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Re: SEISMIC DESIGN to UBC'97

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A couple of issues that about thermal movement that should be considered
when making the decision when to add thermal  expansion joints.

1.  The thermal mass of a concrete building is such that even when it is
subject to significant temperature changes you do not see corresponding
changes in length.  Simply put, the period of the temperature variations is
smaller than the time it takes to change the temperature of the concrete. 
As a result the effective temperature variation is less than the ambiant
temperature changes.

2.  The building envelope and the heating and air conditioning systems in
the building insure that the building's structure does not see significant
temperature variations.

3.  Problems with temperature variation are most significant between the
ground floor and the next level up.  This is because the foundation is
embedded in the ground and does not see any effective temperature change. 
In the upper floors the temperature variation at each level is effectively
the same thus resulting in little if any differential floor movement.  Thus
the height has essentially nothing to do with the need for thermal
expansion joints.

4.   A seasonal tempertaure variation of 30-35 degrees celcius is not that
much.  There are many bigger buildings that have performed acceptably
without a  thermal expansion joint when subject to larger variations in
temperture.

Mark Gilligan


______________________________________________________


>>>According to a study " Earthquakes and Seismic Zones in The Middle East
".
Kuwait is located in Zone 1, moreover there is no history of seismic
activity in that area. My experience is mainly in a nearby country the
United Arab Emirates. Regarding spacing of expansion joints, local
authorities there usually do not encourage spacings greater than 50 meters,
due to the high seasonal tempertaure variation which may reach 30-35
degrees
celcius.
However I reached a spacing of 70 meters for a 22 storey r.c. rectangular
building. Authorities there accepted that but requested the submittal of
calculations. The usual expansion joint thickness adopted in that region is
20-25 mm.

Regards,

Hasan Hindawi<<<