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[SEAOC] Re: [SEAOC] Re: [SEAOC] Footings' Tie Beams

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In a message dated 96-06-17 00:41:54 EDT, you write:

>The requirement really is intended for deep foundation types.  The reason
>being that in the eventuality that there is normal soil settlement,
>earthquake induced consolidation, or liquefaction, the top portions of the
>piles and pile caps will be exposed with no lateral support; by providing
>ties the piles and caps act more like columns and with the tie beam they
>act as a frame.

This is a valid reason and only in deep footings. I also think it helps
distribute lateral loads when caissons are used for such resistance,
particularaly where soil conditions are variable. Soils engineers seem to
require tie beams as a method of limiting differential settlement. But this
is clearly ineffective since the stiffness of such beams is very low. The
only possible effect they might have is to increase the effective area of the
footing and reduce, therefore, the soil pressure. The tensile properties can
prevent lateral movement of perimeter footings where settlement may occur
near a slope. 

I think that an effective tie system can be incorporated into the slab on
grade for tensile resistance.