Two way slab ? Top bar column strip alternately continuous or all continuous ? 2

[Penpendrum]

Hello everyone

In the two way slab holding only gravity loads . . is it okay to alternately continue the top bars along the column strip rather than to make
it all continues ? if so ? what is the real reason why other engineers preferred it to be all continuous , and others alternately continuous,
why is it that we dont provide temperature top bars for the middle strip.?
is there a section of the aci code that could support all this?

a.) alternate column strip

b.) continuous column strip

 

[BAretired]

It is not necessary to make any of the top bars continuous. Most flat slabs are reinforced with a bottom mat which is continuous and a top mat which is discontinuous. The ACI and CSA codes show minimum requirements for curtailing reinforcement.

It is always permissible to use additional reinforcement at the discretion of the engineer, but it is not a requirement.

BA

 

[Penpendrum]

hello BAretired .. thanks for your reply

can you please tell me in which section of the ACI code that could support your statement..

 

[BAretired]

Either the ACI code has changed substantially or you haven't looked very hard. I cannot cite the section in the current ACI code. The attached sketch is from ACI-1963 and shows the arrangement of bars. Bent bars turned out to be troublesome to place correctly, so recent practice is to use all straight bars.

BA

 

[KootK]

why is it that we dont provide temperature top bars for the middle strip.?

Temperature and shrinkage reinforcing isn't actually required in both faces of a slab.[pre][/pre]

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Penpendrum]

thank you so much BAretired. . I have seen the latest minimum requirements I thought that the temperature bars are not included in the ACI skecth. . .

hello KootK . . do you mean that the bottom bars of the two way slab is enough for the temperature bars?

correct me if I am wrong KootK. . the continuous top bars of the slab would only serve as a hanger for the other top bar perpendicular to its direction ? and the continuous top bar at the middle of the column strip is no temperature bar?

 

[KootK]

hello KootK . . do you mean that the bottom bars of the two way slab is enough for the temperature bars?

Exactly.

correct me if I am wrong KootK. . the continuous top bars of the slab would only serve as a hanger for the other top bar perpendicular to its direction ?

They could serve that purpose if desired for constructability. The point is that, normally, they do not serve a purpose related to structural performance.

and the continuous top bar at the middle of the column strip is no temperature bar?

It doesn't have to be temperature reinforcing where adequate temperature reinforcing is already provided at the bottom of the slab.

A number of prominent firms have taken to eliminating all middle strip top bars and, instead, are moving that reinforcing to the column strip. As I understand it:

1) This allows convenient lanes for construction traffic that are free of interfering top bars.

2) Slab performance seems to be unaffected by the change.

3) This allows all top steel at interior locations to be prefabricated and lifted into place if desired.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[BAretired]

What I was doing before I retired was to place a top mat wide enough so that it entered the middle strip on each side. In that way, the middle strip received the correct amount of reinforcement but it was at each edge rather than uniformly distributed across the strip. This still permitted wide enough lanes for construction traffic to move about.

BA