Field Blast Tests Research Articles

Numerical investigation on dynamic performance of reinforced ultra‐high ductile concrete–ultra‐high performance concrete panel under explosion

AbstractUltra‐high ductile concrete (UHDC) is known for ultra‐high tensile ductility, and ultra‐high performance concrete (UHPC) has ultra‐high compressive strength. Reinforced UHDC–UHPC panels that are made of UHDC and UHPC (i.e., hybrid panels) are expected to have excellent blast‐resistance capacity. However, only limited research is devoted to study the dynamic performance of the panels under explosion. To further investigate the dynamic performance of such kind of composite structural system, numerical simulations are carried out through LS‐DYNA. The developed material models are used for describing the mechanical properties of UHDC, UHPC and steel bars at high strain rate. Based on the corresponding field blast test results, the feasibility and accuracy of the adopted finite element models are validated. Furthermore, parameter analysis is applied for investigating the effects of scale distance, reinforcement ratio and concrete type on the dynamic performance. It is concluded that the maximum deflection of reinforced UHDC–UHPC panels reduces with increasing scale distance and reinforcement ratio. Reinforced UHDC–UHPC panels possess excellent blast‐resistance capacity in comparison with reinforced concrete panels.

Damage Mechanism and Stress Distribution of Gypsum Rock Pillar Subjected to Blasting Disturbance

The room-pillar mining technology of underground gypsum resources results in numerous gypsum rock pillars for controlling and supporting mined gobs, which forms a large area of roof hanging gobs. Owing to weathering and mining activities, gypsum rock pillar damage and failure will occur, thereby inducing a large area of gypsum mined-gob collapse accidents and disasters. Blasting is vital to the stability of gypsum rock pillars and is indispensable in mining engineering. Based on field blasting tests and using wave velocity as the basic parameter to characterise the integrity of gypsum rock, the damage mechanism of gypsum rock pillars subjected to blasting disturbance is investigated. With ten blasting tests, the maximum damage rate is 7.82% along the horizontal direction of pillar, and 3.52% along the vertical direction. The FLAC numerical simulation calculation software is used to analyse the stress distribution law of gypsum rock pillars with disturbances of different strengths from different distances. As the disturbance strength increased, the stress increased with no clear linear relationship; as the disturbance distance increased, the stress decreased gradually with a linear relationship. All stress after disturbance is greater than the original static stress, and lower than the ultimate compressive strength. However, the correlation between blasting tests results and numerical simulation results is poor and is discussed for many factors. The results can provide important guidance and reference for clarifying the damage mechanism of gypsum rock pillars subjected to blasting disturbance, as well as reveal the collapse mechanism of gypsum mined gobs.

Mitigation of blast effects through novel energy-dissipating connectors

Explosions generate overpressures that can cause irreparable damage to structures. For many buildings, especially critical infrastructure, continued operation after an explosive attack is essential. The use of energy-dissipating methods will enable the protection of a structure and occupants from a blast and permit the timely repair and re-occupation of the building after an event. The concept behind the system presented is the creation of panels that can be used as cladding for structures. The panels are connected to the main structure using energy-dissipating component assemblies around the panel edge. When subjected to a blast load the panels transfer the blast pressure through the assemblies, thereby reducing the forces transmitted to the underlying structure. After an event, the panels and energy-dissipating component assemblies can be replaced quickly and easily, allowing the building to be reoccupied in a short time after an attack. This study focuses on the characterization of energy-dissipating component assemblies using static and dynamic laboratory testing. A predictive theory, supported by a single degree of freedom model, is developed and a general evaluation method proposed. Further laboratory testing expands the characterization of behaviour of the assemblies through experiments, with a blast generator in tension tests and in simulated blast panel tests. The time histories developed from tension tests are then compared to examine the effect of loading rate. The investigations on blast panels also include a comparison with predictions to determine whether the latter can describe the global behaviour of the system. Lastly, the response of the energy-dissipating component assemblies is evaluated in full-scale field blast tests on cladding panels.

