2.0 SHEAR
2.1 Concrete Breakout Failure Mode
Results ϕ seismic
Results ACI 318-19 Chapter 17 Provision Comments for PROFIS Engineering
ϕ seismic
17.10.5.4 The anchor design tensile strength shall be calculated from ( a ) through ( e ) for the failure modes given in Table 17.5.2 assuming the concrete is cracked unless it can be demonstrated that the concrete remains uncracked :
( a ) ϕN sa for a single anchor or for the most highly stressed individual anchor in an anchor group
[ ϕN sa corresponds to steel failure ( tension ) in Table 17.5.2 ] ( b ) 0.75ϕN cb or 0.75ϕN cbg except that N cb or N cbg need not be calculated if anchor reinforcement satisfying 17.5.2.1 ( a ) is provided [ ϕN cb or ϕN cbg correspond to concrete breakout failure ( tension ) in Table 17.5.2 ]
( c ) 0.75ϕN pn for a single anchor or for the most highly stressed individual anchor in an anchor group [ ϕN pn corresponds to pullout failure ( tension ) in Table 17.5.2 ] ( d ) 0.75ϕN sb or 0.75ϕN sbg [ ϕNsb or ϕNsbg correspond to side-face blowout failure ( tension ) in Table 17.5.2 ]
( e ) 0.75ϕN a or 0.75ϕN ag
[ ϕN a or ϕN ag correspond to bond failure ( tension ) in Table 17.5.2 ] where ϕ is in accordance with 17.5.3 .
17.5.3 Strength reduction factor ϕ for anchors in concrete shall be in accordance with Tables …… ……….. 17.5.3 ( b )…………………
Table 17.5.3 ( b ) — Anchor strength governed by concrete breakout , bond , and side-face blowout
Supplementary reinforcement
Supplementary reinforcement present
Supplementary reinforcement not present
Type of anchor installation
Cast-in anchors
Postinstalled anchors
Cast-in anchors
Postinstalled anchors
Anchor Category [ 1 ] from ACI 355.2 or ACI 355.4
Not applicable
Strength reduction factor ϕ
Tension ( concrete breakout , bond , or side-face blowout )
0.75
1 0.75 2 0.65 3 0.55
Not applicable
0.70
1 0.65 2 0.55 3 0.45
Shear ( concrete breakout )
PROFIS Engineering calculations for concrete breakout failure in tension when seismic load conditions are being modeled : single anchor : design concrete breakout strength = ϕ seismic ϕ concrete
N cb
. anchor group : design concrete breakout strength = ϕ seismic ϕ concrete
N cbg
.
PROFIS Engineering calculations for concrete breakout failure in shear when seismic load conditions are being modeled : single anchor : design concrete breakout strength = ϕ concrete
V cb
. anchor group : design concrete breakout strength = ϕ concrete
V cbg
.
0.75
0.70
When designing an anchorage for seismic tension load conditions , ACI 318-19 provisions for concrete breakout failure in tension require calculation of a nominal concrete breakout strength ( N cb or N cbg
). The nominal strength is multiplied by two strength reduction factors ( ϕ-factors ): one ϕ-factor for concrete breakout failure in tension , and one ϕ-factor for seismic tension load conditions , to obtain a design strength ( 0.75ϕN cb or 0.75ϕN cbg
).
PROFIS Engineering designates the 0.75 seismic tension reduction factor noted in ACI 318-19 Section 17.10.5.4 “ ϕ seismic
”. This reduction is only considered with respect to non-steel tension failure modes when calculating tension design strengths for both cast-in-place and post-installed anchors subjected to seismic tension loads .
When designing an anchorage for seismic shear load conditions , ACI 318- 19 strength design provisions for concrete breakout failure in shear require calculation of a nominal concrete breakout strength ( V cb or V cbg
) that is only multiplied by one ϕ-factor to obtain a shear design strength ( ϕV cb or ϕV cbg ).
PROFIS Engineering designates this ϕ-factor “ ϕ concrete ”. The 0.75 seismic strength reduction factor ( ϕ seismic
) required per Section 17.10.5.4 is only relevant to tension calculations , and is therefore not applied to V cb or V cbg when the anchorage is being designed for seismic shear load conditions . The PROFIS Engineering report always shows ϕ seismic equal to 1.0 for shear concrete breakout calculations when seismic shear load conditions are being modeled .
When calculating the design concrete breakout strength in shear for cast-in-place anchors , the parameter “ ϕ concrete
” in the PROFIS Engineering report is taken from Table 17.5.3 ( b ). When calculating the design concrete breakout strength in shear for post-installed anchors , the parameter “ ϕ concrete
” in the PROFIS Engineering report is taken as follows :
• if “ Condition B ” is selected in PROFIS Engineering as a design parameter , “ ϕ concrete
” is taken from the ϕ-factor for shear given in the ICC-ES evaluation report ( ESR ) for the anchor .
• if “ Condition A ” is selected in PROFIS Engineering as a design parameter , “ ϕ concrete
” is taken from the ϕ-factors in Table 17.5.3 ( b ) corresponding to “ supplementary reinforcement present ”.
Reference the Results section of the PROFIS Engineering report for more information on the following parameters :
V cb or V cbg : nominal concrete breakout strength in shear ϕV cb or ϕV cbg : design concrete breakout strength in shear ϕ concrete
: strength reduction factor for shear concrete failure .
202 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-19 Provisions