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https://nap.nationalacademies.org/catalog/27432/critical-issues-in-transportation-for-2024-and-beyond

SEISMIC FRAGILITY OF EXISTING CONVENTIONAL REINFORCED CONCRETE HIGHWAY BRIDGES

Seismic fragility is estimated for an existing conventional reinforced-concrete highway bridge using nonlinear-dynamic finite element analysis. The bridge selected for analysis is the Meloland Road Overcrossing located near El Centro, California. It is representative of a large class of two-span continuous bridges in California and other locations in the United States. The column supporting the deck is assumed to govern the damage state for the entire bridge. The column is about 20 feet high and has an outside diameter of 5 feet. Flexure is assumed to be the critical damage mode for the column. The fundamental response modes of the bridge affecting this damage mode involve a three-dimensional interaction between deck flexure/torsion and column flexure. A beam-column damage element is used which allows for such an interaction between the column element and the plate elements used to represent the multi-cell hollow box girder deck. The column element uses a practical fiber modeling approach that models the basic kinematic interaction between axial force and biaxial bending moments using one-dimensional nonlinear constitutive relations that require only a few basic stress and strain parameters. Confinement effects are specified through the concrete parameters and an effective dimension for the confined zone. The constitutive relations consist of envelope curves and loading/unloading rules which permit time and load-path dependent modeling of key damage mechanisms including concrete cracking, concrete crushing, concrete spalling and reinforcing steel plasticity. The damage element is first shown to adequately predict the capacity and ductility of cantilever specimens tested by others without showing sensitivity to either scale or geometry effects. The selected bridge is then analyzed using the damage elements. By tuning the elastic moduli for the deck plate elements to match measured frequencies for the bridge under the moderate seismic event, a fixed-base model is able to predict acceleration time history records for the event. A soil-structure interaction model is developed from the fixed-base model by adding lumped spring and lumped mass effects of the foundations at the abutments. The predicted column base moments of the soil-structure interaction model are shown to be in excellent agreement with the fixed-base model considering the complexities of the foundation response. Artificially generated random motions are input to the soil-structure model to predict damage response over a range of input intensities. A damage index analogous to interstory drift is computed and is shown to correlate well with peak ground acceleration of the simulated time histories. Fragility curves are computed on the basis of linear regression analysis of the simulated data. The effect of span length on the curves is examined using the identical time histories applied to replicas of the bridge proportioned according to California Department of Transportation design guidelines.

Language

  • English

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Filing Info

  • Accession Number: 00758977
  • Record Type: Publication
  • Report/Paper Numbers: Technical Report, NCEER-97-0017
  • Files: NTL, TRIS
  • Created Date: Jan 29 1999 12:00AM