Italics are used for text within Sections 1903 through 1905 of this code to indicate provisions that differ from ACI 318.
About this chapter: Chapter 19 provides minimum accepted practices for the design and construction of buildings and structural components using concrete—both plain and reinforced. Chapter 19 relies primarily on the reference to American Concrete Institute (ACI) 318, Building Code Requirements for Structural Concrete. Structural concrete must be designed and constructed to comply with this code and all listed standards. There are also specific provisions addressing concrete slabs and shotcrete.
Code development reminder: Code change proposals to this chapter will be considered by the IBC—Structural Code Development Committee during the 2022 (Group B) Code Development Cycle.
Structural concrete shall conform to the durability requirements of ACI 318.
Exception: For Group R-2 and R-3 occupancies not more than three stories above grade plane, the specified compressive strength, f´c, for concrete in basement walls, foundation walls, exterior walls and other vertical surfaces exposed to the weather shall be not less than 3,000 psi (20.7 MPa).
DETAILED PLAIN CONCRETE STRUCTURAL WALL. A wall complying with the requirements of Chapter 14, including 14.6.2.
ORDINARY PRECAST STRUCTURAL WALL. A precast wall complying with the requirements of Chapters 1 through 13, 15, 16 and 19 through 26.
ORDINARY REINFORCED CONCRETE STRUCTURAL WALL. A cast-in-place wall complying with the requirements of Chapters 1 through 13, 15, 16 and 19 through 26.
ORDINARY STRUCTURAL PLAIN CONCRETE WALL. A wall complying with the requirements of Chapter 14, excluding 14.6.2.
Modify ACI 318 Sections 22.214.171.124 and 126.96.36.199 to read as follows:
Special moment frames and special structural walls shall also satisfy 18.2.4 through 18.2.8.
Modify ACI 318, Section 18.5 by adding new Section 188.8.131.52 and renumbering existing Sections 184.108.40.206 and 220.127.116.11 to become 18.104.22.168 and 22.214.171.124, respectively.
- 126.96.36.199 — 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.
- 188.8.131.52 — Elements of the connection that are not designed to yield shall develop at least 1.5 Sy.
- 184.108.40.206 — In structures assigned to SDC D, E or F, wall piers shall be designed in accordance with 18.10.8 or 18.14 in ACI 318.
Modify ACI 318, Section 220.127.116.11 to read as follows:
- 18.104.22.168 — Special structural walls constructed using precast concrete shall satisfy all the requirements of 18.10 for cast-in-place special structural walls in addition to 18.5.2.
Modify ACI 318, Section 22.214.171.124 to read as follows:
- 126.96.36.199 — Foundations resisting earthquake-induced forces or transferring earthquake-induced forces between a structure and ground shall comply with the requirements of 18.13 and other applicable provisions of ACI 318 unless modified by Chapter 18 of the International Building Code.
Modify ACI 318, Section 14.6 by adding new Section 14.6.2 to read as follows:
- 14.6.2 — Detailed plain concrete structural walls.
- 188.8.131.52 — Detailed plain concrete structural walls are walls conforming to the requirements of ordinary structural plain concrete walls and 184.108.40.206.
220.127.116.11 — Reinforcement shall be provided as follows:
Delete ACI 318, Section 14.1.4 and replace with the following:
- 14.1.4 — Plain concrete in structures assigned to Seismic Design Category C, D, E or F.
18.104.22.168 — Structures assigned to Seismic Design Category C, D, E or F shall not have elements of structural plain concrete, except as follows:
- • Structural plain concrete basement, foundation or other walls below the base as defined in ASCE 7 are permitted in detached one- and two-family dwellings three stories or less in height constructed with stud-bearing walls. In dwellings assigned to Seismic Design Category D or E, the height of the wall shall not exceed 8 feet (2438 mm), the thickness shall be not less than 71/2 inches (190 mm), and the wall shall retain no more than 4 feet (1219 mm) of unbalanced fill. Walls shall have reinforcement in accordance with 14.6.1.
• Isolated footings of plain concrete supporting pedestals or columns are permitted, provided the projection of the footing beyond the face of the supported member does not exceed the footing thickness.
Exception: In detached one- and two-family dwellings three stories or less in height, the projection of the footing beyond the face of the supported member is permitted to exceed the footing thickness.
• Plain concrete footings supporting walls are permitted, provided the footings have at least two continuous longitudinal reinforcing bars. Bars shall not be smaller than No. 4 and shall have a total area of not less than 0.002 times the gross cross-sectional area of the footing. For footings that exceed 8 inches (203 mm) in thickness, a minimum of one bar shall be provided at the top and bottom of the footing. Continuity of reinforcement shall be provided at corners and intersections.
Modify ACI 318 Sections 22.214.171.124, 126.96.36.199(d) and 188.8.131.52 to read as follows:
• 184.108.40.206 — Where the tensile component of the strength-level earthquake 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 220.127.116.11. The anchor design tensile strength shall be determined in accordance with 18.104.22.168.
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 22.214.171.124(d).
- • 126.96.36.199(d) — The anchor or group of anchors shall be designed for the maximum tension obtained from design load combinations that include E, with E increased by Ω0. The anchor design tensile strength shall be calculated from 188.8.131.52.
• 184.108.40.206 — Where the shear component of the strength-level earthquake force applied to anchors exceeds 20 percent of the total factored anchor shear force associated with the same load combination, anchors and their attachments shall be designed in accordance with 220.127.116.11. The anchor design shear strength for resisting earthquake forces shall be determined in accordance with 17.7.
The thickness of concrete floor slabs supported directly on the ground shall be not less than 31/2 inches (89 mm). A 6-mil (0.006 inch; 0.15 mm) polyethylene vapor retarder with joints lapped not less than 6 inches (152 mm) shall be placed between the base course or subgrade and the concrete floor slab, or other approved equivalent methods or materials shall be used to retard vapor transmission through the floor slab.
Exception: A vapor retarder is not required: