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Re: Shotcrete on URM

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Michael, Marlou,

I have done shotcrete on URM overlays on a number of projects.  While I
think Michael has a point technically (" ... ignoring the contribution of
the urm resistance to in-plane demands is not correct") I cannot think of
why your approach (which is the one I've always taken) would not be
conservative.

It seems to me that a good argument can be made that distributing the demand
in proportion to the moduli of the dissimilar materials (based on some
assumed elastic modulus) and then designing your shotrcrete, "... so it
carries enough demand to reduce the urm stresses at or below the value
obtained from the brick mortar testing program," is a bad idea.  While the
more complex mathematical model Michael proposes undoubtedly more accurately
describes the behaviour of the composite construction under moderate (i.e.,
design level) loads, the elastic moduls of the URM is (a) unpredictable, (b)
not determined by standard mortar tests, and (c) likely to degrade more
rapidly than that of the reinforced shotcrete during a severe seismic event.

My point is general -- the more accurate model is not necessarily the one
that is more appropriate for design -- something that it seems to me we are
more apt to forget in the age of easy access to computational power.

I would not want to reduce the amount of rebar in a shotcrete overlay on
account of the contribution of URM regardless of what my computer might be
able to tell me about relative stiffness and distribution of stress.  Given
this fact, I can't imagine why I would want to make the more complex
analysis Michael suggests.

Drew

----- Original Message -----
From: "Michael Krakower" <mkrakower(--nospam--at)earthlink.net>
To: <seaint(--nospam--at)seaint.org>
Sent: Saturday, October 21, 2000 2:14 PM
Subject: Shotcrete on URM


> Marlou:
>
> In my opinion, . The shotcrete and the URM have stiffness and
> demands should be proportioned accordingly. The shotcrete should be
> designed . I have used an E
> for brick at around 100,000 psi to evaluate URM stiffness.
>
> Michael Krakower SE
> Arcadia,CA.
>
>
>