Seismic evaluation of Clark County critical bridges using nonlinear static procedures

Bridges are vital connective elements in community transportation systems. In the past, bridges have been severely damaged by earthquakes. However, with proper mitigation techniques, such as bridge retrofit, severe earthquake damage to bridges can be avoided. Since the 1970's, design codes underwent major changes with regard to seismic analysis and design provisions of structures and bridges. Meanwhile, one third of the nation's 600,000 inventoried highway bridges are considered as either structurally deficient or functionally obsolete.;This study is a part of the "Earthquakes in Southern Nevada" project. Earlier in this project, buildings and bridges in southern Nevada were studied in order to prioritize their need for rehabilitation. This prioritization was based on a risk assessment that combines both vulnerability and importance. In this study, bridges with the highest risk scores were structurally evaluated against earthquake loads using performance-based approach. Performance-based approach was chosen for the evaluation process of the bridges as it had been recognized as an efficient and practical procedure to perform analysis and evaluation of structures. A nonlinear static procedure, specified by the Federal Emergency Management Agency, was used in the evaluation process. This procedure was modified by AlAyed (2002) for the applicability to bridges rather than buildings.;The Maximum Considered Earthquake (MCE) level was used for the evaluation of five bridges. Seismic loads were applied in two horizontal directions of each bridge: transverse and longitudinal directions. Nonlinear behavior of the bridge substructure components (columns) were evaluated and compared to the acceptance criteria. The acceptance criteria of the bridges set in this study was the Immediate Occupancy performance level, as these bridges are of high importance and are expected to be fully operational maintaining the pre-earthquake strength and stiffness of their components. Most of the evaluated bridges violated the acceptance criteria under the aforementioned level of earthquake in one or more of the analysis cases. The main two deficiencies identified in these five bridges were: (1) the insufficient flexural capacity of some columns at the plastic hinge regions and (2) the inadequate development lengths provided in the longitudinal reinforcement of the columns, either at the lap splice locations or at the beam-column joints.