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RE: Grade @ Anchor Bolts

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Nels-
Unless you are relying on yielding of the vertical steel with multiple bolt
installations, I would be careful of a multiple nut configuration (assuming
you mean they are spaced so that the cones don't overlap vertically) since
the failure of a grouted concrete block wall shear cone would be a brittle
failure.  If there is sufficient vertical steel, such a detail might be o.k.

Regards,
Bill Cain, S.E.
Oakland CA


	-----Original Message-----
	From:	Nels Roselund [SMTP:n.roselund(--nospam--at)worldnet.att.net]
	Sent:	Friday, August 18, 2000 9:30 PM
	To:	seaint(--nospam--at)seaint.org
	Subject:	Re: Grade @ Anchor Bolts

	Do multiple nuts on a threaded rod improve the anchorage
performance?  I've
	done that to develop a holddown into a grouted concrete block wall.

	Nels Roselund
	Structural Engineer


	>> >With a head or nut (but no plate) at the end of the
	>> embedment(s), the mode
	>> >of failure on anchorage devices is a cone-type failure in
	>> the concrete,
	>> >assuming that limit state is the controlling limit state.
	>> The intersection
	>> >of cones often reduced the total strength of the embedment
	>> group, but you
	>> >can still count on a cone-type failure.
	>> >
	>> >With a plate at the bottom of the anchors, the mode of
	>> failure is likely to
	>> >change from a lot of individual cones to one big chunk
	>> (technical term)
	>> with
	>> >a flat bottom. If so, and since this has less surface area,
	>> it reduces the
	>> >strength.
	>> >
	>> >Charlie



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