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A common misconception regarding pre-engineered metal buildings (PEMBs) is that manufacturers serve as the Engineer of Record (EOR) for the projects they undertake. While manufacturers do provide stamped drawings and calculations for their buildings, they do not function as the EOR. Instead, they deliver a product based on design loads and code information supplied by the EOR.
As metal building contractors, it is essential for us to obtain loads and code information from the EOR. However, since PEMBs are frequently utilized in design-build projects, companies often seek our input before engaging an EOR. Understanding building codes and design loads is crucial for us to create accurate preliminary designs and budgets.
One of the most important factors to establish early in the process is the Risk Category of the building. The Risk Category significantly influences every load that the building is designed to withstand. Buildings assigned a lower Risk Category are designed for lower loads and importance factors compared to those in higher categories.
The 2018 International Building Code (IBC) Table 1604.5 outlines four Risk Categories (I–IV):
Risk Category I: Low-Hazard Occupancy
These buildings present minimal risk to human life in the event of failure. Examples include agricultural buildings, temporary structures, and small storage facilities. They are designed using lower loads due to their low risk of causing injury or death during a collapse.
Risk Category II: Standard Occupancy
Most buildings fall into this category. Standard occupancy structures include all buildings not classified in Risk Categories I, III, or IV. This is the most prevalent classification used in PEMB design.
Risk Category III: Hazardous or Special Occupancy
These buildings pose a significant hazard to human life if they fail. Examples include buildings for public assembly, certain schools, and industrial sites that handle hazardous materials (e.g., chemical or tire manufacturing).
Risk Category IV: Essential Facilities
Essential facilities encompass hospitals, police and fire stations, power plants, and buildings containing highly toxic materials. These structures are vital for community safety and continuity during and after catastrophic events.
To demonstrate how Risk Categories influence design loads, consider a PEMB in Tonawanda, NY (ZIP 14150). The design wind speed varies by Risk Category:
The 19 mph range illustrates the significant differences in design requirements between Risk Categories. Incorrectly selecting a lower Risk Category, such as Category II (Standard Occupancy), for a building that should be classified as Category IV (Essential Facility) could lead to underestimating the design loads. This oversight may affect both the structural integrity and the overall costs of the project.
Understanding the structural design criteria, including Risk Categories and their implications on loads, is crucial for accurate PEMB design and pricing. As contractors, being well-informed about these criteria allows us to better serve our clients, whether we are providing preliminary consultations or collaborating with the EOR.
Stay tuned for the next article in this series, where we will delve into additional design criteria and their applications in PEMB projects.