Close-in Blast Research Articles

Blast Resistance of Reinforced Concrete Slabs Based on Residual Load-Bearing Capacity.

In this paper, the blast-loading experiment and numerical simulation are carried out for RC slabs with two typical reinforcement ratios. The time history of reflected shockwave pressures and displacement responses at different positions on the impact surface of the specimens are obtained, and the influence of the reinforcement ratio on the dynamic responses and failure modes of the RC slabs is analyzed. Based on the experimental data, the simulation model of the RC slab is verified, and the results indicate good agreement between the two methods. On this basis, the residual load-bearing capacity of the damaged RC slabs is analyzed. The results show that the load distribution on the impact surface of the slab is extremely uneven under close-in blast loading. The resistance curve shape of the RC slabs varies markedly before and after blast loading, and its load bearing capacity and bending stiffness deteriorate irreversibly. Increasing the reinforcement ratio can impede crack extension, reduce the slab’s residual displacement, and, at the same time, reduce the decrease of the damaged slab’s load-bearing capacity. The findings of this study will provide insights into the anti-explosion design and damage evaluation of RC slabs.

Dynamic response of GFRP-reinforced UHPC beams under close-in blast loading

Combined use of ultrahigh-performance concrete (UHPC) with glass fiber reinforced polymer (GFRP) reinforcement has the potential for further blast resistance enhancement of reinforced concrete (RC), due to the improved toughness of UHPC and the high strength-to-weight ratio of GFRP. This paper aims to fill the gap on the effectiveness of GFRP bars on the blast response of UHPC beams. The blast resistance of UHPC beams built with GFRP bars (UHPC-GFRP beams) is experimentally and numerically investigated in this paper. In the experimental scheme, twelve beams strengthened with various types of concrete and reinforcement are tested under near-field explosions. The properties of UHPC beams reinforced with GFRP bars are compared with specimens reinforced with normal-strength steel (NSS) and high-strength steel (HSS) bars. GFRP bars reduce the maximum displacements, which enhances the blast performance of UHPC beams. However, reinforcing UHPC beams with GFRP bars results in large rebound displacements. In addition, the coupled finite element model is adopted to predict the response of test beams. The numerical method using LS-DYNA achieves reasonable accuracy. Moreover, the damage process, energy characteristics, reaction forces, stress response and the effect of the compressive reinforcement are examined to better depict the damage mechanism of the UHPC-GFRP beams.

Experimental investigation into the close-in blast performance of RC columns with axial loading

The high cost and long consuming time of field blast test result in that the experimental study on the blast performance of reinforced concrete (RC) column subjected to blast loads and axial loading is limited in the previous study which focuses on the numerical investigation. As the critical reference which is utilized to verify the accuracy of the numerical simulation, it is necessary to carry out the experimental study for the RC column subjected to close-in blast loads and axial loadings. In this study, the lateral displacement and failure characteristic of RC column with initial axial loading subjected to close-in blast loads are analyzed based on the field blast test. The influence of charge mass, detonation distance and axial load on the lateral displacement and failure mode of RC column subjected to close-in blast loads is discussed. The experimental result shows that the close-in blast loads can induce serious local damage, which is characterized as the concrete crushing at the front blast surface and concrete spallation at the rear blast surface. The decrease of scaled distance has a negative influence on the close-in blast performance of RC column, while the increase of axial compression ratio has different influences on the close-in blast performance of RC column under different scaled distances. In order to assess the damage degree of RC column subjected to close-in blast loads, the residual bearing capacity test of blast-damaged RC column is carried out. The decrease of scaled distance makes the blast damage degree of RC column transform from low damage to medium damage under the certain combination of scaled distance and axial loads. The increase of axial compression ratio makes the blast damage degree of RC column transform from low damage to medium damage under the certain combination of scaled distance and axial loads.

