Concrete & Masonry (IBC Chapters 19 & 21)—Part 3.
This multi-part series discusses significant structural changes to the 2024 International Building Code (IBC) by the International Code Council (ICC). Part 3 includes an overview of changes to IBC Chapter 19 on concrete and IBC Chapter 21 on masonry. Only a portion of these chapters’ total number of code changes are discussed in this article. More information on the code changes can be found in the 2024 Significant Changes to the International Building Code, available from ICC (Figure 1).
Concrete
Structural Concrete with GFRP Reinforcement
New provisions and referenced standards have been added to the IBC for structural concrete with glass-fiber reinforced polymer (GFRP) reinforcement. New provisions and referenced standards ACI 440.11
Building Code Requirements for Structural Concrete Reinforced with Glass Fiber Reinforced Polymer (GFRP) Bars (Figure 2) and ASTM D7957 Standard Specification for Solid Round Glass Fiber Reinforced Polymer Bars for Concrete Reinforcement for GFRP bars are added to the IBC expanding options for their use. The addition of these new standards allows the design and construction of cast-in-place reinforced concrete using non-metallic reinforcement.
1901.2.1 Structural concrete with GFRP reinforcement. Cast-in-place structural concrete internally reinforced with glass fiber-reinforced polymer (GFRP) reinforcement conforming to ASTM D7957 and designed in accordance with ACI 440.11 shall be permitted where fire-resistance ratings are not required and only for structures assigned to Seismic Design Category A.
CHAPTER 35 REFERENCE STANDARDS
ACI 440.11-22 Building Code Requirements for Structural Concrete Reinforced with Glass Fiber Reinforced Polymer (GFRP) Bars
ASTM D7957/D7957M-17 Standard Specification for Solid Round Glass Fiber Reinforced Polymer Bars for Concrete Reinforcement
Change Signicance: Design and construction requirements in ACI 440.11 allow the use of GFRP in Seismic Design Category (SDC) A for the structural frame and in SDC B and SDC C for concrete members that are not part of the seismic force-resisting system.
Reasons to use GFRP bars in concrete structures include resistance to corrosion in the presence of chloride ions, lack of interference with electromagnetic fields, and low thermal conductivity. GFRP-reinforced concrete is especially suitable in highly corrosive environments, such as reinforced concrete exposed to salt water, salt air, or de-icing salts. It is primarily used to reinforce highway bridge decks where deicing salts are used on the roads and cause severe corrosion to conventional steel reinforcement. Other applications where GFRP-reinforced concrete is being considered include marine and coastal structures, parking garages, water tanks, and structures supporting magnetic resonance imaging (MRI) equipment.
ACI 440.11 establishes minimum requirements for GFRP-reinforced concrete comparable to ACI 318 which establishes minimum requirements for structural concrete with steel reinforcement. Since GFRP reinforcement behaves differently than steel reinforcement, specific standards for this application are required. Among the subjects covered in ACI 440.11 are:
- Design and construction for strength, serviceability, and durability
- Load combinations, load factors, and strength reduction factors
- Structural analysis methods
- Deflection limits
- Development and splicing of reinforcement
- Construction document information
- Field inspection and testing
- Methods to evaluate the strength of existing structures
IBC Section 1901.2.1 and the standard prohibit the use of internally GFRP-reinforced concrete for applications where fire-resistance ratings are required. For a building where reinforced concrete elements require fire-resistance ratings (e.g. in IBC Tables 601 and 705.5), the fire-resistance-rated members and assemblies will continue to need steel reinforcement.
See the April 2023 issue of STRUCTURE for an article on GFRP use in new construction and repair of existing structures.
Seismic Requirements for Structural Concrete
IBC Section 1902.1.1 has been revised and IBC Section 1905 has been reorganized and revised. The section no longer amends sections of ACI 318, rather focusing on provisions that supplement ACI 318 for seismic design.
1902.1.1 Design displacement. Design displacement shall be the Design Earthquake Displacement, δDE, defined in ASCE 7 Section 12.8.6.3. For diaphragms that can be idealized as rigid in accordance with ASCE 7 Section 12.3.1.2, δdi, displacement due to diaphragm deformation corresponding to the design earthquake, is permitted to be taken as zero. Design displacement at each level shall be the total lateral deffection at the level calculated for the design earthquake using the procedures defined in Section 12.8.6 of ASCE 7.
SECTION 1905 SEISMIC REQUIREMENTS MODIFICATIONS TO ACI 318
1905.1 General. In addition to the provisions of ACI 318, structural concrete shall comply with the requirements of Section 1905.
