Analyzing existing concrete structures reinforced with smooth rebars? 4

[abusementpark]

It is my understanding that a lot older concrete structures were reinforced with smooth rebars before deformed bars became the standard practice. Are there any special considerations associated with this when evaluating and analyzing existing concrete structures?

Should you calculate the capacity of members any differently if you know or suspect that smooth rebars were used for reinforcment?

 

[civeng80]

Theory is the same with plain bars.
However check that development length is achieved for the reo bar to yield.
The development length in a plain bar is greater than that for a deformed bar.

 

[abusementpark]

The development length in a plain bar is greater than that for a deformed bar.

That's my main concern.

Does ACI actually give development length provisions for plain bars? I guess I assumed that wasn't even allowed these days for reinforced concrete construction.

 

[BAretired]

One of the problems with plain bars is that when the stress in the bar rises to the yield point and beyond, Poisson's ratio comes into effect and the diameter decreases, resulting in reduced bond with the surrounding concrete. This is not true of deformed bars because a slight reduction in diameter does not prevent the ribs from bearing against concrete.

If I remember correctly, it is usual to consider the bond of a plain bar to be about 2/3 that of a deformed bar. Of course, if there is any oil or impurity on the bar before pouring, all bets are off.

BA

 

[hokie66]

ACI318-63 specified that the bond of plain bars should be taken as 1/2 of that permitted for deformed bars, but not more than 160 psi.

 

[TomDOT]

When were plain bars in common usage? All I tend to see in older bridges around here are the square cross-secton ribbed bars. Early 1900s.

 

[abusementpark]

Good question, Tom.

I've seen plain bars in early 1900s buildings, but they did have very small ribs. I've been assuming the ribs aren't nearly equivalent to the deformation standards of today.

 

[BAretired]

Here is an article with some information on that:

http://www.google.ca/url?sa=t&rct=j..._szl0peIIrRxKaA&bvm=bv.46340616,d.cGE&cad=rja

BA

 

[abusementpark]

Thanks for the link BA!