Irregular diaphragm 1

[Wazk]

Wondering what your thoughts are on the following irregular diaphragm. 10m high warehouse with mezzanine at 4m. each block (A, B, C) has a dimension of 8x8m roughly.
I have problem arranging the steel roof framing for stability purpose. Can anyone share your opinions?
Can I not have portal frame to resist wind in latitude direction but use the roof bracing to cantilever with block B & C as back spans?
For longitudinal direction, I find it hard to place portal frame or (braced wall) due to the irregularity of the lightweight frame. What do you suggest? Thank you.

 

[phamENG]

What is your proposed roof framing? Steel beams? Open web joists? Steel deck diaphragm or discreet, in plane bracing?

 

[KootK]

- If this is a high seismic application, the general consensus on this forum seems to be that some kind of lateral system along the LSF side is prudent, even if that's just relatively soft moment frames.

- In an application dominated by wind and general stability, I'd be willing to cantilever the diaphragm off of that long concrete wall so long as the diaphragm is rationalized in a way that makes it tractable and somewhat predictable. See the sketch below for one idea.

 

[Aesur]

I second KootK's response above.

 

[Wazk]

Thank you.

Sorry. It is steel beams + purlins on top + rob bracing.

 

[Wazk]

It is in low seismic zone

I have done the sketch for the latitude wind as below. Can you please explained how 'cantilever' works for longitudinal wind? (also I forgot to add that the RC wall will be precast).

 

[Wazk]

Also, for the irregular steel frame shown in blue, there are voids in mezzanine level, meaning the height the frame will be 10m.
The architect wants keep them within 100mm thick. I was thinking having shs columns span from footing to roof with internal restraints by wind beams at mezzanine floor to reducing its unbraced length. (See below what I was proposing for block B & C). But I have problem doing the same thing for block A due to its shape. Any suggestions?

Thank you.

 

[KootK]

Can you please explained how 'cantilever' works for longitudinal wind?

Like this. It's also commonly referred to as three sided building design.

 

[KootK]

The architect wants keep them within 100mm thick. I was thinking having shs columns span from footing to roof with internal restraints by wind beams at mezzanine floor to reducing its unbraced length. (See below what I was proposing for block B & C). But I have problem doing the same thing for block A due to its shape. Any suggestions?

My gut feel is that large wind beams won't be practical and, rather, the architect may have to accept a deeper wall section.

 

[jayrod12]

10m wall only 100mm thick, that's not reasonable. Could you do vertical wind posts and then have the glazing/cladding span between them? Sure. But even at that, the vertical posts would need to be fairly substantially sized and fairly regularly spaced. I would bet you're into the 175mm +/- mullion back section depth at those heights.

 

[sticksandtriangles]

Just because it is counterintuitive, I think the diaphragm deflection will have opposite curvature as shown in Kootk image, see this thread [URL unfurl="true"]https://www.eng-tips.com/viewthread.cfm?qid=450755[/url]

S&T

 

[KootK]

Yup, in my rush to make the analogy I've forgotten my own past work on this. It's the difference between a thing dominated by flexural deformation and a thing dominated by shear deformation. Thanks for the correction SnT.

 

[Wazk]

Thank you.

I was considering 300 PFC (strong axis horizontal). Can you explain why this is not practical? (My problem with this is for block A since it is curved) Without internal restraint, the wall will span 10m long and required around 200mm mullions with closed spacing from my first guess...

 

[Wazk]

Thank you.
With wind beam placed at 4m height, the mullions will be a 4+5+1 (parapet) two back spans cantilever beam. I will expect it works at 1.2m spacing. That said, I can increase them to say 150 shs if required. Now my issue is for block A. Can curved wind beam be placed at first level as restraints? Do you see any problems with this idea? Without wind beam the mullions will be 200mm+ deep..

 

[Wazk]

https://www.eng-tips.com/viewthread.cfm?qid=450755[/URL]]

Noted. Thank you for this helpful information.