Shrinkage & temperature reinforcement in thick members
Shrinkage & temperature reinforcement in thick members
(OP)
I need some insight on the AASHTO LRFD Bridge Design specs.
Section 5.10.8.2 states shrinkage & temperature reinforcement should be 0.18% of the gross sectional area for members less than 48" thick. The AASHTO LFD code required 0.125in² per ft of surface.
I am designing a bent cap that is 42" square. The LRFD code requires 3.18in² temp steel, while the LFD code requires only 0.44in² - this is a BIG difference.
The AASHTO LRFD commentary cites use of ACI 318. In that code, the discussion is limited to slabs only (§7.12).
My inclination is to use the smaller value, but I cannot justify this decision within the limits of the LRFD code.
Thanks in advance for your help!
Section 5.10.8.2 states shrinkage & temperature reinforcement should be 0.18% of the gross sectional area for members less than 48" thick. The AASHTO LFD code required 0.125in² per ft of surface.
I am designing a bent cap that is 42" square. The LRFD code requires 3.18in² temp steel, while the LFD code requires only 0.44in² - this is a BIG difference.
The AASHTO LRFD commentary cites use of ACI 318. In that code, the discussion is limited to slabs only (§7.12).
My inclination is to use the smaller value, but I cannot justify this decision within the limits of the LRFD code.
Thanks in advance for your help!





RE: Shrinkage & temperature reinforcement in thick members
This still only equates to 1.75 in2 of T&S steel, and without the LRFD code in front of me I can't think of where the difference might be....
Anyone know the logic behind this LRFD provision?
RE: Shrinkage & temperature reinforcement in thick members
This would be #4 ties at 3", or #5 ties at 4½" -- much more than needed for the shear requirements.
Thanks, RAF
RE: Shrinkage & temperature reinforcement in thick members
RE: Shrinkage & temperature reinforcement in thick members
I concur the LRFD results seem excessive. The "break even" point occurs around 24" thickness.A square member eventually requires double the reinforcement at the 48" limit. Below the break pt, the LRFD requires slightly less. (let Ag = s²; plot 4s vs. 0.0018Ag)
Any idea if anything has been published or posted regarding this individual's comments?
Thanks for your help! RAF