Required tension reinforcement

[Awre]

There is a clause in the code that states:

A minimum area of flexural reinforcement, As[sub]min[/sub], shall be provided at every section where tension reinforcement is required by analysis.

My question (s):
What does it mean that the tension reinforcement "would be required by analysis"?
When this would be?
For example, if we have a very small moment (almost none), does it mean that tension reinforcement is required because we have a moment (of any magnitude)? What is the borderline to require tension steel...

Thanks

 

[Just Some Nerd]

Tension reinforcement would be required wherever the concrete can't resist tensile forces on its own. With a typical assumption that concrete can't resist any tensile stress, you'd need bottom steel anywhere with a positive moment and top steel anywhere it is negative. Pre-stresses members have the potential to remain completely in compression in spite of non-zero moment and can bypass this to a certain degree if moments aren't too large.

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Why yes, I do in fact have no idea what I'm talking about

 

[Awre]

Thanks @Just Some Nerd, does this apply even If I have a very small moment such as 0.2 kip-ft/ft or even less (0.03 k-ft/ft, etc)?
Should I add moment steel because of this moment?
Note that there are also minimum steel requirements, max spacing, etc. so, I may end up with more steel than it really needs, while I think the plain concrete may itself take this moment... Thanks again

 

[jayrod12]

some codes still have plain concrete provisions, and if you meet those(if your code has them) then I don't see why you must have steel.

That being said, where I am, no one uses the plain concrete provisions and just put minimum steel.

 

[KootK]

I'm guessing that you probably can forgo the tension reinforcement. The "analysis" that the code refers to is not necessarily the results of an elastic FEM but, rather, whatever analysis you've selected to ensure that equilibrium is ensured. This can be -- and very often is -- an elastic analysis with some degree of plastic redistribution being exploited to rationalize the rebar layout.

 

[wrantler]

Adding the min steel is cheap insurance I would think...A few bars is not too much $$$.

What happens if something settles and puts this member under mores stress than anticipated? What if someone wants to modify the bldg later? Are you worried about shrinkage cracks?