1905.2 ACI 318 Section 2.3. Modify existing definitions and add the following definitions to ACI 318, Section 2.3.
CAST-IN-PLACE CONCRETE EQUIVALENT DIAPHRAGM. A cast-in-place noncomposite topping slab diaphragm, as defined in Section 18.12.5, or a diaphragm constructed with precast concrete components that uses closure strips between precast components with detailing that meets the requirements of ACI 318 for the Seismic Design Category of the structure.
DETAILED PLAIN CONCRETE STRUCTURAL WALL. A wall complying with the requirements of [ASCE 7] Chapter 14, and Section 1905.5 of the International Building Code.
ORDINARY PLAIN CONCRETE STRUCTURAL WALL. A wall complying with the requirements of [ASCE 7] Chapter 14, excluding 14.6.2.
PRECAST CONCRETE DIAPHRAGM. A diaphragm constructed with precast concrete components, with or without a cast-in-place topping, that includes the use of discrete connectors or joint reinforcement to transmit diaphragm forces.
1905.3 Intermediate precast structural walls. Intermediate precast structural walls shall comply with Section 18.5 of ACI 318 and this section.
1905.3.1 Connections designed to yield. 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.
1905.4 Foundations designed to resist earthquake forces. Foundations resisting earthquake-induced forces or transferring earthquake-induced forces between a structure and ground shall comply with the requirements of Section 18.13 of ACI 318 and other applicable provisions of ACI 318 unless modified by Chapter 18.
1905.5 Detailed plain concrete structural walls.
1905.5.1 Reinforcement.
1905.6 Structural plain concrete.
1905.6.1 Seismic Design Categories A and B.
1905.6.2 Seismic Design Categories C, D, E and F.
1905.7 Design requirements for anchors
1905.7.1 Anchors in tension.
1905.7.2 Anchors in shear.
Deleted text and text associated with IBC Sections 1905.5 through 1905.7.2 are not shown for brevity.
Change Significance: IBC Section 1905 previously contained modifications to ACI 318. Many of the modifications were related to the seismic design of concrete structures. IBC Section 1905 now contains information supplemental to ACI 318 provisions specific to seismic design. Additional edits to IBC Sections 1901, 1902, and 1903 were made to harmonize with changes to IBC Section 1905. Due to the extensive reformatting of IBC Section 1905 and related provisions, Table 1 is provided as a summary of changes.
These changes reorganize IBC Section 1905 and related provisions without introducing any substantive change. The new format is believed to be more user-friendly. As part of this format change, existing provisions have been relocated to the following new IBC subsections: 1905.3.1, 1905.5.1, 1905.6.1, 1905.7.1, and 1905.7.2.
Masonry
Updated Masonry Standards
IBC Chapter 21 covers the materials, design, construction, and quality of masonry. Within the chapter are references to masonry design standards and material standards. TMS 402 Building Code Requirements for Masonry Structures, TMS 403 Direct Design Handbook for Masonry Structures and TMS 602 Specification for Masonry Structures are the IBC-referenced design standards for masonry. These standards are developed and published by The Masonry Society (TMS).
The masonry provisions comprise allowable stress design, strength design, empirical design, and requirements for glass masonry and masonry fireplaces and chimneys. Masonry veneer is covered in IBC Chapter 14 and TMS 402 Chapter 13. TMS 402 Chapter 1 lists specific masonry items that need to be included in the construction documents.
TMS has updated TMS 402 and TMS 602 which are placed in a single volume and often referenced as TMS 402/602 (Figure 3). The new 2022 editions have been revised throughout to update the standards to include new provisions in ASCE 7-22 as well as changes to numerous ASTM Standards.
2101.2 Design methods. Masonry shall comply with the provisions of TMS 402, TMS 403 or TMS 404 as well as applicable requirements of this chapter.
CHAPTER 35 REFERENCED STANDARDS
TMS 402-22 Building Code Requirements for Masonry Structures
TMS 602-22 Specification for Masonry Structures
Change Significance: Table 2 provides a summary of changes to TMS 402/602-22. Significant changes include:
- Compression-controlled section requirements added for Strength Design (Chapter 9) of reinforced masonry under combinations of flexure and axial load
- Updated mortar requirements for adhered masonry veneer (see IBC Section 2103.2.4 in this article for more information)
- New Appendix D on Glass Fiber Reinforced Polymer (GFRP) Reinforced Masonry which is limited to Seismic Design Categories A through C for elements not designated as part of the seismic-force-resisting system (see IBC Section 1901.2.1 in this article for similar provisions for structural concrete)
- Removal of TMS 402 Appendix A: Empirical Design of Masonry (Empirical design of Adobe Masonry remains in IBC Section 2109 with a specific reference to TMS 402-16; see IBC Section 2109 in this article for a discussion of empirical design)
Mortar for Adhered Masonry Veneer
IBC Section 2103.2.4 previously listed the types of mortars that can be used for adhered masonry veneer (Figure 4). Additional general requirements for adhered masonry veneer can be found in IBC Chapter 14. Mortar requirements for adhered veneer have been updated to meet new TMS 402-22 requirements.
