Masonry Intersecting Wall Load Transfer

[LearningAlways]

Thank you all for your help on this.

The EOR I'm working with wants me to show how load is transferred between two intersecting masonry walls. These walls are non-load bearing walls that sit on top of precast double tees. They are walls to a mechanical vent shaft and take a lot of wind as they are on the roof level of a 9-story garage. I'm not approaching these walls to act as a composite section.

My intention is for perpendicular walls provide lateral stability, a pilaster if you will, for walls taking wind in a given direction and vice versa depending on which direction wind you are talking. Walls are designed for two-way action, fixed at the bottom (where wall meets double tee stem) and braced at the perpendicular wall. The walls must be free to move opposite to the pinned and fixed connections as it is at an expansion joint in these locations.

The overall design of these walls is totally fine. I've proven everything else by numbers except how this load is transferred.

There are two cases in the attached as these walls are laid in running bond. Case 2 has me questioning how shear is transferred to the bracing wall. It seems as if it must be transferred via horizontal joint reinforcing which is currently typical 9 gauge ladder reinforcing at 8" o/c. The allowable shear from the 9 gauge ladder alone is about 567 lb/ft which seems horribly low which I might be calculating wrong.

Is my approach correct for case 2? It seems since the only way to transfer load between the wall taking wind and its bracing wall is through the horizontal ladder.

Case 1 is a more obvious load transfer and I'm getting about 2.2 kip/ft using a very conservative allowable stress.

My calcs are attached. Please give critique and guidance if possible.

I found in a TEK the empirical design requirements for intersecting walls to transfer load is ladder reinforcing at 8" o/c. No hard numbers form this note and I don't know if my EOR will accept a note like this from TEK but I'm going to try anyway.

 

[BAretired]

A bond beam at the top reinforced with a couple of bars would provide a more positive tie.

BA

 

[dhengr]

LearningAlways:
Redraw the two plan/sections of the wall corner, which you show with/as case 1 and case 2, one course high and/or one course lower, and then tell us which direction case 1 & 2 are acting in. What would happen if there was no horiz. joint reinforcing at the corner? Is there no mortar in the head and bed joints btwn. the conc. blks? Are they not interlocked together at the corner by the mortar joints and their alternating overlap? Doesn’t the filled and reinforced core at the corner help tie the two wall sections together? And then, you say…, “I'm not approaching these walls to act as a composite section.” Are they not acting as a single structural unit at the corners?

 

[LearningAlways]

Thank you both for your feedback.

BAretired: Yeah, there will be a bond beam (at least one) towards the top of the wall. However, the intersecting wall will be able to support the intersected wall continuously and provide stability in its weak axis direction, I'm trying to find a way to justify how that wall is supported by numbers. Intuitively it is clear that the wall transfers load.

dhengr: Yes, they're composite. There are three ways that a wall can be considered composite by code: running bond, bond beams, metal straps. So yeah, they're composite. I'm trying to avoid adding bond beams every 4'-0" o/c(for ease of construction) and rely only on interaction between these two walls.

What approach should be taken to find the maximum load that an intersecting wall can take? What limiting factors should be taken into account to make sure load is transferred? I've looked at shear of an unreinforced grouted cell but is there anything else that requires investigation?