supporting top (compression) chord of truss beam? 1

[greznik91]

Hi, I am designing a steel canopy.

I need your opinion about supporting of top chord (to prevent buckling as a result of compression in top chord). Is this the appropriate way to do it?

Thanks for replies.

 

[jayrod12]

That is one way to do it yes. That is likely the simplest and most effective route.

There are other ways to analyze the web members as cantilevers however the amount of analysis and detailing required to get that to work might not be worth it if the client is willing to accept those diagonals.

 

[phamENG]

Just make sure you consider the combined stiffness of the brace and the beam it connects to. The combined axial and flexural stiffness of that system will determine its effectiveness as a brace for your top chord.

 

[KootK]

That's likely the most structurally efficient way to provide the bracing stiffness required. It kinda messes with the roofing however. Given that you've already got your beams aligned with your truss verticals, I'd consider moment connecting the two to prevent rollover of the truss and forgoing the diagonals. Alternately, if you could drop the truss a couple of feet, you could put the diagonals in the ceiling.

 

[rb1957]

is a symmetric cap vulnerable to lateral bending ?

how about making the tension cap unsupported ? (raise the ceiling, drop the beam)

another day in paradise, or is paradise one day closer ?

 

[Ron247]

If you do the diagonals, I would sheet the slope of the diagonals so the roof covering stops at the diagonals rather than have all the penetrations in the covering. Roofing and waterproofing "inside" the area under the diagonal could get messy.

 

[phamENG]

If dropping the truss isn't an option, you can provide enough strength in the braces to support a sloped roof section. Think of it as a GIANT cant strip. I've done that on several light gauge parapets. It removes the need for the troublesome pitch pockets, and really doesn't add much to the roofing.

 

[phamENG]

Ron beat me to it.

 

[Ron247]

KootK's and rb1957's suggestion of raising the roof make more sense. No parapet to trap debris. Less waterproofing headaches. About the same amount of wind to deal with. Extra headroom inside. Same amount of clearance at the entrance.

 

[canwesteng]

You might even have enough capacity in the end plate connection to the verticals to resist buckling the top chord.

 

[r13]

Check the limit state compressive strength of the top chord, you may need fewer braces than proposed.

 

[greznik91]

Thank you for replies.

Lowering the ceiling can be an option, but in this case I still need to support bottom chord because of uplift wind (bottom is in compression in this case and not supported along whole lenght of truss beam)?
Top chord is no longer a problem because it is laterally braced by IPE 180 beams.