Reinforced CMU shear wall (ASD) with dowels into reinforced concrete foundation (ACI 318-02)

[RHTPE]

I need the collective wisdom of those who frequent this site regarding the connection between a reinforced CMU shear wall and a cast-in-place reinforced concrete (RC) foundation wall.

With a reinforced CMU shear wall, ACI 530-02 limits the steel stress (grade 60) to 24 ksi.

In trying to determine the proper embedment length for the chord dowels in the RC foundation wall, as well as the design tensile force in those dowels (for a post-installed situation), would it be acceptable to apply the 1.6 load factor to the ASD stress to evaluate the dowels under 318-02?

Given #7 bars (As = 0.60), ASD tension force would be 0.60 * 24 ksi = 14.4 kips. Force applied to the dowels under ACI 318-02 would be 14.4 kips * 1.6 = 23 kips.

I am most concerned about the post-installed dowels as it is not possible to fully develop the #7 using an adhesive anchor such as Hilti's HIT-HY 200.

Your thoughts?


Ralph
Structures Consulting
Northeast USA

 

[wannabeSE]

Why don't you calculate the strength design loads on the chord? While it seems reasonable converting with 1.6 might, it might not be conservative with the code's load combinations.

One severe case would be if the dead load counteracting the tension is 144.0 kips and the wind load is 100.8 kips
ASD = -0.6(144) + 101 = 14.6 kips
LRFD = -0.9(144) + 1.6(101) = 32.0 kips

If D = 36.0 kips and W = 36.0 kips, then ASD = 14.4 kips and LRFD = 25.2 kips
If D = 10.3 kips and W = 20.6 kips, then ASD = 14.4 kips and LRFD = 23.7 kips

 

[RHTPE]

wannabeSE:

I have calculated the load in each of the #7 dowels & chord dowels assuming a linear strain distribution decreasing as one approaches the neutral axis of the shear wall (assuming a cantilevered beam). I can't develop the chord dowels using an adhesive anchor given the maximum tension load. Their spacing is 8" c/c so I've been looking at a group of 3 with a fictitious plate. Adhesive bond strength & concrete break-out just isn't working. Development length for a #7 in 4 ksi concrete is 41" (ACI 318-02) in a CIP condition. It seems to me that the most expeditious solution is to remove the top 42" of the foundation wall for the length of the shear wall (10'-8"), preserving the existing #5s (12"c/c EW, EF) and then recasting it.


Ralph
Structures Consulting
Northeast USA

 

[JLNJ]

Maybe there is a way to core and grout the dowels deep emough that you feel good about developing the #5s in the wall. A set of deep cores might be prefereable to attempting pick apart 42" of wall without damaging the rebar. And when they do damage the rebar, you are right back in the same development length boat.

(Also, the area of #7s at 8" significantly exceeds (2) #5s at 12".)

 

[RHTPE]

JLNJ: The #5s are 12" c/c in both faces. The #7s are one line at the center of the wall at 24" c/c


Ralph
Structures Consulting
Northeast USA