Sloped Top of CMU Shear Wall

[cmbseng]

I've had a contractor request forming and pouring grout in place of cutting block at the top of a CMU shear wall where the roof deck slopes. The contractor would like to stop the CMU 8" below the low point of the sloped wall, place the bond beam at that elevation and then pour 8" to 16" of grout (the wall slopes a total of 8"). Everything else in the attached detail would remain the same. In concept, the approach seems acceptable, but I'm not sure how this would affect the shear transfer through the wall or any uplift loading. I'm thinking if the bars themselves could transfer the shear load and could resist the tension from any uplift with proper development lengths that would be sufficient. Has anyone had any experience with this? Any comments would be appreciated.

 

[UcfSE]

I use a raked concrete tie beam at the top of sloping walls. I think that is common, at least in my area. The top of the beam is sloped (raked) and the bottom is stepped with the cmu. Typically I make this 16 inches minimum depth and some minimum longitudinal bars and stirrups 2ft-4ft oc to hold it together.

 

[SteelPE]

Not to bust your chops......but I believe the SJI does not recommend using x bridging next to rigid supports like this. If you have x bridging they recommend using a piece of horizontal bridging between the last joist and the wall. The allows for the joist do deflect properly.

 

[hokie66]

What is described is a raked concrete tie beam as UcfSE noted, not grout.

 

[a2mfk]

Ditto UcfSE.

Are concrete tie beams not common in your area?

 

[cmbseng]

I've used concrete tie beams to strap isolated footings together in the past, but never at the top of the CMU wall. What the contractor was suggesting wasn't a beam per se, as he just wanted to keep the wall vertical reinforcing in the grout (essentially a very fluid concrete mix with pea gravel) beam but wasn't suggesting any additional longitudinal bars or stirrups. Adding the longitudinal bars and stirrups makes me feel a little more comfortable with the suggestion. Thanks for the input.

 

[a2mfk]

Tie beams on top of CMU walls are very common in many areas, so don't hesitate to use them. But I would use a min 3-4 ksi concrete and a beam mix, not grout. Also, longitudinal bars will not just "hold everything together", but act as a chord for your diaphragm and help transfer any uplift forces from the roof into your vertical cells.