Two way slab plan designations (1965) 4

[n8structural]

I am trying to determine the maximum allowable live load for a 7" thick concrete floor slab. Originally designed in 1965, I cannot determine the meaning of the abbreviations shown on the plan (please see attached).
For instance, "10 #5 BT", or "10 #5 ST".
Does anyone know what the "BT" and ST" designate?
I as assuming the bars are perpendicular to the arrow shown, based on the 20' bay dimension having (7)#5's rather than (6)#5's. But the bar placement is eluding me.
Has anyone seen or used these designations before? Thanks.

http://files.engineering.com/getfil...b0c-e45a39780815&file=floor_investigation.pdf

 

[hokie66]

I think ST means straight, BT means bent. There would have been details elsewhere to define the lengths and position of bends.

 

[cap4000]

Try to get the book by Clarence Dunham 1965 titled "The Theory and Practice of Reinforced Concrete". On pages 396 and 397 it gives the -/+ moment coefficients for your two way slab. I agree with hookie's post above.

 

[msquared48]

I agree with Hokie too.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[hokie66]

Hang on...I read your post again, and disagree with the direction you assumed for the bars. The bars are parallel to the calls. There is more reinforcement in the longer span direction, as the moments are greater in that direction.

Without the bending details, you don't know how much top steel you have, because you don't know whether the BT bars are bent one end or both.

 

[JAE]

Generally the standard for older structural designs was for the bent bars to be extended over both supports and extend into the next span some defined, fixed distance...usually 25% of the span length.

If there was an end span, the bent BT bars would be hooked at the edge of slab or beam.

Usually there was a typical slab or beam reinforcement diagram that would define all this.

 

[dhengr]

N8:
Can I assume you have read the above, and followed their good advice? Did you find a typical slab section on the drawings giving reinforcing layout and bend locations, etc. Also, look in the structural notes for some direction. Several rebar detailing books covered this, also. And, finally find a copy of the “CRSI Design Handbook, Vol. II”, 1963 ACI Code, (green cover), Sec. 8, Flat Slabs, Flat Plates. CRSI covers what you need to know, and in fact you should be able to back out the moments and slab loads from their tables.

 

[dik]

Looking at the reinforcing, it appears that the bars are 'straight' and 'trussed', ie. bent at each end to become part of the top reinforcing. This is consistent with both the middle strip and column strip bottom reinforcing. In addition the bars denoted as 'T' or top are a supplemental mat over the column supports. I've seen the designation "B" and "BT" used, but not "BT" and "ST"

Dik