Seismic Response of Nonstructural Elements
There is no doubt that the cost of damage to contents and to nonstructural features of buildings will far exceed the cost of structural damage.
James L. Stratta, 1987
Nonstructural elements are those systems and components attached to the fl oors and walls of a building or industrial facility that are not part of the main or intended load-bearing structural system of the building or industrial facility. Although not part of the main structural system, they may, nevertheless, also be subjected to large seismic forces and depend on their own structural characteristics to resist these seismic forces. In general, nonstructural elements may be classifi ed into three broad categories: (a) architectural components, (b) mechanical and electrical equipment, and (c) building contents. Examples of the fi rst category include elevator penthouses, stairways, partitions, parapets, heliports, cladding systems, signboards, lighting systems, and suspended ceilings. Examples of the second category are storage tanks, pressure vessels, piping systems, ducts, escalators, smokestacks, antennas, cranes, radars and object-tracking devices, computer and data acquisition systems, control panels, transformers, switchgears, emergency power systems, fi re protection systems, boilers, heat exchangers, chillers, cooling towers, and machinery such as pumps, turbines, generators, and motors. Among those in the third category are bookshelves, fi le cabinets, storage racks, decorative items, and any other piece of furniture commonly found in offi ce buildings and warehouses. Nonstructural elements are also known by alternative names such as “appendages;” “nonstructural components;” “building attachments;” “architectural, mechanical, and electrical elements;” “secondary systems;” “secondary structural elements;” and “secondary structures.” Perhaps the name that best describes their nature is “secondary structures” since it refl ects the fact that they are not part of the main structure but must possess, nonetheless, structural properties to maintain their own integrity.