PART 4 SHEAR LOAD
Pryout Failure Mode ( Pryout Bond )
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
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 .
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 .
Variables т k , uncr
Variables 318-14 Chapter 17 Provision Comments for PROFIS Engineering
т k , uncr
17.4.5.1 ………………………….. where
and the constant 1100 carries the unit of lb / in 2 .
c Na
= 10d a т uncr 17 . 4 . 5 . 1d 1100
17.4.5.2 The basic bond strength of a single adhesive anchor in tension in cracked concrete , N ba
, shall not exceed The characteristic bond stress т cr shall be taken as the 5 percent fractile of results of tests performed and evaluated according to ACI 355.4 .
For adhesive anchors located in a region of a concrete member where analysis indicates no cracking at service load levels , т uncr shall be permitted to be used in place of т cr in Eq . ( 17.4.5.2 ) and shall be taken as the 5 percent fractile of results of tests performed and evaluated according to ACI 355.4 .
It shall be permitted to use the minimum characteristic bond stress values in Table 17.4.5.2 provided ( a ) through ( e ) are satisfied :
( a ) Anchors shall meet the requirements of ACI 355.4 ( b ) Anchors shall be installed in holes drilled with a rotary impact drill or rock drill ( c ) Concrete at time of anchor installation shall have a minimum compressive strength of 2500 psi ( d ) Concrete at time of anchor installation shall have a minimum age of 21 days ( e ) Concrete temperature at time of installation shall be at least 50 ° F
The parameter “ т uncr
” corresponds to the characteristic bond stress in uncracked concrete . It is used to calculate the parameter “ c Na
”, which is defined in ACI 318-14 Equation ( 17.4.5.1d ). If uncracked concrete conditions are assumed ,
т uncr is also used to calculate the parameter “ N ba
”, which is defined in ACI 318-14
Equation ( 17.4.5.2 ).
ACI 318 anchoring-to-concrete provisions default to a design assumption that cracked concrete conditions exist ; however , c Na is always calculated using т uncr regardless of whether cracked or uncracked concrete conditions are assumed .
N ba can be calculated for either cracked or uncracked concrete conditions . PROFIS Engineering calculates c Na and N ba using the characteristic bond stress values given in the ICC-ESR for the adhesive anchor system . The ICC-ESR designates the ACI 318 parameter “ т uncr
” as “ т k , uncr ” and the PROFIS Engineering report designates “ т uncr “ as “ т k , c , uncr
”.
Testing per the ICC-ES acceptance criteria AC308 and the ACI test standard ACI 355.4 is used to derive characteristic bond stress values for adhesive anchor systems . Values derived from this testing are provided in an ICC-ESR . Values designated “ т k , uncr
” in the ICC-ESR correspond to the characteristic bond stress in uncracked concrete . The values designated ” т uncr
“ in ACI 318-14 Table 17.4.5.2 are intended to be used as guide values in the absence of product-specific data . When uncracked concrete conditions are assumed , PROFIS Engineering uses the
т k , uncr values given in the ICC-ESR for adhesive anchor bond strength calculations . Although noted in the ICC-ESR as a “ strength ”, т k , uncr is stress parameter having units of psi .
219 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-14 Provisions