2.4 Importance of Nonstructural Damage
Historically, earthquake engineers have focused on the performance of structural systems and ways to mitigate structural damage. As the earthquake engineering community moves toward more comprehensive earthquake standards and expectations of improved seismic performance, and as the public demands a higher level of earthquake protection, it is important to understand the significance of nonstructural damage.
The failures of nonstructural components during an earthquake may result in injuries or fatalities, cause costly property damage to buildings and their contents; and force the closure of residential, medical and manufacturing facilities, businesses, and government offices until appropriate repairs are completed. As stated previously, the largest investment in most buildings is in the nonstructural components and contents; the failures of these elements may be both dangerous and costly. The potential consequences of earthquake damage to nonstructural components are typically divided into three types of risk:
- Life Safety (LS)—Could anyone be hurt by this component in an earthquake?
- Property Loss (PL)—Could a large property loss result?
- Functional Loss (FL)—Could the loss of this component cause an outage or interruption?
Damage to a particular nonstructural item may present differing degrees of risk in each of these three categories. In addition, damage to the item may result in direct injury or loss, or the injury or loss may be a secondary effect or a consequence of the failure of the item.
The focus of this guide is on nonstructural hazards; nevertheless, existing structures may also have structural hazards that pose risks to life safety, property, and functionality. While it may make sense to implement simple and inexpensive nonstructural protection measures even in a building with structural hazards, the relative structural and nonstructural risks should be considered, so that limited resources can be used in the most effective manner. It would give little comfort to know that the pipes and ceilings were all well anchored in an unreinforced masonry structure that could collapse during an earthquake.
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The first type of risk is that people could be injured or killed by damaged or falling nonstructural components. Heavy exterior cladding dislodged during earthquakes has killed passersby (Tally, 1988; Adham and Brent, 1985). Even seemingly harmless items can cause death if they fall on a victim. If a 25-pound light fixture not properly fastened to the ceiling breaks loose during an earthquake and falls on someone's head, the potential for injury is great. Life safety can also be compromised if the damaged nonstructural components block safe exits in a building. Damage to life safety systems such as fire protection piping can also pose a safety concern should a fire start following an earthquake. Examples of potentially hazardous nonstructural damage that have occurred during past earthquakes include broken glass, overturned tall heavy cabinets and shelves, falling ceilings and overhead light fixtures, ruptured gas lines and other piping containing hazardous materials, damaged friable asbestos materials, falling pieces of decorative brickwork and precast concrete panels, dislodged contents stored overhead, and collapsed masonry parapets, infill walls, chimneys, and fences.
- More than 170 campuses in the Los Angeles Unified School District suffered nonstructural damage during the 1994 Northridge, California earthquake. At Reseda High School, the ceiling in a classroom collapsed and covered the desks with debris. The acoustic ceiling panels fell in relatively large pieces, 3 feet or 4 feet square, accompanied by pieces of the metal ceiling runners and full-length sections of fluorescent light fixtures. Because the earthquake occurred during hours when the building was unoccupied, none of the students were injured (Los Angeles Times, 1994).
- A survey of elevator damage following the 1989 Loma Prieta Earthquake revealed 98 instances in which counterweights came out of the guide rails and six instances where the counterweight impacted the elevator cab, including one case in which the counterweight came through the roof of the cab. No injuries were reported (Ding, 1990). An elevator survey following the Northridge Earthquake indicated 688 instances in which counterweights came out of the guide rails, in addition to reports of other types of elevator damage. An occurrence of a counterweight becoming dislodged and impacting the elevator cab was captured on film during the 2010 Chile Earthquake.
- One hospital patient on a life-support system died during the 1994 Northridge Earthquake because of failure of the hospital's electrical supply (Reitherman, 1994).
- During the 1993 Guam Earthquake, the fire-rated nonstructural masonry partitions in the exit corridors of one resort hotel were extensively cracked, causing many of the metal fire doors in the corridors to jam. Hotel guests had to break through the gypsum wallboard partitions between rooms in order to get out of the building, a process that took as long as several hours. It was fortunate that the earthquake did not cause a fire in the building and no serious injuries were reported.
- Damage to industrial storage racks commonly used in “big box” stores has been reported in most recent earthquakes. Damage has ranged from dislodged contents to partial collapse of racking systems. Collapsed racking systems have been documented in both the 1994 Northridge Earthquake and the 2010 Christchurch New Zealand Earthquake. To date, related deaths and casualties have been avoided due to limited occupancy at the time of earthquake shaking.
Figure 2.4.1-2 Shards of broken untempered glass that fell several stories from a multistory building in the 1994 Northridge Earthquake. Failures of this type can be very hazardous, especially if glazing is located above exit ways (FEMA 74, 1994).
As discussed previously, nonstructural components, such as mechanical, and electrical equipment and distribution systems, and architectural components, account for 75-85% of the original construction costs of a typical commercial building. Contents belonging to the building occupants, such as movable partitions, furniture, and office or medical equipment, represent a significant additional value at risk. For example, a high tech fabricating facility may have contents that are worth many times the value of the building and built-in components of the building. Immediate property losses attributable to contents alone are often estimated to be one third of the total earthquake losses (FEMA, 1981).
