I’m designing a connection using ACI 318-11 Appendix D provisions and a Hilti anchor installed in uncracked concrete.
*Posted on behalf of a Hilti customer.
Hey Customer,
well this is a good question. ACI 318-11 Part D.5.2.6 states “for anchors located in a region of a concrete member where analysis indicates no cracking at service load levels” ψc,N = 1.4 “for post-installed anchors, where the value of kc used in Eq. (D-6) is 17.” D.5.2.6 continues: “where the value of kc used in Eq. (D-6) is taken from the ACI 355.2 or ACI 355.4 product evaluation report for post-installed anchors qualified for use in uncracked concrete, ψc,N shall be taken as 1.0”.
ACI 318-11 Equation (D-6) is given as: Nb = kc λa √f’c hef1.5. Hilti post-installed anchor values for kc are based on testing per ACI 355.2 (Mechanicall anchor) or ACI 355.4 (adhesive anchor). The tested value for kc will specific to cracked concrete or uncracked concrete, and will be shown in the ICC-ES evaluation report for the anchor. Per Part D.5.2.6, since uncracked concrete conditions can be accounted for via the parameter kc in Equation (D-6), the modification factor ψc,N should not be increased for uncracked concrete conditions. Similarly, since cracked concrete conditions are also accounted for via the parameter kc in Equation (D-6), the modification factor ψc,N is always equal to 1.0 for cracked concrete conditions.
When designing cast-in anchors, cracked concrete conditions are assumed for the parameter kc in Equation (D-6). Per D.5.2.6, the modification factor ψc,N = 1.0 for cracked concrete conditions, but it is increased to a value of 1.25 for uncracked concrete conditions.
Please feel free to reach out any time, if you need additional information.
Best Regards
Justin