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The presence of air voids, moisture, and chlorides inside tendon systems on segmental posttensioned (PT) bridges has been cited as a reason for the early age corrosion and failure of strands in these bridges. This paper develops probabilistic models to predict the time-variant tension capacity of PT strands exposed to wet-dry conditions. A total of 384 unstressed and 162 stressed strand test specimens were exposed to various void, moisture, and chloride conditions for 0, 12, 16, and 21 months; the residual tension capacities of the strands were then determined. Using these experimental data, a Bayesian approach is used to develop probabilistic capacity models for unstressed and stressed strands. The tension capacities of stressed strands under potential void, wet-dry, and chloride conditions in the field are predicted using the developed models. Probabilistic time-variant models are formulated in such a way that they can be updated by other researchers using additional information from the testing of unstressed strands only, avoiding expensive and cumbersome testing of stressed strands. The mean absolute percentage errors of these models are less than 3.2%, indicating good overall model accuracy. [ABSTRACT FROM AUTHOR]

This paper provides an approach to conduct a probabilistic assessment of structural damage due to seismic events with an application to typical building structures in mid-America. The developed methodology includes modified damage state classifications based on the Applied Technology Council (ATC)-13 and ATC-38 damage states and the ATC-38 database of building damage. Damage factors are assigned to each damage state to quantify structural damage as a percentage of structural replacement cost. To account for the inherent uncertainties, these factors are expressed as random variables with a Beta distribution. A set of fragility curves, quantifying the structural vulnerability of a building, is mapped onto the developed methodology to determine the expected structural damage. The total structural damage factor for a given seismic intensity is then calculated using a probabilistic approach. Prediction and confidence bands are also constructed to account for the prevailing uncertainties. The expected seismic structural damage is assessed for three types of building structures in the mid-American region using the developed methodology. In addition, a sensitivity analysis for the probabilistic parameters is conducted. The developed methodology provides a transparent procedure where the structural damage factors can be updated as additional seismic damage data becomes available. [ABSTRACT FROM AUTHOR]

A probabilistic fatigue assessment methodology for riveted railway bridges is presented. The methodology is applied to a typical, short-span, riveted U.K. railway bridge under historical and present day train loading. On the loading side, the problem is randomized through dynamic amplification and traffic volume; on the resistance side, the S-N curves and the cumulative damage model are treated probabilistically. Model uncertainty is represented by the ratio between actual and calculated stresses, the latter obtained through finite element analysis. Annual response spectra for a fatigue-critical connection are developed through Monte Carlo simulation, which show that there is a continual and accelerating increase in the mean stress range experienced by the connection with time. S-N curves proposed in United States and United Kingdom codes are used in combination with Miner’s rule, to estimate the remaining fatigue life of the connection for different target failure probabilities. Parametric studies revealed that fatigue life estimates exhibit the highest sensitivity to detail classification, to S-N predictions in the region of high endurances, and to model uncertainty. This highlights the importance of field monitoring for old bridges approaching the end of their useful life. [ABSTRACT FROM AUTHOR]

Literature on the probability distribution function (PDF) of annual maximum flood discharges is extensive, yet the literature on the PDF of the flood of record (FOR) is sparse. This is partially due to two facts: (1) the PDF for record events is more complex than the PDF for annual maxima; and (2) data sets for observed FORs are much smaller than for the annual maximum flood series from which they derive. We show that, if annual floods arise from a generalized extreme values (GEV) distribution, then the FOR also arises from another GEV distribution, which we term GEVmax. We also derive the moments and L-moments for the PDF of GEVmax. Using record flood observations at over 1,500 basins in the United States, we compared theoretical and empirical properties of observed values of the FOR. We found that, at both regional and national scales, the FOR values are on average more extreme than would be expected if they occurred randomly, and that they tend to form spatial clusters. [ABSTRACT FROM AUTHOR]

A fragility analysis methodology is developed for assessing the response of light-frame wood construction exposed to stipulated extreme windstorms and earthquakes. Performance goals and limit states (structural and nonstructural) are identified from a review of the performance of residential construction during recent hurricanes and earthquakes in the United States. Advanced numerical modeling tools provide a computational platform for risk analysis of light-frame wood building structural systems. The analysis is demonstrated for selected common building configurations and construction (defined, e.g., by roof sheathing, truss spacing, and roof or shear wall nailing patterns). Limit state probabilities of structural systems for the performance levels identified above are developed as a function of 3-s gust wind speed (hurricanes) and spectral acceleration (earthquakes), leading to a relation between limit state probabilities and the hazard stipulated in ASCE Standard 7, "Minimum design loads for buildings and other structures." [ABSTRACT FROM AUTHOR]