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Concrete Movement Joints

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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.

 -----Original Message-----
From: Hasan Hindawi [mailto:hasanh(--nospam--at)go.com.jo]
Sent: Thursday, September 02, 1999 6:01 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: SEISMIC DESIGN to UBC'97


Greetings,

1- In Kuwait the temperature may reach 55 degrees celcius during the summer
days and may drop to 20 during summer nights.  And may even drop below 10
during the winter. So the actual temperature  change is actually greater
than 30-35 degrees celcius. But nevertheless the drop occurs. And special
measures should be adopted when casting during the summer.
2- It is true that heating and air-conditioning systems reduce the effect of
temperature variations, however most cracking problems occur during
construction stage. The duration between pouring a slab and operating
heating or a.c. is a minimum of 1 year in these parts of the world.
3- Yes I agree that critical stresses occur in the bottom floors due to the
fixity of the columns to the footings. Therefore, regardless of the number
of floors of a building, it is sufficient to analyze up to 6-7 floors for
temperature variations

Regards

Hasan Hindawi