8/9/2019 Questions on ACI 318 Appendix D, Anchoring to Concrete
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68 MAY 2005 / Concrete international
Questions in this column were asked by users of ACI documentsand have been answered by ACI staff or by a member or membersof ACI technical committees. The answers do not represent theofcial position of an ACI committee. Only a published committeedocument represents the formal consensus of the committee andthe Institute.
We invite comment on any of the questions and answerspublished in this column. Write to the Editor, Concrete International,38800 Country Club Drive, Farmington Hills, MI 48331; contact usby fax at (248) 848-3701; or [email protected].
Q. What values should be used for effective embedmentdepth and effective edge distance in calculating the
projected concrete failure areas for an anchor groupinfluenced by three or four edges?
A. For tension loads, the effective embedment depthhef to be used in calculating the projected concrete
failure area in tension A Nc is defined in 318-05 provisionD.5.2.3 in terms of the maximum distance from the centerof an anchor shaft to the edge of the concrete ca,max , andthe maximum spacing between the anchors:
“Where anchors are located less than 1.5 hef from threeor more edges, the value of hef used in Eq. (D-4) through(D-11) shall be the greater of ca,max /1.5 and one-third of themaximum spacing between anchors within the group.”
Commentary Fig. RD.5.2.3 provides an example calculation
of A Nc, using the term h′
ef to distinguish the effective
Questions on ACI 318 Appendix D, Anchoring to Concrete
When compared with previous editions, ACI 318-05 provides significant clarification as well as more consistentnomenclature. To highlight a small portion of the revisions, the following questions, commonly asked in reference toACI 318-02 Appendix D, are repeated here.
embedment depth from the actual embedment depth.For shear loads, the edge distance ca 1 (the distance
from the center of an anchor shaft to the edge of theconcrete in the direction of the applied shear) to be usedin calculating the projected concrete failure area in shear
AVc is defined in D.6.2.4 in terms of the edge distance inthe direction perpendicular to the applied shear ca 2, thethickness of the member ha , and the maximum spacingbetween the anchors:
“Where anchors are influenced by three or moreedges, the value of ca1 used in Eq. (D-23) through (D-28)shall not exceed the greatest of: ca 2/1.5 in either direction,ha /1.5; and one-third of the maximum spacing betweenanchors within the group.”
Commentary Fig. RD.6.2.4 provides an examplecalculation of AVc, using the term c
′
a 1 to distinguish theeffective edge distance from the actual edge distance.
Q. How is pryout shear calculated for a connection withmultiple anchors?
A. As in the previous edition of 318, 318-05 provisionD6.3.1 defines the coefficient for pryout strength kcp
as a function of hef . In 318-05, however, kcp is applied tothe nominal concrete breakout strength in tension foreither a single anchor N cb per Eq. (D-4) or a group ofanchors N cbg per Eq. (D-5). For a group of anchors, forexample, the nominal pryout strength V cpg is given by
Eq. (D-30) as V cpg = kcp N cbg .