Damage mechanism of U-shaped ribs stiffened steel flat plates subjected to close-in explosion

The U-shaped ribs stiffened plates are widely used in civil and marine engineering structures for their high bending resistance performance. Moreover, these structures may be exposed to blast scenario especially terrorist and accidental explosions. Based on this background, this investigation carried out a study on the damage modes and the damage mechanisms of the U-shaped ribs stiffened plates subjected to close-in blast loads. The work used both field experimental and numerical methodologies. In this investigation, field blast tests were conducted on two flat plates and a stiffened plate. Furthermore, a fine numerical model was developed on the LS-DYNA platform and validated by the experimental results. Numerical analysis was conducted follow the validated model, and three typical damage modes (five detailed damage modes) of the single U-shaped stiffener stiffened plates subjected to blast loads were revealed through the numerical calculation of 40 specimens. Furthermore, a new damage number (Φ) was proposed for the classification of the damage modes. Meanwhile, maximum incident angle (α) and relative stiffness (κ) were put forward for further identification of the damage modes. It is proven that the damage modes of the single U-shaped stiffener can be well identified by the combination of damage number, maximum incident angle, and relative stiffness. Damage mode I occurred when Φ is less than Φ1 (0.042). And while the Φ is more than Φ2 (0.071), the stiffened plates exhibited mode IIIb damage. For Φ is between Φ1 and Φ2, the damage modes can be classified as mode IIa (κ < 0.0032) and IIb (κ≥ 0.0032) when α is less than 45°. While α is greater than 45°, the damage modes can be classified as mode IIa (κ < 0.001), IIIa (0.001 ≤κ < 0.0032) and IIIb (κ≥ 0.0032).

Experimental study on damage magnification effect of lightweight auxetic honeycomb protective panels under close-in blast loads

Sandwich panels/sacrificial cladding systems composed of an auxetic core sandwiched between two faceplates can be considered an effective protective measure for reinforced concrete structures from blast loads. In this study, the effectiveness of re-entrant honeycomb core sandwich (RHS) protective panel systems, which exhibit a negative Poisson’s ratio, to protect one-way simply supported reinforced concrete (RC) slabs subjected to a close-range detonation from high explosive charges was experimentally evaluated. Three large-scale field blast trials were carried out, namely an RC slab without protection as the reference test and two RC slabs with RHS protective systems under similar blast loading conditions. The RC slabs with RHS protective systems experienced catastrophic failure, unlike the unprotected reference slab that experienced only localised concrete damage. LS-DYNA numerical models were validated and agreed well with the experimental results. It was demonstrated that the transferred blast impulse to the main structure can be magnified by a factor of 1.6 by using an RHS protective system compared to an unprotected structure. Furthermore, the effect of the mass of the protective system was numerically studied. The numerical results showed that the blast protection level of the main structure is governed by the inertial resistance of the protective system rather than through energy absorption of the auxetic honeycomb core structure.

Performance of (1) concrete-filled double-skin steel tube with and without core concrete, and (2) concrete-filled steel tubular axially loaded composite columns under close-in blast

Composite structural members such as concrete-filled double-skin steel tube (CFDSST) and concrete-filled double steel tubular (CFDST) columns are increasingly being utilized in modern structures owing to their capability to integrate the beneficial properties of constituent materials to carry heavy loads as compared to conventional reinforced concrete columns. Axial compression performance of such composite columns has been extensively investigated and available in the open literature. However, their response under impulsive loadings such as those induced by explosions is not very well studied because not many investigations have been conducted on these columns. Performance of composite compression members under short-duration/high-magnitude blast loading is of considerable interest under the prevailing environment of hi-tech wars, subversive activities, and accidental explosions. The recent devastating accidental Ammonium Nitrate explosion at Beirut port (Lebanon), and the ongoing invasion of Ukraine by Russia raise the concern of researchers and engineers for the safety of structural elements/components. In this study, a 3-D finite element model of axially loaded 2500 mm long CFDSST column of ultra-high-strength concrete (170 MPa) is developed in ABAQUS/Explicit-v.6.15 computer code equipped with Concrete Damage Plasticity (CDP) model, and investigation has been carried out for its blast performance under the 50kg-TNT explosive load at a standoff distance of 1.50 m in free-air. The effects of strain rate on the compressive strength of the concrete are considered as per fib Model Code 2010 (R2010) and UFC-3-340-02 (2008). The non-linear behavior of the steel is also taken into account. Damages in the form of (1) a - concrete crushing on the explosion side of the column and b - concrete cracking on the tension side and their spread over the column length, and (2) yielding of tubes are observed. Computational results are validated with the available experimental observations. To improve the column response, the analysis has been extended to investigate the blast performance of axially loaded CFDSST columns with and without core concrete having an inner steel tube of circular/square cross-section and their response have been compared with the equivalent single skin concrete-filled steel tubular circular/square columns of same axial load capacity.

