Transient responses of double-curved sandwich two-layer shells resting on Kerr's foundations with laminated three-phase polymer/GNP/fiber surface and auxetic honeycomb core subjected to the blast load

This work uses refined first-order shear theory to analyze the free vibration and transient responses of double-curved sandwich two-layer shells made of auxetic honeycomb core and laminated three-phase polymer/GNP/fiber surface subjected to the blast load.Each of the two layers that make up the double-curved shell structure is made up of an auxetic honeycomb core and two laminated sheets of three-phase polymer/GNP/fiber.The exterior is supported by a Kerr elastic foundation with three characteristics.The key innovation of the proposed theory is that the transverse shear stresses are zero at two free surfaces of each layer.In contrast to previous first-order shear deformation theories,no shear correction factor is required.Navier's exact solution was used to treat the double-curved shell problem with a single title boundary,while the finite element technique and an eight-node quadrilateral were used to address the other boundary requirements.To ensure the accuracy of these results,a thorough comparison technique is employed in conjunction with credible statements.The problem model's edge cases allow for this kind of analysis.The study's findings may be used in the post-construction evaluation of military and civil works structures for their ability to sustain explosive loads.In addition,this is also an important basis for the calculation and design of shell structures made of smart materials when subjected to shock waves or explosive loads.

Sensitivity analysis and probability modelling of the structural response of a single-layer reticulated dome subjected to an external blast loading

The structural response of a single-layer reticulated dome to external explosions is shaped by many variables,and the associated uncertainties imply non-deterministic results.Existing deterministic methods for predicting the consequences of specific explosions do not account for these uncertainties.Therefore,the impact of the uncertainties associated with these input variables on the structures’response needs to be studied and quantified.In this study,a parametric uncertainty analysis was conducted first.Then,local and global sensitivity analyses were carried out to identify the drivers of the structural dynamic response.A probabilistic structural response model was established based on sensitive variables and a reasonable sample size.Furthermore,some deterministic empirical methods for explosion-resistance design,including the plane blast load model of CONWEP,the curved blast load model under the 50%assurance level,and the 20%mass-increased method,were used for evaluating their reliability.The results of the analyses revealed that the structural response of a single-layer reticulated dome to an external blast loading is lognormally distributed.Evidently,the MB0.5 method based on the curved reflector load model yielded results with a relatively stable assurance rate and reliability,but CONWEP did not;thus,the 1.2MB0.5 method can be used for making high-confidence simple predictions.In addition,the results indicated that the structural response is very sensitive to the explosion parameters.Based on these results,it is suggested that for explosion proofing,setting up a defensive barrier is more effective than structural strengthening.

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/kg^(1/3);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 singleend 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.

Numerical Study on the Behaviour of Hybrid FRPs Reinforced RC Slabs Subjected to Blast Loads

The safety of civilian and military infrastructure is a concern due to an increase in explosive risks,which has led to a demand for high-strength civil infrastructure with improved energy absorption capacity.In this study,a Finite Element(FE)numerical model was developed to determine the effect of hybrid Fibre Reinforced Polymer(FRP)as a strengthening material on full-scale Reinforced Concrete(RC)slabs.The reinforcing materials under consideration were Carbon(CFRP)and Glass(GFRP)fibres,which were subjected to blast loads to determine the structural response.A laminated composite fabric material model was utilized to model the failure of composite,which facilitates the consideration of strain rate effects.The damaged area of the laminate is determined in the FE model,and it is in good agreement with the corresponding experimental results in the literature.Models containing different stacking sequences were built to demonstrate their efficiency in resisting blast loads.In general,the damaged area was reduced when a hybrid reinforcement with CFRP as the top layer was used.

Dynamic caustics test of blast load impact on neighboring different cross-section roadways

Using digital laser dynamic caustics experimental system and conducting simulation experiment researched the influence rule of blasting excavation of a new roadway on neighboring existed different cross-section roadways. The experimental results show that the influence of blast load on adjacent roadway has a good relationship with the cross-section of roadway. The expansion distance of precrack existed in circular, arch-wall, rectangular roadway is respectively 1.76, 1.61 and 0 cm under blast load.At the same time, the direct-blast side of rectangular roadway has more obvious damage compared with circular and arch-wall roadway. It explains that plane reflects more stress wave than arc, so that it exerts more tensile failure in the direct-blast side, which leads to less stress wave diffracting to the precrack in the back-blast side. When the precrack extends, higher value dynamic stress intensity factor in circular roadway works longer than that of arch-wall roadway. Indirectly, it explains that plane's weakening function on stress wave is significantly stronger than arc. Stress wave brings about self-evident influence on the upper and bottom endpoints of the rectangular roadway, and it respectively extends 1.03, 2.06 cm along the line link direction of the center of the blasthole and the upper and bottom endpoints on the right wall.

Numerical investigation on free air blast loads generated from center-initiated cylindrical charges with varied aspect ratio in arbitrary orientation

In current guidelines, the free air blast loads(overpressure and impulse) are determined by spherical charges, although most of ordnance devices are more nearly cylindrical than spherical in geometry. This may result in a great underestimation of blast loads in the near field and lead to an unsafe design.However, there is still a lack of systematic quantitative analysis of the blast loads generated from cylindrical charges. In this study, a numerical model is developed by using the hydrocode AUTODYN to investigate the influences of aspect ratio and orientation on the free air blast loads generated from center-initiated cylindrical charges. This is done by examining the pressure contours, the peak overpressures and impulses for various aspect ratios ranged from 1 to 8 and arbitrary orientation monitored along every azimuth angle with an interval of 5°. To characterize the distribution patterns of blast loads,three regions, i.e., the axial region, the vertex region and the radial region are identified, and the propagation of blast waves in each region is analyzed in detail. The complexity of blast loads of cylindrical charges is found to result from the bridge wave and its interaction with primary waves. Several empirical formulas are presented based on curve-fitting the numerical data, including the orientation where the maximum peak overpressure emerges, the critical scaled distance beyond which the charge shape effect could be neglected and blast loads with varied aspect ratio in arbitrary orientation, all of which are useful for blast-resistant design.

Analytical Solutions to Strain Rates of Reinforced Concrete Simply Supported Slabs under Blast Loads

Based on the Duhamel integral, a couple of analytical solutions are derived to predict the strain rates of concrete and steel reinforcement in reinforced concrete slabs under blast loads and to estimate their variation over depth of a cross-section along the entire length of the member. The analytical approach utilizes the single-degree-of-freedom mode for the analysis of reinforced concrete simply supported one-way panels subjected to blast loads. These analytical solutions can give the strain rate profile for any cross-section at any time and permit variations of strain rate in each time step of numerical iteration method, thus making it possible to directly incorporate strain rate effects into non-linear dynamic response analysis of structural members subjected to blast loads.

Responses of HFR-LWC beams under close-range blast loadings accompanying membrane action

The load-carrying capacities and failure patterns of reinforced concrete components can be significantly changed by membrane effects.However,limited work has been carried out to investigate the blast resistance of Hybrid Fiber Reinforced Lightweight Aggregate Concrete(HFR-LWC)members accompanying membrane action.This paper presents a theoretical approach to quantitatively depicting the membrane behavior and its contribution on the behavior of HFR-LWC beams under close-range blast loadings,and the suitability of the proposed model is validated by a series of field tests.An improved Single-Degree-of-Freedom(SDOF)model was employed to describe the dynamic responses of beam-like members under blast loadings accompanying membrane action,where the mass-load coefficient is determined according to the nonuniformly distributed load induced by close-range explosion,and the membrane action is characterized by an in-plane(longitudinal)force and a resisting moment.The elastoplastic and recovery responses of HFR-LWC beams under the combined action of blast load and membrane force were analyzed by the promoted model.A specially built end-constrain clamp was developed to provide membrane action for the beam member when they are subjected to blast load simultaneously.It is demonstrated that the analytical displacement-time histories are in good agreement with experimental results before peak deflections and that the improved SDOF model is an acceptable tool for predicting the behavior of HFR-LWC beams under blast loadings accompanying membrane action.

Numerical damage evaluation of perforated steel columns subjected to blast loading

The structural performance of perforated steel columns(PSCs)is significantly more complex than the one of solid web I-shaped elements under the diversity of blast loading scenarios.The damage criterion of PSCs is not only related to initial deformation response during the blast but also the residual axial load capacity and it can be considered as a reliable index after the blast effects.Therefore,the PSCs damages will be studied in two stages;direct and post blast effects.In the present study,the dynamic response of PSCs was numerically evaluated under different levels of blast threats using LS-DYNA software.Extensive explicit finite element(FE)analyses are carried out to investigate the effect of various parameters,such as web opening shapes,boundary conditions and strengthening details on the damage index and toughness of the PSCs compared to the parent steel sections.The results of the comparative study show that the damage and toughness decrease when the support condition changes from pinned to fixed ends through the two stages of loadings.PSCs give high toughness compared to its parent sections during blast shock stage while,a remarkable decrease in toughness is observed during the application of axial gravity after blast shock.Furthermore,the web opening shapes have slight effects on the global dynamic behavior of PSCs,particularly in terms of residual capacity.On the contrary,the retrofitting strategy using both closed holes at end and vertical stiffeners have an effective enhancement to get higher toughness in case of the extreme blasts.

