2024 IBC Significant Structural Changes

By John “Buddy” Showalter, PE, and Sandra Hyde, PE

This 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 31 on temporary structures. Only a portion of the chapter’s total number of code changes is discussed. More information on the code changes can be found in the 2024 Significant Changes to the International Building Code available from ICC.

Temporary Structures

Special requirements that apply to temporary structures are included in IBC Section 3103. For applying the applicable code provisions, “temporary” is considered as being erected for a period of less than 180 days. The International Fire Code (IFC) also has a significant number of provisions applicable to such structures. Additionally, the IBC identifies key criteria that must be applied to temporary structures, including conformity with structural strength, fire safety, means of egress, accessibility, light, ventilation, and sanitary requirements. Permits are typically required, as are construction documents. The scope of IBC Section 3103 includes special event structures, tents, umbrella structures, and other membrane structures.

202
DEFINITIONS

PUBLIC-OCCUPANCY TEMPORARY STRUCTURE. Any building or structure erected for a period of one year or less that serves an assembly occupancy or other public use.
SERVICE LIFE. The period of time that a structure serves its intended purpose. For temporary structures, this shall be the cumulative time of service for sequential temporary events which may occur in multiple locations. For public-occupancy temporary structures this is assumed to be a minimum of 10 years.
TEMPORARY EVENT. A single use during the service life of a public-occupancy temporary structure at a given location which includes its installation, inspection, use and occupancy, and dismantling.
TEMPORARY STRUCTURE. Any building or structure erected for a period of 180 days or less to support temporary events. Temporary structures include a range of structure types (public-occupancy temporary structures, temporary special event structures, tents, umbrella and other membrane structures, relocatable buildings, temporary bleachers, etc.) for a range of purposes (storage, equipment protection, dining, workspace, assembly, etc.).
3103.1 General. The provisions of Sections 3103.1 through 3103.4 3103.8 shall apply to structures erected for a period of less than 180 days. Temporary special event structures, tents, umbrella structures and other membrane structures erected for a period of less than 180 days shall also comply with the International Fire Code. Those Temporary structures erected for a longer period of time and public-occupancy temporary structures shall comply with applicable sections of this code.
Exceptions:

1. Public-occupancy temporary structures complying with Section 3103.1.1 shall be permitted to remain in service for 180 days or more but not more than 1 year where approved by the building official.
2. Public-occupancy temporary structures erected within the confines of an existing structure are not required to comply with Section 3103.6.

3103.1.1 Extended period of service time. Public-occupancy temporary structures shall be permitted to remain in service for 180 days or more without complying with requirements in this code for new buildings or structures where extensions for up to 1 year are granted by the building official in accordance with Section 108.1 and where the following conditions are satisfied:

1. Additional inspections as determined by the building official shall be performed by a qualified person to verify that site conditions and the approved installation comply with the conditions of approval at the time of final inspection.
2. A qualified person shall perform follow up inspections after initial occupancy at intervals not exceeding 180 days to verify the site conditions and the installation conform to the approved site conditions and installation requirements. Inspection records shall be kept and shall be made available for verification by the building official.
3. An examination shall be performed by a registered design professional to determine the adequacy of the temporary structure to resist the structural loads required in Section 3103.6.
4. Relocation of the public occupancy temporary structure shall require a new permit application.
5. The use or occupancy approved at the time of final inspection shall remain unchanged.
6. A request for an extension is submitted to the building official. The request shall include records of the inspections and examination in Items 1 and 3.

3103.1.1 3103.1.2 Conformance. (No changes to text)
3103.1.2 3103.1.3 Permit required. (No changes to text)
(No changes to IBC Sections 3103.2 through 3103.4)
3103.5 Bleachers. Temporary bleachers, grandstands and folding and telescopic seating that are not building elements shall comply with ICC 300.
3103.6 Structural requirements. Temporary structures shall comply with the structural requirements of this code. Public-occupancy temporary structures shall be designed and erected to comply with the structural requirements of this code and Sections 3103.6.1 through 3103.6.4.
Exception: Where approved, live loads less than those prescribed by Table 1607.1 shall be permitted provided a registered design professional demonstrates that a rational approach has been used and that such reductions are warranted.
Temporary non-building structures ancillary to public assemblies or special events structures whose structural failure or collapse would endanger assembled public shall be assigned a risk category corresponding to the risk category of the public assembly. For the purposes of establishing an occupant load for the assembled public endangered by structural failure or collapse, the applicable occupant load determination in Section 1004.5 or 1004.6 shall be applied over the assembly area within a radius equal to 1.5 times the height of the temporary non-building structure.
3103.6.1 Structural loads. Public-occupancy temporary structures shall be designed in accordance with Chapter 16, except as modified by Sections 3103.6.1.1 through 3103.6.1.6
3103.6.1.1 Snow loads. Snow loads on public-occupancy temporary structures shall be determined in accordance with Section 1608. The ground snow loads, pg, in Section 1608 shall be modified according to Table 3103.6.1.1.
Exception: Ground snow loads, pg, for public-occupancy temporary structures that employ controlled-occupancy procedures per Section 3103.8 shall be permitted to be modified using a ground snow load reduction factor of 0.65 instead of the ground snow load reduction factors in Table 3103.6.1.1.
Where the public-occupancy temporary structure is not subject to snow loads or not constructed and occupied during times when snow is to be expected, snow loads need not be considered, provided that where the period of time when the public-occupancy temporary structure is in service shifts to include times when snow is to be expected, one of the following conditions is met:

1. The design is reviewed and modified, as appropriate, to account for snow loads.
2. Controlled-occupancy procedures in accordance with Section 3103.8 are implemented.

