Title:
Concrete Q & A Modification Factors for Post-Installed Anchors
Author(s):
Publication:
Concrete International
Volume:
34
Issue:
4
Appears on pages(s):
87
Keywords:
DOI:
Date:
4/1/2012
Abstract:
ACI 318, Section D.5.2.7, provides a modification factor ψcp,N “for post-installed anchors designed for uncracked concrete in accordance with D.5.2.6 without supplementary reinforcement to control splitting.”1 The factor reduces the basic concrete breakout strength based on the minimum distance from the centerline of the connector to the edge of the concrete. The commentary to Section D.5.2.7 tates,“If supplementary reinforcement to control splitting is present or if the anchors are located in a region where analysis indicates cracking of the concrete at service loads, then the reduction factor ψcp,N is taken as 1.0.”
First, this seems counterintuitive. If cracking is present, shouldn’t there be a reduction in the basic concrete breakout strength?
Second, rather than conduct an analysis to show that the concrete will be cracked, can I make the conservative assumption that the concrete is cracked and take ψcp,N as 1.0?
I will be using Eq. (D-6) to calculate the basic concrete breakout strength in tension for a single anchor Nb , where Nb = kc λa√f′c h 1.5 ef (D-6) using kc = 17 for post-installed anchors.