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Title: Assessment of conservativeness in design of FRP-based structural strengthening systems
Author: Kansara, Kunal
ISNI:       0000 0004 5357 3654
Awarding Body: University of Bath
Current Institution: University of Bath
Date of Award: 2014
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Conservativeness (or conservatism), in general, is a measure of the lack of confidence in any activity that we do in the spheres of life. It is a reflection of our apprehension for the consequences of failure, and hence we instinctively tend to be conservative in order to be safe. Engineering design involves incorporation of various physical characteristics of the materials and systems through various mathematical models and design criteria. These models and criteria are developed based on empirically observed, experimentally measured, logically anticipated, analytically testified and/or hybrid behaviours and responses of materials and systems. All these processes invariably involve uncertainties arising from the deficiency in terms of knowledge, data and time-testimony. Uncertainties also arise from the lack of precision in expressing a phenomenon or mechanics, or from the inherent variability associated with them. All these factors lead to lack of confidence in the use of materials and systems, and compels our designs to be conservative. Comprehending uncertainties in engineering design, and refining their design treatment can pay big dividends. Design of fibre reinforced polymer (FRP) based structural strengthening systems involves an interesting interplay of uncertainties between those inherent in the existing structure being strengthened and those arising from the lack of complete knowledge and time-testimony of using FRP composites for structural strengthening. Most strengthening design guidelines tend to be more conservative than the conventional structural design norms in order to meet the safety targets. A popular approach for achieving this requirement is through prescribing a set of safety factors within the strengthening design, which are substantially higher compared to those used in structural design using conventional materials like concrete and steel. However, FRP composites in general, and their use as externally bonded reinforcement in particular, involve considerable peculiarities compared to the conventional structural materials. Also, the type and form of post-strengthening failure modes exhibit substantial qualitative distinctions compared to the pre-strengthening failure modes. Therefore, the design processes for strength (for new constructions) and additional strength (for strengthening existing structures) can have conflicting design requirements and objectives. A strategy of prescribing quantitatively higher safety factors, under this condition, could be ineffective in producing required conservativeness for some design scenarios, and can instigate undesirable side-effects. This thesis aims at assessing performance of flexural and shear strengthening design processes under the identified contradictory and contrasting features of the safety format used in strengthening design. It also provides a deeper interpretation of conservativeness in strengthening design by identifying implications of the means employed for producing conservativeness on the course of strengthening design process and on the quality of the resultant strengthening design solutions. An exhaustive review of literature, spanning over past three decades, on the design for structural strengthening using externally bonded FRP reinforcement has been carried out. This review has identified various sources of uncertainties, gap in knowledge and design conflicts associated with the mechanics of FRP-based structural strengthening systems. Detailed taxonomies of uncertainties and safety parameters concerning FRP-based structural strengthening systems have been proposed. The uncertainties are classified into constitutive and behavioural uncertainties. The former are attributed to the variability in constitutive material properties of FRP, while the latter are due deviations between the ideally expected or real behaviours of FRP composites and that predicted within the design process. It is suggested that the utility of this study can further be increased by developing an expert system based on the directions and knowledge-based presented within this study. The applicability of this study can be expanded by converting it into probability-based reliability format that can inform us on the fragility and risk profiling. It is also shown that the concept of conservativeness can also be extended to cover issues related to structural robustness and resiliency.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available