Numerical Assessment and Repair Method of Runway Pavement Damage Due to CBU Penetration and Blast Loading

This paper addresses the protection capability of a runway pavement by executing a field blast test on an airfield pavement subjected to blast loading from a CBU (cluster bomb unit), and by confirming the numerical simulation of warhead penetration and the form of damage. The CBU’s blast loading applies the BAP 100 of an air-to-ground munition in a similar scale. Penetration depth is calculated by a formula which incorporates the terminal speed of a free-falling cluster munition dispersed 20 km above the ground. According to the result of the calculation, the penetration depth by a cluster munition is 33 cm from the surface of the pavement. The field blast test was conducted based on this result. Furthermore, LS-DYNA software simulation was used to assess the condition of damage, determined by the depth of penetration and explosive pressure from a free-falling CBU landing on the airfield pavement from 20 km above the ground. The condition was ultimately used to verify the result of field testing and to confirm the scale of damage repair. The depth of explosion was 78 cm, from the surface to the crushed stone and sand layer below the pavement, and the diameter was 30 cm. The size of the crushed concrete that needed to be removed was an average diameter of 156 cm. The simulation result confirms that the diameter and depth of the crater are 67.6 cm and 67 cm, respectively, when the CBU is detonated under the same depth as the field testing, and the height of upheaval is 12 cm. The most appropriate method for repair, after a series of reviews, is to cut and remove a concrete slab 1.8 m × 1.8 m and cast the crushed stone layer disrupted from the explosion, followed by repairing the removed damaged concrete slab sections using rapid hardening concrete.

Experimental Performance Assessment of Thermobaric Explosives in Free Field and Internal Blast Tests

Experimental Performance Assessment of Thermobaric Explosives in Free Field and Internal Blast Tests

Experimental Performance Assessment of Thermobaric Explosives in Free Field and Internal Blast Tests

Experimental Performance Assessment of Thermobaric Explosives in Free Field and Internal Blast Tests

Experimental and numerical investigation of normal reinforced concrete panel strengthened with polyurea under near-field explosion

In this paper, field blast tests and numerical simulations were conducted to investigate the strengthening effect of polyurea on the blast resistance of the normal reinforced concrete (NRC) panels under near-field explosion. Five specimens were fabricated and tested, including two NRC panels, and three NRC panels sprayed with polyurea at the rear side. The experimental results showed that polyurea could effectively improve the blast resistance of the NRC panel with less damage and smaller residual displacement. Furthermore, with the existence of the polyurea, the integrity of the specimen could be maintained, and the deadly fragments of the concrete panel were captured, thereby reducing the secondary damage to surrounding personnel and structures. The finite element (FE) model of NRC panels strengthened with polyurea under near-field explosion was established using the Arbitrary-Lagrangian-Eulerian (ALE) method, and validated with the experimental results. Thereafter, the validated FE models were used to investigate the effects of scaled distances and polyurea thickness on the blast resistance of the NRC panel. This research is of direct importance to both practitioners and researchers involved with strengthening design for NRC components against explosion.

Improved resistance functions for RC elements accounting for compressive and tensile membrane actions

Membrane actions commonly present in reinforced concrete elements as a result of restrained boundary conditions and geometry of deformations, which could substantially improve the ultimate flexural load-resistance as compared to that using yield line theory. Nevertheless, most current design manuals do not consider membrane effect because of a short of proper analysis method. This paper proposed an improved resistance model for RC (reinforced concrete) elements which considers both compressive and tensile membrane actions. Firstly, the derivation of the proposed membrane model was presented in detail. It was then validated with available testing data, in which good agreement was found on the load-deflection relationship of RC element between the estimation using the proposed model and testing data. Combining with the equivalent SDOF (single-degree-of-freedom) analysis method, the dynamic responses of structural elements subjected to blast loads could be more accurately predicted as compared to the common elastic-perfectly-plastic resistance assumption in design guides. The proposed method was further verified with existing field blast testing results. Parametric studies were then carried out to examine the influences of critical design parameters for membrane behaviors including reinforcement ratio, span-to-depth ratio, and restraint stiffness. Last but not the least, based on the proposed analytical method a series of diagrams for modifying the design loading capacity estimated by UFC (Unified Facilities Criteria) design guides without considering the membrane effects were derived for more accurate and easy predictions of loading capacities in engineering applications.