Damage behavior and assessment of polyurea sprayed reinforced clay brick masonry walls subjected to close-in blast loads

As a means to lessen the threat of an accidental blast, the polyurea sprayed reinforcement of masonry walls has attracted extensive attention. In this research, the detailed micro numerical models which can predict the nonlinear dynamic response of unreinforced clay brick masonry walls (URWs) and polyurea reinforced clay brick masonry walls (PRWs) under close-in blast were developed. The numerical simulation results were in good agreement with the field test results. Through numerical simulation and structural resistance model, the blast resistance mechanism of polyurea was revealed, and the damage behavior of polyurea rear spraying reinforced walls (PRRWs) and polyurea double-sided spraying reinforced walls (PDRWs) under different blast scaled distance was clarified. By defining the damage parameters, i.e., internal crack rate and mass loss rate, the comprehensive effects of polyurea spraying position and blast scaled distance on the damage degree of wall were summarized. Finally, the retrieval map of damage modes for PRWs under close-in blast was established, which could provide specific guidance for the anti-blast protection design of PRWs.

Evaluation of critical damage location of contact blast on conventionally reinforced one-way square concrete slab applying CEL-FEM blast modeling technique

Nowadays, accidental explosions in residential and factory buildings are common owing to poor maintenance and mishandling of fuel gas and chemical explosive appliances leading to grievous injuries and infrastructure damages. Contact blast on slabs using explosives is noticed as a simpler act of subversion as compared to other components of the building and is more damaging than a close-in blast. In general, damage caused by contact blast is localized in the form of concrete cratering, scabbing, and rupture of the reinforcement. A recently published state-of-the-art review on the performance of reinforced concrete (RC) slabs under contact and close-in explosion loading scenario by the authors (Anas et al., 2021b) reveals the common perception for the location of contact blast to cause maximum damage is the centroid of the slab. It develops a curiosity with sufficient interest to investigate the effect of the location of contact explosive charge on the damage response of the slab. Several numerical techniques such as empirical, ConWEP (semi-empirical), Smooth Particle Hydrodynamics (mesh-free method), and Coupled-Eulerian-Lagrangian (CEL) are in use for simulation of blast loading on structures. Current literature reveals that the CEL is the most advanced and realistic blast modeling technique. This study applies Coupled-Eulerian–Lagrangian (CEL) formulation with finite element method (FEM) using the dynamic computer code ABAQUS/Explicit-v.6.15 to investigate the performance of singly reinforced one-way spanning concrete slab subjected to concentric contact blast loading. The numerical model is validated with the experiment results in the open literature. The validated model is then employed to investigate whether or not the maximum damage is really caused by the central location of the contact blast. For this purpose, one-quarter of the slab with nine symmetrical points (or locations) of contact blast of explosive charge, which reflect the coverage of the entire slab, in contact with the top face of the slab is considered in the study. Two constitutive material models, Concrete Damage Plasticity and Johnson–Cook, with strain rate effects are used to simulate the non-linear behavior of the concrete and steel, respectively. The results reveal that the most critical location of maximum damage to the slab is along the line of symmetry parallel to the supports at an eccentricity of B/4 from the centroid of the slab, where “B” is the width of the one-way slab.

