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Abstract
Dissertation deals with the problem of fatigue changes in compressed concrete and their influence on the bridge piers from the reliability point of view. An assessment of the reliability of R/C columns as an integral part of hammerhead bridge piers, subjected to axial load and biaxial bending, is carried out in this study.
To determine if there is a dierence in safety level (and eventually how big it is) after including fatigue in the analysis, two major cases are considered. First one covers analysis of the strength of the bridge piers based on the statistical parameters available at the time of the last code preparation. Some of the available statistical data at that time was very limited, i.e. live load. In the second part analogous analysis is carried out using newer statistical parameters. Additionally in this part, influence of cyclic load caused by truck traffic passing the bridge is considered in a form of weakening of concrete internal structure expressed in statistical parameters obtained in a separate analysis. The newest available statistical parameters of all variables are used to estimate safety level (expressed in reliability index, β) of the considered element, including the fatigue influence.
Combinations of different span lengths, concrete grades, reinforcement ratios, dimensions proportions, and normalized eccentricities in two orthogonal directions were considered in order to perform the sensitivity analysis. Resistance parameters are determined on the basis of statistical data for materials (material factors) and other factors (fabrication and professional factors). The statistical parameters of resistance are obtained using Monte Carlo techniques. For this purpose complex software program is developed in MATLAB.
Based on these analyses, recommendations for modifying the design resistance factors are proposed for the safer design of the bridge piers subjected to repetitive load.
Moreover, review of analytical fatigue models for concrete is performed. Order of listed models reflects their level of advancement and complexity. All models are described and the most important mathematical expressions are introduced.