Influence of Hole Arrangement on the Section of Cavity Formed by Cutting Blast

In order to optimize the arrangement of cutting holes in tunnel blast in Dahongshan Copper Mine, theoretical analysis and numerical simulation were combined to preliminarily determine the diameter of the hollow hole and the distance between the charge hole and the hollow hole during cut blast, which was verified through the field blast test. The research results show that with the increase of the hole diameter, the peak compressive stress of rock surrounding the empty hole gradually decreases, and the peak tensile stress gradually increases, which is consistent with the calculation results; when the hole diameter is 10 cm, the two first blast holes are arranged horizontally and 30 cm from the empty hole, two second blast holes are arranged vertically and 40 cm away from the empty hole, and the four third blast holes are arranged at a horizontal distance of 45 cm and a vertical distance of 45 cm from the empty hole; the contour area in numerical simulation is the maximum. The difference in contour area, contour width, and contour and contour height between the measured value and the simulation result is 5.3%, 3.3%, and 3.4%, respectively, indicating that the combination of theoretical calculation and numerical simulation is suitable for prediction of cavity section after blast in tunnel excavation.

Experimental investigation on blast load resistance of reinforced concrete slabs retrofitted with epoxy resin impregnated glass fiber textiles

Blast mitigation of civil and transportation infrastructure is in focus due to the ever-present volatile geopolitical situation. Structures are not designed to withstand blast load, and in areas of an imminent attack, their sensitive elements require blast retrofit. The retrofit technique selected follows three criteria: speed and ease of application and relatively low price. Commercially available glass fibers, in the form of textiles and mats, were applied on RC slabs using epoxy resin. The test program consisted of two phases. The first phase consisted of laboratory four-point static bending tests of RC slabs to determine the feasibility and efficiency of devised retrofit. The second phase consisted of field blast tests of RC slabs to study blast behavior and determine the applicability of devised retrofits. Applied retrofit has been proved useful in reducing flying debris and maximum deflection in the tested range of explosion.

Experimental investigation on the residual axial capacity of close-in blast damaged CFDST columns

Concrete-filled double-skin steel tubes (CFDSTs) are comprised of two concentrically placed steel tubes and concrete core filled in the annulus between the two tubes. A number of studies have demonstrated the excellent structural performance of CFDSTs as load-bearing columns under various loading conditions, which have attracted lots of interests of engineers and researchers. Despite the increasing popularity of using CFDSTs as load-bearing structural columns, there is limited knowledge on blast resistant performance of CFDST columns particular under close-in explosion. In this paper, an experimental study was conducted to investigate the residual axial load-carrying capacity of CFDST columns after being subjected to close-in explosion. Field blast tests were firstly carried out on CFDST columns. Then, the blast-damaged columns were subjected to axial compression till failure under quasi-static condition in the laboratory to examine their residual axial load-carrying capacities. Seven half-scale CFDST column specimens were constructed and tested, of which one column serves as a reference column that was directly tested under axial compression to check the ultimate axial load-carrying capacity of CFDST columns without blast damage. The influences of design factors including charge weight, stand-off distance, charge orientation, and section hollow ratio on blast resistant performance of CFDST columns were quantitatively assessed based on the residual axial capacity index. It was found that under close-in blast loading CFDST columns showed localized cross-section denting with slight global deformation. The damaged columns can maintain up to 60% of its ultimate axial load-carrying capacity and exhibited good strength and ductility.

