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[kajal.chopra]

 
I have been reading the book "Seismic Design of Reinforced Concrete and Masonry Buildings"- Paulay and Priestley:

I have the following question pertaining to the "Design for Flexural Strength for beams" in the potential plastic hinge zone:

Now, as per the page 188 of the book , it's stated that,due to reversed nature of bending moment or code requirement beam secions are always doubly reinforced.Fine.

It's stated that due to reversed cyclic inelastic displaacements , both the top and bottom beam reinforcement are expected to yield in tension.Fine.

It is given that , when the flexural bars have yielded in one face of the beam wide cracks in the concrete will occur.Fine.

But, the next sentence says that these cracks cannot close upon moment reversal unless the bars in the compression zone yield or slip.

I don't understand this part.Why is it said that the  cracks cannot close upon moment reversal unless the bars in the compression zone yield or slip?????

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[nrupeny]

The explaination for this as i feel is that,

Under reversal any crack to close it should come under compressive zone,
its not possible expect closure (crack) untill slip or deformation (bar)
occurs because of.

- Anchoring of bars.

-Bonding of concrete with steel.

REGARDS
NRUPEN.R.Y

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[kajal.chopra]

Thanks for the response--

You said :
"Under reversal any crack to close should come under compresion zone."
Fine

Then,in the compression zone, under compressive stresses the crack should close.What is the significance of the relation between:

Yielding of compresion reinforcement with Anchoring of bars.
and Bonding of concrete with steel.

I have not understood what you are trying to point out.

Please help!!!

On Fri, 10 Nov 2006 nrupeny[AT]des... wrote :
[quote]The explaination for this as i feel is that,

Under reversal any crack to close it should come under compressive zone,
its not possible expect closure (crack) untill slip or deformation (bar)
occurs because of.

- Anchoring of bars.

-Bonding of concrete with steel.

REGARDS
NRUPEN.R.Y

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[nrupeny]

The Bonding of concrete with steel/ yields,

When crack occurs in a state mentioned below by u, the yielded steel of
addnl length at crack (may be of micro scale) cant be expected to retain it
position in normal way, to attain this the force should of such a magnitude
as to slip the steel (as i feel curtailed ones), n if crack is wide enough
and if small dia bars used may deflect locally because of slender effect /
if large dia bars then may deflect (i feel uncomfortable 2 call as yielding)
due to restrain in slip by end anchorage. There is good bond b/w Reinf and
conc.

REGARDS
NRUPEN.R.Y

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