Al-Mosawe, Doha
(2019)
Reliability analysis of deteriorated post-tensioned concrete bridge decks.
PhD thesis, University of Nottingham.
Abstract
During the last fifty years, there has been an increase in the development of pre-stressed highway bridges to accommodate the increasing of the road traffic. The construction of post-tensioned (PT) segmental concrete bridges is one of the most important developments in highway bridges since they represent a proven method for delivering durable bridges. The inspection of existing PT bridges
has shown that significant corrosion can occur in tendons and, eventually, lead to tendon failure. Corrosion results from, fundamentally, two phenomena: the ingression of chloride ions into partially grouted ducts and the ingression of deicing salts through the expansion points. Therefore, periodic on-site inspections are very important to ensure their safety and durability. However, it is very difficult to find visual evidence of corroded tendons and, in some locations, almost impossible. Accordingly, reliability analysis should be applied to assess the safety of PT concrete bridges with corroded tendons. The primary purpose of this thesis is to establish a framework to assess the reliability of segmental PT concrete bridges, by considering a real case study in UK. Reliability analysis methods, in particular FORM and Monte-Carlo simulation (MCS), are firstly studied and applied on a simple example of a RC beam. Then, the non-linear behaviour of concrete beams tested experimentally were modeled numerically using the Concrete Damage Plasticity (CDP) model in ABAQUS. The results were compared with the experimental data available in the literature. This work is essential because it can be considered as a calibration of the modelling approach. The modelling approach is then used to model the non-linear behaviour of the real case study. Then, FORM and MCS are integrated with a numerical model using a newly developed approach to apply time-dependent reliability analysis on a simple example of a deteriorated RC beam. The developed method connects MATLAB and ABAQUS using a Python script file, to speed up the application of reliability analysis. The proposed method helps to solve one of the main limitations in reliability analysis, computational cost. Finally, a time-dependent reliability analysis of the selected case study, Ynys-y-Gwas bridge, is carried out considering the deterioration due to corrosion of pre-stressing strands, which is the most concerning cause of PT concrete bridges degradation. The temporal and spatial variability of localized corrosion are considered through the existing time-dependent model and the uniform capacity length of the tendon according to Stewart (2004) method. The available data in the literature has been used to prepare the model and to identify the degree of corrosion in tendons. The adopted procedure shows that localized corrosion along the joints has strongly reduced the reliability of the bridge. Additionally, the reliability index after 32 years (the time of failure) is very low (near to zero) which is compatible with the observed bridge failure. The effect of bond degradation associated with localized and generalized corrosion is analysed and its effect is very significant in case of general corrosion. The most relevant variables were the model uncertainties, traffic load and the resistance moment. This method can be used to assess any identical bridges after getting the most important data (chloride concentration and degree of corrosion) from inspection.
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