Property losses may be the result of direct damage to a nonstructural item or of the consequences produced by its damage. If water pipes or fire sprinkler lines break, then the overall property losses will include the cost to repair the piping (a primary or direct loss), plus the cost to repair water damage to the facility (a secondary or indirect loss). If the gas supply line for a water heater ruptures and causes a fire, then clearly the property loss will be much greater than the cost of a new pipe fitting. Many offices and small businesses suffer losses as a result of nonstructural earthquake damage but may not keep track of these losses unless they have earthquake insurance that will help to cover the cleanup and repair costs.
The nonstructural property losses can be much larger if they occur at library and museum facilities whose function is to store and maintain valuable contents. For example, as a result of the 1989 Loma Prieta Earthquake, two libraries in San Francisco each suffered over a million dollars in damage to building contents; the money was spent primarily on reconstructing the library stacks, rebinding damaged books, and sorting and reshelving books. At one of these facilities, $100,000 was spent rebinding a relatively small number of rare books alone (Wong, 1993; Dobb, 1993).
In addition to life safety and property loss considerations, there is the additional possibility that nonstructural damage will make it difficult or impossible to carry out the functions that were normally accomplished in a facility. After life safety threats have been addressed, the potential for postearthquake downtime or reduced productivity is often the most important risk. For example, if a business loses the use of its computers, filing system, or other instruments of service as a result of earthquake damage, then the dollar loss of replacing the damaged items may be relatively small, but the loss in revenue associated with downtime during recovery can be tremendous. In light of the global economy, loss of function can also translate to longer term loss of market share for some businesses as consumers find alternate suppliers for needed goods or services.
Many external factors may affect postearthquake operations, including power and water outages, damage to transportation systems, availability of materials and contractors to repair damage, civil disorder, police lines, and curfews. These effects are generally outside the control of building owners and tenants and beyond the scope of this discussion.
The following are examples of nonstructural damage that resulted in interruptions to postearthquake emergency operations or to businesses:
- During the 1994 Northridge Earthquake, nonstructural damage caused temporary closure, evacuation, or patient transfer at ten essential hospital facilities. These hospitals generally had little or no structural damage but were rendered temporarily inoperable, primarily because of water damage. At the majority of these facilities, water leaks occurred when fire sprinkler, chilled-water, or other pipelines broke. In some cases, personnel were unavailable or unable to shut off the water, and water was flowing for many hours. At one facility, water up to 2 feet deep was reported at some locations in the building as a result of damage to the domestic water supply tank on the roof. At another facility, the emergency generator was disabled when its cooling water line broke where it crossed a separation joint. Other damage at these facilities included broken glass, dangling light fixtures, elevator counterweight damage, and lack of emergency power due to failures in the distribution or control systems. Two of these facilities, shown in the following figures, Los Angeles County Olive View Medical Center and Holy Cross Medical Center, both in Sylmar, California, that had suffered severe structural damage or collapse during the 1971 San Fernando Earthquake had been demolished and entirely rebuilt by the time of the 1994 Northridge Earthquake (Reitherman, 1994).
Figure 2.4.3-1 Broken sprinkler pipe at Olive View Hospital in Sylmar, California as a result of the 1994 Northridge, Earthquake. Pipe ruptured at the elbow joint due to differential motion of the pipe and ceiling (FEMA 74, 1994).
Figure 2.4.3-2 HVAC damage at Holy Cross Medical Center in Sylmar in the 1994 Northridge Earthquake. Damage to signage and louvers was caused when suspended fans in the mechanical penthouse swung and impacted the louver panels. HVAC service outage caused the temporary evacuation of patients (FEMA 74, 1994).
- Of 32 commercial data processing facilities surveyed following the 1989 Loma Prieta Earthquake, at least 13 were temporarily out of operation for periods ranging from 4 to 56 hours. The primary cause of outage was loss of outside power. Reported damage included overturning of equipment at two facilities, damage to access floors at four facilities, movement of large pieces of computer equipment over distances ranging from a few inches to 4 feet at 26 facilities, and dislodged ceiling panels at 13 facilities. Twenty of these facilities reported having an earthquake preparedness program in place at the time of the earthquake, three reported having no program, and information was unavailable for nine facilities (Ding, 1990).
- The 1971 San Fernando Earthquake caused extensive damage to elevators in the Los Angeles area, even in some structures where no other damage was reported. An elevator survey indicated 674 instances in which counterweights came out of the guide rails, in addition to reports of other types of elevator damage. These elevators were inoperable until they could be inspected and repaired. Many thousands of businesses were temporarily affected by these elevator outages. The State of California instituted seismic elevator code provisions in 1975 with the intent of allowing for safe elevator shutdown during and after an earthquake (not to make the elevators so earthquake-resistant that they can be relied upon for exiting buildings immediately after an earthquake). While these provisions appear to have helped reduce elevator damage, there were still many instances of counterweight damage in the San Francisco area following the 1989 Loma Prieta Earthquake, and 688 cases in the Northridge Earthquake in 1994 (Ding, 1990; Reitherman, 1994). Since the State of California seismic elevator code provisions have not been adopted nationally, elevator damage—including the potential for life-threatening conditions—remains a concern.
In some cases, cleanup costs or the value of lost employee labor are not the key measures of the postearthquake impact of an earthquake. For example, data processing facilities or financial institutions must remain operational on a minute-by-minute basis in order to maintain essential services and to monitor transactions at distant locations. In such cases, spilled files or damage to communications and computer equipment may represent less tangible but more significant outage costs. Hospitals and fire and police stations are facilities with essential functions that must remain operational after an earthquake.