Beam supporting reinforced masonry deflection limit 1

[milkshakelake]

What's the deflection limit of a steel beam supporting reinforced masonry? I use L/600, but my beams are getting too massive, so I'm wondering if L/240 is appropriate.

ACI 530-13 5.2.1.4.1 uses L/600 for unfactored dead plus live loads. However, the commentary has something interesting.

5.2.1.4.1. The deflection limits apply to beams and lintels of all materials that support unreinforced masonry. The deflection requirements may also be applicable to supported reinforced masonry that has vertical reinforcement only.

The commentary says that the limit "might" apply to reinforced masonry that has vertical reinforcement only. All my reinforced masonry walls have ladder trusses at 16" on center vertically, which might count as horizontal reinforcement. All this reinforcement gives the masonry some crack control and ductility. Is that enough of an argument to definitively allow L/240?

Bonus question: Separately from the previous question, let's say I have to use L/600, like if it was theoretically unreinforced masonry. Would the deflection limit apply to the long beams in the picture below? The distance between them is about 6' average. My thinking is that it does apply to long beams. Although I usually consider local deflection of the beam directly under the masonry, in this case they're pretty rigid and most of the deflection would come from the long beams. On the other hand, they'd all deflect pretty much the same amount (they're all controlled by deflection), so I don't see a lot of potential for differential deflection.

I did see an old thread about this, but it's maybe referring to some outdated code commentary:

https://www.eng-tips.com/viewthread.cfm?qid=125144

 

[KootK]

XR can drive over and we can spend December drinking Scotch and sailing rather than huddled in your house trying to keep warm.

Uhh... ok!!! Sold. I'm hugely attracted to sailing. Especially navigation and knot tying.

There's a sad, puddle based sailing club down the street from my house: Link. I hear they offer decent lessons. I've been meaning to sign up but, to date, haven't really had a decent, post-lesson opportunity to make it worthwhile. Most of my bike rides are around that same body of water so I get plenty of opportunities to drool.

I've been toying with the idea of getting a cheap sextant so that I can pretend to be Admiral Lord Nelson while in my hot tub on clear fall evenings.

 

[phamENG]

To the OP's topic: lexpatrie is correct - the hard limit for masonry deflection was removed from the code. The Brick Industry Association still recommends its use, though, so I still incorporate it into my design criteria.

To the more important topic:

A friend got me a 1915 US Naval Academy textbook on celestial navigation for my birthday a few years back. I, too, would like to pick up a sextant and learn to use it. Haven't, though. I'm also more likely to imagine myself as Jack Aubrey, though. Fictional characters have marginally less baggage, not to mention the bad blood between old Horatio and one of my distant cousins...

 

[milkshakelake]

@phamENG That's what I was thinking, that the relative deflection between the beams shouldn't really be an issue. JAE suggested patterned live loading, which makes sense, but I'll just put expansion joints and call it a day.

@Tomfh The short beams that the CMU walls are resting on are only 6' long, so they won't reach L/600 or 0.3". Thanks for the explanation though. I generally stick to L/600 in all cases, even if the client cries; this was just a weird one.

@lexpatrie The CMU will sit on a concrete slab on metal deck with dowels into it. I don't want to make the diaphragm discontinuous and put it directly on the steel beams. It'll help even out the load a tiny bit. And yeah, I thought it was weird that I didn't see a hard deflection limit in the code. I could've sworn I saw it somewhere. I'm glad I'm not going crazy. I didn't quite understand what you meant about reducing the dead/live load though. So I only need to consider the deflection when the CMU is being laid? What about the live load afterward? This is a place of assembly, so there will be a whole bunch of 100 psf live loads.

Look at all of you talking about interesting things, like socializing and going outside. I don't think I had time for that for half a decade now. *cries*