Damage response of high elastic polyurea coated liquid-filled tank subjected to close-in blast induced by charge with prefabricated fragments

The fuel tank related to the safety and normal operation of vehicle equipment has become a vulnerable component under the attack from conventional ammunition and terrorist explosion. It is an important subject to improve the protection ability of fuel tank against strong impact loads. In order to explore the feasibility of polyurea coating on the protection of thin-walled liquid-filled tank under the combined action of fragments and blast shock waves, a series of experiments concerning prefabricated fragment charge impacting on polyurea coated fuel tank (PCFT) under close-in blast were conducted. The results showed that polyurea can not only reduce the perforation rate and damage area on PCFT, but the excellent self-healing characteristics can also inhibit the leakage of inner liquid. The micro morphology indicated that the "self-healing" of polyurea originated from the intricate overlap of tensile deformed filaments. Meanwhile, numerical simulation was carried out to reproduce the experimental results and expand the working conditions (blast scaled distance varies from 0.096 to 0.385m/kg1/3, and polyurea thickness from 0 to 8mm). The interaction mechanism of fragments and shock waves was revealed, and the protection enhancement mechanism of polyurea was clarified together with fourier transform infrared spectroscopy. According to the summarized four types of damage modes on PCFT, the retrieval map of damage modes influenced by polyurea thickness and blast scaled distance was finally established. The research provides support for the application of polyurea on improving the impact resistance of liquid storage container.

Blast resistance of prestressed steel-grouting composite beams under close-in explosions: Experiment and numerical analysis

To increase the blast resistance of reinforced concrete or steel–concrete composite structures with long span, an innovative prestressed steel-grouting material composite beam with a hollow web is proposed. In the beam, the flange is filled with grouting material, and an I-type steel web is used to strengthen the shear capacity, and a prestressed tendon is placed in lower flange to improve the flexure resistance. The following three specimens were designed: a double hollow tube, a double tube filled with grouting material, and a prestressed double tube filled with grouting material. The specimens were tested against close-in blast, and overpressure, deformation, and strain were recorded. In order to further understand the blast-resistant performance of the beam, a finite element model was developed by commercial software LS-DYNA. A good agreement between the numerical predictions and test data was observed. It is indicated that the proposed prestressed steel-grouting material composite beam with hollow web exhibits excellent blast-resistant performance.

The Influence of Cowper-Symonds Coefficients on the Response of Stiffened Steel Plates Subjected to Close-In Blast Loads

The Cowper-Symonds relationship is the most common empirical equation used to model the influence of strain rates in steel structures subjected to blast loads. The simplicity of this relationship makes it as the preferred choice due to the minimum number of coefficients used in the equation. However, different coefficients were reported from experimental results where it was found that the coefficients could be influenced by the thickness of the specimens, types of materials and method of testing. Even so, the actual coefficients even for the same type of material such as for mild steel could be differ. It is known that strain rates effect increases the yield strength of steel, and this could reduce the maximum displacement of steel structures such as steel plates subjected to blast loads. This influence could be more significant if the steel plate was stiffened. Therefore, this study investigated the influence of Cowper-Symonds coefficients for steel plates with stiffeners subjected to close-in blast loads. The numerical investigations were performed using finite element software, Abaqus. The target plate was a 0.4 m x 0.4 m plate with 0.002 m of thickness subjected to a 0.012 kg of Plastic Explosive No. 4 (PE4) at 0.04 m stand-off distance. The influenced of stiffeners were investigate first where five stiffeners’ configurations were used and, in each configuration, the stiffeners come with different geometry ratios. Two best stiffened steel plates have been chosen to study the influence of different Cowper-Symonds coefficients. Different coefficient values of dominator, D and hardening coefficients, q was used. The results shows that any possible coefficient combinations of Cowper-Symonds relation are possible to use in predicting response of steel plates subjected to blast loads. From this study, the most ideal stiffened square steel plates for offshore platform could be identified.

