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# ACI 10.5.3 Minimum Flexural Reinforcement

• To: <seaint(--nospam--at)seaint.org>
• Subject: ACI 10.5.3 Minimum Flexural Reinforcement
• From: "Wontae Kim" <Wontae.Kim(--nospam--at)unistresscorp.com>
• Date: Tue, 31 Aug 2004 16:30:25 -0400

```Hi!
This is a strict application question of ACI.

ACI318-02    10.5.3 (Minimum reinforcement of flexural members)
"The requirements of 10.5.1 and 10.5.2 need not be applied if AT EVERY
SECTION
the area of tensile reinforcement provided is at least one-third
greater than required
by analysis."

1.	If phi Mn >= 1.33 Mu, don't I need any flexural reinforcement at
all?
How about temperature and shrinkage reinforcement? (if I can ignore
21.3.2.1)

2.	If some portion of  a flexural member has phi Mn >= 1.33 Mu and
other portions
have phi Mn < 1.33 Mu, can't I apply 10.5.3  to the areas of phi Mn >=
1.33 Mu?

3.	What's the relationship 10.5.3 and cracking moment?
(In my opinion, Eq 10-3 is related with Mcr, which is dependent upon
section and material properties.)
If phi Mn >= 1.33 Mu and Mu < Mcr, no flexural reinforcement is
required.
How about if phi Mn >= 1.33 Mu and Mu > Mcr, so phi Mn > 1.33 Mcr?
In this case, 10.5.3 says that minimum reinforcement is not required
for phi Mn >= 1.33 Mu.
But, its load Mu > Mcr says it will crack.
Do I need reinforcement smaller than minimum reinforcement, which will
resist Mcr?
If this is true, I need small amount of flexural reinforcement
although I do not need minimum flexural reinforcement. Correct?

****Wontae Kim****
Unistress Corp.
Pittsfield, MA 01201
(Tel)  413-629-2031
(Fax) 413-499-0824

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