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RE: APPENDIX D - EQUATION (D-5)

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As best I can tell this effect occurs with or without the edge effect as John has noted in his initial post.  The An/Ano ratio decreases, approaching unity (1) for large embedment depths.  At large embedment depths the projected failure surface for a single bolt is nearly identical to the projected failure surface of a closely spaced bolt group.  At shallow embedments the the failure surface of a 4-bolt pattern is almost 4 times the failure surface of a single bolt.  Hence the unexpected effect.  Equation (D-5) should still behave properly however since Nb increases so dramatically with embedment depth and overides the reduction in the An/Ano ratio.  The capacity of the bolt group increases with embedment depth when the edge distances are held constant.   
 
 
Christopher A. Banbury, PE
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