Modeling the blast load induced by a close-in explosion considering cylindrical charge parameters

Structural damage is significantly influenced by the various parameters of a close-in explosion. To establish a close-in blast loading model for cylindrical charges according to these parameters, a series of field experiments and a systematic numerical analysis were conducted. A high-fidelity finite element model developed using AUTODYN was first validated using blast data collected from field tests conducted in this and previous studies. A quantitative analysis was then performed to determine the influence of the charge shape, aspect ratio (length to diameter), orientation, and detonation configuration on the characteristics and distributions of the blast loading (incident peak overpressure and impulse) according to scaled distance. The results revealed that the secondary peak overpressure generated by a cylindrical charge was mainly distributed along the axial direction and was smaller than the overpressure generated by an equivalent spherical charge. The effects of charge shape on the blast loading at 45° and 67.5° in the axial plane could be neglected at scaled distances greater than 2 m/kg1/3; the effect of aspect ratios greater than 2 on the peak overpressure in the 90° (radial) direction could be neglected at all scaled distances; and double-end detonation increased the radial blast loading by up to 60% compared to single-end detonation. Finally, an empirical cylindrical charge blast loading model was developed considering the influences of charge aspect ratio, orientation, and detonation configuration. The results obtained in this study can serve as a reference for the design of blast tests using cylindrical charges and aid engineers in the design of blast-resistant structures.

Performance of composite and tubular columns under close-in blast loading: A comparative numerical study

In the present scenario, rapid industrialization and political conflicts across the globe result rise in malicious terrorist activities in the form of blasts and explosions targeting specific civil engineering structures. Damage caused by such blast loading may be of serious consequences in terms of huge material loss and fatalities. Therefore, investigations on construction and strengthening technique to improve the blast resistance of the critical components of the structure are of considerable interest. In the present study, an experimentally tested square RC column with seismic lateral reinforcement carrying axial load subjected to an explosive charge of 100 kg ANFO (82 kg-TNT equivalent) at a scaled distance of 1.00 m/kg1/3 with 10 mm mesh size using ABAQUS/CAE software equipped with concrete damage plasticity model is considered for validation. To have the superior performance of the RC column, efforts have been made by considering eight equivalent RC columns including composite, CFST, CFST with in-plane cross reinforcement, and CFDST to the experimentally tested one under close-in blast are analyzed. The numerical models have been developed by considering equivalent peak pressure of 8.71 MPa under the close-in blast. Parameters such as maximum transverse displacement, stresses, crack depth, and damage to the columns are studied and compared. It has been found that the CFST column with in-plane cross reinforcement and the composite column with seismic reinforcement give superior blast performance under the close-in blast loading. The two superior columns are strengthened with C-FRP wrapping over the mid-height region and analyzed under the same loading. Improved performance of the columns is discussed and compared and the column giving the best performance is identified.

Performance of axially loaded square RC columns with single/double confinement layer(s) and strengthened with C-FRP wrapping under close-in blast

Very recently a new variant of reinforced concrete (RC) columns confined with a double layer of transverse steel has been introduced by researchers and investigated its performance under axial compression and seismic loading. Analysis of blast performance of such columns is of considerable interest. Most of the columns in a building structure are found to be of square or rectangular cross-section. Being axisymmetric, the circular columns perform better than square/rectangular ones under impulsive loadings. The stability of a structure supported mainly on columns subjected to such loadings depends upon the performance of the columns. Therefore, it is important to enhance the response of supporting RC compression members of square or rectangular cross-sections of a structure subjected to high intense loadings. In this research work, one 3000 mm long, 300 mm × 300 mm square RC column with conventional transverse steel carrying an axial working load of 950kN subjected to 82 kg-TNT-equivalent close-in blast loading at scaled distance 1.0 m/kg1/3 tested experimentally has been first analyzed using the high-fidelity dynamic computer code, ABAQUS/Explicit-v6.15. For comparison, another singly confined concrete column with seismic reinforcement over its entire length is also analyzed. By comparing the numerical results with the experimental results in the open literature, the accuracy of the numerical model is verified. To improve the response, doubly confined RC columns having outer transverse confining steel stirrups of square and inner ones’ diamond/circular geometry with different combinations of stirrup spacing have been considered and investigated. The columns are of the same area of compression steel and carry the same axial load (950kN). Carbon-fiber-reinforced-polymer (C-FRP) wrapping of 2 mm thickness is also considered and modeled using Hashin’s damage initiation criteria and energy-based damage evolution to investigate the blast resistance of the columns. Blast performance in terms of displacement, damage dissipation energy, concrete crushing, and cracking are compared and discussed.

