Contact Detonation Research Articles

Response of structural elements of temporary wooden bridges subjected to contact detonation

Response of structural elements of temporary wooden bridges subjected to contact detonation

Secondary debris resulting from concrete slabs subjected to contact detonations – Spatial velocity distribution and influence of steel fibers

Secondary debris resulting from concrete slabs subjected to contact detonations – Spatial velocity distribution and influence of steel fibers

Experimental and numerical study of G-HPC slabs rapidly repaired by G-HPC canvas and G-UHPC under contact detonations

The rapid repair of engineering structures damaged due to explosions can enhance the structural impact resistance after an explosion, thereby reducing the potential for casualties and property losses. A novel concrete canvas was firstly proposed based on G-HPC (geopolymer-based high performance concrete), UHMWPEWF（ultra-high molecular weight polyethylene woven fabric), and 3D BFG (basalt fiber grid) to rapidly repair engineering structures and render their blast resistance. A sequence of contact blast tests was systematically conducted to verify the feasibility of the proposed G-HPC canvas. A normal reinforced concrete slab and a steel-wire mesh (SWM) reinforced G-HPC slab were initially damaged by the contact blast loading, afterwards, the damaged concrete slabs were rapidly repaired by G-UHPC (geopolymer-based ultra-high-performance concrete) and the novel G-HPC canvas. The rapidly repaired concrete slabs were subsequently tested by contact blast loading. A precise 3D finite element model was then developed and calibrated based on the experimental results. Eventually, numerical simulations were performed to better understand the contribution of main parameters including repair materials filling the internal slab, steel-wire mesh, G-HPC canvas location and its thickness towards the improvement of the rapidly repaired slabs against the contact blast loading. The experimental and numerical results indicated that the SWM reinforced G-HPC slab has superior blast-resistance compared with the RC slab and the proposed method to rapidly repair the damaged slabs was feasible. The G-HPC canvas should be placed properly since the location of the G-HPC canvas is related to whether fragments are produced on the rear surface of the damaged slab. Increasing the G-HPC canvas thickness and the layers of SWM could significantly reduce the damage area of the repaired slab.

Blast Resistance of SIFCON against Contact Detonation and Development of a Blast-Resistant Member using SIFCON

Blast Resistance of SIFCON against Contact Detonation and Development of a Blast-Resistant Member using SIFCON

Local damage of precast concrete columns with grout sleeve connections under contact detonation

Over the past several decades, the global terrorism is looming large and public buildings have become targets of terrorist bomb attacks. To obtain the blast performance of precast concrete (PC) columns with grout sleeve connections at the background of terrorist attacks, the contact detonation is concerned in this paper. An experimental program with six PC columns and one reinforced concrete column against contact detonation was conducted in a blast testing vessel, in which the effects of charge weight and location as well as connection type of columns on blast damage were studied. Then the finite-element-based (FE) numerical models were built up with LS-DYNA and validated with comparison of experimental results. In the FE model, blast load is simulated using multi-material Arbitrary-Lagrangian-Eulerian (MM-ALE) algorithm. After careful validation, the numerical models are extended to conduct parametric studies, including the effects of longitudinal and transverse reinforcement ratio, column section depth (or aspect ratio), charge weight and location, axial compression ratio on the blast damage of PC columns. Finally, curve-fitting-based models are derived to build up relationships between local damage sizes and the studied parameters, and then verified with part of numerical results. The results show that contact detonation destroyed all the concrete cover at the front face supporting the charge, and resulted in severe spall damage along the four corners and side faces, in which the corner connecting the side and rear face suffered larger damage than that connecting the side and front face. Moreover, the grout sleeves are able to mitigate the damage if the detonation is at the splicing segments. Increasing reinforcement ratio, section depth and axial compression ratio are able to reduce damage sizes, but the beneficial effect differs for the local damage at the column corners and front face.

