6.1 Protective Measures
- 6.1.1 Commonsense Measures
- 6.1.2 Nonstructural Component Protection Measures
- 6.1.3 Building Protection Measures
Reducing nonstructural hazards requires a combination of commonsense measures and additional protective measures that involve the installation of seismic anchorage and bracing. The protective measures recommended in this chapter will go a long way towards reducing the earthquake hazards from nonstructural components.
A facility survey may identify components that represent a high or moderate risk in their present location but that could readily be relocated or rearranged, in order to reduce the potential risk. The answers to the following questions may help identify commonsense measures available to reduce many of these risks:
- Which areas of the building have a higher occupant load and hence a potentially higher life safety risk?
- Are there heavy, unstable items currently located near a desk or bed, which could be moved?
- Are the exits and exit pathways clear, or are there items that could block doors, corridors, or stairways if they were to fall?
- What is the probability that someone will be injured by falling objects?
- Can items no longer serving a useful function be removed?
- Are all hazardous materials stored properly?
- Which items can be relocated to prevent possible injury and do not need to be anchored, in order to prevent damage or loss?
- If something slides or falls, in what direction is it likely to move?
- Is a suspended item currently hanging where it may impact a window, wall, or another item?
While the answer to these questions may not always be obvious, some simple steps may go a long way toward reducing the related nonstructural risks. The primary investment here is the time required to relocate furniture, reshelf items, or rearrange hazardous chemicals. For instance:
- Tall or heavy objects can be relocated, so that they cannot block an exit or fall onto a desk or bed.
- Shelved items might be rearranged so that heavier items are near the bottom and lighter ones are near the top.
- Falling hazards, such as curios, potted plants, and flower vases can be relocated, so that they will not fall on a bed or desk.
- Hanging objects can be relocated to a place where they will not impact one another or a window.
- Incompatible chemicals can be separated, in order to prevent mixing if the containers should break.
- Excess supplies or inventory can be stored in their original shipping containers until ready for use, in order to reduce the possibility of breakage.
- Rarely used files or materials can be moved to an offsite storage facility or be disposed of.
- Important electronic files should all be backed up to an offsite facility in a different geographic area, which would not be affected by the same earthquake.
There are many techniques available to reduce potential nonstructural earthquake damage. Possible upgrade schemes might include one or more of the following seismic protection measures:
- Using anchor bolts to provide rigid anchorage to a structural floor or wall
- Bracing the item to a structural floor or wall
- Providing a tether or safety cable to limit the range of movement if the item falls or swings
- Installing bracing or anchors for architectural appendages such as chimneys, parapets, canopies, marquees, or signs; anchoring masonry veneer and cornices
- Providing stops, bumpers or snubbers to limit the range of movement if the item is on vibration isolators or can slide or swing
- Providing flexible connections for piping and conduit where they cross seismic joints or connect to rigidly mounted equipment
- Attaching contents to a shelf, desktop, or countertop
- Providing base isolation or seismic shock absorbers for individual pieces of vital equipment
Some of these methods are designed to protect the functional integrity of a particular item; some are designed merely to reduce the consequences of failure. It is important to understand the applicability and limitations of the various upgrade schemes and to select an appropriate scheme for a particular item in a specific context. It is also important to select upgrade details that are consistent with the program objectives: measures required for immediate occupancy or continued operations are typically more complex than those required solely to reduce falling hazards. Measures used to restrain new items may differ from those used to restrain existing items, particularly if the restraint for the existing items is intended to meet only limited objectives and to reduce falling hazards. Critical and expensive items, library and museum collections, hospitals, essential facilities, laboratories, and industrial clean rooms may all require special attention.
Some structural upgrades may also be required in order to meet the operational objectives such as larger seismic gaps to prevent pounding between adjacent structures, or stiffer structural systems such as shear walls to avoid excessive distortion of the structural framing. Structural measures to reduce seismic hazards are addressed in Seismic Evaluation of Existing Buildings (ASCE/SEI 31-03) and Seismic Rehabilitation of Existing Buildings (ASCE/SEI 41-06) but are beyond the scope this document.
Requirements for Postearthquake Operations
Facilities to be upgraded to Immediate Occupancy or Operational performance level following a major earthquake may require extensive modifications and implementation of an ongoing risk reduction program. In order to achieve these enhanced objectives, any or all of the following elements may be needed in order to provide an appropriate level of nonstructural protection:
- Specialized engineering expertise form design professionals experienced with nonstructural seismic protection
- Higher design forces than those required by code for the basic safety objective
- Experienced specialty contractors
- Special construction inspection
- Load-rated hardware and specialty seismic restraint items
- Active equipment that is certified by the vendor to remain operational either by shake table testing or experience data
- Components with hazardous contents that are certified to maintain containment either by analysis, shake tables testing, or experience data
- Equipment or piping with special design details such as dampers or base isolation
It is possible to greatly reduce nonstructural damage and improve the probability of operability following an earthquake by reducing the earthquake demands that nonstructural components are subjected to. Conventional seismic design of building structures is based on the concept of increasing resistance against earthquake forces through the use of shear walls, braced frames, or moment resisting frames. Stiffer building systems often result in higher floor accelerations that are potentially damaging to many nonstructural components. More flexible buildings tend to have increased interstory drift that is potentially damaging to other nonstructural components. One building design concept that has been successfully used to resist earthquakes and greatly reduce both acceleration and drift demands (by factors of 4 or more) and therefore corresponding reducing or eliminating damage to nonstructural components is seismic isolation. Both floor accelerations and interstory drift are reduced in seismically isolated buildings through the use of specially designed interfaces that are typically located at the structure base. These interfaces take advantage of the properties of known earthquake ground motion and trade off significant displacement demands at the base of the structure with reduced acceleration and structure deformation above the base by significantly increasing the fundamental period of the building system. Seismic isolation essentially decouples the building response from the earthquake ground motions in a controlled manner.
The benefits of seismic isolation have been demonstrated in recent large earthquakes including the 1994 Northridge, 2010 Chile and 2011 Japan Earthquakes. The benefits have been most recently observed in full-scale testing of a 5-story building conducted on the large outdoor shake table at University of California San Diego in 2012. In this project (in part sponsored by the National Science Foundation and FEMA), a full-scale reinforced concrete building was constructed and outfitted with an array of nonstructural components included cladding, interior partitions, mechanical and electrical equipment, stairs and elevator and floors dedicated to hospital facilities, servers facilities, laboratories and residential areas. The building was tested with identical strong earthquake motions with and without seismically isolators. The building response with isolators was dramatically reduced with seismic isolators as compared to building response without isolators. More data, papers, reports, and videos from the testing project are expected to be made available in 2013 and 2014.