Blast performance enhancement prediction of circular column with helical mesh reinforcement and strengthened with UHPFRC plaster, and CFRP wrapping under close-in blast

Blast performance enhancement prediction of circular column with helical mesh reinforcement and strengthened with UHPFRC plaster, and CFRP wrapping under close-in blast

Response of strengthened unreinforced brick masonry wall with (1) mild steel wire mesh and (2) CFRP wrapping, under close-in blast

In the past few decades, the world is experiencing a number of frequent and unanticipated blast explosions. Property loss and casualties caused by these blasts are of great concern to state authorities and are of sufficient interest to the structural engineers and researchers. A common structural member in the buildings used for both commercial and residential formats is load-bearing brick masonry walls. For the safety of a structure, the masonry walls which are more vulnerable against such loadings are required to be strengthened. Many retrofitting techniques to strengthen the masonry walls are in vogue. In the present study, a detailed micro-model of 1600 mm × 2100 mm × 240 mm (length × height × thickness) clay brick unreinforced masonry wall has been developed, analyzed, and validated with the available experiment results, using the ABAQUS/Explicit software under the 5 kg-TNT blast load at scaled distance 0.58 m/kg1/3. The Concrete Damage Plasticity (CDP) model including the strain rate effects is used to model the masonry material behavior to blast loading. To improve the response of the wall, it has been strengthened with (1) mild steel wire mesh of different thicknesses 2.50, 3.50, and 4.50 mm (i) on the rear face only, and (ii) on both the faces of the wall; and (2) carbon fiber-reinforced polymer (CFRP) wrapping (i) 0.50 and 0.60 mm thick on the rear face only, and (ii) 0.30 mm thick on both the faces of the wall. Response of the strengthened walls is discussed and compared. The equivalent thickness of the wrapping to the steel wire mesh from displacement and damage point of view has been evaluated.

Experimental and numerical investigations on ultra-high toughness cementitious composite slabs subjected to close-in blast loadings

This study investigated the dynamic response of one-way square ultra-high toughness cementitious composite (UHTCC) slabs under close-in blast loadings. Six UHTCC slabs and two ordinary concrete slabs with dimensions of 600 mm × 600 mm × 60 mm were subjected to blast loadings at scaled distances of 0.043 m/kg1/3, 0.085 m/kg1/3, 0.136 m/kg1/3, 0.271 m/kg1/3, 0.407 m/kg1/3 and 0.356 m/kg1/3 by varying both charge and distance to the slab. The results indicate the UHTCC displayed better blast resistance performance than the ordinary concrete. Under 200 g TNT blast loadings, the UHTCC slabs presented breaching damage and several cracks and could still bear the load, while the ordinary concrete slabs were broken severely and could not bear load anymore. The existing empirical formulae, including McVays’ and UFC 3-340-02, were employed and discussed to predict the failure modes of UHTCC slabs under blast loading. And a formula was proposed to estimate the residual load-carrying capacity of UHTCC slabs and was fitted well with the experimental data. Furthermore, Finite Element (FE) models were developed to study the dynamic response of slabs in LS-DYNA. The findings of this study indicate that the UHTCC has good potential for the constitution of protective structures.

