New technique to protect RC structures against explosions

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Numerical analysis of small-scale concrete beams strengthened with CFRP under impact loading

Reinforced concrete structures are vulnerable to impact loads (e.g. rock-fall, vehicle collision or ship impact) during their service life. It is of interest to understand the impact load behaviour of reinforced concrete and its potentially catastrophic failure. This paper presents a preliminary study, on small-scale reinforced concrete beams strengthened with carbon fibre reinforced polymer (CFRP) under low-velocity impact. This study comprises both experimental work, making use of a drop-weight set-up, and a non-linear finite element model (FEM). The FEM was validated using the results achieved from the experiments. On overall, the simulation yielded promising results in a consistent prediction of the displacement and failure behaviour mechanism, though further sensitivity analysis is needed with respect to the modelling of the specimen boundary conditions. In line with observations in literature, the CFRP strengthening of the test specimens demonstrated to be an effective technique to improve the resistance of the reinforced concrete beams under impact load

Low-velocity impact behaviour of plain concrete beams

Concrete structures are designed and constructed to serve their anticipated service life, generally with minimal consideration of accidental loads such as impact or explosion. The behaviour of reinforced concrete structures under impact loads has been widely discussed in the last decades, however, there are few studies on the behaviour of plain concrete under impact loading. This paper presents a finite element model of plain concrete beams using nonlinear finite element analysis. The numerical results are compared to experimental data taken from an existing study. The experiments consist of drop-weight tests with varying drop-heights. A parametric study is conducted with respect to the concrete material model and mesh size of elements in order to fine-tune the model and to understand the dynamic response of the beam under low-velocity impact load

Numerical analysis of debonding between CFRP strips and concrete in shear tests under static and blast loads

The present paper deals with the finite element (FE) analysis of the bond slip between concrete and carbon fiber reinforced polymer (CFRP) strips in a single bond shear test under static loads and in a double bond shear test under blast loading. A plastic damage material model and an elastic material model are used to model the concrete prism and the unidirectional CFRP strip, respectively. The bond interface between concrete and CFRP strip is simulated using a cohesive bond model. For the static loads, the numerical model is validated with experimental tests available in the literature. The debonding failure mode, the delamination loads and the strain distribution along the CFRP strip are predicted. The numerical results show a good agreement with the experimental data using the cohesive bond model. For the blast loads, the validated cohesive bond model is used. A parametric study with respect to the width and the length of the CFRP is conducted. Moreover, the reflected pressure and impulse are varied to highlight the effect of the propagation of the blast wave in the debonding process under blast loads

Numerical analysis of retrofitted RC slabs with CFRP strips under blast loading

This paper investigates the effectiveness of carbon fiber reinforced polymer (CFRP) as externally bonded reinforcement (EBR) to improve the flexural resistance of reinforced concrete (RC) slabs under blast loads. Three simply supported RC slabs are subjected to blast loading using an explosive driven shock tube (EDST). The obtained experimental results of the RC slabs without and with EBR are presented and discussed with the aim of evaluating the influence of EBR on the blast response of the RC slabs. A numerical analysis is carried out using the finite element software LS-DYNA to complement the experimental results. The bond interface between CFRP strips and concrete is simulated with a specific contact algorithm including the normal and shear stresses at the interface with failure criteria. The numerical analysis shows good agreement with the experimental results for the maximum deflection at the mid span of the slabs and good prediction of the distribution of cracks. CFRP strips as EBR increase the flexural capacity and the stiffness of the slabs. A reduction in the blast induced maximum deflection is recorded for the slabs retrofitted with CFRP strips

Blast response of RC slabs with externally bonded reinforcement under two independent explosions

The use of carbon fiber reinforced polymer (CFRP) as externally bonded reinforcement (EBR) for strengthening reinforced concrete (RC) structures that are loaded by a blast wave is confirmed as an efficient solution. This in addition to other advantages of CFRP such as high tensile strength, light weight and durability. This paper aims to investigate the blast response of reinforced concrete (RC) slabs retrofitted with carbon fiber reinforced polymer (CFRP) as externally bonded reinforcement (EBR) under two independent explosions. In order to achieve this objective, four simply supported slabs were tested using an explosive driven shock tube (EDST) to generate a reflected pressure equal to 3 MPa in the first explosion and a reflected pressure equal to 7.5 MPa in the second explosion. Digital image correlation (DIC) is used to measure the strain evolution in the concrete and the CFRP strips during the first explosion. The slabs retrofitted with increasing the quantity of fibers show a reduction in the residual deflection after two independent explosions. The results show that for the first explosion, EBR increases the flexural response and the stiffness of the RC slabs. In the second explosion, a total debonding of the CFRP strips occurs and initiates from the midspan of the slabs toward the supports. When the total debonding of the CFRP strips occurs, the strain distribution in the steel rebars are the same for all slabs regardless of the quantity of applied EBR

New technique to protect RC slabs against explosions using CFRP as externally bonded reinforcement

In recent years, numerous explosions related to industrial accidents and terrorist attacks causing loss of life and severe damage to infrastructures have occurred all over the world. However, existing reinforced concrete (RC) structures are not designed to resist blast loads and could collapse after the incident. As a consequence, the emerging challenge of critical infrastructure protection has been recognized and nowadays there is a desire to upgrade the blast resistance of existing RC structures. The present paper provides an experimental and numerical analysis of the efficiency of using carbon fiber reinforced polymer (CFRP) as externally bonded reinforcement (EBR) on RC slabs under blast loads to increase the flexural resistance of the structure. Moreover, the effect of the propagation of the blast wave within the retrofitted specimens and how it affects the bond interface between the CFRP strip and concrete during the blast loading is discussed