PROFIS ENGINEERING REPORT SHEAR LOAD
Concrete Breakout Failure Mode
Calculations A Vc
Calculations 318-14 Chapter 17 Provision Comments for PROFIS Engineering
A Vc
17.5 . 2.1 The nominal concrete breakout strength in shear , V cb of a single anchor or V cbg of a group of anchors , shall not exceed : ( a ) For shear force perpendicular to the edge on a single anchor
V cb
=
A vc ψed , V ψ c , y ψ h , V
V b
( 17.5.2.1a )
A vc0
( b ) For shear force perpendicular to the edge on a group of anchors
V cbg
= A vc ψ ec , V ψ ed , V ψ c , V ψ h , V
V b
( 17.5.2.1b )
A vc0
………….…….. 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 a group of anchors . 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 halfpyramid is given by the axis of the anchor row selected as critical . The value of ca1 shall be taken as the distance from the edge to this axis .
Reference Fig . R17.5.2.1b — Case 1 .
……………………………………..
A Vc is a modification factor that accounts for the area of influence assumed to develop at the edge of a concrete member when a shear load acting on a single anchor or a group of anchors is applied towards that edge . A Vc calculations are predicated on the parameter c a1
, which is assumed to be the distance in the direction of the applied shear load from “ the axis of the anchor row selected as critical ”. ACI anchoring-to-concrete provisions do not set a maximum limit on the value for c a1
. Minimum edge distance values ( c min
) are given in ACI 318-14 Sections 17.7.2 , 17.7.3 and in post-installed anchor approvals .
Fig . R17.5.2.1b in the commentary R . 17.5.2.1 provides some suggestions for determining c a1
, and using this value to calculate A Vc . 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 . AWS D1.1 headed studs are rigidly attached to a fixture . Per Fig . R17.5.2.1b — Case 2 , a c a1
-value corresponding to the distance from the anchor row farthest from the fixed edge where concrete breakout is assumed to occur can be used to model this type of anchor .
The geometry for A Vc is defined by ( a ) projected edge distances perpendicular to the direction of the applied shear load acting on the anchors , ( b ) anchor spacing perpendicular to the direction of the applied shear load and ( c ) a projected distance down from the surface of the concrete at the edge where concrete breakout in shear is assumed to occur . The maximum projected distance assumed for ( a ) and ( c ) is limited to 1.5c a1
. The maximum spacing assumed for
( b ) equals 3.0c a1 . Minimum anchor spacing values ( s min
) are given in ACI 318-14
Section 17.7.1 and in post-installed anchor approvals . The figure below illustrates how A Vc can be calculated for a group of four anchors in shear with a fixed edge distance ( c a1
) in the direction of the applied shear load ( V ua ), and a fixed edge distance ( c a2
) perpendicular to the direction of Vua . Concrete breakout in shear is assumed to occur at the y- edge , and c a1 is being considered as the distance from anchor row 1 to the y- edge . Only the spacing sx perpendicular to the direction of V ua is considered when calculating A vc for this application . s x for this application is assumed to be less than or equal to 3.0c a1
; otherwise , the anchors would not be considered to act as a group with respect to s x
. c a2 for this application is assumed to be less than 1.5c a1
. There is no fixed edge perpendicular to V ua in the x + direction , so the projected distance in the x + direction used to calculate A Vc is limited to a maximum value of 1.5c a1
. The maximum projected distance down from the concrete surface at the y- edge that is considered when calculating A Vc equals the smaller of the concrete thickness
( h a ) and 1.5c a1
. h a for this application is assumed to be less than 1.5c a1
. Minimum concrete thickness values for post-installed anchors are given in the anchor approvals .
Reference Fig . R17.5.2.1b — Case 2 .
Reference Fig . R17.5.2.1b — Case 3 .
188 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-14 Provisions