Composite Design - Masonry wall on steel beam 2

[RFreund]

I guess I should first ask - Can/should a masonry wall on a steel beam be designed as a composite beam or is this a bad idea?
Second, can anyone provide any references for composite design of a masonry wall on a steel beam? I was thinking this would be similar to composite steel beam and concrete deck, no? I would think though that the height of the studs would need to be increased to 'help' engage more of the masonry.

The wall in my case is pretty shallow on the order of 2' tall for a 34' span. I could switch to light gauge but I would like to 'transfer shear' between a high/low roof and every thing else is masonry so I would like to 'maintain the stiffness'.




EIT

http://www.HowToEngineer.com

 

[johnbridge231]

Since you prevent the relative slip between the steel beam and masonry, by carrying the corresponding longitudinal shear with adequate studs count, I think you can assume a composite connection. This will result into a smaller steel section, but it is maybe more convenient to design the steel beam as is (without composite action) as there is a lack in code provisions regarding such things..
I hope this has helped you.

Analysis and Design of arbitrary cross sections
Reinforcement design to all major codes
Moment Curvature analysis

http://www.engissol.com/cross-section-analysis-design.html

 

[JAE]

I would be concerned that there would be gaps in the masonry - with grout fill sometimes the small re-entrant ends of the blocks don't get grouted and you would have non-continuous compression in the masonry.

 

[BAretired]

Is the steel beam laterally braced? Is the top of wall laterally braced? For a 34' span, you will likely need some sort of lateral bracing to prevent lateral torsional buckling.

BA

 

[RFreund]

Yes it would be braced but that brings up a good point (in combination w/ JAE's comment) that the 'discontinuity' from the joists framing into the beam could be a problem?

Attached is the section.
Ideally I would like to provide a something that can transfer shear between the high and low roof. Although if not possible I believe I can account these forces else where if I have to.
I am open to alternatives but I'm also still interested in hearing more about the composite beam as well.

Apparently there is some research on this however I am neither Canadian nor a member of the NRC research press...

http://www.nrcresearchpress.com/doi/abs/10.1139/l82-010?journalCode=cjce#.URWWKqV9K2E

Thanks!

EIT
www.HowToEngineer.com

 

[msquared48]

With such a small compression block in the CMU, I'm wondering how much steel you could really save here, let alone the lateral bracing issues previously mentioned.

It is good that you are thinking out of the box though...

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[BAretired]

There is no question that the materials will act in a composite way if properly constructed. To avoid the issue that JAE brought up, you could use knockout blocks for the three courses of block between high and low roofs. But unless the steel beam is to be shored at midpoint, it still has to carry the dead load over a 34' span.

BA

 

[RFreund]

Hmmmm, yeah, I'll have to give this one some thought. I may go through the exercise just to see what I can get out of it, but ultimately I will probably provide a beam large enough to carry the masonry or switch to light gauge and resolve the diaphragm forces elsewhere. However if anyone has any further thoughts, or text references feel free to let me know.

Thanks again!

EIT

http://www.HowToEngineer.com

 

[BAretired]

One feature that I don't like about the idea is that the steel erector has to wait until the mason builds the wall before he can place the upper joists. I would prefer to use steel to support both levels, then fill in with masonry afterwards. The 2' difference in height could be used effectively if the top chord of a truss supports the upper level while the bottom chord supports the lower level.

BA

 

[RobertHale]

BA raises an interesting point. If you used his approach you could then use a hybrid steel - infill masonry system to resist the shear. NCMA has Tek Note 14-9A that covers these systems.

 

[RFreund]

BA - Good point. I think I may go this route.

Robert - Thanks for the reference. Interesting stuff.




EIT

http://www.HowToEngineer.com

 

[KootK]

I've done something similar to what you've proposed RFreund (out of desperation). Here's what I came up with:

1) I used deformed bar anchors welded to the beam instead of studs. I transferred the horizontal shear through shear friction.
2) I used the out of plane flexural stiffness of the CMU wall to brace the steel beam from LTB. That's why I went with the deformed bar anchors which I lapped to the CMU wall reinforcement.
3) I only counted on the contribution of the steel beam to resist shear. This seemed prudent given the realities on control jointing (my beam spanned a window).
4) I had bond beams installed in the upper two courses to encourage a solid load path for the compression block.
5) I kept the stresses pretty low. My main purpose was to limit deflections.
6) I made a point of performing the field review of the beam myself.

Alas, I know of no additional references for designing composite CMU / Steel beams.

 

[RFreund]

KootK - A few questions:

RE 1) Shear friction between steel and masonry? How tall were the bars?

RE 2) I'm not sure I see the difference if you were to use bars or studs here. The welded bars were vertical correct? Then you had horizontal bars which you lapped into the wall. Unless you are saying that the deformed bars were used for additional height (to 'engage' more of the masonry)?

RE 4) When you say you "Bond beam in the upper two courses" What courses are you referring to here? Directly above the beam? Entire masonry 'compression' area was grouted solid, correct?

Thanks again for the info.





EIT

http://www.HowToEngineer.com

 

[KootK]

In response to your questions:

1) The bars lapped to full height bars in the masonry. They only needed to be developed for shear friction.

2) The welded bars were vertical. My goal was to use the out of plane flexural resistance in the block wall above the steel beam to prevent lateral torsional buckling of the steel beam. Transferring torque in the steel beam to flexure in the block requires a vertical tension and compression couple at the interface between the steel beam and the masonry. I used the rebar for the tension force. Studs may well be able to perform the same function. However, I didn't feel too great about the tension capacity of a stud pulling out of the bottom of a grouted masonry cell. In theory, there may have been no tendency for the steel beam to laterally torsionally buckle. No part of it was supposed to be in tension after all. I just like to cover my butt a few different ways when I'm making up my own design procedures.

4) The upper two courses were the two courses at the very top of the block wall segment constructed above the steel beam. Someone else mentioned concern about potential gaps at the head joints in the block in the compression region. I had that same concern. By using bond beam units rather than simple grouted cells, I eliminated the head joints altogether.

 

[RFreund]

Makes sense. Thanks!

EIT

http://www.HowToEngineer.com

 

[RFreund]

Sorry Kootk one more question as I keep working through this (even though I plan to go a different route).

Can you elaborate on "transfer through shear friction"?

Do you mean similar to the concrete equation for shear friction? If so I do not recall this equation for masonry but I suppose it is basically the same.

EIT

http://www.HowToEngineer.com

 

[KootK]

No problem. I used shear friction to handle the horizontal shear between the steel beam and masonry above. I used the concrete equations as you've suggested.