External blast load factors for dome structures based on reliability

Dome structures have been used extensively for industrial,residential,and military infrastructure.Therefore,it is necessary to understand the damage risk potential for such structures for blast-resistant design considerations.This paper investigates the effect of blast load variability on the design value and the structural dynamic response.Therefore,the sources of uncertainty in the external blast load on dome structures were discussed firstly.Then based on the probabilistic blast load model for the dome,the rationality of a deterministic mass-increase safety method was assessed.It was found that previous deterministic design method cannot provide a consistent and sound assurance factor or reliability index on the entire dome roof.In addition,it was also proved that the assurance-based load method fails to ensure compliance with structural safety design standards on the dome roof when compared with the reliability-based blast method.A sensitivity analysis on the probabilistic blast load was conducted,and the results indicate that stand-off distance and explosive mass both act as dominant sources to influence the mean and variability of blast load.Therefore,based on the Latin hypercube sampling method,a reliability-based external blast load factor technique was proposed.This technique was further used to estimate structural damage levels of a single-layer reticulated dome under different reliability requirements,associated with a low,medium,and high level of protection grades for a specific explosion scenario,and it indicated that this technique can be useful in the building design to achieve a higher structural anti-explosion capacity.This study herein can serve as a reference for the calculation method of designed blast load.

Some aspects affecting the response of RC compartment structures subjected to internal blast loads

Protective compartments are typically used to protect some specific structures from internal explosions,such as industrial buildings that contain devices that may explode in certain circumstances.This research investigates how the response of reinforced concrete(RC)compartment structures subjected to internal blast loads are affected by the following aspects:introduction of material nonlinearity in the analysis,reinforcement ratio,and aspect ratio of the compartment.To achieve this goal,a calibrated and sophisticated FE numerical model is introduced,and a parametric study for the intended aspects is carried out.A discussion of the results and conclusions are offered,which show the role of each aspect in the dynamic performance of the compartment structures.The main conclusions are as follows:introduction of material nonlinearity in this type of analysis and for these structures is very important and significant in obtaining accurate outputs that are similar to actual behavior;the reinforcement ratio has a significant effect on the response and its effect varies depending on the thickness of the compartment;in general,increasing the reinforcement ratio enhances the behavior and reduces the stresses in the compartment;and the aspect ratio of the compartment does not show a clear pattern on the response of such structures under internal blast loads.

A Review of Current Researches on Blast Load Effects on Building Structures in China

The damages of building structures subjected to multifarious explosions cause huge losses of lives and property. It is the reason why the blast resistance and explosion protection of building structures become an important research topic in the civil engineering field all over the world. This paper provides an overview of the research work in China on blast loads effect on building structures. It includes modeling blast shock wave propagation and their effects, the dynamic responses of various building structures under blast loads and the measures to strengthen the building structures against blast loads. The paper also discusses the achievements and further work that needs be done for a better understanding of the blast loads' effects on building structures, and for deriving effective and economic techniques to design new or to strengthen existing structures.

Numerical Analysis of Structural Progressive Collapse to Blast Loads

After the progressive collapse of Ronan Point apartment in UK in 1968, intensive research effort had been spent on developing guidelines for design of new or strengthening the existing structures to prevent progressive collapse. However, only very few building design codes provide some rather general guidance, no detailed design requirement is given. Progressive collapse of the Alfred P. Murrah Federal building in Oklahoma City and the World Trade Centre (WTC) sparked again tremendous research interest on progressive collapse of structures. Recently, US Department of Defence (DoD) and US General Service Administration (GSA) issued guidelines for structure progressive collapse analysis. These two guidelines are most commonly used, but their accuracy is not known. This paper presents numerical analysis of progressive collapse of an example frame structure to blast loads. The DoD and GSA procedures are also used to analyse the same example structure. Numerical results are compared and discussed. The accuracy and the applicability of the two design guidelines are evaluated.

Pressure-impulse diagram with multiple failure modes of one-way reinforced concrete slab under blast loading using SDOF method

Two loosely coupled single degree of freedom (SDOF) systems were used to model the flexural and direct shear responses of one-way reinforced concrete slabs subjected to explosive loading. Blast test results show that the SDOF systems are accurate in predicting the failure mode of the slab under blast loads by incorporating the effects of the strain rate effect caused by rapid load application. Based on different damage criteria, pressure-impulse (P-I) diagrams of the two failure modes were analyzed with the SDOF systems. The effects of span length, concrete strength, and reinforcement ratio of the slab on the P-I diagram were also investigated. Results indicate that a slab tends to fail in direct shear mode when it is of a smaller span length and tends to fail in flexure mode when it is of a larger span length. With the increase of the concrete strength or reinforced ratio, both the flexure and shear capacity increase. Based on numerical results, a simplified method and a semi analytical equation for deriving the P-I diagram are proposed for different failure modes and damage levels.

