Top Bars for Concrete Joists

[jike]

This is a question for the old timers .....

What year did they change the ACI code for one way joists where they started to require top bars to be distributed rather than concentrated over the top of the joists?

If I remember correctly it had to do with controling crack widths, but I cannot find the reference that I am looking for. Can anyone help me out?

 

[JAE]

The oldest ACI 318 that I have (318-77) has section 10.6.6 in it where T beams are required to distribute negative reinforcing over the width of the flange. I don't have anything older than that. This section (10.6.6) doesn't seem to have changed much since then.

 

[jike]

I am sure it is older than that! I am thinking that it is either '63 or '71.

 

[SlideRuleEra]

Don't have access to the code, but if I remember correctly, strength design was introduced in '63 (to begin the phase out of working stress). Major changes were made in '71. Best guess: 1971

http://www.SlideRuleEra.net

 

[tincan]

ACI 318-63
Part V 2001(d)"....such slabs shall be reinforced at right angles to the joists wit at least the amount of reinforcement required for flexure....."

Never throw away your old references...Best, Tincan, one of the old timers.

 

[JAE]

tincan - that refers to "right angles to teh joists" - jike above was referring to distributing longitudinal reinforcing across the flange of the joists (i.e. the top negative reinforcing at each end of the span)

Is there anything in the '63 that mentions this?

 

[tincan]

JAE, sorry 'bout that.
Unfortunately, ACI-63 contaied 2 pages on Joist constructin with the best advice reading..the slab shall be designed by approved methods taking into the account the effect of contunuity...I liked the old methods, it made you engineer a job.
Checked CRSI working stress handbook (1963 ACI CODE)it gives the Ex distance (top bar distance measured from face of support beam to the end of negative reinforcement)as whichever is greater:
Ex = l'/4
= l"/4
= 21D for #5 bars and larger when d > 12"
there is a note in CRSI stating "ACI require top bars to extend to l'/16 or the effective depth of the member past the point of inflection"
Could not find this reference...hope this helps
Tincan

 

[SacreBleu]

I found my ACI318-71 (It was the first Code I ever owned, a required "book" for my college concrete course)
It does have the requirement that you are looking for. Based on the above posts, I am assuming that is the edition where it first appears.
I also have a CRSI 1975 Handbook. It also shows in great detail how to check the top bars for crack control. It is based on the ACI318-71.