Configuration

DOE-STD-1020-2002

Characteristics of the lateral force-resisting systems are at least as important as the

earthquake load level used for design or evaluation. These characteristics include redundancy;

ductility; tying elements together to behave as a unit (to provide redundancy and to reduce

potential for differential displacement); adequate equipment anchorage; non-uniform,

non-symmetrical configuration of structures or equipment; detailing of connections and

reinforced concrete elements; and the quality of design, materials, and construction. The level of

earthquake ground shaking to be experienced by any facility in the future is highly uncertain. As

a result, it is important for facilities to be tough enough to withstand ground motion in excess of

their design ground motion level. There can be high confidence in the earthquake safety of

facilities designed in this manner. Earthquakes produce transient, limited energy loading on

facilities. Because of these earthquake characteristics, well-designed and well-constructed

facilities (i.e., those with good earthquake design details and high quality materials and

construction which provide redundancy and energy absorption capacity) can withstand

earthquake motion well in excess of design levels. However, if details that provide redundancy

or energy absorbing capacity are not provided, there is little real margin of safety built into the

facility. It would be possible for significant earthquake damage to occur at ground shaking

levels only marginally above the design lateral force level. Poor construction could potentially

lead to damage at well below the design lateral force level. Furthermore, poor design details,

materials, or construction increase the possibility that a dramatic failure of a facility may occur.

A separate document providing guidelines, examples, and recommendations for good

seismic design of facilities has been prepared as part of this project (UCRL-CR-106554, Ref.

C-21). This section briefly describes general design considerations that are important for

achieving well-designed and constructed earthquake-resistant facilities and for assessing existing

facilities. Considerations for good earthquake resistance of structures, equipment, and

distribution systems include: (1) configuration; (2) continuous and redundant load paths; (3)

detailing for ductile behavior; (4) tying systems together; (5) influence of nonstructural

components; (6) function of emergency systems; and (7) quality of materials and construction.

Each is briefly discussed below. While the following discussion is concerned primarily with

buildings, the principles are just as applicable to enhancing the earthquake resistance of

equipment, distribution systems, or other components.

Configuration - Structure configuration is very important to earthquake response.

Irregular structures have experienced greater damage during past earthquakes than uniform,

symmetrical structures. This has been the case even with good design and construction;

therefore structures with regular configurations should be encouraged for new designs, and

existing irregular structures should be scrutinized very closely. Irregularities such as large

reentrant corners create stress concentrations which produce high local forces. Other plan

irregularities can result in substantial torsional response during an earthquake. These include

irregular distribution of mass or vertical seismic resisting elements or differences in stiffness

between portions of a diaphragm. These also include imbalance in strength and failure

mechanisms even if elastic stiffnesses and masses are balanced in plan. Vertical irregularities

can produce large local forces during an earthquake. These include large differences or

eccentricities in stiffness or mass in adjacent levels or significant horizontal offsets at one or

more levels. An example is the soft story building which has a tall open frame on the bottom

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