Offset Tie Beam 1

[BrianApex]

For a 3 story all masonry residential home, The architect wanted to have a small offset from the 1st story to the second story (about 2"). I have attached a picture of what they had in mind. All of the buildings we have done do not have anything like this. Do I need to be concerned with anything? Will I have to consider torsion in the beam? I am just wondering if there is anything that I am missing that I should consider.

 

[BAretired]

I would be concerned about specifying a concrete beam in that situation as it would probably be unfamiliar to the contractor. Structurally, there is nothing wrong with using a concrete beam, but if possible, it would be easier to construct a masonry transition, using blocks two inches larger than the typical wall thickness.

If the lower wall is vertically reinforced to take the eccentric load from above, and if the floor system can be laterally tied to the wall, torsion of the beam is likely not an issue except perhaps, in locations where the floor does not reach the wall, such as stair openings.

BA

 

[MIStructE_IRE]

The only thing I’d be concerned about is the architects mental health... it seems ridiculous to do all that work for the sake of what looks like an inch?!

 

[BrianApex]

Just talked to the Architect and that is what he wants to do. I would like to do the Masonry as you have suggested BAretired but I think there might be an issue with availability of 10" block. I have always had problems with it. I guess I'll tell the Contractor good luck.

 

[BAretired]

I didn't think 10" block would be difficult to find, but if it's not available, you may have to resort to the concrete tie beam. Or perhaps the contractor has some other suggestion.

BA

 

[KootK]

I certainly have no objection to the concrete beam from a structural performance perspective. And I agree with your assessment of the torsion situation. The sketch below shows how I might handle this from a design perspective.

I don't actually love setups that assume flexural demand right at the top or bottom of a pin ended wall. It's sketchy, from a bar development perspective, how that's supposed to work. You can play some games with unreinforced masonry and/or carrying the reinforcing into the tie beam but, in my opinion, life's just a bit simpler if all of that is obviated.

Some objections I've heard voiced in the past regarding the 10" block:

1) Sometimes contractors avoid block larger than 8" as it may require two people to carry each block safely.

2) Most anything that gets ordered in small quantity tends to be expensive, relatively speaking. That said, the tie beam formwork may not be cheap.

 

[KootK]

Of course the forces will tend to go where they go base on stiffness. It's also entirely possible that the eccentricity of force in the walls may ne be enough to overcome the axial compressive stresses there.