Secondary debris resulting from concrete slabs subjected to contact detonations

As a consequence of terrorist attacks with explosives and malfunction of machinery detonations can lead to secondary debris on the protective side of a concrete wall. The term secondary debris in this context describes the debris resulting from a breakup of the loaded concrete structure in contrast to primary debris which results from the explosive or its casing. A test series has been conducted in order to investigate the physical phenomenology of the damaging process. A total of 15 reinforced concrete slabs with scaled thicknesses between 1.6 and 2.8 cm g−1/3 were loaded by contact detonations. The protective side of the concrete slabs was recorded with high-speed cameras during testing, and the damaged concrete slabs were measured with 3D-scans afterward. The acquired data will be evaluated for the velocity and mass of the secondary debris, to build the basis for an empirical model, which can make predictions about the occurring secondary debris. The objective of this paper is, to present the conducted experiments and propose the first part of an empirical model. This model predicts the geometry of the spalling crater on the protective side of the concrete slab, as well as the maximum velocity of the secondary debris. In following papers, the correlation between the mass and the velocity of the secondary debris will be derived from numerical simulations. With this, predictions can be made about the effects of the secondary debris on humans and installations on the protective side of the concrete slabs.

Blast-induced dynamic responses of reinforced concrete structures under progressive collapse

To study the response of reinforced concrete structures under progressive collapse induced by an actual blast event, an experimental programme on reinforced concrete frames subjected to contact detonation was conducted. The tested structure included a double-span beam with a middle joint, side columns and beam extensions connected to external restraints. The experimental programme employed similar geometry, reinforcing arrangement, material properties and boundary restraints from previous quasi-static as well as free-fall dynamic test series, which focused on the effects of horizontal restraint conditions on the mobilisation of catenary action. Compared to the corresponding static and free-fall tests conducted previously, the blast-induced tests simulated the condition of a progressive collapse event triggered by an explosive charge which is close to actual accidental/terrorist situations. As a result, initial effects/damages created by the initial blast effects – that is uplift of the double-span beam and blast pressure on beam and column – were witnessed and well captured. Damage patterns and failure modes from the blast tests were compared with those from related quasi-static and free-fall tests to emphasise the actual behaviour of structures under realistic explosive attacks. Finally, the blast tests also indicated the limitations of some simplified dynamic assessment methods when applying the single column removal assumption.

Field tests of fiber reinforced concrete slabs subjected to close-in and contact detonations of high explosives

This paper presents an experimental research to study the behavior of fiber-reinforced concrete slabs with varying fiber volume and type, subjected to contact and close-in detonations. A total of 25 full-scale blast tests were carried out. The results are analyzed, discussed and compared to fast-running tools. For the close-in detonations, the damage was manifested by a global flexural response and the fiber volume did not affect slab performance. For the contact blasts, localized damage in the forms of cratering, spalling, and in some cases perforation, was observed. For these tests, increasing fiber volume was found to improve slab performance.

An analytical model to predict spalling and breaching of concrete plates under contact detonation

Under contact and close-in detonation, severe local failure is commonly observed on concrete elements and structures. So far prediction tools are available as empirically-based design diagrams, PC tools through replication scaling, or as physics based Finite Element Models (FEM). The last tool requires significant computational efforts and expertise from the modeler. As a fast and physics-based alternative, an analytical model is proposed in Tu et al.’s work [1], to quantitively predict compressive damage forming on the impacted face. In this paper, subsequent studies are conducted to (1) predict spalling damage size on the rear face and (2) predict whether concrete plates are breached by contact detonation. The analytical predictions are validated against a range of experimental data from published references. Good agreement shows the capability of the proposed model in effectively predicting local damage size and breaching of concrete plates subjected to contact detonation.

