2.3 Extent of Nonstructural Damage
There are many factors affecting the performance of nonstructural components during an earthquake and the extent to which they will sustain damage. The degree of damage caused by the four principal effects previously described depends upon considerations such as the components' dynamic characteristics, their location in the building, and their proximity to other structural or nonstructural components. Other factors include the type of ground motion, the structural system of the building, the location and placement of the loads, the type of anchorage or bracing, if any, the strength of the structural supports used for anchorage, potential interaction with other nonstructural components, and the potential for secondary damage.
A survey of 25 damaged commercial buildings following the 1971 San Fernando Earthquake revealed the following breakdown of property losses: structural damage, 3%; electrical and mechanical, 7%; exterior finishes, 34%; and interior finishes, 56%. A similar survey of 50 damaged high-rise buildings, which were far enough away from the earthquake fault rupture to experience only mild shaking, showed that whereas none had major structural damage, 43 of the buildings suffered damage to drywall or plaster partitions, 18 suffered damaged elevators, 15 had broken windows, and 8 incurred damage to their air-conditioning systems (Steinbrugge and Schader, 1973).
Reducing the Risks of Nonstructural Earthquake Damage—State-of-the-Art and Practice Report (ATC 69) summarizes the current state of knowledge and practice regarding the seismic performance of nonstructural components of buildings. This study confirmed the lack of systematic and comprehensive post-earthquake documentation of nonstructural performance and recommended development of a standardized framework for the collection of future nonstructural earthquake damage data.
- Unique characteristics of the ground shaking at the site (e.g., high or low frequency motion, proximity to fault)
- Characteristics of the structural system supporting the nonstructural elements (e.g., the structure may be tall and flexible, short and stiff, or short and flexible)
- Location of the nonstructural item within the building (e.g., items may be at the basement, at mid-height or roof level; items may cross seismic joints or may be located in close proximity to deforming structural elements)
- Distribution and placement of loads (e.g., heavy loads situated near the bottom of shelving units and lighter items above, or the reverse; countertop lab equipment close or far from the edges of counters)
- Anchorage or restraint conditions (e.g., items may be unanchored, marginally anchored, or well anchored)Condition of structural elements used for anchorage (e.g., location and strength of studs in a wall used to anchor tall cabinets or shelving, location of reinforcing bars in concrete used to anchor heavy items, condition of mortar in old masonry walls)
- Potential interaction with structural elements or other nonstructural elements (e.g., rigid granite veneer covering a flexible steel column or a well-anchored ceiling grid with unbraced sprinkler lines)
- Potential for secondary damage caused by release of fluids, gases, toxins, asbestos, and other hazardous substances (e.g., damage to asbestos insulation requires evacuation, a gas leak results in a fire)