Seismic Codes For Nonstructural Engineering

While most people know that earthquakes can cause buildings, bridges, and other structures to crack, distort, and even fail, mechanical, electrical, and plumbing system failures often get overlooked. People fear earthquakes because they can be injured from falling structural elements like columns or beams or architectural components like brick facades or windows. But what about the lights overhead, the rooftop units, pipes, or storage tanks? These nonstructural components can injure people when their supports and attachments fail.

The number-one goal of a building code is to protect people. The building code that governs the majority of the United States is the International Building Code (IBC), which is published by the International Code Council (ICC). IBC Chapter 16, as well as Chapters 11-13 and 15-23 of American Society of Civil Engineers (ASCE) 7—Minimum Design Loads for Buildings and Other Structures, address seismic design. Although the main purpose of the IBC is to safeguard against major structural failures and loss of life, this does not imply that damage should be limited or the function of the building be maintained. Buildings and other structures that support the mechanical, electrical, or plumbing (MEP) components are divided into occupancy categories (IBC Table 1604.5), which are used to determine the level of seismic loads and detailing required.

Essential facilities such as hospitals, police and fire stations, power plants, or water treatment facilities are examples of higher level occupancy categories (III or IV), which can require a higher level of analysis, design, and detailing than a lower occupancy category building in the same region of the country. Essential facilities like these require immediate occupancy or continued use after an earthquake, which can require continued function of MEP components after an earthquake as well. Life safety systems such as fire sprinkler systems and essential electrical systems require seismic bracing to stay in service.

To determine the level of analysis, design, and detailing that will be required for the structural, architectural, and MEP components, the structural engineer will need to calculate the seismic design category. This calculation takes into account the location of the building near a fault, the occupancy category of the building (as previously mentioned), and the soil characteristics of the site. Seismic design categories A, B, or C are deemed low to moderate, whereas categories D, E, or F are deemed high to severe. Structures located in California, for example, will typically fall into a high to severe category, while structures located in Wisconsin will fall into low to moderate. Once the seismic design category has been determined, the analysis and design begins. The design of MEP supports and anchorages is covered in ASCE sections 13.3, 13.4, and 13.6.

Below is a partial list of some important items that should be considered and shown by MEP engineers on the construction documents. The list is culled from three very useful documents produced by the Federal Emergency Management Agency (FEMA)—412, 413, 414—as well as from the authors’ personal experience. The FEMA documents are only guides; in all instances local building codes, such as the IBC, control the design.