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Re: Concrete Joist Shear

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Thanks for the heads up Jake. Unfortunately the use is in a garage and fire
exposure would produce a design consideration. Another constraint may be the
large dead load with a small live load. I think these products are probably more
suitable in the live load range.

Soil mixture has already been laced with peat and tested to a weight of 113 pcf.
Saturation is necessary to maintain plantings.

I'll look into your other suggestions also. Thanks again.

Barry H. Welliver
South of Salt Lake City

Jake Watson wrote:

>         If you are leaning toward carbon fiber (SIKA CarboDur?) be aware that
> generally, it creates a fire rating issue.  The carbon can't be used as
> a "primary force element" because as it gets hot, it will delaminate and
> you will lose your load carrying capacity.  This could lead to a
> catastrophic failure.  You could look a fire protection systems, but I
> don't have any suggestions there.
> Does the soil have to be saturated?
> Could you use a peat or other highly organic (light weight) soil?
> What about a nonlinear strain distribution in the concrete?  You could
> use a parabolic stress block.  May help, never done it before.
> Worst case: Sister a steel plate along side (dowel and epoxy?) the
> joist.  Check plate bucking etc., but you could probably use the beam to
> stabilize the plate.
> Post tension along side the existing joist?  If I remember right, by
> post tensioning you get better shear values as well.
> Just thinking out loud (sorta....)
> Good luck,
> Jake Watson, E.I.T.
> Salt Lake City, UT
> "Barry H. Welliver" wrote:
> >
> > I'm looking at possible ways of increasing shear resistance in a
> > tapered concrete joist system. The original design allowed for a depth
> > of soil which is less than the present proposal which also includes
> > some large rocks, trees and a pond.
> >
> > So far I have been able to define a "light" weight soil (113pcf
> > saturated), and am using records of test results to use a slightly
> > higher in-place concrete strength.
> >
> > The results of my analysis produce shear (and some bending)
> > requirements somewhat greater than allowable (15%+). I've sharpened my
> > pencil enough for now and would like any comments regarding possible
> > solutions.
> >
> > So you are aware, there is a possibility of replacing some of the soil
> > volume with styrofoam (or other such material) but this may not
> > completely solve the problem (nor is it preferred solution by the
> > design team). Also, the rocks could become "Disney" like and
> > significantly lighter if absolutely necessary. No immediate thoughts
> > about using lighter water (nuclear), but I'm sure someone will bring
> > it up. :-)
> >
> > I've started looking at SIKA CarboDur for possible moment improvements
> > but have no hands-on experience.
> >
> > Would appreciate any comments.
> >
> > Barry H. Welliver