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# RE: Two way slab designed as one way

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: Two way slab designed as one way
• From: "Alex C. Nacionales" <anacio(--nospam--at)skyinet.net>
• Date: Tue, 13 Oct 1998 13:06:24 +0800

```Dick, Walther,etc

Thank you for your explanation.  I checked my concrete design textbook and
you are correct.

Alex C. Nacionales, C.E.

-----Original Message-----
From:	Horning, Dick/CVO [mailto:dhorning(--nospam--at)CH2M.com]
Sent:	Monday, October 12, 1998 11:57 PM
To:	'seaint(--nospam--at)seaint.org'
Subject:	RE: Two way slab designed as one way

Alex, the slab never went to college, it knows nothing about one-way or
two-way action.  That's just a mathematical model we structurals have
devised so that we can hang numbers  on the action and think we know what's
really happening.

As the slab deflects, it will form a surface with curvature in both
directions, because all 4 edges are supported.  Bending moment goes
hand-in-hand with curvature, so moments will be developed in both
directions.  We use the simplification that for a 1:2 ratio of span lengths,
the long span ceases to be significant, but your example is closer to square
than this.  Sure, if you design it one-way, it won't fall down, but will you
have enough reinforcing in the long direction to distribute flexural cracks
and keep them from being unsightly and objectionable?  Depends also on the
use of the slab - is it in an office or apartment building where it will be
covered with finish material, is it the bottom of a water-holding tank, etc.

-----Original Message-----
From:	Alex C. Nacionales [SMTP:anacio(--nospam--at)skyinet.net]
Sent:	Friday, October 09, 1998 9:26 PM
To:	seaint(--nospam--at)seaint.org
Subject:	RE: Two way slab designed as one way

Dick,

How can there be flexural cracking  if   it  is designed to have one
way
action.
In my opinion, the moments will be redistributed in the short
direction
before any failure occurs.

-----Original Message-----
From:	Horning, Dick/CVO [mailto:dhorning(--nospam--at)CH2M.com]
Sent:	Saturday, October 10, 1998 7:52 AM
To:	'seaint(--nospam--at)seaint.org'
Subject:	RE: Two way slab designed as one way

You also need more than shrinkage/temp steel in the 16' direction,
or there
will be flexural cracking

-----Original Message-----
From:	Alex C. Nacionales [SMTP:anacio(--nospam--at)skyinet.net]
Sent:	Friday, October 09, 1998 4:31 PM
To:	seaint(--nospam--at)seaint.org
Subject:	Two way slab designed as one way

I would like your opinion on designing two way slabs as one
way.

Ex.   12 ft x   16 ft  slab designed as one way  on the 12'
direction.

My opinion is that it  is possible but it would be more
economical
to design
it as two way slab.

Alex C. Nacionales
A.C. Nacionales Construction

```