them accordingly and call it a day.

 

[swearingen]

Actually, StructuralEIT, it does work on paper - it just doesn't work in reality!


If you "heard" it on the internet, it's guilty until proven innocent. - DCS

http://www.eng-tips.com/supportus.cfm

 

[steve1]

I work for a firm that designs cogeneration facilities. We have this discussion concerning bracing for equipment supports all the time. A braced frame is stiffer than a moment resistant frame, hence it provides a higher frequency of response. There is often a frquency criteria associated with equipment supports and we have found that bracing the column legs we help us meet this criteria. Mt personal belief is that moment frames should be avoided for equipment supports.

For a simple platform that is not to tall a moment frame, or even a horizontal bracing system at the top of the platform will suffice.

 

[Lion06]

This seemed to be a platform for workers, not equipment. I agree with you, though, that if it is for equipment then the frequency (and dynamic characteristics) of the platform is important.

 

[beton1]

StructuralEIT:
No offence intended. Keep up the good work.

 

[L17Aurora]

Thanks for all the input. it was just a general question from "not a structural Engineer" about a frame supporting a lump of something.

 

[csd72]

L17Aurora,

Basically it either needs to be braced, cantilvered or portalised (i.e. acting like a rigidly connected portal frame).

Most codes specify that the minimum lateral loads allowed for should be 1% of the vertical loads. This is to allow for any out of plumb in the columns which would tend to induce sway.

If you are in a seismic area then you also need to check the seismic loads.