secondary beams VS cold formed section purlin

[h-badawy]

dear experts

i am reviewing now steel structural building drawings from a prominent steel vendor , and his structural system Consists of parallel hot rolled main frames run in the short direction with a perpendicular cold formed section purlins rested above the main frames,and all base supports are hinge connections , and there is no secondary beams in the long direction .
my inquiry as the following : can this building be stable against the lateral loads (ex. wind loads) in case of absence of the secondary beams which can make lateral connection between the main frames and work like a diaphragm to distribute the loads , or purlins can do this function without need to the secondary beams . .
please see attachment photo .

Thank you

 

[jayrod12]

Usually in this type of building there is horizontal rod bracing in the roof structure in lieu of a diaphragm, and there is vertical rod bracing along the long walls. The short walls can be either a rigid frame with infill, or steel columns, a ridge beam and vertical rod bracing.

What you are looking at in that picture is the basic intent for gravity loading. That image does nothing to show the final lateral stability component.

 

[Ron247]

Please define secondary beams. I am not sure what you are referring to. Are the soldier columns fix base? What is the purpose of the soldier columns? You also need to define which direction the lateral loads you are inquiring about are directed. Are they in the short or long direction?

 

[h-badawy]

jayrod12 : this phpoto is just indication for the main stru. system , yes you are right there is a horizontal rod bracing but between the two first and end main frames and the same locations there is also a vertical rod bracing but my problem in the long direction of the building how the lateral loads will transfer between the frames especially that purlins are very thin and strength is very weak to resist the normal forces .

Ron247 : ignore the soldier columns , i am used to run the hot roller section wide flange between the main frames in the long direction .

Thank you

 

[KootK]

...but my problem in the long direction of the building how the lateral loads will transfer between the frames especially that purlins are very thin and strength is very weak to resist the normal forces

With the discrete diaphragm bracing in play, you don't need to transfer appreciable axial loads between frames. Or, at least, that is the story that we usually tell.

HELP! I'd like your help with a thread that I was forced to move to the business issues section where it will surely be seen by next to nobody that matters to me:

http://www.eng-tips.com/viewthread.cfm?qid=456235

 

[h-badawy]

Krook : but imagine there are two or three frames in the middle of the building without any horizontal/vertical bracing from two sides and it’s base connection is hinge , i feel this case is unstable in the direction of out of plan of the frame when frame under lateral load .

Thank you

 

[KootK]

i feel this case is unstable in the direction of out of plan of the frame when frame under lateral load .

I agree. But, then, it doesn't take a whole lot of axial strength or stiffness in the diaphragm to get the job done. Usually the purlins are capable of doing that job.

HELP! I'd like your help with a thread that I was forced to move to the business issues section where it will surely be seen by next to nobody that matters to me:

http://www.eng-tips.com/viewthread.cfm?qid=456235

 

[Ron247]

Most PEMBs only have one bay of bracing to stabilize the entire building in the long direction. With one bay stable, all other bays are connected to it for stability. The purlins strut the lateral wind load from the endwall to the braced bay. It is the roof purlin that is nearest the intersection of the rods to the rafter that is designed for the strut load.

Longer and wider buildings tend to have more than one braced bay and may have struts installed to transfer larger loads to the bracing.