Concrete Beam Load Sharing (Tie-Beam to Lintel)

[StrEng007]

I have a two story structure, where the 2nd floor is attached directly to the tie-beam.
This exterior wall line is designed as a concrete moment frame, where the tie beam supports the lateral (as top of frame) and also the gravity and coupled shear wall OT's from the 2nd floor/roof.

I've got several openings along this wall line that have varying R.O's and I'm looking to put a varying CIP lintel across the opening.

•During construction, the CIP lintel will support the gravity load from the CMU infill and tie-beam construction above.
•In its final completed state, I'd like the tie-beam/columns to act as the moment frame without concern that the CIP lintel is going to be affected.

My questions are:
1. How much will the CIP be loaded due to total loading of the structure? I know this has to do with stiffness of the tie-beam relative to the lintel but really don't have a way (or budget) to figure this out. If it's any value, the tie-beam is 2x the depth of the CIP lintel.
2. If the moment frame is designed to take the load, can I regard the CIP lintel as an ancillary element that initially took gravity?


Edit: The source of lateral is due to wind. No special moment frames due to seismic or anything fancy.

 

[KootK]

Unless the masonry is gapped, neither beam will participate in reisting the wind shear flexurally. Instead, you'll develop compression struts through the block that will produce a truss of sorts.

Might it make sense to just make these walls solid concrete. I would think that all of the beam formwork would be a bit much for what this is.

 

[StrEng007]

Might it make sense to just make these walls solid concrete. I would think that all of the beam formwork would be a bit much for what this is.

Yeah... I've had situations where I cast the entire beam depth and that's not accepted by the GC. Other situations where I provide staged beam construction and that's also not OK. CMU bond beam should have been a CIP tie-beam one day, and CIP tie-beam should have been a CMU bond beam on another day...

 

[KootK]

Well, if we're just going stick our heads in the sand about the strutting through the block, I might:

1) Design the upper beam as though the lower didn't exist.

2) Design the lower beam, column, and joint such that they could form a plastic hinge early in the load history.

For wind, I don't feel that there's too much that can go wrong here. Realistically, even the dead load on the low beam probably arches over it in a pretty advantageous manner. Maybe hook the low beam bottom bars and provide generous stirrups for good measure.

 

[StrEng007]

Thanks for the information! I haven't written off the compression strut method yet.

2) Design the lower beam, column, and joint such that they could form a plastic hinge early in the load history.

What would that do for the remainder of the column vertical up from the the joint? That would go back to hinging the column and relying on strut action, no?

 

[KootK]

It just provides shear capacity where it might wind up being needed if the strut materializes. You'd want to have solid shear capacity at both the lower and upper regions of the upper columns so might as well do the whole thing.