Pushover Analysis - Bridge Piers: Performance Categories and Criteria#
Introduction#
Performance-based seismic design (PBSD) is an advanced engineering approach that focuses on designing structures to achieve specific performance objectives under seismic events. Unlike traditional seismic design, which aims to meet basic safety standards, PBSD allows engineers to tailor the design to meet various performance levels, such as a desired level of operability or collapse prevention. Performance objectives are defined based on the desired level of performance for different seismic events (e.g., frequent, occasional, rare, or very rare earthquakes). The performance levels used in this tutorial are:
OLE (Operational Level Earthquake): Minimal damage associated with initial cracking and spalling of concrete cover.
CLE (Contingency Level Earthquake): Substantial spalling of piles, such as damage that exposes the spiral.
DE (Design Earthquake): Broken connection due to spalling into the core, fractured dowel bars, or buckled strands.
Performance levels are assigned to materials along with the specification of corresponding strain limits. These strain thresholds mark the maximum permissible damage level that is regarded compatible with the intended structural performance. In a pushover analysis, an equivalent seismic force is applied to a structure. The loading is gradually increased, possibly until a specified target displacement is reached. The resulting capacity curve (base shear vs. top displacement) represents the structure’s overall seismic capacity. During force application, material response is monitored. Once a material reaches a strain limit corresponding to a certain performance level that has not been reached before, a mark on the capacity curve appears, indicating that the given performance level has been surpassed. This allows engineers to assess the performance of the structure for a target displacement related to a seismic event quickly and in a straightforward manner.
Definition of Performance Categories and Criteria#
The definition of performance limits introduces the concept of strain-based damage classification to the plastic hinge. User-defined performance categories and corresponding performance criteria can be linked to the materials used in the section for which a plastic hinge is derived, allowing classification of the sectional performance.
Performance Assessment of Structures#
Using plastic hinges with assigned performance limits enables performance assessment of the pushed structural along the capacity curve. Performance tracing of single hinges during the load application is also possible.
