This is a quick blog post on some errors recently identified in 2021 IBC Section 1905.1.8. This section modifies the requirements contained in Chapter 17 of ACI 318-19 for anchors in concrete subjected to seismic forces. The errors are twofold:

1. Wrong section reference: In ACI 318-19, the special seismic requirements for anchors in concrete have been moved to a stand-alone Section 17.10. However, this change is not reflected in the 2021 IBC modification. As a result, Section 1905.1.8 of the 2021 IBC still references the old section numbers from ACI 318-14.

Similarly, a reference to AISI S100 Section E3.3.1 is also outdated due to the changes that have taken place in that standard since this provision was first introduced in the 2012 IBC.

2. Wrong text formatting: Yes, this is actually important. When IBC Section 1905 adds or revises text in any section of ACI 318, it reproduces the whole ACI 318 section, but prints the added/revised text in italics in order to indicate where the revisions are made. However, this was not done in a number of places. These are indicated by yellow highlights below.

Section 1905.1.8 of the 2021 IBC is reproduced below (in blue) with the corrected section numbers of ACI 318-19 as well as correct formatting. The corrections in the reference sections are indicated by strikeout/underline whereas the corrections in text formatting are indicated by highlight. Some minor editorial differences exist between the relevant text in ACI 318-14 and that in ACI 318-19. The text reproduced below has been updated to the revised text of ACI 318-19. However, those editorial changes are not indicated in order to avoid distracting from the primary issue. Note that the errors do not cause any substantive change in the provisions themselves.

Finally, although not relevant to the topic of this blog post, it is still worth noting that ACI 318-19 Section 17.10.5.3(d) now specifies that only the effect of the horizontal seismic forces, E_h, is to be amplified by the overstrength factor, Ω₀, not the vertical seismic force effect E_v. This resolves a disconnect that used to exist between ACI 318 and ASCE 7. You can read a detailed discussion on this issue in this blog post.

The International Code Council is currently in the process of issuing an errata to address these problems. So, keep an eye out for that on the ICC Errata Central page.

1905.1.8 ACI 318, Section 17.2.3 17.10. Modify ACI 318 Sections 17.2.3.4.2, 17.2.3.4.3(d) and 17.2.3.5.2 17.10.5.2, 17.10.5.3(d) and 17.10.6.2 to read as follows:

• 17.2.3.4.2 17.10.5.2 – If the tensile component of the strength-level earthquake-induced force applied to anchors exceeds 20 percent of the total factored anchor tensile force associated with the same load combination, anchors and their attachments shall be designed in accordance with 17.2.3.4.3 17.10.5.3. The anchor design tensile strength shall be determined in accordance with 17.2.3.4.4 17.10.5.4.

Exception:Anchors designed to resist wall out-of-plane forces with design strengths equal to or greater than the force determined in accordance with ASCE 7 Equation 12.11-1 or 12.14-10 shall be deemed to satisfy Section 17.2.3.4.3(d) 17.10.5.3(d).

• 17.2.3.4.3(d) 17.10.5.3(d) – Anchor or anchor groups shall be designed for the maximum tension obtained from factored load combinations that include E, with E_h increased by Ω₀. The anchor design tensile strength shall be calculated from 17.2.3.4.4 17.10.5.4.

[Author’s note: Based on the updated language of ACI 318-19, it appears that this IBC revision to ACI 318 Section 17.10.5.3(d) is probably not necessary anymore. All this is doing is changing “in accordance with” to “from” in the last sentence.]

• 17.2.3.5.2 17.10.6.2 – If the shear component of the strength-level earthquake-induced force applied to anchors exceeds 20 percent of the total factored anchor shear associated with the same load combination, anchors and their attachments shall be designed in accordance with 17.2.3.5.3 17.10.6.3. The anchor design shear strength for resisting earthquake-induced forces shall be determined in accordance with 17.5 17.7.

Exceptions:

1. For the calculation of the in-plane shear strength of anchor bolts attaching wood sill plates of bearing or nonbearing walls of light-frame wood structures to foundations or foundation stem walls, the in-plane shear strength in accordance with 17.5.2 and 17.5.3 17.7.2 and 17.7.3 need not be computed and 17.2.3.5.3 17.10.6.3 shall be deemed to be satisfied provided all of the following are met:
1. 1.1 The allowable in-plane shear strength of the anchor is determined in accordance with        ANSI/AWC NDS Table 12E for lateral design values parallel to grain.
2. 1.2 The maximum anchor nominal diameter is ⅝ inch (16 mm).
3. 1.3 Anchor bolts are embedded into concrete a minimum of 7 inches (178 mm).
4. 1.4 Anchor bolts are located a minimum of 1 ¾ inches (45 mm) from the edge of the        concrete parallel to the length of the wood sill plate.
5. 1.5 Anchor bolts are located a minimum of 15 anchor diameters from the edge of the        concrete perpendicular to the length of the wood sill plate.
6. 1.6 The sill plate is 2-inch (51 mm) or 3-inch (76 mm) nominal thickness.
2. For the calculation of the in-plane shear strength of anchor bolts attaching cold-formed steel track of bearing or nonbearing walls of light-frame construction to foundations or foundation stem walls, the in-plane shear strength in accordance with 17.5.2 and 17.5.3 17.7.2 and 17.7.3 need not be computed and 17.2.3.5.3 17.10.6.3 shall be deemed to be satisfied provided all of the following are met:
1. 2.1 The maximum anchor nominal diameter is 5/8 inch (16 mm).
2. 2.2 Anchors are embedded into concrete a minimum of 7 inches (178 mm).
3. 2.3 Anchors are located a minimum of 13/4 inches (45 mm) from the edge of the concrete        parallel to the length of the track.
4. 2.4 Anchors are located a minimum of 15 anchor diameters from the edge of the concrete        perpendicular to the length of the track.
5. 2.5 The track is 33 to 68 mil (0.84 mm to 1.73 mm) designation thickness.
6. Allowable in-plane shear strength of exempt anchors, parallel to the edge of concrete, shall be permitted to be determined in accordance with AISI S100 Section E3.3.1 J3.3.1.
3. In light-frame construction bearing or nonbearing walls, shear strength of concrete anchors less than or equal to 1 inch [25 mm] in diameter attaching sill plate or track to foundation or foundation stem wall need not satisfy 17.2.3.5.3 17.10.6.3(a) through (c) when the design strength of the anchors is determined in accordance with 17.5.2.1 17.7.2.1(c).