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RE: Shortening existing concrete joist

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What makes you think that the reinforcing would comply with the 1963 CRSI?
I would have some non-destructive testing done to verify the actual rebar
sizes and locations, whether there are trussed bars or not.

Just because CRSI has that sized joist in it does not mean that the designer
reinforced it per CRSI.  Perhaps the designer used heavier reinforcing for
loads not shown on the drawings, or all straight bars for ease of
construction, or not enough bars because he did not know what he was doing.
just because there was a standardized design table available at the time,
does not mean the designer used it.  Test the in-place joists.


Charles F. Espenlaub, III, P.E.
Martin-Espenlaub Engineering
Tel  215-665-8570
Fax 215-561-5064



-----Original Message-----
From: Roland Bokma [mailto:bokmar(--nospam--at)progressiveae.com]
Sent: Monday, February 26, 2001 5:27 PM
To: 'seaint(--nospam--at)seaint.org'
Subject: Shortening existing concrete joist



	I have a condition where I would like to shortening the span of an
existing concrete joist.

Information:	Approx 19 ft (single span) 
		Bearing on loadbearing masonry walls
		Existing drawings only identify joists as an 8" channel
slab, nothing else
		The building was built in the early sixties

		Shortening span approx 3 ft
		Floor use is not increased
		For my reference, I have a 1963 CRSI Design Handbook Vol II.
		No old geezers in the office

	I haven't run any numbers yet, but the joist should be good for
moment and shear (no tapered ends).  The CRSI manual lists bottom and truss
bars, which are both at the bottom of the beam at a distance equal to the
span/7 from each end (in the manual).  As long as the maximum moment isn't
within this distance, the concrete joist should be okay to cut.  Am I right?
Is there anything else that I should check?

	TIA
	Roland Bokma, E.I.T.
	ProgressiveAE
	Grand Rapids, MI
	www.progressiveae.com