Structural protection against the effects of a nearby explosive detonation is an area of growing importance. Spray-on elastomer coatings are of interest as a practical and low cost protective solution. Recent research has demonstrated the effectiveness of such coatings for blast mitigation. However, there are two loading scenarios of concern for these applications: blast pressures and fragment impacts. To date, there remains a need to understand the merits of this protective solution for impact indentation of concrete structural elements. In this work, we examine whether, and by what mechanism, an elastomer coating can offer protection in this case. A series of quasi-static indentation and dynamic impact experiments are performed using a 0.1 kg circular cylindrical (i.e. blunt) projectile. It is demonstrated that the coating displays a significant protective capability over the full range of impact velocities considered, c. 45 − 150 m s −1. The coating remains intact until impacted at a velocity of c.120 m s −1 when it fails by a ductile, tearing mechanism, forming a plug which undergoes large elastic contraction after projectile penetration. A finite element model of the impact indentation of uncoated and coated concrete cubes is developed and validated against the experiments. Focusing on the early time steps and damage initiation in the concrete, the numerical model is used to interrogate the mechanism by which the elastomer achieves its mitigating effect. It is found that the way in which the elastomer alters the stress distribution in the concrete, and its time evolution, is key to its performance. These findings provide a basis for optimising protective coatings for concrete structural elements.
The fluid-structure interaction (FSI) effect experienced by an elastomer-coated concrete slab subjected to blast loading in air is studied numerically. The aim is to establish whether a flexible coating alters blast-structure interactions and whether this can explain the apparent blast mitigating capability of this retrofit solution as reported in published experimental investigations. Numerical models for a typical concrete and spray-on elastomer coating are established and a Coupled Eulerian-Lagrangian (CEL) model is employed to predict the air blast response. A 1D FSI analysis suggests that the elastomer coating increases the peak compressive stress in the concrete during short timescale pressure wave interactions. But the effect on the total imparted momentum is small, across a range of target mass and blast intensity. However, due to momentum sharing, the impulse imparted to the concrete plate is reduced in the coated configuration. By extending the analysis into 2D, it is found that the displacement of a concrete slab is marginally reduced when coated on either the blastreceiving or non-blast-receiving face. Thus, it is postulated that the elastomer contributes a small, beneficial mechanical effect. Finally, the need for a fully coupled (CEL) approach to model the blast-structure interaction is interrogated. For a wide range of cases, the results suggest that using a purely Lagrangian approach, in which a pressure-time history is directly applied to the structure (thereby neglecting full representation of FSI effects), is sufficient to capture the deflection behaviour of coated concrete plates. However, it is shown that the significance of the error associated with this simplification depends on the blast intensity and slab geometry under consideration.While new buildings can be designed with higher threat levels in mind, existing structures 12 remain vulnerable if the threat level changes. Retrofitting buildings and infrastructure for 13 enhanced blast resistance is one approach to solving this problem. One particular retrofit 14 solution that has gained attention in recent years is the use of a spray-on elastomer coat-15 ing. Early experiments on masonry structures yielded encouraging results regarding the 16 elastomer's ability to contain blast debris [2, 3]. Further work on elastomer application to 17 steel plates has suggested that it is also capable of significantly reducing peak deflections 18 due to dynamic loading [4][5][6]. However, there is some debate in the literature regarding the 19 optimum coating location i.e. whether it is more beneficial to coat the blast-receiving or 20 non-blast-receiving face. Indeed, some researchers have reported that the coating can have 21 detrimental effects if applied to the load-receiving face of a steel substrate [4, 5]. 22Comparatively little work has focused on spray-on elastomers applied to a concrete sub-23 strate, despite concrete representing a significant proportion of the aging, vulnerable infras-24 2 tructure in today's built environment that could ben...
The use of a spray application elastomer coating as an effective retrofit strategy for blast and impact mitigation has gained increasing attention in recent years. Despite some encouraging studies in the literature, there remains a great deal yet to be understood, particularly regarding the coating's impact mitigating capabilities when applied to structural elements. In this work, we consider the application of a spray-on elastomer coating to the impacted face of a concrete cube. High-speed, gas gun experiments are performed on concrete cubes in their uncoated and coated configurations and it is observed that the coating provides a significant protective benefit across the range of test velocities, 45-150 m/s. Quasi-static compression and indentation experimental tests are performed on uncoated and coated concrete cubes to inform the development of a numerical model. Despite a number of modelling challenges, we validate our model against experimental measurements and conclude it provides accurate predictions of behaviour at early time steps, before the concrete becomes severely damaged. Future work will focus on using this validated numerical model as an analysis tool for understanding the mechanism by which the elastomer alters the damage response of the underlying concrete substrate.
Elastomer coatings have been found to offer protection to structural components when subjected to dynamic load cases, such as impact and blast. One such application of interest is the protection of concrete structures. Elastomer coatings have the potential to provide a cost effective and practical protective solution. The dynamic response of quasi-brittle concrete structures to blast loading is complex, with a range of dynamic response regimes. It remains to be identified in which regimes of response an elastomer coating can offer a protective benefit. Numerical and analytical modelling of thin, one-way reinforced concrete slabs subjected to varying intensities of simulated blast loading is carried out, in order to ascertain the protective effect of an elastomeric coating. Three configurations are considered: uncoated, coated with elastomer on the blast-receiving face and coated with elastomer on the non-blast-receiving face. It is found that the slab is relatively insensitive to the elastomer coating during response regimes where concrete damage is minimal. At higher load intensities, where the slab exhibits severe damage, the numerical results indicate a substantial reduction in slab deflections may be achieved by coating on the non-blast-receiving face. At the highest loading intensities, a shift in failure mechanism is observed to one dominated by transverse shear at the supports. An analytical model quantitatively predicts a substantial coating benefit in protecting against this failure mechanism.
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