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RE: Concrete anchorage (ACI 318-99 appendix D)

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These provisions, as I read them, require failure to be ductile, either by yielding of the bolt or yielding of one side of the connection. I haven't used Appendix D in practice yet.
 
I looked at this design method a couple of years ago when it was first published by PCA (Appendix D is pretty much the same version.) The thing that caused me the most heartburn was the formulas for computing the anchorage capacity of the concrete.
 
I was looking at anchorage of a tall steel water reservoir for seismic loads using closely spaced, high capacity, large diameter anchor bolts mounted in a concrete ringwall with the bolt heads and washers close to the bottom of the wall. The bolts were greased near the top to prevent bond so they could be pretensioned.
 
The modification factors for edge distance and spacing required significant capacity reductions that seemed excessive to me and resulted in depth and thickness requirements much greater than what was customary or computed from older methods. Maybe I'm missing something but perhaps Appendix D needs a little amplification, at least for special situations such as the one I described.
-----Original Message-----
From: Jake Watson [mailto:jwatson(--nospam--at)utahisp.com]
Sent: Wednesday, June 25, 2003 7:13 AM
To: Structural Engineering Association International
Subject: Concrete anchorage (ACI 318-99 appendix D)

How many people have though about the new CCD approach and its integration into the IBC?  Reading between the lines I have drawn the conclusion that the new CCD approach & the IBC wants us to begin to think of concrete connections the same way we think of concrete beams.  Connections should be designed to fail in a ductile manner.  We are not necessarily making a better building by over-sizing anchors.  But instead, we should design the steel to yield before the concrete fails similar to a concrete beam.
 
Am I on the right track?  How many people still just use standard "over-sized" connections that are strong enough, but don't fail in a ductile manner?  Or is this another code provision that will be repealed in a few code cycles?  Any thoughts?
 
Jake Watson, P.E.
Salt Lake City, UT