Finite element analyses of constitutive models performance in the simulation of blast-induced rock cracks

This study analyzed the performance of the Riedel-Hiermaier-Thoma (RHT) model and the Holmquist-Johnson-Cook (HJC) model in the numerical simulations of blast-induced cracks in granite. The two models implemented in the LS-DYNA software were firstly adopted to simulate a single blasting process in granite. Further, the HJC model was improved by coupling an additional failure criterion and used to describe the tensile damage of rock materials. The feasibility of the two models in simulating the extent of damage zone and fracture patterns in rock mass under cyclic blast loading was explored based on the field blast tests. The results show that both the RHT model and the improved HJC model are able to describe the formation of crushed zone and the propagation of tensile cracks in single blasting problems. For cyclic blasting problems, the simulation results based on the RHT model are consistent with experimental ones, but the improved HJC model is not applicable. Both the RHT and the improved HJC models are suitable for the numerical simulation of single blasting problems and the RHT model should be the first choice for the simulation of cyclic blasting problems.

Numerical study on the behavior of blasting in deep rock masses

High in-situ stress can limit the generation of rock fractures induced by blasting, which usually shows different states of rock fragmentation with those under low-stress conditions. In this paper, the stress distribution around the blasthole under coupled in-situ stress and blasting load was theoretically analyzed. Then, the single-blasthole blasting process, which is calibrated by field blasting tests, was numerically investigated using the Riedel-Hiermaier-Thoma (RHT) model, and the effects of in-situ stress magnitudes and lateral pressure coefficients on the crushed zone and the crack propagation were investigated. After that, influences of lateral pressure coefficients, buried depths, and blasthole layouts on the behavior of double-blasthole blasting were studied. It is concluded that in-situ stresses can increase the compressive stress and reduce the tensile stress caused by blasting load. The area of the crushed zone decreases with increasing in-situ stresses. The crushed zone is elliptical in shape in anisotropic pressure conditions. The gap between the long axis and the short axis of the crushed zone widens as the difference between the stress in the horizontal and vertical directions increases. Cracks preferentially propagate in the higher stress direction. At a buried depth of 1000 m, connecting cracks can be formed at lateral pressure coefficients ranging from 0.25 to 3.0 when blastholes are drilled along the horizontal direction. The rise in buried depths and the angle between the centerline of adjacent blastholes and the higher stress direction can limit the formation of connecting cracks. The research results can provide guidance for analyzing the behavior of rock blasting in deep underground.

Improving Blast Performance of Reinforced Concrete Panels Using Sacrificial Cladding with Hybrid-Multi Cell Tubes

The utilization of sacrificial layers to strengthen civilian structures against terrorist attacks is of great interest to engineering experts in structural retrofitting. The sacrificial cladding structures are designed to be attached to the façade of structures to absorb the impact of the explosion through the facing plate and the core layer progressive plastic deformation. Therefore, blast load striking the non-sacrificial structure could be attenuated. The idea of this study is to construct a sacrificial cladding structure from multicellular hybrid tubes to protect the prominent bearing members of civil engineering structures from blast hazard. The hybrid multi-cell tubes utilized in this study were out of staking composite layers (CFRP) around thin-walled tubes; single, double, and quadruple (AL) thin-walled tubes formed a hybrid single cell tube (H-SCT), a hybrid double cell tube (H-DCT), and a hybrid quadruple cell tube (H-QCT). An unprotected reinforced concrete (RC) panel under the impact of close-range free air blast detonation was selected to highlight the effectiveness of fortifying structural elements with sacrificial cladding layers. To investigate the proposed problem, Eulerian–Lagrangian coupled analyses were conducted using the explicit finite element program (Autodyn/ANSYS). The numerical models’ accuracy was validated with available blast testing data reported in the literature. Numerical simulations showed a decent agreement with the field blast test. The proposed cladding structures with different core topologies were applied to the unprotected RC slabs as an effective technique for blast loading mitigation. Mid-span deflection and damage patterns of the RC panels were used to evaluate the blast behavior of the structures. Cladding structure achieved a desired protection for the RC panel as the mid-span deflection decreased by 62%, 78%, and 87% for H-SCT, H-DCT, and H-QCT cores, respectively, compared to the unprotected panels. Additionally, the influence of the skin plate thickness on the behavior of the cladding structure was investigated.

