However, beware: If your portable unit is stacked (two-story portable office), the 7-22 code prohibits the free-rocking exception. Stacked portables must be treated as fixed-base structures with explicit seismic connections. Inside a portable building, everything moves: server racks, lockers, medical equipment, and furniture. ASCE 7-22 Section 13.2.1 now requires that portable structures with casters or wheels have all internal components independently braced for ( F_p = 0.6 S_DS W_p ) (up from 0.4 in 7-16). This is a 50% increase in internal bracing loads.
| Risk Category | Typical Portable Application | Importance Factor (Wind/Ice) | | :--- | :--- | :--- | | | Unoccupied tool shed, construction blind, agricultural portable shelter (low hazard to life) | 0.87 | | II | Job site office (standard occupancy), portable classroom, ticket booth | 1.00 | | III | Portable medical triage unit, emergency response trailer, event stage with >300 people | 1.15 | | IV | Portable command center for nuclear/dam failure alerts (rare, but exists) | 1.25 | asce 7 22 portable
ASCE 7-22 Table 1.5-1 outlines four Risk Categories (I, II, III, IV). For portable units: However, beware: If your portable unit is stacked
This article dissects the new standard’s application to portable structures, covering risk categories, wind design for non-permanent anchorage, seismic "free-rocking" analysis, and the three most common pitfalls engineers face when applying a "building" code to a movable asset. Before we dive into load combinations, we must define the subject. ASCE 7-22 does not have a dedicated chapter titled "Portable Buildings." Instead, portability falls under the umbrella of Chapter 15: Nonbuilding Structures and specific provisions for Chapter 13: Nonstructural Components . ASCE 7-22 Section 13
Design every portable unit as if it will be anchored in the worst possible location—because eventually, it will be. Disclaimer: This article is for informational purposes. Always consult a licensed structural engineer and the full ASCE 7-22 standard for your specific portable structure application.
By: Senior Structural Engineer & Modular Construction Specialist