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Re: Caissionse

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In a message dated 98-03-10 20:40:52 EST, you write:

<< To All:
 We are designing a USD$400 million airport in Manila.  The foundation
 system will be caissions bored into natural bedrock is about 3m.  The
 existing ground above the bedrock has a large amount a expansive
 properties.  Therefore we are using a structural slab system for thr
 first level of a five level airport.  The distancd to the bedrock from
 level 1 varies from 1/2m to 2-1/2m.  The structural slab is a two-way
 flat plate with drop panels, the thickness of the slab is 300mm (12").
 The UBC94 code is concerned, Section 1807.2,  states that we will need
 tie beams for our caisson foundation scheme. The code states that:
 Individual pile caps and caissons of every structure subjected to
 seismic forces shall be interconnected by ties. Such ties shall be
 capable of resisting, in tension or compression, a minimum horizontal
 force equal to 10 percent of the larger column vertical load.
 EXCEPTION: Other approved methods may be used where it can be
 demonstrated that equivalent restraint can be provided.
 I think that the flat slab alone on level 1 could meet the above
 restraint requirement mentioned above? What do you think? Please comment
 on this. Does anybody have any feedback.
 Best Regards
 Tom Long
 PCI Asia >>

The code specify that all caissons be tied in both directions, but does not
specify which method to use (grade beams or pile caps).  Since the slab act as
a pile cap for the enitre group, it satisfy this requirement, provided that
slab is adequately doweled into the piles.  Good luck.

Long T. Tang