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Re: ACI 318 section 12.2.4

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Warren,

	I don't have a copy of the code but the scientific reason is that bleed
water from the initial setting of concrete below the bars may rise and
reduce the actual contact area between the concrete and the
reinforcing.  This is compensated for by increasing the bar length.

				Regards,

				H. Daryl Richardson

Foy, Warren wrote:
>
> Can anyone provide information regarding the alpha factor used in
> determining development lengths?
>
> Why is development length increased for bars with 12" of concrete cast below
> the bar?
>
> What constitutes 12" of concrete cast below?  Is this applicable only to
> beams or does it apply to horizontal reinforcement in walls?  If applicable
> to beams, is it also applicable to vertical tension bars in columns and
> walls with 12" or more to the compression face?
>
> TIA
>
> Warren.Foy(--nospam--at)confusedRI.com
>
> Warren S. Foy
> Structural Design Manager
> The Mason & Hanger Group Inc.
>
>
> 300 West Vine Street, Suite 1300
> Lexington, KY   40507-1814
> voice: 859.252.9980
> fax: 859.389.8870
> web: http://www.mhgrp.com
>
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