Search

Abstract: Deterioration of concrete structures caused by corrosion have caused worldwide concerns especially for pre-stressed concrete (PC) structures because of their extensive use in important infrastructure, such as highway bridges. PC girders that have been in service for a long time in natural environment are highly susceptible to various corrosion-induced deteriorations, which can in turn affect the structural behaviour of PC girders. Therefore, it is important to understand and quantify the corrosion effects on the flexural and shear behaviours of PC bridge girders. In parallel with the experimental testing of the PC girders salvaged from a decommissioned 28-year old bridge, this thesis aims to take an analytical approach to investigate the residual performance of PC girders with various deteriorations. In this thesis, two-dimensional (2D) non-linear finite element (FE) method was used to model the flexural and shear behaviour of concrete beams/girders, and relevant modeling strategies were first validated using experimental tests of reinforced concrete beams with artificial corrosion defects. After that, 2D FE models for PC girders were developed to study the flexural and shear behaviours of corroded PC bridge girders. A 2D FE model was developed for the PC girder #1, which was in a visually intact condition, and it was firstly used to back-calculate the possible pre-stress loss (30% - 40%) in this PC girder as a preliminary forensic analysis. This was verified by the 2D FE models for the flexural and shear girder tests, as well as the one-dimensional beam model using fibre-based beam elements for the flexure test. The 2D FE models were validated against the tests to be capable of predicting both the flexural and shear behaviour of PC girders. The validated 2D FE models were then used to conduct comprehensive parametric studies for both flexural and shear critical girders, respectively, focusing on the corrosion effects on the structural behaviour (e.g., stiffness, residual strength). The deterioration features considered in the parametric studies include pre-stress loss, the steel cross-sectional area loss, material degradation, concrete spalling, and complete or intermediate loss of bond between steel and concrete, which were all related to corrosion degrees. It was found that the pre-stress loss, the steel cross-sectional area loss, and bond loss played significant roles on the residual capacities of corroded PC girders. In contrast, the material degradation and concrete spalling on the tension side played less role on the residual load bearing capacities. Based on the parametric analysis results and the FE modeling of girder #1, the 2D models were used to understand the possible deteriorations inside other corroded girders (i.e., girder #2) with severe corrosion or to predict the behaviour of other girders (i.e., girder #3). The models provided fairly good results for both flexural and shear behaviour of girders under different deterioration levels. Eventually, to further understand the effect of corrosion on the capacity of PC girders, the FE models for corroded girders were integrated with probabilistic analysis algorithms (e.g., subset simulation) to study the residual capacity of PC girders. The probabilistic capacities for specific corrosion scenarios with three different corrosion degrees (0%, 10%, and 30%) were compared. It is found corrosion affects both the mean and variance of the residual capacities of PC girders, especially for high corrosion degrees (e.g., 30%).