ACI 21.6.1 Requirements being applied to Gravity Columns?

RE: ACI 21.6.1 Requirements being applied to Gravity Columns?

Seth Guthrie — Wed, 05 Sep 2018 22:42:15 GMT

What version are you using? What size column and bar pattern? (or send the file using Secure File Upload)

RE: ACI 21.6.1 Requirements being applied to Gravity Columns?

Amber Hoey — Wed, 05 Sep 2018 15:09:32 GMT

I am getting a similar problem with my concrete gravity columns when running the analysis with ACI 318-14. My columns are concrete, gravity only, the project is SDC D and the shear walls take all the lateral load.

When I run the column analysis I am getting the following warning: Column section dimensions are not acceptable per ACI 318-14 Sec. 18.7.2

Per the ACI 318-14 code section 18.7.2 (as noted below) is for columns of special moment frames. So its unclear why the columns (gravity only) are being required to meet a standard they are not part of?

ACI 318-14 REFERENCED SECTION

18.7—Columns of special moment frames
18.7.1 Scope
18.7.1.1 This section shall apply to columns of special moment frames that form part of the seismic-force-resisting system and are proportioned primarily to resist flexure, shear, and axial forces.

18.7.2 Dimensional limits
18.7.2.1 Columns shall satisfy (a) and (b):
(a) The shortest cross-sectional dimension, measured on a straight line passing through the geometric centroid, shall be at least 12"
(b) The ratio of the shortest cross-sectional dimension to the perpendicular dimension shall be at least 0.4.

RE: ACI 21.6.1 Requirements being applied to Gravity Columns?

Seth Guthrie — Thu, 29 Sep 2016 17:59:22 GMT

I did some further review and here's what I observed. The gravity columns are getting checked for Section 21.6.1.1 only when Pu > Ag*f'c / 10. We get here via 21.13 -> 21.13.4.3. 21.13.4.3 references section 21.6.3, 21.6.4, 21.6.5 and 21.7.3.1 but NOT 21.6.1. I will file a defect to have 21.6.1 and 21.6.2 exempted for gravity columns. In the meantime, if this is the only failure or warning on your small columns it should be fine to use them.

Defect 569895: ACI 318-08 (ACI 318-11) section 21.13 when Pu / Ag*f'c/10 incorrectly checks 21.6.1.1 and 21.6.1.2 for gravity columns

RE: ACI 21.6.1 Requirements being applied to Gravity Columns?

Amber Hoey — Thu, 29 Sep 2016 17:33:39 GMT

and I just ran as ordinary results "Story 1
* Column section dimensions are not acceptable per ACI 318-11 Sec. 21.6.1.1"

RE: ACI 21.6.1 Requirements being applied to Gravity Columns?

Seth Guthrie — Thu, 29 Sep 2016 17:19:34 GMT

I've actually reproduced your symptom in a test file. I'll report back when I understand the design flow better.

RE: ACI 21.6.1 Requirements being applied to Gravity Columns?

Seth Guthrie — Thu, 29 Sep 2016 17:06:16 GMT

Yes, and I assume you will use Special Concrete Shear Walls when you get around to the wall design, but since you don't actually have any moment frames I wanted you to test using the Ordinary Moment Frame option to see what happens in relation to the gravity columns.

RE: ACI 21.6.1 Requirements being applied to Gravity Columns?

Amber Hoey — Thu, 29 Sep 2016 17:02:16 GMT

Don't all buildings that are SDC D need to be special?

RE: ACI 21.6.1 Requirements being applied to Gravity Columns?

Seth Guthrie — Thu, 29 Sep 2016 16:56:44 GMT

A shear wall structure in SDC D still needs to have the gravity columns checked against 21.13. Presumably the design displacement in such a structure would be smaller than that of a Moment Frame structure, however.
The link from 21.13 back to 21.6 should start with 21.6.3 however. I don't see any reason for 21.6.1.1 to be checked on gravity columns. Make sure your frame type is correct (ordinary moment frame in your case) and confirm if you are using the latest version 15.03.

RE: ACI 21.6.1 Requirements being applied to Gravity Columns?

Amber Hoey — Thu, 29 Sep 2016 16:42:56 GMT

And also, i don't see anywhere in 21.13 that references 21.6.1.1 & 21.6.1.2 which is the section RAM is telling me I am violating. It says the column does not meet the dimensions of 21.6.1.1 & 21.6.1.2?

RE: ACI 21.6.1 Requirements being applied to Gravity Columns?

Amber Hoey — Thu, 29 Sep 2016 16:40:43 GMT

I don't have a moment frame. The building is designed for Shear Walls but we are in SDC D. Do you have to assume you have some sort of Moment frame in RAM?

RE: ACI 21.6.1 Requirements being applied to Gravity Columns?

Seth Guthrie — Thu, 29 Sep 2016 15:35:56 GMT

I assume we are talking about ACI 318-08 (or 11) here. The governing section of the code is 21.13, 'Members not designed as part of the seismic-force resisting system'. This section is applied to gravity columns when the SDC is D, E or F (note this is set in Criteria - Frame Type).

This section essentially forces the gravity columns to be designed with more reinforcement and references other sections such as 21.6. For a complete list of the code sections that 21.13 cross references, see the Ram Concrete Column Manual, section 4.8.4.