3103.6.1.2 Wind loads. The design wind load on public-occupancy temporary structures shall be permitted to be modified in accordance with the wind load reduction factors in Table 3103.6.1.2.
Exceptions:

1. Design wind loads for public-occupancy temporary structures that implement controlled occupancy procedures per Section 3103.8 shall be permitted to be modified using a wind load reduction factor of 0.65.
2. For public-occupancy temporary structures erected in a hurricane-prone region outside of hurricane season, the basic wind speed, V, shall be permitted to be set as follows, depending on Risk Category:
   2.1. For Risk Category II: 115 mph.
   2.2. For Risk Category III: 120 mph.
   2.3. For Risk Category IV: 125 mph.

3103.6.1.3 Flood loads. Public-occupancy temporary structures need not be designed for flood loads specified in Section 1612. Controlled occupancy procedures in accordance with Section 3103.8 shall be implemented.
3103.6.1.4 Seismic loads. Seismic loads on public-occupancy temporary structures assigned to Seismic Design Categories C through F shall be permitted to be taken as 75 percent of those determined by Section 1613. Public-occupancy temporary structures assigned to Seismic Design Categories A and B are not required to be designed for seismic loads.
3103.6.1.5 Ice loads. Ice loads on public-occupancy temporary structures shall be permitted to be determined with a largest maximum nominal thickness of 0.5 inch (13mm), for all risk categories. Where the public-occupancy temporary structure is not subject to ice loads or not constructed and occupied during times when ice is to be expected, ice loads need not be considered, provided that where the period of time when the temporary structure is in service shifts to include times when ice is to be expected, one of the following conditions is met:

1. The design is reviewed and modified, as appropriate, to account for ice loads.
2. Controlled occupancy procedures in accordance with Section 3103.8 are implemented.
   

1. Surfaces on which snow or ice accumulates shall be monitored before and during occupancy of the public-occupancy temporary structure. Any loads in excess of the design snow or ice load shall be removed prior to its occupancy, or the public-occupancy temporary structure shall be vacated in the event that either the design snow or ice load is exceeded during its occupancy.
2. Wind speeds associated with the design wind loads shall be monitored before and during occupancy of the public-occupancy temporary structure. The public-occupancy temporary structure shall be vacated in the event that the design wind speed is expected to be exceeded during its occupancy.
3. Criteria for initiating occupant evacuation procedures for flood and tsunami events.
4. Occupant evacuation procedures shall be specified for each environmental hazard where the occupant management plan specifies the public-occupancy temporary structure is to be evacuated.
5. Procedures for anchoring or removal of the public-occupancy temporary structure, or other additional measures or procedures to be implemented to mitigate hazards in snow, wind, flood, ice, or tsunami events.

CHAPTER 35
REFERENCED STANDARDS

ANSI E1.21-2020 Entertainment Technology: Temporary Structures Used for Technical Production of Outdoor Entertainment Event
ANSI ES1.7-2021 Event Safety Requirements – Weather Preparedness
Change Significance: Four new definitions have been added to the IBC: temporary structures, public-occupancy temporary structures, service life, and temporary event. Public-occupancy temporary structures are new buildings or structures that are used by the public, or that support public events, where the public expects similar levels of reliability and safety as offered by permanent construction. Public-occupancy temporary structures are often assembled with re-useable components and designed for a particular purpose and limited period, which is defined as a temporary event when the period is less than one year. Public-occupancy temporary structures in service for a period that exceeds 1-year must meet IBC requirements for new buildings.

While temporary structures are developed for use up to 180 days, many of these structures are used repeatedly at different locations. Thus, their actual service life may be on the order of 5 to 10 years. Such structures are typically subjected to repeated assembly and dismantling with associated wear and tear. Therefore, service life for temporary structures is defined to provide a consistent basis of reliability relative to that of new buildings, and a service life of 10 years is assumed for public-occupancy temporary structures when determining snow and wind load reductions in IBC Section 3103.6.

IBC Section 3103.1.1 deals with extension of a public-occupancy temporary structure’s service time. The owner and their “qualified person” are to perform any additional inspections required by the building official, and ongoing inspections every 6 months. For the ongoing inspections, the qualified person must keep records should the building official wish to review them. These provisions are comparable to the process for special inspections in IBC Chapter 17, where a building official relies on a special inspector or agency for many of the details of construction. Relocation of a public-occupancy temporary structure (not all temporary structures) requires the owner to apply for a new permit. A request for an extension must be submitted to the building official, and reports resulting from inspections by the qualified person and the registered design professional’s examination must be submitted along with the request.

