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RE: Slab punching shear

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I haven't heard from ACI but I did speak with one of the professors that developed the Equivalent Frame Method in the early 60's.

Following is an outline of my discussion with him:

4f'c^.5 was experimentally determined on a uniformally loaded slab (no moment) at a distance d/2 from the column face at the University of Illinois. The Code method to determine shears with moment is an approximate one and is definitely intended to be applied to columns uniaxially with each direction limited to a max stress of 4f'c^.5.

It is obvious that the actual behavior at corner columns is biaxial but a biaxial stress limit is not known and limiting a calculated combined stress to 4f'c^.5 is acceptable but not necessary.

There is a full-scale 3 story test scheduled this summer (at Purdue, I believe) and the investigation of punching stress with flexure (via lateral loading) is part of the program. In the mean time, the current methods of analysis are definitely approximate but they are the best we have and have been proven over time.

Regards,

Byron Benson


-----Original Message-----
From: Byron Benson [mailto:byronatseaint(--nospam--at)hotmail.com]
Sent: Thursday, March 25, 2004 9:43 AM
To: seaint(--nospam--at)seaint.org
Subject: Slab punching shear

Why isn't a biaxial analysis of moment required for corner columns when
analyzing by the Equiv. Frame Method?  Are the ACI stress limits calibrated
to the independent, orthogonal methods in the Code (Direct Design and Equiv
Frame) and therefore indirectly account for out of plane moments via a
lowered capacity? If so, if a 'whole floor' analysis is performed (with the
'real' highest stress on the inside corner) wouldn't a higher material
capacity be justified since both axes are considered simultaneously?

The sources I have discuss moment and stress calculation in one direction
very well but don't even mention the perpendicular direction.  I would
appreciate it if someone could point me to the literature that discusses
this.

Byron Benson

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