Does 2012 IBC Chapter 19 work with ACI 318-11? Part 2
In last week’s blog post, we discussed some inconsistencies that exist between 2012 IBC Section 1905 and ACI 318-11. The 2012 IBC adopts the 2011 edition of ACI 318 for the design and construction of concrete buildings. However, the adoption was done through an administrative process at a time when ACI 318-11 was not available. As a result, the modifications made in 2012 IBC Section 1905 to certain ACI 318 provisions remained based on the 2008 edition of that standard, and some of the provisions became inconsistent with the 2011 edition.
Additionally, ACI 318-11 Appendix D now includes adhesive anchors for the first time. This also necessitates certain changes in the 2012 IBC, especially in the verification and inspection requirements for concrete construction (Chapter 17).
The 2012 IBC errata failed to resolve these issues.
So, this week, we follow up with those additional changes that need to be made to the 2012 IBC to make it consistent with ACI 318-11. As mentioned before, jurisdictions that have not adopted the 2012 IBC can make the following amendments (and those in our last blog post) in their adoptive ordinance, and those that have adopted the 2012 IBC can approve the changes under Section 104.11 of the IBC, “Alternative materials, design and methods of construction and equipment.”
The changes are shown using strikeouts and underlines to the IBC provisions as they appear in the 1st printing of the 2012 IBC, without applying the errata. A clean version of the final outcome of all these changes is also shown.
A comprehensive discussion of these changes can also be found here.
Changes to 2012 IBC Section 1905
Revise as follows:
1905.1 General. The text of ACI 318 shall be modified as indicated in Sections 1905.1.1 through 1905.1.10 1905.1.9.
1905.1.1 ACI 318, Section 2.2. Modify existing definitions and add the following definitions to ACI 318, Section 2.2.
WALL PIER. A wall segment with a horizontal length-to-thickness ratio of at least 2.5, but not exceeding 6, whose clear height is at least two times its horizontal length.
(Retain other definitions)
1905.1.3 ACI 318, Section 21.4. Modify ACI 318, Section 21.4, by adding new Section 21.4.3 and renumbering existing Sections 21.4.3 and 21.4.4 to become 21.4.4 and 21.4.5, respectively. and adding new Sections 21.4.3, 21.4.5, 21.4.6 and 21.4.7 to read as follows:
21.4.3 – Connections that are designed to yield shall be capable of maintaining 80 percent of their design strength at the deformation induced by the design displacement or shall use Type 2 mechanical splices.
21.4.4 – Elements of the connection that are not designed to yield shall develop at least 1.5Sy.
21.4.5 – In structures assigned to SDC D, E, or F, wall piers shall be designed in accordance with 21.9 or 21.13 in ACI 318.
21.4.5 – Wall piers in Seismic Design Category D, E or F shall comply with Section 1905.1.4 of the International Building Code.
21.4.6 – Wall piers not designed as part of a moment frame in buildings assigned to Seismic Design Category C shall have transverse reinforcement designed to resist the shear forces determined from 21.3.3. Spacing of transverse reinforcement shall not exceed 8 inches (203 mm). Transverse reinforcement shall be extended beyond the pier clear height for at least 12 inches (305 mm).
Exceptions:
1. Wall piers that satisfy 21.13.
2. Wall piers along a wall line within a story where other shear wall segments provide lateral
support to the wall piers and such segments have a total stiffness of at least six times the sum of the stiffnesses of all the wall piers.
21.4.7 – Wall segments with a horizontal length-to thickness ratio less than 2.5 shall be designed as columns.
1905.1.4 ACI 318, Section 21.9. Modify ACI 318, Section 21.9, by deleting Section 21.9.8 and replacing with the following:
21.9.8 – Wall piers and wall segments.
21.9.8.1 – Wall piers not designed as a part of a special moment frame shall have transverse reinforcement designed to satisfy the requirements in 21.9.8.2.
Exceptions:
1. Wall piers that satisfy 21.13.
2. Wall piers along a wall line within a story where other shear wall segments provide lateral
support to the wall piers and such segments have a total stiffness of at least six times the sum of the stiffnesses of all the wall piers.
21.9.8.2 – Transverse reinforcement with seismic hooks at both ends shall be designed to resist the shear forces determined from 21.6.5.1. Spacing of transverse reinforcement shall not exceed 6 inches (152 mm). Transverse reinforcement shall be extended beyond the pier clear height for at least 12 inches (305 mm).
21.9.8.3 – Wall segments with a horizontal length-to thickness ratio less than 2.5 shall be designed as columns.
Clean Version:
1905.1 General. The text of ACI 318 shall be modified as indicated in Sections 1905.1.1 through 1905.1.9.
1905.1.3 ACI 318, Section 21.4. Modify ACI 318, Section 21.4, by adding new Section 21.4.3 and renumbering existing Sections 21.4.3 and 21.4.4 to become 21.4.4 and 21.4.5, respectively.
21.4.3 – Connections that are designed to yield shall be capable of maintaining 80 percent of their design strength at the deformation induced by the design displacement or shall use Type 2 mechanical splices.
21.4.4 – Elements of the connection that are not designed to yield shall develop at least 1.5Sy.
21.4.5 – In structures assigned to SDC D, E, or F, wall piers shall be designed in accordance with 21.9 or 21.13 in ACI 318.
Changes Related to Inclusion of Adhesive Anchors in ACI 318-11 Appendix D
Revise 2012 IBC Table 1705.3 as follows:
Clean Version:
In addition to the revisions to Table 1705.3, a new Section 1901.3 is also to be added (and subsequent sections renumbered) and the current Section 1909 is to be deleted as shown below:
1901.3 Anchoring to concrete. Anchoring to concrete shall be in accordance with ACI 318 as amended in Section 1905, and applies to cast-in (headed bolts, headed studs, and hooked J- or L-bolts) anchors and post-installed expansion (torque-controlled and displacement-controlled), undercut, and adhesive anchors.
1909 Anchorage to concrete – strength design. This section is deleted without substitution or revision.
