Browsing by Author "Kirchner, Hugo"

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    Structural assessment of ASR-affected concrete bridge deterioration
    (Stellenbosch : Stellenbosch University, 2022-11) Kirchner, Hugo; Van Zijl, Gideon P. A. G.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: ASR has long been acknowledged as a key consideration that needs to be accounted for when designing structures in South Africa. The main purpose of this study was to inform industry practitioners of the influence of ASR on the structural behaviour of RC bridge structures within the Western Cape. It was found that the aggregate type and size plays a role in how the ASR develops over the life cycle of the structure. For this study the greywacke aggregate was found to be the most prominent component in ASR-affected structures within the Western Cape region and the structure investigated. From here, the influence of ASR on the three main mechanical properties namely, tensile strength, compressive strength, and E-modulus, were investigated and a decrease in all three properties over time was observed. A tool for decision making was developed in the form of the structural behavioural matrix, which was developed specifically for ASR-affected structures. It aims to quantify what components of the overall structural behaviour may be at risk due to ASR induced effects. This study focused on the effect of compressive strength at the ultimate limit state for the Sir Lowry’s Pass Viaduct. The overall condition of the bridge and the critical element were determined from existing reports and drawings. The South African STRUMAN BMS was utilized as a tool to form a better understanding of the service-life of a specific structure by making use of the routine field inspection reports. The critical bridge element was identified through obtaining the condition indices, crack widths, expansion index, and structural severity rating. The reduced material properties, due to the presence of ASR, were determined according to existing studies. ASR development curves for the affected elements were established. From these curves the extent of the ASR propagation could be determined. Through the available documentation the critical structural element is identified and investigated further through structural analysis. Three bridge design standards, namely the CPA (1977) and TMH7 (1981) along with the more novel WIM approach considered together with Eurocode provisions, were used to determine the maximum design bending moment and shear action and resistance. To develop a standardised approach that can be replicated on other bridge structures within the region it was decided to analyse a rectangular RC bridge deck slab. The slab was modelled according to the construction drawings along with the reinforcement detailing to subsequently obtain the ultimate shear and moment resistance of the actual element according to the CP110 (1974) code used for the initial bridge design, and current EN 1992-1-1 (2004) Eurocode standards. These designs were performed for the case of standard unaffected concrete and ASR-affected concrete respectively. Due to compressive strength being the least affected material property by ASR deterioration, the resistance to original design loads is found to be sufficient.