PART 4 SHEAR LOAD
Pryout Failure Mode ( Concrete Breakout )
Variables k cp
Variables 318-14 Chapter 17 Provision Comments for PROFIS Engineering
k cp
17.5.3.1 The nominal pryout strength , V cp for a single anchor or V cpg for a group of anchors , shall not exceed : ( a ) For a single anchor
V cp
= k cp
N cp
( 17.5.3.1a )
For cast-in , expansion , and undercut anchors , N cp shall be taken as N cb determined from Eq .
( 17.4.2.1a ), and for adhesive anchors , N cp shall be the lesser of N a determined from Eq . ( 17.4.5.1a ) and N cb determined from Eq . ( 17.4.2.1a ). ( b ) For a group of anchors
V cpg
= k cp
N cpg
( 17.5.3.1b )
For cast-in , expansion , and undercut anchors , N cpg shall be taken as N cbg determined from Eq .
( 17.4.2.1b ), and for adhesive anchors , N cpg shall be the lesser of N ag determined from Eq . ( 17.4.5.1b ) and N cbg determined from Eq . ( 17.4.2.1b ). In Eq . ( 17.5.3.1a ) and ( 17.5.3.1b ), k cp
= 1.0 for h ef < 2.5 in .; and k cp
= 2.0 for h ef ≥ 2.5 in .
The parameter “ k cp
” is defined in ACI 318-14 as the “ coefficient for pryout strength ”. The commentary R17.5.3.1 states :
“ ……………………… the pryout shear resistance can be approximated as one to two times the anchor tensile resistance with the lower value appropriate for h ef less than 2.5 in .”
PROFIS Engineering applies k cp per Section 17.5.3.1 for the cast-in anchors and post-installed anchors in its portfolio .
Variables h ef
Variables 318-14 Chapter 17 Provision Comments for PROFIS Engineering
h ef
17.4 . 2.1 …….. A Nc is the projected concrete failure area of a single anchor or group of anchors that shall be approximated as the base of the rectilinear geometrical figure that results from projecting the failure surface outward 1.5h ef from the centerlines of the anchor , or in the case of a group of anchors , from a line through a row of adjacent anchors ……..
17.4 . 2.1 …….. A Nc0 is the projected concrete failure area of a single anchor with an edge distance greater than 1.5h ef .
A Nc0
= 9h ef
2
( 17.4.2.1c ) 17.4.2.4 The modification factor for anchor groups loaded eccentrically in tension , ψ ec , N shall be calculated as ψ ec , N
=
1
1 + 2e ́N
3h ef
( 17.4.2.4 ) h ef is defined as the “ effective embedment depth of an anchor ”. This parameter corresponds to the embedded portion of the anchor that is “ effective ” in transferring tension load from the anchor into the concrete . Excerpted ACI 318-14 anchoring-to-concrete provisions that include h ef for calculating concrete breakout strength in tension are shown to the left . These provisions are also used to calculate concrete pryout strength in shear . It is important to understand that the calculated value for some of the parameters defined in these provisions will be dependent on whether concrete breakout failure in tension is being considered or concrete pryout failure in shear is being considered since the number of anchors in tension may be different from the number of anchors in shear . However , the parameter h ef will not change when used in these provisions to calculate either concrete breakout in tension or concrete pryout in shear .
For cast-in-place anchors , PROFIS Engineering permits users to input h ef values ranging between 4d anchor and 25 ”. cast-in-place headed studs
4d anchor
≤h ef
≤ 25 ”
265 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-14 Provisions