ACI 17.6.2.1.3 - Concrete Tension breakout Strength

[billdance]

ACI 17.6.2.1.3 If an additional plate or washer is added at the head of the anchor, it shall be permitted to calculate the projected area of the failure surface by projecting the failure surface outward 1.5hef from the effective perimeter of the plate or washer. The effective perimeter shall not exceed the value at a section projected outward more than the thickness of the washer or plate from the outer edge of the head of the anchor.

I'm having a hard time visualizing this language, specifically the last part. Does this mean that if I attach a 6" square X 1/4" thick plate washer at the end of a single tieback anchor rod, where the anchor rod has 6" effective embedment, then I can calculate the projected area of failure out as [(width of plate washer) + 2x(effective embedment*1.5)]^2? assuming sufficient edge distances. Essentially increasing the area calculation of Anc?

This is with respect to concrete tension breakout strength, not pull-out strength, which very conveniently considers the bearing area of the bearing area of the anchor plate.

 

[icebloom]

See below snapshot of my understanding. Blue is washer and red is the anchor head - by capping the section based on the plate/washer thickness I think the clause is basically giving you a 45 degree dispersion angle (pink) through the washer/plate for which you can claim the effective perimeter from which to then project your failure cone.