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29 Demand Displacement: The peak displacement profile of the structure based on seismic analysis for a given ground motion level. Full Ductility Design: A design criteria that allows for full inelastic behavior in selected mem- bers without reference to a targeted damage level, and generally based on simple elasto-plastic material behavior (See reference (2), Fig C4.9-1) only limited by (reduced) ultimate material strains [See reference (2), Table 8.4.2-1]. Functional Event (FEE): A seismic event level for which the bridge is expected to operate imme- diately after the event, with only minimal damage that can be repaired without closing the bridge. Kinematic System: Dynamic behavior of the assemblage of members and joints of the structure undergoing a time history of displacement associated with ground motion input. Limited Ductility Design: A design criteria that sets limits on damage and/or element strains in members based on computation of damage conditions that are less than full ductility, generally for the purpose of maintaining function or limiting the amount of repair to the structure after the earthquake event. Liquefaction (of soils): A condition where soil strength diminishes from the normal static strength due to pore water pressure accumulation within the soil framework, which in turn can greatly reduce strength and stiffness, and in the case of a sloped ground surface, cause dislocation of the soil mass by lateral flow. Minimal Damage: A damage level to components of the bridge where local repairs and patching may be needed, similar to the level of distress assumed for strength design of bridge elements for normal loads. Nonlinear Time-History (NLTH) (Analysis): A dynamic analysis of the structure and founda- tion system for ground motion time-history input that accounts for geometric and material nonlinearity in the model. Probabilistic Site Hazard Analysis (PSHA): A site-specific study that combines analysis of local and regional seismicity, source fault conditions, attenuations from those sources, and the probability of earthquake occurrence along those source faults that is used to determine the probabilities and magnitudes of seismic events for design at the bridge site. Pushover (Analysis): A static analysis procedure where seismic demand displacement is applied to a structural system to verify that ductility demand does not exceed the limits for a full ductility design and that non-ductile member demands remain essentially elastic. Glossary of Terms
30 Seismic Design of Non-Conventional Bridges Repairable Damage: A damage level to components of the bridge where ductile elements experi- ence considerable damage that is limited to a level that can be repaired in order to place the bridge back into normal service. Repairable damage levels may require short-term closures of the bridge. Safety Event (SEE)*: A significant seismic event level with the longest return period considered to represent a life safety design-level seismic event where the bridge is expected to experience considerable damage but not collapse. Significant Damage: A damage level that precludes structural collapse, may or may not be repairable, and generally will require extended closure or demolition of the bridge. Strain-Based Criteria: Design criteria based on a computation of peak strain levels in elements of members that have been correlated to acceptable damage levels in the members. Strong-Column Weak-Beam: A seismic resistance system where the ductility is assigned to the beams, with the columns remaining essentially elastic. This is the standard configuration for tall buildings. Weak-Column Strong-Beam: A seismic resistance system where ductility is assigned to the columns, with the beams remaining essentially elastic. This is the standard configuration for conventional bridges. *Note that in the criteria document for Project 11 in Chapter 3, the SEE term is defined as the service evaluation event, with the typical SEE event then termed the NCE for no-collapse event. However, this is not standard terminology.