deflection of an infilled steel frame 2

[Ayham Shahoud]

I have an infilled steel frame system with a total height of 21'. I need to check both horizontal & vertical deflections. I used the value of (L/600) for vertical optimization under (D+L) as mentioned on (Masonry Building Code1-3-02) page12 /pls see the attached image/. However, it didn't mention the lateral deflection, so I used IBC2012 as a guide. IBC2012 /page 366/recommends for the plaster or stucco finishes to use the value (L/360) to check against wind load /pls see image/. Actually, I am concerned about the difference between both values since the wall inertia is the same for both directions in the plan.

ANY RECOMMENDATIONS PLEASE

 

[Lomarandil]

For out-of-plane deflection of a reinforced masonry wall, the masonry code limits mid-panel deflection (δ) to 0.007h at service levels, including the effects of cracking and of P-Δ from the frame elements.

So while I'm not aware of a code requirement for the lateral deflection of a structural system supporting masonry walls (excluding seismic drift limits and the general IBC limit that you show), at some point a flexible building frame will create large P-Δ that makes it impossible to satisfy the 0.007h limit in the infill panel.

Griffiths published an article that provides a better guide, although I'm not sure it ever made it into the code:

https://www.aisc.org/Serviceability-Limit-States-Under-Wind-Load

For in-plane deflection, Appendix B limits the displacement of a participating infill panel to 25mm maximum. Or you'll need to provide a 10mm isolation gap all around the infill to prevent it from attracting in-plane load, and appropriate out-of-plane restraint. That gets messy.

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just call me Lo.

 

[Ayham Shahoud]

Thank you, Lo.
Actually, the walls aren't reinforced masonry but thermally insulated blocks. So, shall we apply the same limit values to them ??

 

[Lomarandil]

I've asked that same question. For unreinforced blocks, I certainly wouldn't exceed 0.007h, although a lower limit might be required.

----
just call me Lo.

 

[Ayham Shahoud]

Thanks, a lot Lo. cuz that was so helpful.

 

[le99]

Note that the 0.007h limit is to prevent structural damage to the framing members, while the IBC recommendation is for limiting damage to the finishing/cladding. You shall apply the limit accordingly.

 

[Lomarandil]

Le99, thats not how I read it in the TMS commentary. It sounded like 0.007h was a limit for the panel itself. What makes you believe it is to protect the framing?

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just call me Lo.

 

[le99]

What does the commentary say? Does it treat the panel as a structural or architectural element? The IBC is more clear on that aspect, which says the deflection of a structural element with sensitive finishing shall be limited to... The limit here is architectural rather than structural.

 

[Lomarandil]

From the TMS commentary: "A wall loaded in this range returns to its original vertical position when the lateral load is removed, because the stress in the reinforcement is within its elastic limit".



----
just call me Lo.

 

[dik]

Is the frame totally infilled? with no gaps between the steel and the masonry?' Would it act as a rigid masonry panel and not require deflection issues?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[Ayham Shahoud]

Dear all,
the frames are fully infilled without gaps between the steel and masonry cuz no cladding will be attached after the thermal block installation, therefore, the block will be in the front line to resist the sun rays. As a result, the block walls will contribute to the frame rigidity and the deflection issues must be taken into consideration carefully.

 

[le99]

The 0.007h limit turns out to be a deflection limit of L/143. Your call.

 

[dik]

I would not normally consider any frame deflection with total infilled walls.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[le99]

Is crack on the masonry blocks acceptable? If not, what is the limiting stress? Does the TMS provide a method to calculate the rigidity of cracked masonry? Can you provide a cross-section of this wall, or it is simply the steel framing with reinforced/unreinforced masonry infilled wall?

 

[Lomarandil]

Dik, I've heard similar sentiments from other designers, but it isnt how I read the code (when applicable).

In the developing world, falling masonry from infill panels and parapets is (anecdotally) the primary hazard to human life in seismic events.

----
just call me Lo.

 

[dik]

I wasn't aware there was a code provision for infilled masonry, other than a rational approach.


Adjustable strap anchors (not the flimsy gauge material ties) generally hold the stuff in place.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik