2.5 Common Types of Nonstructural Earthquake Damage
Many types of nonstructural components can be damaged in earthquakes, but the items that are most vulnerable and most likely to result in injuries, significant property losses, and interruption will be described here in terms of the risk posed to life safety, property, and functionality.
Heavy exterior cladding
Cladding is an architectural element used to provide the exterior skin for buildings. Often constructed of heavy precast concrete panels, these panels typically have four support points, two at the top of the panel connecting it to the beam above, and two at its base connected to the level below. Unless specifically designed to accommodate the anticipated inter-story drift and out-of-plane seismic forces, these supports can fail. A female student was killed in the 1987 Whittier Narrows Earthquake when a 5,000-pound precast panel fell 25 feet off of the exterior of a parking garage at California State University, Los Angeles. The student was attempting to exit from the ground floor parking level when she was struck by the falling panel (Taly, 1988).
Heavy interior walls
Nonstructural walls in older buildings are often built of heavy, unreinforced masonry materials such as brick, concrete block, or hollow clay tile. These materials are advantageous for fire and sound proofing and thermal insulation, but are brittle since they do not have a grid of horizontal and vertical steel reinforcing bars embedded in them. Falling masonry in hallways and stairwells is a particular hazard for occupants attempting to exit buildings during an earthquake.
Unbraced masonry parapets or other heavy building appendages
Unreinforced masonry parapets are a common feature of vintage commercial construction in many parts of the country. Parapets are the short walls around the perimeter of a roof, constructed to help prevent fire from jumping from one roof to the next, to provide guardrail protection for people on the roof, to hide roof-mounted equipment, or to provide an architectural effect of greater height. While some communities have enforced ordinances that require unreinforced masonry parapets to be braced or anchored, many jurisdictions have no such mandatory provisions. As these parapets often fail at the roofline and fall outwards onto the sidewalk, they represent a particular hazard for pedestrians and occupants attempting to exit damaged buildings. Two children were killed on their way to school due to falling unreinforced stone masonry in Challis, Idaho during the 1983 Borah Peak, Idaho earthquake (Adham and Brent, 1985). Unreinforced masonry parapets have also fallen inward and penetrated through the roof of buildings.
Unreinforced masonry chimneys
Residential chimneys are typically built of brittle unreinforced brick masonry that may be damaged even in relatively small earthquakes. This is also true of many commercial chimneys. Broken chimneys can fall through the roof and pose a safety risk to building occupants. The 1992 Landers Earthquake caused one related fatality where a child was sleeping next to a fireplace. A similar fatality occurred in the 2000 Napa earthquake where a child sleeping next to a fireplace was killed during a slumber party. Chimneys can also fall against the side of the building, onto an adjacent building or onto a public sidewalk, posing a hazard to neighbors or passersby. Use of a cracked flue chimney can cause an indirect hazard when carbon monoxide enters a home or leads to ignition of a fire.
Suspended overhead lighting is prone to damage in earthquakes, especially if the lights are supported solely by unbraced suspended ceilings, or if they interact with unbraced piping or other suspended components. There were several instances where suspended lighting fixtures in Los Angeles school district classrooms fell during the 1994 Northridge Earthquake. No casualties occurred since school was not in session at the time of the earthquake.
Large, heavy ceilings
Heavy suspended ceilings and soffits can be damaged during earthquakes, sometimes causing heavy and dangerous material to fall and injure people below. Figure 2.4.1-2 shows a failed stucco soffit above a building entrance damaged in the 1994 Northridge Earthquake. During the 1989 Loma Prieta Earthquake, the proscenium arch ceiling at the Geary Theatre in San Francisco fell and covered the first six rows of seats in the auditorium; the theater was not in use at the time and no one was injured (Ding, 1990).
Tall, slender, and heavy furniture such as bookcases and file cabinets
Tall slender shelving, bookcases, or file cabinets frequently overturn during earthquakes if they are unanchored or poorly anchored. These items are particularly hazardous if they are located adjacent to a desk or bed or located where they can jam doors or block corridors and exits. Recent shaking table tests conducted in Japan predict injuries to occupants represented by mannequins crushed by tall unanchored pieces of furniture.
Heavy unanchored or poorly anchored contents, such as televisions, computer monitors, countertop laboratory equipment, and microwaves
Heavy contents situated above the floor level include a wide range of items that could become falling hazards in an earthquake. Many rooms have overhead wall- or ceiling-mounted televisions and monitors, offices have desktop computer monitors, or microwaves may be perched high on counters or shelves. Any of these items could cause injury if they fell and hit someone; damage to fallen items can add to property loss and downtime. During the 1989 Loma Prieta Earthquake, an overhead monitor fell at the San Francisco International Airport, hitting a passenger on the shoulder.
Damage to storefront windows in older commercial buildings is common during earthquakes, often causing hazardous conditions on sidewalks in commercial areas. Glazing failures were relatively common in high-rise buildings in Mexico City in the 1985 Earthquake. U.S. earthquakes have not yet caused numerous high-rise glazing failures, though it remains a possibility.
Fire protection piping
Damage to suspended fire protection piping and other system components can render the system inoperable following an earthquake. The resultant loss of fire life safety protection can pose a serious risk to the life safety of building occupants.
Hazardous materials release
There have been a number of examples of hazardous materials release resulting from earthquake damage to piping, stored chemicals, commercial, medical, or educational laboratory facilities. Breakage of containers of chemicals can cause them to mix and lead to hazardous reactions. Exposure of asbestos materials due to earthquake activity has also resulted in the postearthquake evacuation of facilities that otherwise had little structural damage.
Gas water heaters
Residential and small commercial water heaters have ignited fires following earthquakes, in instances where the gas supply line was damaged. As water heaters are typically tall and slender, the gas supply line can break if the water heater tips over.
The following components pose a high risk of direct injury requiring hospitalization, or possibly causing death, if installed without seismic bracing, seismic anchorage, seismic restraint or allowance for differential movement in zones of high seismicity. Other components posing indirect risks to life safety are also identified.
- Exterior walls (including veneer, prefabricated panels, glazing, glass block, curtain wall and storefront window systems)
- Partitions (hollow clay tile, unreinforced masonry or similar)
- Ceilings (plaster or other heavy material, particularly if suspended)
- Parapets and appendages (unreinforced masonry)
- Canopies, marquees and signs
- Chimneys and stacks (unreinforced masonry)
- Suspended equipment weighing over 20 pounds
- Fuel tanks
- Fuel or hazardous material piping
- Suspended light fixtures (recessed, surface-mounted or pendant) weighing over 20 pounds
- Tall and slender shelves, bookcases, file cabinets, vending machines, lockers or similar
- Industrial storage racks and contents
The following components pose life safety concern when located in path of egress:
- Glazed partitions
- Demountable partitions
- Metal stud partitions with heavy veneer such as tile or stone
- Suspended acoustic tile ceiling including light or other components supported by the ceiling grid only and weighing 20 pounds or more
- Clay or concrete roof tiles
The following components pose indirect life safety risk:
- Emergency generation system (in hospitals, emergency communication centers or similar)
- Fire protection systems
For a more detailed list of components and risk ratings, refer to Appendix E.
Masonry damage has long been used to estimate earthquake ground motion intensity in the absence of instrumental recordings. The Modified Mercalli Intensity (MMI) scale identifies levels I to XII to characterize the seismic intensity. MMI Intensity VI and VII both include descriptions of cracked masonry that can be used to estimate the level of ground shaking (Richter, 1957).
Recent efforts to correlate the MMI scale with recorded peak ground accelerations (PGAs) suggest that the threshold for masonry damage, MMI Intensity VI, is associated with low levels of seismic excitation with PGAs in the range 0.10g to 0.15g (CISN, 2009).
Suspended piping for water or waste
Failures of suspended piping have lead to costly property loss in past earthquakes. While such failures are not often associated with life threatening injuries, they often result in costly property loss: both the cost to replace the damaged system and the cost to repair damage caused by the release of both clean and contaminated or hazardous fluids. Secondary damage due to fluid release is often a large component of nonstructural property losses.
Suspended fire protection piping
Failures of suspended fire protection piping have resulted in both direct and indirect property loss following earthquakes. Some of these systems have failed or fallen and had to be replaced. More costly are the failures of sprinkler piping, connections, or sprinkler heads. These have resulted in the release of great volumes of water in plenum or occupied spaces. Flooded plenums have resulted in collapsed ceilings which cause the consequent loss of property and disruption of operations. In extreme cases, entire floors or buildings were abandoned as a result of the water damage. Flooding in occupied spaces has resulted in water damage to furniture, files, computer equipment, and interior finishes. As fire sprinkler lines are widespread in occupied spaces, this type of failure has been one of the most costly types of nonstructural damage.
