| Popis: |
Concrete is a commonly used construction material in both civil and military infrastructures. Over the last few decades, it has been widely demonstrated that the use of externally bonded fibre reinforced composites (FRP) is an efficient technique to strengthen such infrastructures to resist increased static loads for which they were not designed for. Nevertheless, the use of these techniques for improving the blast capacity of reinforced concrete (RC) structures has only recently been studied. Although such studies have highlighted an effective enhancement of the bearing capacity of RC members under explosions, no particular attention has been paid to the influence of blast loading on the performance of the bonded interface. This work presents a set of experimental campaigns to investigate and quantify the influence of blast loading on the structural resistance of FRP strengthened concrete structures with the focus on the performance of the bonded joint. Primarily, this research experimentally examines the quasi-static and blast performance of RC beams with externally bonded FRP strips. Experimental findings reveal that although the structural performance is comparable between both loading cases, the failure mechanism of FRP is different. Finite element models are developed and calibrated against experimental data and used to investigate in detail the reasons behind such difference. Secondly, a combined experimental/numerical investigation is performed on the influence of externally bonded FRP strips on the damage extent of concrete subjected to contact detonations. Twenty-seven contact detonations were conducted on concrete plates to verify the influence of bonding area, mass of attached material and concrete strength. Results reveal that FRP strips have a clear influence on the damage extent of concrete. By developing a finite element model of the experimental setup, it is found that the combination of momentum transmitted to the FRP together with the bonding effect gives rise to a complementary damage mechanism, leading to larger damaged areas. Additionally, current analytical methods to predict the structural performance of RC structures under blast loading, such as the single-degree-of-freedom, rely on the assumption that full bond is kept upon the structural failure, and as such are inadequate at providing a valid prediction of structural performance when disruption of FRP is an issue, as this directly influences the establishment of force-deflection characteristics of the member. To this end, commonly accepted design approximations for the establishment of force-deformation characteristics are discussed and an innovative method is proposed. SDOF analysis are conducted using the different modelling approaches and results are compared and discussed against experimental data. This PhD thesis highlight the complex behaviour of concrete structures strengthened with externally bonded FRP under blast loading, mostly when disruption of FRP is achieved, and should dissipate the idea that a design is accurate if disruption of FRP is neglected. This research can also be used by engineers to determine the likely effect that the disruption of FRP will have on the overall structural performance of RC structures. |
