code UPDATES 2024 IBC Significant Structural Changes Loads (IBC Chapter 16)—Part 6
By John “Buddy” Showalter, PE, and Sandra Hyde PE
T
his multi-part series discusses significant structural changes to the 2024 International Building Code (IBC) by the International Code Council (ICC). This article includes an overview of changes to IBC Chapter 16 for environmental loads including snow, rain, wind, tornado, and earthquake. Only a portion of the chapter’s total number of code changes is 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).
ASCE 7-22 and Hazard Tool ASCE/SEI 7-22 Minimum Design Loads and Associated Criteria for Buildings and Other Structures includes a significant number of revisions for nearly all environmental loads. Changes throughout the 2024 IBC, most significantly in IBC Chapter 16, match changes to ASCE 7. To easily determine new environmental loads based on location and risk category, use the ASCE Hazard Tool (asce7hazardtool. online) – a free resource.
Snow Loads New ground snow load (GSL) maps based on ASCE 7-22 are included in the IBC and are now based on the risk category of the building (Figure 2). 1608.2 Ground snow loads. The ground snow loads to be used in determining the design snow loads for roofs shall be determined in accordance with the reliability-targeted (strength-based) ground snow load values in Chapter 7 of ASCE 7 or Figures 1608.2(1) and through 1608.2(24) for the contiguous United States and Table 1608.2 for Alaska. Site-specific case studies shall be determined in accordance with Chapter 7 of ASCE 7 and shall be approved by the building official. made in areas designated “CS” in Figures 1608.2(1) and 1608.2(2). Ground snow loads
for sites at elevations above the limits indicated in Figures 1608.2(1) and 1608.2(2) and for all sites within the CS areas shall be approved. Ground snow load determination for such sites shall be based on an extreme value statistical analysis of data available in the vicinity of the site using a value with a 2-percent annual probability of being exceeded (50-year mean recurrence Figure 1. More information on the code interval). Snow loads are zero changes can be found in the 2024 for Hawaii, except in moun- Significant Changes to the IBC available tainous regions as approved by from the International Code Council. the building official. (Additional related technical and editorial changes throughout the IBC are not shown for brevity) Change Significance: ASCE 7-22 includes updated national GSL datasets in electronic and map form. The new snow loads are based on 25 years of additional snow load data and updated procedures for estimating snow loads, as well as using strength design-based values. Additionally, this approach incorporates advanced spatial mapping that has reduced the number and size of case study regions in mountainous areas significantly and eliminates discontinuities in design values across state boundaries. Given that GSL values have been provided as allowable stress loads up to this point, many provisions within the IBC and the IRC rely on allowable stress design (ASD) values. Therefore, a new Section 1608.2.1 is added to provide a conversion from the strength-based values now provided in the IBC reliability-targeted GSL maps to an equivalent ASD value. Note that the ASCE Hazard Tool also provides ASD ground snow loads.
Wind Loads Wind speed maps and associated provisions are updated to the newly referenced ASCE 7-22 load standard. SECTION 202 DEFINITIONS
Figure 2. Ground snow loads (psf) for Risk Category III buildings.
BASIC WIND SPEED, V. Basic design wind speeds. The wind speed used for design, as determined in Chapter 16. WINDBORNE DEBRIS REGION. Areas within hurricane-prone regions located: (1.) Within 1 mile (1.61 km) of the mean high-water line where an Exposure D condition exists upwind at the waterline and the
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