Unanchored and poorly anchored equipment, particularly roof-mounted equipment and unrestrained vibration-isolated equipment
Roof-mounted HVAC equipment is often vulnerable to earthquake damage, in part because the seismic accelerations are typically larger at the roof level than they are at the lower levels of the building. Such equipment is often mounted on vibration-isolation springs to prevent the transmission of the equipment vibrations to the building and building occupants. While these springs allow the equipment to move vertically a small amount in order to isolate its rapid vibratory motion from the building, this equipment is especially vulnerable to the much larger motions caused by an earthquake, unless it is also designed with seismic restraints. Damage to roof-mounted equipment, as well as other suspended or floor-mounted equipment, can disable the infrastructure of a building.
Non-load-bearing gypsum board partitions can be detailed to reduce the impact of seismic distortions of structural systems, with a connection detail at the top of the partition that allows the interface with the floor or roof above to accommodate sliding. However, this often is not detailed properly, resulting in extensive cracking and tearing at joints and points of attachment. Heavy partitions constructed of concrete masonry units, brick, or hollow clay tile are also often damaged in earthquakes and are costly to repair. Even when partition damage is minor to moderate, it may still necessitate complete interior patching and painting and may cause business interruptions in the affected interior spaces. Pacific Gas & Electric Company, which operates throughout much of Northern California, reported close to $50 million in area-wide property damage following the 1989 Loma Prieta Earthquake, much of which was from damage to gypsum board partitions, glazing, and air conditioning units. While this nonstructural damage represented relatively minor losses for each building, it added up to large aggregate losses for the firm (Ding, 1990).
Suspended ceiling systems have failed in many earthquakes resulting in major repair or replacement costs for the ceilings and interconnected lighting or fire sprinkler lines as well as interruption in the use of the occupied spaces.
Hazardous materials release
Release of some hazardous materials can create a point of ignition for a fire. An entire three story university chemistry building burned down to the steel frame as a result of a hazardous materials release in the 2010 Chile Earthquake (see Section 126.96.36.199).
Emergency generators for critical facilities and related components such as day tanks, batteries, and mufflers
Continued operations of critical facilities following an earthquake depend on the integrity not only of the emergency generator itself but also of many related subcomponents such as batteries, battery racks, day tanks, exhaust and sometimes water-cooling connections, electrical connections to control panels, and mufflers. All of these items must be adequately restrained or anchored in order for the emergency systems to remain operational.
Suspended piping for water or waste
As noted above, damage to these systems results not only in primary damage to the piping and connected systems but also can result in costly outages resulting from the release of fluids into occupied spaces. Also, many facilities cannot operate without water and sanitary sewage service. As an additional concern, process piping may require extensive inspection prior to equipment restart, whether it appears damaged or not, resulting in additional time for functional loss.
Suspended fire protection piping
Failures of suspended fire protection piping have resulted in costly business interruption as well as disabling hospitals in past earthquakes. The small bore lines and sprinkler heads often are built in a grid with ceiling and lighting systems; incompatible motions of these systems have sometimes resulted in damage to the sprinkler heads and subsequent overhead water release.
Hazardous materials release
Breakage of containers of chemicals can cause them to mix and lead to hazardous reactions. Also, due to disruption of building materials, asbestos release has occurred during earthquakes. Any of these types of releases can cause building closures, evacuation, and costly delays until specially trained HAZMAT crews can be brought in to identify and clean the spills.
Failure of equipment needed for functionality, such as computer data centers, controls, servers, hubs, routers, switches, and communication systems
Computer networks form the backbone of many operations. Earthquake damage can result in extended downtime.
Equipment needed for functionality, including HVAC systems
Many facilities cannot maintain operations without HVAC equipment because temperature control and air filtration systems are required in many hospitals, laboratories, and high tech manufacturing facilities.
Equipment needed for functionality, such as elevators and conveyors
Many facilities cannot resume normal operations without the use of passenger and freight elevators or material conveyors. Hospitals need elevators to move gurneys and portable equipment from floor to floor. Occupants of multistory buildings depend upon the use of elevators to move work materials, supplies, and equipment.