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The article discusses the study which presents a new technique for strengthening concrete beams and girders for aging structures. It includes the analytical formulation of equations to determine the adjustments in the load-carrying capacity of simple-span beams that needed to be strengthened. It cites the rehabilitation project of the Pier 39 parking structure in San Francisco, California where the post-tensioned beams were strengthened by external post-tensioning.

Damage fragilities describe the probability that a bridge will incur certain (discrete) damage states conditioned on the intensity of the earthquake it may experience. Reinforced concrete box girder highway overpass bridges are prevalent among the total inventory of bridges in California. For this class of bridges, a method for computing damage fragilities for three damage states (concrete cover spalling, longitudinal bar buckling, and column failure) based on the bridge force reduction factors (R-factors) is derived in this paper. Bridge damage fragilities are described by equations relating the median intensity and uncertainty of ground motion to discrete damage states of column concrete cover spalling, column bar buckling, and column failure using the bridge R-factor as the principal parameter describing the bridge structure. Such damage fragility equations are furnished for earthquake intensities measured using pseudospectral acceleration (Sa) and cumulative absolute displacement (CAD) in both the bridge longitudinal and transverse directions. [ABSTRACT FROM AUTHOR]