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Anchoring to concrete

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A fixture anchored to concrete with 4 anchor bolts in a rectangular pattern is subject to overturning: two bolts are subject to tension, two are in compression.  Using ACI 318-02, Appendix D to determine the tension capacity of the bolts of a single fixture in tension, with the distance between bolts being 5-1/2", hef being 10", would you base the value of AN on 1.5 x hef each side of the bolts in tension, ignoring the bolts in compression?
 
The installation I am working on has several identical fixtures in a line at 16" spacing sharing in connecting the lateral force to the top of a concrete shear wall.  Thus, the bolts in tension are at 16" spacing, with an intervening compression zone.  One approach that I have in mind, in figuring the tension capacity of the bolts in a fixture: to use 1/2 x 16" = 8" as the longitudinal dimension factor [instead of hef] in determining AN.
 
However, this approach seems to ignore that the compression due to overturning will supplement the strength of the concrete in resisting breakout of the tension bolts, and it provides for no benefit for anchors of greater depth, which is counter-intuitive.
 
Perhaps it would make more sense to treat this like a single installation with a line of tension anchors at 16" spacing.  This is better, but still allows no benefit for anchors longer than slightly over 10"
 
How would you approach this?
 
Regarding a previous question to the List, the effect of grout under a plate on the strength of an anchor bolt in shear, Section D.6.1.3 says, "Where anchors are used with built-up grout pads, the nominal strengths  of [a steel anchor in shear] shall be multiplied by a 0.80 factor".  I find nothing related to surface preparation or grout quality, or gap thickness, etc.
 
Nels Roselund
Structural Engineer
South San Gabriel, CA
njineer(--nospam--at)att.net