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RE: SEISMIC DESIGN to UBC'97

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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
----- Original Message -----
From: Mark Gilligan <MarkKGilligan(--nospam--at)compuserve.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Thursday, 02 September, 1999 7:39 AM
Subject: Re: SEISMIC DESIGN to UBC'97


> 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<<<
>
>