CMU WALL SUPPORT W/ TEMPORARY SHORING

[sedesigner06]

I have a long span wall (53.5 ft from column support to column support). It is support as varying brick veneer from 9' on the high side and ' on the low side. This is the only load that beam will be carrying. With limiting the deflection to 0.3'' the beam is huge as you can imagine (W36x182). Has anyone utilized temporary shoring in situations like this.

My thought is that if I can utilize a temporary support at midspan I reduce the size greatly. I plan on putting a bond beam at the top and bottom of the wall, this should allow me to analyze the section as a deep beam and make it easier to meet the deflection requirements.

Thanks in advance for any input,

Thanks,

Eric

 

[KootK]

I've done this in the past. Essentially, the steel beam becomes just formwork. A couple of things to watch out for:

1) Make sure that your contractor's okay with leaving the shoring in place while you attain f'm. This can be a construction sequencing issue.

2) Make sure that you have a good handle on where control joints might be placed and what effect that might have on your CMU beam. The sides of windows are popular control joint locations.

3) If the beam will not be solid grouted, be sure to consider that in your beam shear evaluation. The usual case for CMU beams is fully grouted cells.

Another strategy that I've used in the past, in conjunction with what you have proposed, is to attempt to make the beam behave compositely with a few courses of solid grouted block above. I had rebar couplers welded to the top of the beam and field installed vertical rebar projecting a few courses into the masonry. I wasn't able to find an established design procedure for this so I wound up being pretty conservative. Locating the couplers properly is an issue as well.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[sedesigner06]

Thanks for your help, see responses below.


1) Make sure that your contractor's okay with leaving the shoring in place while you attain f'm. This can be a construction sequencing issue.
I am in the process of preparing construction documents. I believe the proper approach would be to show the beam size and add a note of temporary shoring at the mid span. If they have a problem with the sequencing I can reissue with the beam size to carry the full wall.

2) Make sure that you have a good handle on where control joints might be placed and what effect that might have on your CMU beam. The sides of windows are popular control joint locations.
There are no windows at the cmu wall above, with a 53.5' wall I was thinking control joints at the 1/3 points. I will detail it such that rebar with a coupler welded to the beam is on each side of the control joint.

3) If the beam will not be solid grouted, be sure to consider that in your beam shear evaluation. The usual case for CMU beams is fully grouted cells.
Will keep a close eye on.

Another strategy that I've used in the past, in conjunction with what you have proposed, is to attempt to make the beam behave compositely with a few courses of solid grouted block above. I had rebar couplers welded to the top of the beam and field installed vertical rebar projecting a few courses into the masonry. I wasn't able to find an established design procedure for this so I wound up being pretty conservative. Locating the couplers properly is an issue as well.
I believe this as a good approach and will implement in my detail.

 

[bookowski]

I haven't done this but like the idea. The one thing that always worries me when doing something clever but atypical is that down the line someone won't understand the system and will modify it in a way that causes issues. Someone looking at this in 10 years will probably see cmu supported on a steel beam and say sure we can punch a bunch of openings in this wall.

Following Kootk's #4 but slightly different - it is common in my area to have a stair divider beam on scissor stairs that consists solely of a strip of the typical slab thickness supporting a cmu dividing wall between stairs, so an 8" wide x 8" deep slab/beam spanning say 15' supporting cmu. Doesn't make sense by calculation unless you follow a similar approach and assume that some composite action occurs effectively making a deep beam. Not the same but similar.

 

[KootK]

There are no windows at the cmu wall above, with a 53.5' wall I was thinking control joints at the 1/3 points. I will detail it such that rebar with a coupler welded to the beam is on each side of the control joint.

The vertical control joints at the 1/3 points make me a bit nervous with regard to shear transfer. Locally, near the control joints, your vertical shear will need to reside in the steel beam, correct? If so, that may introduce complexity with regard to the getting the shear out of, and back into, the masonry at those locations.

The one thing that always worries me when doing something clever but atypical is that down the line someone won't understand the system and will modify it in a way that causes issues.

Further to this point, whenever I attempt to "innovate", I detail the crap out of the innovation for just this reason. It won't help a potential, plan-less renovator in the future but it will greatly increase the odds of getting things done correctly in the original build. Besides, technology as it is these days, any building owner who fails to retain PDF copies of the structural plans deserves what he gets.

it is common in my area to have a stair divider beam on scissor stairs that consists solely of a strip of the typical slab thickness supporting a cmu dividing wall between stairs, so an 8" wide x 8" deep slab/beam spanning say 15' supporting cmu. Doesn't make sense by calculation unless you follow a similar approach and assume that some composite action occurs effectively making a deep beam.

Wowsers! I'm surprised that the strip beam would even work in shear. Is there any chance that the CMU wall below the beam is built up snuggly to the underside of the beam before the upper level block is installed? If one could somehow assemble all of the crazy, yet successful details that work in various markets, I feel that we could obviate the need to run calcs altogether. In my neck of the woods, we do some really whacky stuff with brick support.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.