New IBC Section 3103.6 differentiates between temporary structures and its subcategory public-occupancy temporary structures. The latter has new specific provisions for structural loads, foundations, installation and maintenance inspection, durability and maintenance of reusable components, serviceability, and controlled occupancy procedures.

Temporary non-building structures (such as stands supporting lights, audio equipment, cameras, etc.) which are associated with either public assemblies or special event structures need to be assigned a risk category consistent with the risk category of the public assembly. Applicable occupant load determination per IBC Section 1004.5 or 1004.6 is to be applied over the assembly area within a radius equal to 1.5 times the height of the temporary non-building structure. This is consistent with recommendations from the California Building Officials Association for the “fall zone” around buildings damaged in earthquakes when conducting building safety evaluations. Those recommendations suggest that building safety evaluators cordon off or barricade for a distance of 1.5 times the height of a damaged building in danger of collapsing to protect the public from building materials that can also shatter and bounce. Determination of the risk category for each temporary non-building structure in a public assembly area is to be done for each structure individually, not cumulatively, as it is unlikely that simultaneous failure of multiple structures will occur during an event. See the risk category determination example shown in Figure 1 containing cases of minimum areas and heights assigned to pole-type temporary non-building structures.

Public-occupancy temporary structures should not pose more risk to occupants than permanent structures, but because the code’s design-level environmental loads are far less likely during a temporary event, these new provisions reduce certain structural load requirements for a consistent level of risk. Minimum uniformly distributed live loads and concentrated loads can be reduced where a registered design professional calls for such reductions based on a rational approach.

Recognizing the relatively short service life of temporary structures, the ground snow load can be reduced to reflect the comparatively low probability that the ASCE/SEI 7 Minimum Design Loads and Associated Criteria for Buildings and Other Structures ground snow loads will occur during the shorter service life of a temporary structure. If controlled occupancy procedures are implemented, an even larger reduction of ground snow loads is permitted. If the service life of the temporary structure will not occur during months when snow is to be expected, snow loads need not be considered.

In hurricane-prone regions outside of hurricane season, the basic wind speed can be prescriptively set at 115 mph for RC II, 120 mph for RC III and 125 mph for RC IV structures. For nonhurricane areas, the wind load reduction factors shown in Table 3103.6.1.2 are believed to provide a reasonable level of reliability, given the ability to evacuate or modify temporary structures for strong wind events. If controlled occupancy procedures are implemented, an even larger reduction of wind loads is permitted.
Seismic loads on public-occupancy temporary structures assigned to Seismic Design Categories C through F can be taken as 75 percent of those required by IBC Section 1613 which results in reduced seismic performance relative to permanent structures. This is consistent with the reduction for the evaluation and upgrade of existing buildings and will result in a similar seismic risk to occupants.
Public-occupancy temporary structures can be supported on the ground with temporary foundations where approved by the building official. Consideration is needed for the impacts of differential settlement. Presumptive load-bearing values for structures supported on pavement, slab on grade, beach sand or grass cannot be assumed to exceed 1,000 psf unless otherwise determined by a registered design professional. IBC Table 1806.2 soil bearing values are applicable for other typical supporting soil conditions.

Provisions for controlled occupancy in IBC Section 3103.8 address cases where an environmental loading hazard cannot be reasonably mitigated and allow for actions based on a preapproved action plan that a building official may use to permit installations that cannot resist code prescribed loads. For example, public-occupancy temporary structures subject to high wind loads may be evacuated and sections of the structure can be removed to reduce the wind load and prevent components from becoming projectiles. Where such plans are required, they must comply with ANSI ES1.7 and an operations management plan in accordance with ANSI E1.21 shall be submitted to the building official for approval as a part of the permit documents. ANSI E1.21 includes requirements for monitoring weather forecasts for high winds, tornadoes, thunderstorms, lightning, and other severe conditions, as well as a requirement for mitigating actions for ice and snow to be specified in the operations management plan.

Temporary structures are designed to be assembled and disassembled and transported to different locations as components or as modules. They may be in service during varying weather conditions. Components may be damaged during transportation or installation. Components also may have been manufactured more than a decade prior to the latest use. Therefore, and unlike a new structure that is typically constructed with new building materials and components that were not previously used, components for temporary structures need to be inspected regularly and their suitability for reuse needs to be assessed. This is typically done by the installation crews, and this is similar to bleachers regulated by ICC 300 Standard on Bleachers, Folding and Telescopic Seating, and Grandstands. The qualified person assigned to perform the regular inspections is identified by the owner.

Additional related technical and editorial changes throughout the IBC including IBC Section 108.1 and multiple sections of IBC Chapter 16 are not shown or discussed here. See code change S116-22 with committee modifications on the ICC website for more details.

Conclusion

Structural engineers should be aware of significant structural changes in the 2024 IBC Chapter 31 on temporary structures. New definitions, reduced environmental loads, as well as installation and maintenance inspections are now included for temporary structures. ■