2.0 SHEAR
2.1 Concrete Breakout Failure Mode
Variables c a1
Variables ACI 318-19 Chapter 17 Provision Comments for PROFIS Engineering
c a1
17.7.2.1.1 A Vc is the projected area of the failure surface on the side of the concrete member at its edge for a single anchor or an anchor group . It shall be permitted to evaluate A Vc as the base of a truncated half-pyramid projected on the side face of the member where the top of the half-pyramid is given by the axis of the anchor row selected as critical . The value of c a1 shall be taken as the distance from the edge to this axis . ……………………………………..
17.7.2.1.3 A Vc0 is the projected area for a single anchor in a deep member with a distance from edges of at least 1.5c a1 in the direction perpendicular to the shear . It shall be permitted to calculate A Vc0 by Eq . ( 17.7.2.1.3 ), which gives the area of the base of a half-pyramid with side length parallel to the edge of 3c a1 and a depth of 1.5c a1 .
A Vc0
= 4.5c a1
2
( 17.7.2.1.3 )
17.7.2 . 2.1 Basic concrete breakout strength of a single anchor in shear in cracked concrete , Vb , shall not exceed the lesser of ( a ) and ( b ):
( a ) V b = 7 l e
0.2 d a d λ a
( c a1 ) 1 . 5 ( 17.7.2.2.1a ) a ƒ ́c
…………………………………………………….. ( b ) V b
= 9λ a f ́c ( c a1 ) 1 . 5 ( 17.7.2.2.1b )
The parameter “ c a1
” corresponds to the distance in the direction of the applied shear load from the center of an anchor , or centerline through a row of anchors , to the fixed edge where concrete breakout in shear is assumed to occur . The ACI 318-19 commentary R17.7.2.1 discusses how the value for c a1 can be taken as the distance from the anchor row nearest the fixed edge being considered for concrete breakout ( Case 1 and Case 3 ), or the anchor row farthest from that fixed edge ( Case 2 ). When the anchor configuration consists of more than two rows of anchors in shear , c a1 could also be considered from intermediate rows . PROFIS Engineering always uses a c a1
-value corresponding to the distance from the anchor row nearest the fixed edge where concrete breakout is assumed to occur unless AWS D1.1 headed studs are being modeled . Per ACI 318-19 Section 17.7.2.2.2 , if the criteria noted in this section with respect to fixture thickness , anchor spacing and corner reinforcement are satisfied ; PROFIS Engineering uses a c a1
-value corresponding to the distance from the anchor row farthest from the fixed edge where concrete breakout is assumed to occur . The provisions of Section 17.7.2.2.2 are only utilized by PROFIS Engineering when AWS D1.1 headed studs are being modeled .
The illustration below show examples of how ca1 can be determined . Reference ACI 318-19 commentary Fig . R17.7.2.1b ( Case 1 ).
17.7.2.2.2 For cast-in headed studs , headed bolts , or hooked bolts that are continuously welded to steel attachments basic concrete breakout strength in shear of a single anchor in cracked concrete , V b
, shall be the lesser of Eq . ( 17.7.2.2.1b ) and Eq . ( 17.7.2.2.2 ) provided that ( a ) through ( d ) are satisfied .
V b
= 8 l e
0.2 d a d λ a
( c a1 ) 1 . 5 ( 17.7.2.2.2 ) a ƒ ́c
……………………………………………………………. 17.7.2.3.1 Modification factor for anchor groups loaded eccentrically in shear , ψ ec , V
, shall be calculated by Eq . ( 17.7.2.3.1 ). ψ ec , V
=
1
e ́V 1 +
1.5c a1
≤ 1.0 ( 17.7.2.3.1 )
177 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-19 Provisions