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Title: Effects of extreme impulsive loads on RC structures with a view to strengthening
Author: Isaac, Philip
ISNI:       0000 0004 5351 067X
Awarding Body: University of Bath
Current Institution: University of Bath
Date of Award: 2014
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Accurately predicting the response of reinforced concrete columns to blast and impact loads is essential if structures are to be designed with sufficient robustness. The failure of load bearing columns can have devastating and costly consequences for the inhabitants of the building as history has shown. Current methods of analysis in this field tend to be either over simplified or too reliant on numerical modelling. It is shown from the literature review that significant gaps exist in our understanding of the complicated response of a member to these types of loads. Presented in this thesis is a range of theoretical modelling and experimental work aimed at addressing some of the limitations identified from the literature review. Impact tests have shown that as the rate of loading increases the failure mode can become increasingly brittle. It has also been shown that in some cases members that are designed to respond flexurally can actually fail in a catastrophic shear mode. Failure in this way can have potentially devastating consequences for a structure, leaving load bearing columns with little or no residual capacity. To address this issue this thesis presents the results of a theoretical model developed to predict the forces acting on an impacted member at the initial stage of the response. This model treats the response as a wave like phenomenon, making use of experimental data which showed that a finite time existed between an impact occurring and the supports experiencing the force. Using this theory it was shown that the initial forces generated from a higher velocity, lighter mass impact were greater than those generated from a lower velocity, heavier mass impact. This model is thought to be the first of its kind which is able to demonstrate this increasing brittleness of failure as the rate of loading increases. The second part of this thesis presents the results of a separate theoretical model, developed to predict the peak displacement of flexurally deforming members subjected to blast and impact loads. The model implicitly assumes that shear failure has been avoided, which, it was shown from the literature and through experimental testing, can be achieved through the application of externally applied fibre reinforced polymers. The model uses a plasticity based energy method to predict peak displacements and is developed predominantly for blast situations, although the extension to impact situations is also discussed. A major benefit of this approach is that the strain-rates in a section can be calculated during the analysis and employed directly to determine a sections capacity through material dynamic increase factors. When compared with the limited test data available, it is shown that this new model is more accurate than other alternative simplified analysis methods. In addition to the theoretical models developed, the results from a comprehensive range of testing, carried out using a purpose built impact test rig, are presented. In particular data for the time delay between an impact occurring, and the supports experiencing the force, were instrumental in the development of the model to predict the initial forces on a member.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available