Finite element modeling of FRP retrofitted RC column against blast loading

Fiber-reinforced polymer (FRP) wrap could considerably improve the shear capacity and ductility of RC columns. FRP is therefore considered a potential material to strengthen the RC column against blast loading. Due to the high expense and safety concern of field blast tests, a very limited number of explosion tests on FRP retrofitted RC columns have been conducted, which hinders the understanding of the response of FRP retrofitted RC columns against blast loading. With advanced computational technology, it is convenient to develop a Finite Element (FE) model that can accurately capture the structural response of FRP retrofitted columns under blast loading. In this paper, a refined FE model was established to simulate the FRP retrofitted RC columns under blast loading. Strain rate effects on the concrete and steel reinforcing bar as well as the FRP composite of which the strain rate effect was commonly ignored, were all considered in the model. Comprehensive modifications were made to the Karagozian and Case concrete (KCC) model to accurately capture the mechanical properties of FRP-confined concrete. Finally, the FE model was validated with several available experimental tests. The developed FE model could capture the blast response of FRP retrofitted columns with good accuracy.

Comparative study on tunnel blast-induced vibration for the underground cavern group

Seismic wave induced by blasting excavation of tunnel may exert adverse effects to the surrounding rock. To study the different characteristics and attenuation of blast-induced vibration in the blasting tunnel and adjacent tunnel, field blasting tests are carried out to record velocity–time histories during blasting in Wanhua Underground Gas Storage. The characteristics and attenuation of vibration velocity and energy are presented based on the field data. And the dynamic finite-element model is established to further study the vibration attenuation law. Results demonstrate that PPV and vibration energy of the adjacent tunnel is greater than that in the blasting tunnel and attenuates more readily when monitoring points are near the blasting area. The dominant frequencies of the adjacent tunnel are higher than that in the blasting tunnel at three orthogonal directions. Adopting vibration energy as the evaluation index of seismic intensity, the fitting formula has favorable prediction accuracy, which will provide more accurate guidance for controlling the adverse effects of tunnel blasting.

Numerical analysis of axial load effects on RC bridge columns under blast loading

Blast load and its effects on transportation infrastructure especially bridge structures have received considerable attention in recent years. The RC bridge columns are considered as the most critical structural members because their failure leads to collapse of the bridge. Although RC bridge columns are typical axial load-carrying components, the studies on blast-resistant capacity of RC bridge columns usually neglect the axial load effect since it is commonly assumed that neglecting the axial load leads to conservative predictions of column responses. This assumption is true when column failure is governed by flexural response since axial compressive load generates a prestress in column which compensates concrete tensile stress induced by bending response. When subjected to blast loads, column response however could be governed by shear response. In this case neglecting axial loading effect does not necessarily lead to conservative predictions of column responses. In this study, high-fidelity finite element (FE) models for both non-contact explosion and contact explosion were developed in LS-DYNA. The FE models were validated with field blast test data. Subsequently, intensive simulations of the RC bridge columns with and without axial load subjected to a wider range of blast loading scenarios, including far-field, near-field and contact explosion were conducted. The influence of axial load on the dynamic performance of RC bridge columns corresponding to different blast loading scenarios was discussed.

