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FW: Concrete Movement Joints

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The size of the joint depends on the movement of each building. 100mm would
obviously not be suited for a 20 story building (especially given
construction tolerances for out of plumb).  My comments concerning 100mm
joints were based on experience and a 1 story building.  By the 1994 UBC (to
make it easier to discuss), drift is limited to .005h.  For a 4m story the
allowable drift is 20mm.  This value needs to be amplified for inelastic
displacements based on the structural system but in general the value is a
factor of 3.  Since each building could move this value towards each other
the joint should be 2 x 3 20mm, which is 120mm, so I rounded down for
simplification.  The most common joint width I've worked with, based on mid
rise buildings is 150mm.

A 25mm joint would have to be for an extremely stiff building or as I
suspect is common, building seismic movements are not considered or deemed
improbable.

Curt La Count
Jacobs Engineering
Portland, OR
 ----------
From: Hasan Hindawi
To: seaint(--nospam--at)seaint.org
Subject: Re: Concrete Movement Joints
Date: Thursday, September 02, 1999 12:52PM

As you mentioned certain measures could be taken to reduce slab cracking due
to drying shrinkage. However, in my opinion , these measures do not help in
reducing flexural stresses in edge columns/shear walls resulting from
temperature changes.Those flexural stresses could be quite high depending on
building length, edge column stiffnesses, ... ,etc.

My question engineers in seismic areas, does a 100mm wide expansion joint
suffice to prevent pounding, taking into consideration the allowable drift
for high-rise buildings.

Hasan Hindawi

 ----- Original Message -----
From: La Count, Curt <Curt.LaCount(--nospam--at)Jacobs.com>
To: 'seaint' <seaint(--nospam--at)seaint.org>
Sent: Thursday, 02 September, 1999 5:57 PM
Subject: Concrete Movement Joints


> On our projects, we've been more concerned about drying shrinkage than
> temperature movements.  Typical drying shrinkage movements are .06 %,
while
> temperature movements are typically .1% per 100 degrees C.   It takes
about
> 60 degrees C to equal drying shrinkage.  Control of the design mix,
> distributed steel reinforcing, fiber reinforcing and pour sequencing are
> methods we've used to pour plates as large as 80m, with only minor
cracking.
>
>
> I have found it common practice, in non-seismic regions, to provide
> expansion joints in buildings with very small joints.  The effects of
> pounding were apparently never investigated or the probability of
occurrence
> thought to be remote enough to ignore.  On the West coast of the US,
> engineers would typically think 100mm joints as minimum separations to
> prevent pounding.
>
> Curt La Count
> Jacobs Engineering
> Portland, OR
>
>
>  ----------
> From: Rex Donahey
> To: seaint(--nospam--at)seaint.org
> Subject: RE: SEISMIC DESIGN to UBC'97
> Date: Thursday, September 02, 1999 6:28AM
>
> A major factor in cracking of large structures is shrinkage of the
concrete
> during the construction phase.  Although it can require a great deal of
> coordination, it is possible to detail closure strips in the building.  If
> the strips are left open for at least 30 days, they will allow most of the
> shrinkage to occur with less constraint.