Slab Flexure Strength Calculation 1

[tmgczb]

I am calculating a valve pit. In our template, there are a group of equations to calculate reinforcement.
In which textbook could I find the theory, like meaning of the parameters Rn and m？I am looking for a full example in textbook.

 

[dik]

You can generate a lot of traffic with this posting. Is your moment +/-? Slab on grade is less than 200 (8") for some folks... this normally has one layer of reinforcing. 12M @ 150 is pretty close, you will have difficulty walking on the rebar for placing concrete. You might want to space it out to 350 or 400 o/c. How did you arrive at the moment? Just some thoughts...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[JoelTXCive]

I have not seen this exact equation setup before, but I think I know what is being done.

These are what I call "shortcut variables". If you know your beam (or slab strip) geometry + material properties, and are trying to solve for the required steel area, then you can combine all the constant values into 1 coefficient. This reduces the number of values in your equations and makes the subsequent calculations easier.

Assuming you have a tension controlled section then below are the full versions of the design equations.

See attached math to see how these two equations are combined and manipulated to get the Rn value. I believe a similar procedure is being used for the shortcut 'm' value.

Wight & MacGregor used the exact same Rn value in their concrete textbook. In the Wight textbook, the Rn value is used in conjunction with tabulated values that speed up design (before everyone had computers and fancy calculators that solve quadratics). Other authors use similar shortcuts.

 

[dik]

It's not the reinforcing calculation... it's the moment, itself.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[OldDawgNewTricks]

JoelTXCive is correct. Rn is the "flexural resistance factor". Most any concrete textbook should explain it. It's just an algebraic substitution/reorganization of the variables in the flexural strength equation. The textbooks typically include tables of Rn values in the appendices. But I don't think anybody really uses the tables anymore. They just solve the flexural strength equations with their calculator or computer.

 

[tmgczb]

I am not able to download it. I'd appreciate if you could attach this book to an email to tmgczb@163.com

 

[centondollar]

Any book on reinforced concrete will do. By drawing the strain distribution (assumed linear across section height) and stress distribution (parabolic or constant with Whitney correction factor for concrete) of concrete and steel, you can find the moment capacity equation directly.

Derive the formula first, and then use it.

 

[JoelTXCive]

Try this version of upload....

We did not use the tension reinforcing index in School, but my boss introduced me to it at my first job.

I wrote this memo to myself several years ago.