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RE: Concrete flat slab strengthening

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I guess that I don't understand the comment.  Most people who subscribe to
this list know that I am not a fan of polypropylene fibers in concrete.  Non
shrink concrete does not have to contain polypropylene fibers.  I have not
seen any evidence that polypropylene fibers reduces shrinkage.  If that is a
contention, please send me the data on standard ASTM shrinkage tests in lieu
of testimonials.

Regards,
Harold Sprague

> -----Original Message-----
> From:	Murat ERBAS [SMTP:merbas(--nospam--at)garanti.net.tr]
> Sent:	Tuesday, January 11, 2000 11:16 AM
> To:	seaint(--nospam--at)seaint.org
> Subject:	Re: Concrete flat slab strengthening
> 
> 
> 
> 
> Non shrink concrete use FIBERMESH fibers www.fibermesh.com
> 
> 
> -----Original Message-----
> From: Sprague, Harold O. <SpragueHO(--nospam--at)bv.com>
> To: seaint(--nospam--at)seaint.org <seaint(--nospam--at)seaint.org>
> Date: 10 Ocak 2000 Pazartesi 23:34
> Subject: RE: Concrete flat slab strengthening
> 
> 
> >Alexander,
> >
> >Conventional Reinforced Concrete:
> > You mentioned the most obvious caveat on the concrete side
> >(shoring). Also consider:
> > 1. Jack the slab to relieve the DL
> > 2. Scarify / prepare / test the surface to get adequate
> >bond from new to old concrete.  Dowels can be used, but they are more
> >expensive.  There is a good history for raking surfaces to get new
> concrete
> >to bond to existing.  With a 4" thickness you don't need to account for a
> >different modulus of elasticity.
> > 3. Use a low shrinkage concrete.  I wouldn't use
> >shrinkage compensating, but you can reduce shrinkage with a good mix and
> >good curing.
> > This is how Filigree wide slab is done.  The also have a
> >mechanical anchor, but it does not see the horizontal shear load.  The
> bond
> >is adequate.
> >
> >Structural Steel:
> > For the "steel beams from above" solution. Also consider jacking the
> >slab to preload the steel beams.
> >
> >Composite steel:
> > Another possibility is a system of composite steel beams:
> > 1. Provide steel beams below the slab connected to the
> >columns
> > 2. Preload the steel beams
> > 3. Drill holes through the slab
> > 4. Shoot shear connectors to the top flange of the
> >steel beam
> > 5. Grout the shear connector holes full
> > 6. Remove preload after grout is cured
> >
> >Post-Tension:
> > Another potential solution is external PT in which the PT strand is
> >harped similar to prestressed concrete.  Use either cast-in-place
> concrete
> >anchor blocks / spacer blocks, structural steel, or a combination.  This
> can
> >be a very cost effective solution.
> >
> >You can get load cells to tell you how much load you are putting on the
> >structural elements during jacking for the shoring / jacking solutions.
> >Obviously the rams will be calibrated to indicate the amount of PT force.
> >
> >You should always factor in long term deflections.
> >
> >Regards,
> >Harold Sprague
> >
> >> -----Original Message-----
> >> From: Alexander Sasha Itsekson [SMTP:sitsekson(--nospam--at)ida-se.com]
> >> Sent: Monday, January 10, 2000 1:41 PM
> >> To: List server
> >> Subject: Concrete flat slab strengthening
> >>
> >> Hello,
> >>
> >> I am working on the renovations for the existing 4 story concrete
> building
> >> with flat slabs (10" thick at the floors and 8" thick at the existing
> >> roof)
> >> and columns on the 23' by 25' grid.  The building is approximately
> >> 155'x166'
> >> in plan with a few oddly sized bays.  The building is a historical
> >> structure.  It is used to be SEARS store and is being converted to
> lofts
> >> (surprise!).
> >>
> >> They are adding an additional story on top of this building.  Obviously
> >> the
> >> new roof is curved and none of the new bearing walls are centered on
> top
> >> of
> >> the columns.  The existing roof slab needs to be leveled and is
> >> overstressed
> >> with all the additional dead and live loads.
> >>
> >> There a two ways of retrofitting of the existing roof slab that were
> >> discussed with the architect:
> >>
> >> 1. Steel framing raised several inches above ex. slab and supported on
> top
> >> of existing columns (columns are fine for the additional loads as the
> >> floor
> >> slabs were designed for 125 psf live loads) with concrete filled metal
> >> deck.
> >> This was my preferred solution.
> >> 2. A minimum 4" reinforced concrete filling to bring the slab thickness
> to
> >> 11".  Of course the existing slab will need to be shored prior to
> pouring
> >> of
> >> new concrete and new topping shall be dowelled into ex. concrete.
> >>
> >> The architect's choice is to use the topping slab, of course.
> >>
> >> Questions:
> >>
> >> 1.  What are the potential problems with the second choice in your
> >> experience?  I have always used steel framing to reinforce existing
> slabs
> >> but this was ruled out by the architect.
> >>
> >> 2. Are there any alternatives?
> >>
> >> 3. Shall we be concerned with long term deflections?
> >>
> >> I appreciate your opinions.
> >>
> >> Thanks in advance,
> >>
> >> Alexander Sasha Itsekson
> >> INGRAHAM DEJESSE ASSOCIATES INC.
> >> Berkeley, CA
> >> (510) 527-7223 ext. 209
> >>
> >>