Performance of an auxetic honeycomb-core sandwich panel under close-in and far-field detonations of high explosive

This paper aims to scrutinise the effectiveness of a re-entrant auxetic honeycomb-core sandwich panel (AHSP) to protect reinforced concrete (RC) slab under close-in and far-field detonations of high explosive. A series of quarter symmetric 3D comprehensive numerical models were developed by using Arbitrary Lagrangian Eulerian (ALE) formulation in LS-DYNA hydrocode. Strain rate effects of the rate sensitive materials were employed in the model to consider dynamic behaviour of the materials during blast loading. The developed numerical model was validated with the documented experimental results. Deformation patterns, energy absorption, overpressure damping, blast pressure deflection, and stress-transmission to the protected structure were investigated with the computational models. Furthermore, the performance of AHSP sacrificial protective structure was compared with an equivalent areal density conventional honeycomb-core sandwich panel (CHSP) structure. The results showed that AHSP not only absorbed higher blast energy but also acted as a pressure deflector by forming a densified concave depression under close-in blast load. AHSP damped higher magnitude of blast overpressure in both close-in and far-field blasts. Moreover, a uniform redistribution of the stress on the protected structure was observed with AHSP protection. The overall response of AHSP was found to be better than CHSP to protect the RC slab.

Experimental study of reinforced UHDC-UHPC panels under close-in blast loading

Ultra-high ductile concrete (UHDC) has excellent tensile ductility, and ultra-high performance concrete (UHPC) possesses ultra-high compressive strength and hardness. It is expected that the combination of UHDC and UHPC should possess better blast-resisting capacity. This paper presents the dynamic performance of reinforced UHDC-UHPC panels under close-in explosion. Four reinforced UHDC-UHPC panels with different steel ratios were tested at scale distances ranging from 0.5 m/kg1/3 to 0.8 m/kg1/3. These panels show excellent resistance to local damage. Concrete cratering and punching failure on the UHPC surfaces are almost eliminated, and only multiple micro-cracks (no more than 100 μm) occur on the UHDC surfaces. The numbers of micro-cracks appeared on the UHDC faces decrease from 391 to 125 with the increase of scale distance. And with decreasing steel ratio, micro-crack number increases from 271 to 937. Moreover, maximum displacement and residual displacement decrease with increasing scale distance or steel ratio. The velocity and average acceleration in nonlinear state increase with decreasing scale distance, and the natural period and damping ratio in linear state reduce as damage level decreases.

Numerical and experimental study of externally reinforced RC slabs using FRPs subjected to close-in blast loads.

The use of woven Fiber Reinforced Polymer (FRP) as strengthening material on full-scale Reinforced Concrete (RC) slabs was studied in this paper. Carbon (CFRP) and E-glass (GFRP) fibers were tested for comparison. The specimens of the trials were subjected to blast loads at scaled distances of 0.83 m/kg1/3, 0.42 m/kg1/3 and 0.21 m/kg1/3, varying both charge and distance to the slab. Furthermore, Finite Element (FE) numerical models have been developed to study, in-depth, the response of the structural elements. A non-reinforced slab facing the highest scaled distance has been used as calibration test. It was monitored with pressure gauges and accelerometers, obtaining errors of around 2% and 5%, respectively, compared with the models’ predictions. Seven other trials were carried out and used as validation tests. The explosive charge model was developed using the *LOAD_BLAST_ENHANCED (LBE) tool available in the LS-DYNA software. Two concrete material models have been tested, CSCM and RHT, achieving better results with the first one. To model the FRP reinforcement, *MAT_058 (LAMINATED_COMPOSITE_FABRIC) was used. Applying CFRP resulted in a generally reduced damage area on both surfaces especially at intermediate scaled distances. Concerning the specimens reinforced with GFRP, further investigation needs to be conducted as the field test outcomes were not entirely conclusive due to the bonding of the fiber on concrete. The experimental results were closely reproduced with the developed numerical models, with errors in terms or surface damage below 15%.