Lintel for openings at curved CMU wall 1

[dcceecy]

does anybody have some experience in analysis of Lintels for CMU wall opening? The CMU wall is curved so the opening (about 6' wide) and lintel are also curved.

for straight walls, we have a schedule. But for curved lintel, it seems some torsion is introduced. How to design such lintel?

thanks.

 

[jike]

In those cases, I have used a tube with a bottom plate. That is the easy part.

The hard part is the anchorage so that it will not just roll off its bearing. I would suggest a column at each end up to the roof or floor above.

 

[msquared48]

I do not know the width of the CMU you are using, but considering the need for closed stirrups for torsion, and the clearance/bending problems for 8" CMU, I would seriously consider an 7 5/8" wide CIP concrete lintel so you can deal with the problems better. The placement will be tight even with the CIP, but dooable.

If you are dealing with 10 or 12" block there should be no problem with placement issues, but there is definitely a problem with 6" block. I consider 8" CMU marginal as there is only roughly 5 1/4" of lateral void space for bent rebar and cover for bond.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[msquared48]

Tube is a good idea - with Nelson studs welded to it as needed.

Good suggestion Jike as tubes are great in torsion.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[dcceecy]

thank you for your replies.

the wall is 8" CMU. the maximum centerline offset is only
1-3/4" (the middle of straight and the middle of curved at the opening), the curve radius is big, the curve is not so much.

The Architect said it is fire rated wall and he prefers the concrete lintel.

Any suggestions I need to do to anchor the beam to the wall at both ends?

Thanks.

 

[msquared48]

1. Continue the lintel reinforcing into the CMU wall for 3 to 4 feet if possible.

2. Use 2 or 3 inverted U shaped #4 bars at the ends extended down into the CMU column at each end of the lintel.

Depending on the load seen by the lintel, which may not be much at only a 6 foot span, I would not really be too concerned with the 1.75" overhang. I've seen a low worse.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[hokie66]

You will just need to extend the lintel into the wall far enough so that you can engage enough wall to resist the torsion, with the vertical reinforced masonry wall resolving the torsion in bending.

 

[dcceecy]

Thank you very much.

Happy Holidays!

 

[engstructural]

Using either the steel or concrete lintel it would be worth looking at a strapping detail at the bearing points. using a 30X5mm strap plugged and screwed to the wall at close centres and screwed/shot fixed to lintel would increase the resistance to overturning.

 

[cntw1953]

How much brick above the lintel? Grouted? Reinforced? It may be designed to lessen

 

[cntw1953]

How much brick above the lintel? How far is the brick extends beside the opening? Grouted? Reinforced? It may be designed to provide better stability, and lessen the twist at lintel ends.

 

[ishvaaag]

I normally would suspend it with rod hangers from the structure above; this way you can reduce almost to nil the torsional effects, and problems at supports.

 

[MultiVar]

I normally would suspend it with rod hangers from the structure above; this way you can reduce almost to nil the torsional effects, and problems at supports.

Sweet idea. I have to model structs like this, typically with more pronounced (out of plane) curvatures.

So do you mean shore up lintel during construction, and eventually tie your rod hangers (tension elements) into the bond beam above, with possible post-tensioning in some situations?

 

[ishvaaag]

That could be. For minor brick structures, the steel hanging parts are either (typically eccentrical) steel straps bolted to the floors above, maybe buttressed by some angle or even another strap (5 to 8 mm use to be common for the straps) to the floor again. In other cases a rod is mechanically drilled and/or fixed, or glued to the floor above, in this case use to be centered with the load. I have not see postensioned cases but if the hanged height would warrant might be a proper solution.

The minor cases that I have seen more frequently have many times the ordinary steel structure built before the brick itself. Needs not even to be shored. If going for hanging rods, I would place some buttressing part ... for curved lintels (in plan) that would be less necessary but still convenient.

 

[csd72]

One option is to have a full window frame with verticals down eiach side and a steel sill to take out the torsion.