Concrete plates with externally bonded FRP under contact detonations

Local damage on concrete elements subjected to a contact detonation include spalling and cratering of the back and front face, respectively. This paper presents the results of a detailed experimental and numerical methodology aiming to analyse the influence of externally bonded fibre reinforced polymers (FRP) on the spalling phenomena of concrete when it is subjected to contact explosions. The influence of externally bonded reinforcement (EBR) on the diameter and depth of the spalling is experimentally investigated, as is also the total momentum transferred to the ejected fragments when their mass increases. The experimental observations enable the development of a computational framework, where a finite element (FE) model is validated and used to perform a through-thickness analysis focused on the stress wave propagation and associated damage mechanisms. It is found that the extent of concrete volumetric damage is highly influenced by the mass of the bonded material, as well as increased bonded areas leading to enlarged surface damage. Additionally, it was verified that the compressive strength of concrete plays a major role in the spall damage.

Experimental and numerical investigations on performance of reinforced concrete slabs under explosive-induced air-blast loading: A state-of-the-art review

Rising fanaticism and rapid industrialization across the globe make the structures more vulnerable to direct threats generated from accidental and explosion-induced air-blast loads. Unlike the response of the reinforced concrete structure under quasi-static loading, it may respond in a brittle manner with highly localized failure like scabbing, cratering, spalling, and crushing of the concrete as well as rupturing of the reinforcement under the near field or contact detonations. Large deflection and high stresses could cause irreparable damage or result in the failure of critical structural elements. Besides, high-speed secondary fragmentation resulting from spalling of concrete may cause injuries to the occupants and other damages in the detonation area. It is therefore important to have a better understanding of the structural response/damage under air-blast loadings. This paper provides a comprehensive review of major (over twenty) publications addressing the blast response of the reinforced concrete slabs. First, the phenomenon of spall damage in the slab and the parameters affecting it are discussed. Then, available experimental investigations on slabs have been reviewed and different damage/failure modes of the slabs exposed to contact or close-in detonations are presented. The damage in the slabs has been observed in the form of spalling of concrete, the formation of punching crater, concrete scabbing/crushing, flexure-shear failure, flexural failure, bending-punching failure, and development of longitudinal, transverse, and radial cracks. Next, numerical modeling of the slabs using various material damage models available in different finite element programs has been discussed by reviewing the numerical /analytical investigations under air-blast loading. It is noted that the vast majority of the papers focused on improving the blast resistance of the slabs using different strengthening techniques. Finally, the major findings and other aspects that need to be considered for subsequent research are discussed.

Experimental and numerical studies of tubular concrete structures subjected to blast loading

The E39 coastal highway route along the west coast in Norway is envisioned a future without ferries. A submerged floating tube bridge built in concrete has been suggested as a means of crossing wide and deep fjords, and an internal blast load against this structure could have disastrous consequences. To investigate the response of tubular concrete structures subjected to blast loading, standard off-the-shelf concrete pipes were tested using live explosives. The tests were monitored by high-speed cameras and pressure sensors. Three different positions for the explosive charges were used and the charge size was varied for each position. It was found that a contact charge detonated from the outside requires approximately twice the explosive amount to breach the pipe than a contact charge detonated from the inside, suggesting a significant confinement effect. Charges placed in the centre of the cross-section produced longitudinal cracking and fragmentation. Measurements show that the pressure inside the pipe is notably higher than immediately outside. As one would expect, reinforcement increased the blast capacity of the pipes significantly. Material test specimens (cubes and cylinders) were cut from the pipes and tested quasi-statically to determine the mechanical properties. The material tests were used to calibrate a concrete material model for finite element simulations, where the blast load was described by a particle-based method. The structural response from the simulations showed good agreement with the experimental data. This applied to the contact charges as well although no special measures were taken to account for the contact detonation.

