Typical Eave Strut Design 1

[SmithJ]

Hello All,

I am in the process of designing a Hangar in Florida. My building is a Pre-Manufactured Metal building with typical purlins, girts and sheeting material. The building has a 3 foot overhang on all sides.

I intend to have two Eave Struts on the building, one along the line of the frame columns and one at the end of the overhang (which will be created using a mill shape). The Eave strut along the frame column line will have sheeting attached to it's top flange and outside web. My questions are:

* What is the laterally unbraced length for the Eave Strut?
* Can I use the AISI 96 requirements for through fastened
flange braces or do I need discrete braces?
* Doesn't the wall sheeting attaching to the web of the
stut provide adequate lateral stability?
* Does the roof panel alone provide enough lateral
stability for both the top and bottom flanges of the
Eave Strut?

Your input as always is greatly appreciated in this case.

Thanks.
JS.

 

[ssdpe]

SmithJ,

* What is the laterally unbraced length for the Eave Strut?
For your case, the eave strut is fully braced since it has panel attached to it. This open section is supported vertically and laterally by the panel. At the eave, the wind edge strip will require the screw spacing to be around 6"-12" on center. Thus, the eave strut will be designed as a fully braced one.

* Can I use the AISI 96 requirements for through fastened
flange braces or do I need discrete braces?
You do not need discrete braces for screw down systems UNLESS your panel is not able to transfer the roll forces to the support points through diaphragm action or the roof slope is beyond certain limit. Your company should have testing available on diaphragm capacity.

* Doesn't the wall sheeting attaching to the web of the
stut provide adequate lateral stability?
If the eave strut were supported only vertically, I would not consider this section as a fully braced one. This open section will buckle when subjected to compressive forces.

* Does the roof panel alone provide enough lateral
stability for both the top and bottom flanges of the
Eave Strut?
No. This section will be subjected to axial plus bending. Thus, the eave strut's bottom flange is fully unbraced.

I will recommend you the following references:

1. Cold-Formed Steel Design, 3rd Edition
By Dr. Wei-Wen Yu

2. NASPEC 2001 Edition
Which is an AISI Standard

I always tell engineers to discuss with others what you have in mind before you take a final desicion. Good luck!

nepe

 

[SmithJ]

Hi,

I know this is an old post but I was wondering if I could raise a question here.

Nepe, In your response to the first question you state that the strut is fully braced. However, in your response to the third quetion, you say that you would not consider the Eave Strut Fully braced if it is only vertically supported.

Are you saying that the wall sheeting provides only vertical support? In a typical metal building, can we assume that the roof sheeting provides horizontal support and, acting together with the wall sheeting, wil result in a fully braced Eave Strut?

Thanks for your input.
JS.

 

[3dboy]

you had better brace the flange opposite the panel in someway to account for compression in that flange due to suction.