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Re: Shotcrete at shear walls boundary elements

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At 06:32 PM 6/27/99 -0700, Lynn wrote:

>I guess my questions is;  Have any of the Engineers who subscribe to the
>list required these mockup tests on their shotcrete projects?  If you
>have, what were the results?  Are some of these shotcrete people
>actually able to get good density inside a wall boundary element with
>very large rebar and tight tie spacing?

Lynn and list:

I will de-lurk for this since my contribution may be meaningful:

My company regularly provides the engineering for air-formed concrete shell
domes that are built with shotcrete. These are design-build or turnkey
projects; our client is the dome contractor. The owner's engineer is
typically not experienced in structures much less shell roofs. Currently,
we have two under construction at the Los Angeles Export Terminal on
Terminal Island, LA, that are each 240 ft diameter hemispheres atop 15 ft
cylindrical walls, for a total height of about 135 ft, to be used for
storage of petroleum coke. They are visible from the Vincent Thomas Bridge.

Near the springlines of the LAXT domes, the shell vertical reinforcement is
#6 bars at 5" each face, and the horizontal (hoop) reinforcement is #10
bars at 4" each face. The outside-face reinforcement is placed, tied, and
shotcreted before the inside-face reinforcement is present. This helps alot
to avoid rebar shadows in the concrete.

I can't think of a shotcrete dome that we've done that hasn't included
mockup tests. I wouldn't dream of not doing them - they are in our standard
general notes / specifications for the domes. We typically get tests
corresponding to 1) the heavily-reinforced but nearly vertical springline
area, 2) halfway or so up where the shell is thinner and reinforcing is
lighter, and 3) the crown area where reinforcement is again heavier and the
nozzle operator is on his back. The contractor we work with typically
passes these tests on the first "shot". (The owner is the chief nozzle
operator.)

For a little background on these shells, the "air-formed" construction
method entails 1) building a footing-ring with short (2') stem wall, 2)
anchoring an inflatable shaped-fabric form to the stem wall, 3) inflating
the form using air pressure, 4) spraying polyurethane foam on the inside of
the form, 5) in multiple passes, tying steel and placing shotcrete on the
inside surface, and 6) depressurizing. When completed, the air-form fabric
provides waterproofing, the foam provides insulation, and the reinforced
shotcrete provides structural support. The controlling design loads are
retaining pressures (think of a ~90 ft or higher retaining wall), headhouse
loads, and seismic.

P.S. We don't have rigid-vs-flexible diaphragm issues on these domes. =8^)

Regards,

____________________________________
Mark Ketchum <mark(--nospam--at)ketchum.org>
http://www.ketchum.org
Berkeley & San Francisco, California