2103.2.4 Mortar for adhered masonry veneer. Mortar for use with adhered masonry veneer shall conform to Section 13.3 of TMS 402. ASTM C270 for Type N or S, or shall comply with ANSI A118.4 for latex-modified Portland cement mortar.
Change Significance: Provisions for adhered masonry veneers have been extensively updated in the 2022 edition of TMS 402 to be more rationally based using a minimum mortar/unit bond strength value. Setting bed mortars are required by TMS 402/602-22 to be latex-modified mortars complying with ANSI A118.4 Specifications for Modified Dry-Set Cement Mortar or A118.15 Specifications for Improved Modified Dry-Set Cement Mortar to gain increased bond strength. Setting bed mortars meeting ASTM C270 Standard Specification for Mortar for Unit Masonry Type N or S are only permitted when testing is conducted on the specific mortar/unit combination to be used in construction.
Empirical Design of Adobe Masonry
The empirical design procedure for adobe masonry is a prescriptive method of sizing and proportioning masonry structures using rules and formulas that were developed over many years. The procedure is based on experience and predates engineering design methods. The empirical method was developed for use in smaller buildings with more interior walls and stiffer floor systems than are commonly built today (Figure 5). The option for empirically designed masonry has been removed from the 2022 edition of TMS 402. However, reference to the previous edition (TMS 402-16) will allow Adobe masonry provisions to remain in the IBC.
SECTION 2109
EMPIRICAL DESIGN OF ADOBE MASONRY
2109.1 General. Empirically designed adobe masonry shall conform to the requirements of Appendix A of TMS 402-16, except where otherwise noted in this section.
2109.1.1 Limitations. The use of empirical design of adobe masonry shall be limited as noted in Section A.1.2 of TMS 402-16. In buildings that exceed one or more of the limitations of Section A.1.2 of TMS 402-16, masonry shall be designed in accordance with the engineered design provisions of Section 2101.2 or the foundation wall provisions of Section 1807.1.5.
Section A.1.2.23 of TMS 402-16 shall be modified as follows:
A.1.2.23 – Wind. Empirical requirements shall not apply to the design or construction of masonry for buildings, parts of buildings, or other structures to be located in areas where Vasd as determined in accordance with Section 1609.3.1 of the International Building Code exceeds 110 mph.
2109.2 Adobe construction. Adobe construction shall comply with this section and shall be subject to the requirements of this code for Type V construction, Appendix A of TMS 402-16, and this section.
Remaining provisions are unchanged.
Change Significance: In recent years TMS 402 has curtailed the application of empirical design for contemporary masonry materials, construction methods, and building types because these modern buildings and materials no longer rely on the smaller number and size of openings, more frequent cross walls, and shorter walls assumed in the empirical design approach.
Additionally, adobe is a material for which there is greater variability in mortar and masonry unit qualities than modern masonry products. As a result, cost-effective adobe construction depends on time-tested and appropriately conservative empirical methods to guide prescriptive solutions for smaller-scale projects, which cannot justify the expense of laboratory testing for each source and product.
While TMS 402 Appendix A: Empirical Design of Masonry will no longer be included in 2022 and future editions, retaining reference to the previous edition (TMS 402-16) will allow adobe masonry provisions to remain in the IBC until a standard specific to adobe construction can be created and approved as an IBC-referenced standard. The Masonry Society has indicated that TMS 402-16 will remain available for the foreseeable future.
A related change corrects a typographical error to a TMS Appendix A section in IBC Section 2109.1.1.
Conclusion
Structural engineers should be aware of significant structural changes in the 2024 IBC for concrete and masonry. New provisions and referenced standards are added for structural concrete reinforced with glass-fiber reinforcement. IBC Section 1905 has been revised and reorganized and no longer amends sections of ACI 318, rather focusing on provisions that supplement ACI 318 for seismic design. TMS 402 and TMS 602 have been updated to 2022 editions. Mortar requirements for adhered veneer are updated to meet new TMS 402-22 requirements. Finally, the option for empirically designed masonry has been removed from the 2022 edition of TMS 402 but reference to the previous edition (TMS 402-16) will allow adobe masonry provisions to remain in the IBC.
Look for Part 1 of the series in the November 2023 issue and Part 2 in the December 2023 issue of STRUCTURE.