PART 4 SHEAR LOAD
Pryout Failure Mode ( Concrete Breakout )
Results ϕ seismic
Results 318-14 Chapter 17 Provision Comments for PROFIS Engineering
ϕ seismic
17.2.3.4.4 The anchor design tensile strength for resisting earthquake forces shall be determined from consideration of ( a ) through ( e ) for the failure modes given in Table 17.3.1.1 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 a group of anchors
ϕN sa corresponds to steel failure ( tension ) in Table 17.3.1.1 ] ( b ) 0.75ϕN cb or 0.75ϕN cbg except that N cb or N cbg need not be calculated where anchor reinforcement satisfying 17.4.2.9 is provided
[ ϕN cb or ϕN1 correspond to concrete breakout failure ( tension ) in Table 17.3.1.1 ] ( c ) 0.75ϕN pn for a single anchor or for the most highly stressed individual anchor in a group of anchors
[ ϕN pn corresponds to pullout failure ( tension ) in Table 17.3.1.1 ] ( d ) 0.75ϕN sb or 0.75ϕN sbg [ ϕNsb or ϕNsbg correspond to side-face blowout failure ( tension ) in Table 17.3.1.1 ]
( e ) 0.75ϕN a or 0.75ϕN ag ϕNa or ϕN ag correspond to bond failure ( tension ) in Table 17.3.1.1 ] where ϕ is in accordance with 17.3.3 .
17.3.3 Strength reduction factor ϕ-for anchors in concrete shall be as follows when the load combinations of 5.3 are used :
……………………………………………………………………………………………………
( c ) Anchor governed by concrete breakout , side-face blowout , pullout , or pryout strength
Condition A
Condition B ( i ) Shear loads 0.75 0.70
Condition A applies where supplementary reinforcement is present except for pullout and pryout strengths .
Condition B applies where supplementary reinforcement is not present , and for pullout and pryout strengths .
PROFIS Engineering calculations for concrete breakout failure in tension when seismic load conditions are being modeled :
single anchor : design concrete breakout strength = ϕ seismic ϕc oncrete
N cb
. anchor group : design concrete breakout strength = ϕ seismic ϕ concrete
N cbg
.
PROFIS Engineering calculations for concrete pryout failure in shear when seismic load conditions are being modeled :
single anchor : design concrete pryout strength = ϕ concrete
V cp
. anchor group : design concrete pryout strength = ϕ concrete
V cpg
.
When designing an anchorage for seismic tension load conditions , ACI 318-14 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 318-14 Section 17.2.3.4.4 “ 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 318-14 strength design provisions for concrete pryout failure in shear require calculation of a nominal concrete pryout strength ( V cp or V cpg ) that is only multiplied by one ϕ-factor to obtain a shear design strength ( ϕV cp or ϕV cpg
). PROFIS Engineering designates this ϕ-factor “ ϕ concrete ”. The 0.75 seismic strength reduction factor
( ϕ seismic
) required per Section 17.2.3.4.4 is only relevant to tension calculations , and is therefore not applied to V cp or V cpg 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 pryout calculations when seismic shear load conditions are being modeled .
When calculating the design concrete pryout strength in shear for cast-in-place anchors , the parameter “ ϕ concrete
” in the PROFIS Engineering report is taken from Section 17.3.3 ( c )( i ). When calculating the design concrete pryout strength in shear for post-installed anchors , the parameter “ ϕc oncrete
” in the PROFIS Engineering report corresponds to the “ Condition B ” ϕ-factor for shear given in the ICC-ESR for the anchor .
Per ACI 318-14 Section 17.3.3 , Condition A is not considered for pryout strength calculations .
Reference the Results section of the PROFIS Engineering report for more information on the following parameters :
V cp or V cpg : Nominal concrete pryout strength in shear ϕV cp or ϕV cpg
: Design concrete pryout strength in shear
ϕ concrete
: Strength reduction factor for shear concrete pryout failure
291 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-14 Provisions