Literature review on blast protection by externally bonded FRP reinforcement

One of today’s state-of-the-art techniques is the use of Fibre Reinforced Polymer (FRP) composites as Externally Bonded Reinforcement (EBR). This method consists in gluing strips or flexible sheet in the tension zone to increase the resistance capacity or service behaviour of structures. The use of FRP as externally bonded reinforcement has been demonstrated as a very efficient technique mainly for static load conditions. More recently, a number of studies have also been conducted regarding the use of FRP EBR for strengthening critical infrastructure (concrete and masonry) against blast loading. This paper presents a brief literature review of research on FRP EBR and blast loading and describes the efficiency of FRP composites for blast protection

New technique to protect RC structures against explosions

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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

Experimental study of blast response of RC slabs with externally bonded reinforcement

The present paper discusses experimental work on the efficiency of externally bonded reinforcement (EBR) on reinforced concrete (RC) slabs under blast loads using an explosive driven shock tube (EDST). This study focuses on four tests which have been performed on simply supported RC slabs retrofitted with carbon fiber reinforced polymer (CFRP) strips and subjected to explosions for the same pressure and impulse. Pressure transducers are fixed at the end of the tube to measure the pressure of each experiment. Maximum deflection and strain distribution in the concrete and CFRP strips are recorded using digital image correlation (DIC) measurements. Due the explosion, the RC slabs are submitted to a dynamic vibration in both directions and during the first inbound displacement phase, the kinetic energy of the retrofitted specimen is stored as elastic strain energy in CFRP strips. All this elastic strain energy stored in FRP strips is violently released as kinetic energy during the rebound phase of the slab. The results indicate that EBR increases significantly the flexural capacity and the stiffness of RC slabs under blast loads

Numerical modelling of the debonding between CFRP strips and concrete in shear tests under static loads using different approaches

The present paper deals with the finite element (FE) analysis of bond slip between concrete and carbon fiber reinforced polymer (CFRP) strips in a single pull-out test under static loads. The commercial software LS-DYNA is used to simulate the test set-up using a plastic damage material model and an elastic material model for the concrete prism and the unidirectional CFRP strip, respectively. The bond interface between the concrete and the CFRP strip is simulated following three different approaches using a perfect bond model, a cohesive bond model and contact algorithms based on recently developed proposed bond slip models. The numerical model is validated based on experimental test results available from literature. The debonding failure mode and the delamination loads of the CFRP strip are predicted. The numerical results show a good agreement with the experimental data using the cohesive bond model. The perfect bond model gives an overestimation of the delamination loads and of the damage distribution in the concrete prism

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

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

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