A Comparative Study on Blast-Resistant Performance of Steel and PVA Fiber-Reinforced Concrete: Experimental and Numerical Analyses

This paper deals with the blast-resistant performance of steel fiber-reinforced concrete (SFRC) and polyvinyl alcohol (PVA) fiber-reinforced concrete (PVA-FRC) panels with a contact detonation test both experimentally and numerically. With 2% fiber volumetric content, SFRC and PVA-FRC specimens were prepared and comparatively tested in comparison with plain concrete (PC). SFRC was found to exhibit better blast-resistant performance than PVA-FRC. The dynamic mechanical responses of FRC panels were numerically studied with Lattice Discrete Particle Model-Fiber (LDPM-F) which was recently developed to simulate the meso-structure of quasi-brittle materials. The effect of dispersed fibers was also introduced in this discrete model as a natural extension. Calibration of LDPM-F model parameters was achieved by fitting the compression and bending responses. A numerical model of FRC contact detonation was then validated against the blast test results in terms of damage modes and crater dimensions. Finally, FRC panels with different fiber volumetric fractions (e.g., 0.5%, 1.0% and 1.5%) under blast loadings were further investigated with the validated LDPM-F blast model. The numerical predictions shed some light on the fiber content effect on the FRC blast resistance performance.

Effects of Fiber Type on Blast Resistance of Slurry-Infiltrated Fiber Concrete Under Contact Detonation

Effects of Fiber Type on Blast Resistance of Slurry-Infiltrated Fiber Concrete Under Contact Detonation

Post-blast performance and residual capacity of CFDST columns subjected to contact explosions

Contact detonations, even with a small charge weight, could cause severe damage to structural columns and result in devastating consequences, associate with significant casualties, economic losses and social impacts. Therefore, to prevent catastrophic structural collapse, the most critical requirement of a blast-damaged column would be the residual axial load bearing capacity. In this paper, the post-blast performance of concrete-filled double-skin steel tube (CFDST) columns subjected to contact explosions was studied by experimental tests and numerical simulations. The experimental study comprised of field blast tests and residual axial load-carrying capacity tests on four CFDST columns. A high-fidelity physics-based numerical model was then developed using the nonlinear dynamic analysis program LS-DYNA and was validated against the test results. It was then used to model the dynamic response and predict the residual axial load-carrying capacity of CFDST columns subjected to contact explosions. An extensive parametric study was then carried out to investigate the influence of charge weight, boundary conditions, axial loading level and column geometries on the column residual axial load-carrying capacity. An empirical formula was derived through multi-variable regression analysis to predict the residual axial bearing capacity of CFDST columns after contact explosions.

Experimental study on the residual axial capacity of ultra high performance cementitious composite filled steel tube (UHPCC-FST) column under contact explosion

Abstract Ultra-high performance cementitious composite filled steel tube (UHPCC-FST) has been widely applied as the load bearing members for long-span bridges, which are the potential bomb explosion attack targets in terroristic activities. This paper aims to experimentally study the residual axial capacity of UHPCC-FST columns under contact explosion by conducting the field contact detonation and the subsequent axial compression tests. Firstly, five UHPCC-FST cylinder columns are fabricated with the column height, outer diameter and core concrete compressive strength being 2000 mm, 203 mm and 131.5 MPa, respectively. Secondly, three of which are tested under contact explosion with the TNT charge weights of 1 kg, 2 kg and 3 kg, in which the impact craters are formed and the integrity of the columns is maintained under 1 kg and 2 kg TNT explosions, while the outer steel tube is seriously ruptured and the core UHPCC is fully crushed for 3 kg TNT explosion. Furthermore, the original axial capacity of intact columns and the residual axial capacity of blast-damaged columns are evaluated though the axial compression tests, and the relationships between the axial load and axial/lateral displacement are derived. It indicates that, (i) both the intact and blast-damaged columns under axial compression show diagonal shear failure, the local bulging of steel tube is induced due to the low confinement of steel tube and high compressive strength of UHPCC; (ii) the quantitative dependence of column damage index on the charge weight is determined.

