No. 3 or No. 4 Horizontal Rebar Minimum
No. 3 or No. 4 Horizontal Rebar Minimum
(OP)
Many of the designs I have seen use #3 at 16" OC horizontal for both CMU and CIP shear walls. However ACI 530 and ACI 318 both list minimum horizontal reinforcement that seem to require a minimum of #4 rebar, even when shear wall capacity exceeds shear requirements.
Is the minimum horizontal requirement strictly for longitudinal reinforcement or does this apply to minimum shear reinforcement as well?
Our colleagues and peers are split in their opinions. Can anyone provide clarity on ACI 530 and ACI 318 for minimum horizontal reinforcement?
Thanks!!!
Is the minimum horizontal requirement strictly for longitudinal reinforcement or does this apply to minimum shear reinforcement as well?
Our colleagues and peers are split in their opinions. Can anyone provide clarity on ACI 530 and ACI 318 for minimum horizontal reinforcement?
Thanks!!!






RE: No. 3 or No. 4 Horizontal Rebar Minimum
ACI 318 specifies minimum horizontal reinforcement for walls, regardless of whether they are part of the lateral system. I think this reinforcement ratio allows less than #4 at 12" OC, but as a personal preference, that is what I start with for each mat of steel.
RE: No. 3 or No. 4 Horizontal Rebar Minimum
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: No. 3 or No. 4 Horizontal Rebar Minimum
In the case we are looking at the shear wall capacity is greater than shear so we will need only minimum reinforcement. ACI says we can use #3 as a tie but then turns around and says min reinforcement is the rhoxbxt which in the case of 8" walls results in #4 bars.
Still wondering!!!
RE: No. 3 or No. 4 Horizontal Rebar Minimum
Chapter 14 of ACI 318-11 does not specify a minimum bar diameter, so I'm not sure where you are getting such a requirement for CIP. The limitation for horizontal reinforcement is usually a function of maximum bar spacing (18" max.) and minimum reinforcement ratio (0.0020 or 0.0025, effectively acting as T&S in the case.) Reinforcement ratios below this are usually considered unreinforced.
RE: No. 3 or No. 4 Horizontal Rebar Minimum
11.9.9 Design of Shear reinforcement for walls
Ratio of horizontal shear reinforcement area to gross concrete area of vertical section shall not be less than 0.0025.
14.3 Minimum reinforcement
14.3.3 Minimum rato of horizontal reinforcement to gross area shall be:
(a) 0.0020 for deformed bars not larger than No. 5 with fy less than 60,000 psi or
(b) 0.0025 for other deformed bars
21.9.2 Reinforcement
21.9.2.1 The distributed reifnrocment ratios for strutcural walls shall not be less than 0.0025, except for ........
The only place I know of that specifes bar sizes for walls is in 14.3.7 that requries not less than No. 5 bars around window, door or similar sized openings.
Bruce
RE: No. 3 or No. 4 Horizontal Rebar Minimum
That was the crux of the problem - does or does not the following end up being #4 minimum because of the reinforcement ratio? For instance - if we want to design horiz reinforcement at 16" OC, then we would have 8 x 16 x .0025 = .32 Sq In. This means that #3 at 16" would be insufficient - or does it?
And one other designer insists that only the grouted cells of a Concrete Masonry Unit (Hollow Block)count for Ag because the CMU's are only 1350 psi strength. Using only the grouted cells for Ag would then make #3 @ 16" well within the reinforcement ratio requirement.
Like to hear your opinions on these as well - and thanks!!
RE: No. 3 or No. 4 Horizontal Rebar Minimum
#3 bars could be used...you would just need more of them.