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RE: Modulus of rupture

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• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: Modulus of rupture
• From: "Stuart, Matthew" <mstuart(--nospam--at)schoordepalma.com>
• Date: Thu, 7 Dec 2006 18:27:47 -0500

```fr is used to calculate Mcr which is compared to Ms (a service moment).

________________________________

From: Gerard Madden, SE [mailto:gmse4603(--nospam--at)gmail.com]
Sent: Thu 12/7/2006 5:01 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Modulus of rupture

fr=7.5(f`c)^.5

It's just a variable. All concrete code is Ultimate Strength. This is just one variable on the path to determining the ultimate strength.

If you are using it to calculate deflections (long term cracking) then the loads are a little more complex than service loads ( i.e. duration of load etc...). It's been a while, but the loads are unfactored I believe but you give them different durations that trigger other multipliers.

ACI has commentary in the code and most concrete textbooks should discuss it.

hth,
-gm

On 12/7/06, Anantha Narayan C.K. <anant_27(--nospam--at)yahoo.com> wrote:

Greetings,

Could anyone tell me if modulus of rupture of concrete is a service limit state or an ultimate limit state?

I think modulus of rupture is an ultimate limit state and using fr to compute Mcr to determine the degree of cracking under service loads is not quite true because of the modulus of rupture being a ultimate limit state.

Could someone throw more light on this?

Thanks
Anantha

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ANANTHA NARAYAN, E.I.
Structural Engineer
Bliss and Nyitray Inc.
Miami, FL - 33134

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-gm
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