Experimental investigation on the blast resistance of framed PVB-laminated glass

PVB-laminated glass has been widely adopted for building windows as safety glass due to its significant post-crack load bearing capacity. To achieve a better understanding of the mechanical behaviour of framed PVB-laminated glass under explosion, a series of field blast tests were carefully designed and conducted aiming to study the dynamic responses and failure modes of framed PVB-laminated glass subjected to various blast loadings. The reflected overpressure and displacement time histories were measured in the tests. In particular, DIC technology was adopted to record the 3-D deflection field of the glass panel, which is essential for analyzing the dynamic response feature of laminated glass panels under blast loading. Three typical failure modes, i.e. global flexural failure, local punching failure and mixed failure, were identified and corresponding failure mechanisms were analyzed. Finally, the test results were used to check the effectiveness of different design approaches. The results from this study can provide reference for further blast resistant analysis and design for framed PVB-laminated glass.

Close-in blast resistance of large-scale auxetic re-entrant honeycomb sandwich panels

The protection of critical infrastructure, including government buildings, airports, religious buildings, military buildings and military vehicles, which are at risk to blast loads, has become important due to increasing terrorist activities in recent years. Sacrificial cladding systems based on negative Poisson’s ratio core topologies have recently received more attention as a protective technology due to its excellent energy absorption capability. In this study, field blast tests were performed on metallic re-entrant honeycomb-cored sacrificial cladding systems as protective structures for steel plate structures. This study focused on the near-field blast loading conditions where liquid Nitromethane (NM) spherical charges were detonated in close proximity to the main structure. Two 6 mm thick mild steel plates and two steel plates protected with re-entrant honeycomb-cored sacrificial cladding systems were among the specimens tested. The proposed auxetic cladding system was fabricated from aluminium sheets using a novel in-house built folding machine. Numerical simulations were conducted utilising LS-DYNA software and the Blast Impact Impulse Model (BIIM). The results obtained from the numerical simulations are in good agreement with the experimental results. It was found that the deformation pattern of the sacrificial auxetic cladding system varies with the intensity of the blast loading, and there is a limit at which the proposed protective system ceases to effectively absorb the applied blast loading. The variation of negative Poisson’s ratio of the system with blast loading was studied. It was found that the auxetic cladding system could become a solid projectile leading to damage amplification for very close-range blast loads due to rapid densification of the auxetic core. The proposed cladding systems with narrow re-entrant angles performed well under blast loads due to relatively low stiffness of the panels. Finally, the optimisation study was performed for the protective system. Overall, the experimental and numerical results assure that auxetic-based cladding systems are suitable for applications requiring blast protection such as armoured vehicles and critical physical infrastructure but need to be carefully designed for the given blast threat to prevent overloading of the protected structures.

Metallic Ribbon-Core Sandwich Panels Subjected to Air Blast Loading

Sandwich structures provide a quite promising solution for blast alleviation techniques owing to their lightweight, high strength, and impressive energy absorption capabilities relative to solo metallic plates with equivalent density. The ability of the sandwich structure to withstand blast loading relies on its core topology. This paper numerically investigates the effectiveness of using ribbon shapes as an innovative core topology for sandwich structures subjected to blast loading. The hydro-code program (Autodyn) supported by the finite element program (ANSYS) is adopted to study the dynamic response of various sandwich panels. The accuracy of the finite element (FE) models were verified using available experimental results for a field blast test in the literature. The results show that the developed finite element model can be reliably exploited to simulate the dynamic behavior of the sandwich panels. The trapezoidal (TZ) and triangular (T) corrugated core topologies were selected to highlight the blast-resistant performance of the new ribbon core topology. Applying the ribbon topology to the traditional corrugated core topologies improved their blast performance. The facing front-plate’s deflection of the trapezoidal corrugated ribbon core sandwich structure (TZRC) has been improved by 45.3% and by 76.5% for the back-plate’s deflection, while for the triangular ribbon corrugated core (TRC), the front plate’s defection has been enhanced by 69.3% and by 112.1% for the back plate. The effect of various design parameters on the blast behavior of the Ribbon-Core Sandwich Panels (RCSPs) was investigated. A parametric study was conducted to evaluate performance indicators, including energy dissipated through plastic deformation and plate deflections. Finally, based on the parametric study, the results of this paper were recommended to be used as a guide for designing metallic ribbon sandwich structures with different protection levels.