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# Re: One way slab design with point load.

• To: seaoc(--nospam--at)seaoc.org
• Subject: Re: One way slab design with point load.
• From: Joe McCormick <jmccormick(--nospam--at)proaxis.com>
• Date: Sun, 28 Sep 1997 16:14:16 -0700

```
At 11:53 PM 9/26/97 -0400, you wrote:
>
>What is an appropriate  effective width for a one-way slab with point load
>occuring at the center span?  I have a 22 foot long span, 12" deep, 4000 psi
>concrete.

I have a photocopy out of an old concrete design book a senior engineer gave
me years ago that has the following simplistic assumption for approximating
participating width of a one way slab under a point load.   Take TAN^-1(0.6)
lines from the point load radiating to the supported sides of the slab.  For
your case with a point load at the center, the participating width would be
2*0.6*11 = 13.2 feet.  Obviously, if the load is not at center span, the
effective width will be smaller at one support than at the other since the
slab cannot form a symmetric "saucer" shape.  I've always thought this was a
little too optimistic for my comfort level though, and usually take no more
than the point load width plus 4x the slab depth in width and provide extra
reinforcing in this strip as necessary.  I'd be curious to hear how other
people handle this situation, too.

Regards,
Joe McCormick

```