Blast-Resistant Performance of Hybrid Fiber-Reinforced Concrete (HFRC) Panels Subjected to Contact Detonation

This paper experimentally investigates the blast-resistant characteristics of hybrid fiber-reinforced concrete (HFRC) panels by contact detonation tests. The control specimen of plain concrete, polypropylene (PP), polyvinyl alcohol (PVA) and steel fiber-reinforced concrete were prepared and tested for characterization in contrast with PP-Steel HFRC and PVA-Steel HFRC. The sequent contact detonation tests were conducted with panel damage recorded and measured. Damaged HFRC panels were further comparatively analyzed whereby the blast-resistance performance was quantitively assessed via damage coefficient and blast-resistant coefficient. For both PP-Steel and PVA-Steel HFRC, the best blast-resistant performance was achieved at around 1.5% steel + 0.5% PP-fiber hybrid. Finally, the fiber-hybrid effect index was introduced to evaluate the hybrid effect on the explosion-resistance performance of HFRC panels. It revealed that neither PP-fiber or PVA-fiber provide positive hybrid effect on blast-resistant improvement of HFRC panels.

An analytical model to predict the compressive damage of concrete plates under contact detonation

Explosions threaten the safety of buildings and occupants by inducing severe damage to concrete structural elements. The effects of close-in and contact loading situations on RC plates have been investigated in literature and the common approaches employ field test results condensed in engineering charts based on cube-root scaling. In this paper, a new analytical model based on a physical framework is developed to (a) investigate shock wave attenuation along the depth of the concrete plate and (b) predict the size of crater damage. The analytical model for shock wave pressure is discussed in comparison to prediction data from established numerical models and existing experimental results. Moreover, consistency of the newly proposed model with established scaling rules is verified with respect to crater size.

Experimental and numerical investigation of steel-concrete (SC) slabs under contact blast loading

Single-side- steel-concrete (SSSC) panel and center steel-concrete (CSC) panel, which consists of concrete infill, steel plate, and shear studs, are usually applied as protective structures in the industrial structures, commercial buildings, and nuclear power plant. In the past, limited research about these types of slabs under blast loads has been studied. In this study, three small-scale RC, SSSC and CSC slabs under contact detonation were tested to obtain the failure modes, mid-span deflection, and dynamic response. Nonlinear 3D finite element models of RC, SSSC, and CSC panels consisting steel plate, concrete infill, and shear connectors were established to assess the blast behaviors using Arbitrary-Lagrange-Eulerian (ALE) coupled with Fluid-structure interaction (FSI) algorithm. The accurateness of the numerical models was verified with the experiments by comparison of damage modes and deflection. The results indicated that the failure modes of these slabs were summarized as three types such as type I, type II and type III from both experimental and numerical results. The damaged areas of concrete in SSSC and CSC slabs were larger than that of RC slab. However, the RC slab suffered severe penetration damage with the loss in loading bearing capacity. The experimental and the numerical results demonstrated that the steel plate plays an important role in the blast resistance of SSSC, and CSC slabs under contact explosion, which had better blast resistances compared with the RC slab.

Experimental and numerical study of damage characteristics of RC slabs subjected to air and underwater contact explosions

Reinforced concrete (RC) is one of the most commonly used construction materials. However, impact and blast loads could completely destroy RC structures, causing tremendous casualties and property losses. Therefore, analyzing the damage mechanism and dynamic behaviour of RC structures under blast loading is significant. This paper presents a study on the behaviour of RC slabs subjected to air and underwater contact detonation. Two RC slabs were tested under real blast loads. One was tested under air contact explosion of 210 g TNT, the other was tested subjected to underwater contact explosion of 6 g TNT. Damage evolution and damage mechanism of the RC slabs subjected to the air and underwater contact explosions are investigated by using high-fidelity numerical models. The damage patterns obtained from the numerical models match well with those of the tests. The effect of experimental environments on the structural behaviour of the slabs subjected to the underwater explosions is also discussed. The different response of the RC slabs subjected air and underwater explosions with identical charge mass are analyzed contrastively by employing the validated coupled method. The results show that the present model can give a reliable prediction of damage characteristics for RC structures under various blast scenarios. The experimental environments have important influence on the structural response and bubble development. The damage of the RC slabs induced by underwater contact explosion is significantly larger than that caused by air contact blast with equal charge mass.