Glossary

Capacity-protected component — A component expected to experience minimum damage and to behave essentially elastic during the design earthquakes.

Concentrically braced frame (CBF) — A diagonally braced frame in which all members of the bracing system are subjected primarily to axial forces.

Connections — A combination of joints used to transmit forces between two or more members.

Design earthquake — Earthquake loads represented by acceleration response spectrum (ARS) curves specified in design specifications or codes.

Displacement ductility — Ratio of ultimate-to-yield displacement.

Ductile component — A component expected to experience repairable damage during the FEE and significant damage but without failure during the SEE.

Ductility — Ratio of ultimate-to-yield deformation.

Eccentrically braced frame (EBF) — A diagonally braced frame that has at least one end of each bracing member connected to a link.

Expected nominal strength — Nominal strength of a component based on its expected yield strength.

Functional evaluation earthquake (FEE) — A lower level design earthquake that has relatively small magnitude but may occur several times during the life of the bridge. It may be assessed either deterministically or probabilistically. The determination of this event is to be reviewed by a Caltrans-approved consensus group.

Joint — An area where member ends, surfaces, or edges are attached.

Link — In EBF, the segment of a beam that is located between the ends of two diagonal braces or between the end of a diagonal brace and a column. Under lateral loading, the link deforms plastically in shear thereby absorbing energy. The length of the link is defined as the clear distance between the ends of two diagonal braces or between the diagonal brace and the column face.

Liquefaction — Seismically induced loss of shear strength in loose, cohesionless soil that results from a build up of pour pressure as the soil tries to consolidate when exposed to seismic vibrations.

Maximum credible earthquake (MCE) — The largest earthquake that is capable of occurring along an earthquake fault, based on current geologic information as defined by the 1996 Caltrans Seismic Hazard Map.

Moment-resisting frame (MRF) — A frame system in which seismic forces are resisted by shear and flexure in members and connections in the frame.

Nominal strength — The capacity of a component to resist the effects of loads, as determined by computations using specified material strength, dimensions, and formulas derived form acceptable principles of structural mechanics or by field tests or laboratory test of scaled models, allowing for modeling effects, and differences between laboratory and field conditions.

Overstrength capacity — The maximum possible strength capacity of a ductile component considering actual strength variation between the component and adjacent components. It is estimated by an overstrength factor of 1.2 times expected nominal strength.

Plastic hinge — A concentrated ''zero length'' hinge that maintains its plastic moment capacity and rotates freely.

Plastic hinge zone — A region of structural components that are subject to potential plastification and thus must be detailed accordingly.

Seismic performance criteria — The levels of performance in terms of postearthquake service and damage that are expected to result from specified earthquake loadings.

Safety evaluation earthquake (SEE) — An upper level design earthquake that has only a small probability of occurring during the life of the bridge. It may be assessed either deterministically or probabilistically. The deterministic assessment corresponds to the maximum credible earthquake. The probabilistically assessed earthquake typically has a long return period (approximately 1000 to 2000 years).

Ultimate displacement — The lateral displacement of a component or a frame corresponding to the expected damage level, not to exceed the displacement when the lateral resistance degrades to a minimum of 80% of the peak resistance.

Upper bound solution — A solution calculated on the basis of an assumed mechanism that is always at best equal to or greater than the true ultimate load.

Yield displacement — The lateral displacement of a component or a frame at the onset of forming the first plastic hinge.

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