Numerical Modeling of Response and Damage of Masonry Walls to Blast Loading

To model the damage process of masonry walls under blast loading, a dynamic continuum damage material model is constructed for brick and mortar separately. The degradation of both the stiffness and strength are governed by a damage variable. By using the proposed material model, damage and fragmentation of a typical masonry wall under blast loading at different scaled distances is calculated. The hazard level of the masonry wall to blast loading is evaluated by analyzing the numerical results.

Numerical Analysis of Dynamic Behavior of RC Slabs Under Blast Loading

In order to reduce economic and life losses due to terrorism or accidental explosion threats, reinforced concrete (RC) slabs of buildings need to be designed or retrofitted to resist blast loading. In this paper the dynamic behavior of RC slabs under blast loading and its influencing factors are studied. The numerical model of an RC slab subjected to blast loading is established using the explicit dynamic analysis software. Both the strain rate effect and the damage accumulation are taken into account in the material model. The dynamic responses of the RC slab sub-jected to blast loading are analyzed, and the influence of concrete strength, thickness and reinforcement ratio on the behavior of the RC slab under blast loading is numerically investigated. Based on the numerical results, some prin-ciples for blast-resistant design and retrofitting are proposed to improve the behavior of the RC slab subjected to blast loading.

Strength and Toughness of Steel Fibre Reinforced Reactive Powder Concrete Under Blast Loading

The blast resistance of structures used in buildings needs to be investigated due to the increased threat of a terrorist attack. The damage done by Composition B or Powergel to steel fibre reinforced reactive powder concrete (SFRPC) panels and ordinary reinforced concrete (RC) panels of equivalent static flexural strength is compared. A 0.5 kg charge was detonated at a distance of 0.1 m from the 1.3 m×1.0 m×0. 1 m (thick) panels, which were simply supported and spaning 1.3m. Dynamic displacement measurements, high-speed video recording and visual examination of the panels for spall and breach were undertaken. The SFRPC panels withstood the bare charge blast better than the reinforced ordinary concrete panels. Neither type of panel was breached using a 0.5 kg charge. The RC panel exhibited more spalling when Composition B was used. Under successive Composition B loading conditions, the RC panel was breached. In comparison the SFRPC panel was not breached. Exposure to fragmenting charge loading conditions confirmed these performance differences between the SFRPC panel and the reinforced ordinary concrete panel.

Numerical Simulation of Dynamic Response and Collapse for Steel Frame Structures Subjected to Blast Load

The progressive collapse of steel frame structures under the blast load was investigated using LS-DYNA. The multi-material Eulerian and Lagrangian coupling algorithm was adopted. A flu-id-structure coupling finite element model was established which consists of Lagrange element for simulating steel frame structures and concrete ground, multiple ALE element for simulating air and TNT explosive material. Numerical simulations of the blast pressure wave propagation, struc-tural dynamic responses and deformation, and progressive collapse of a five-story steel frame structure in the event of an explosion near above ground were performed. The numerical analysis showed that the Lagrangian and Eulerian coupling algorithm gave good simulations of the shock wave propagation in the mediums and blast load effects on the structure. The columns subjected to blast load may collapse by shear yielding rather than by flexural deformation. The columns and joints of steel beam to column in the front steel frame structure generated enormous plastic defor-mation subjected to intensive blast waves, and columns lost carrying capacity, subsequently lead-ing to the collapse of the whole structure. The approach coupling influence between struc-tural deformation and fluid load well simulated the progressive collapse process of structures, and provided an effective tool for analyzing the collapse mechanism of the steel frame structure under blast load.

Analysis on Dynamic Response of Hard-Soft-Hard Sandwich Panel Under Blast Loading

Surface contact explosion experiments have been performed for the study of dynamic response of the hard-soft-hard sandwich panel under blast loading. Experimental results have shown that there are four damage modes, including explosion cratering, scabbing of the backside, radial cracking induced failure and circumferential cracking induced failure. It also illustrates that the foam material sandwiched in the multi-layered media has an important effect on damage patterns. The phenomena encountered have been analyzed by the calculation with ALE method. Meanwhile, the optimal analysis of foam material thickness and position in the sandwich panel were performed in terms of experimental and numerical analysis. The proper thickness proportion of the soft layer is about 20% to the thickness of sandwich panel and the thickness of the upper hard layer and lower hard layer is in the ratio of 7 to 3 under the condition in this paper when the total thickness of soft layer remains constant.

Numerical Simulation of Dynamic Response of an Existing Subway Station Subjected to Internal Blast Loading

In order to design and retrofit a subway station to resist an internal blast, the distribution of blast loading and its effects on structures should be investigated firstly. In this paper, the behav-ior of a typical subway station subjected to different internal blast loadings was analyzed. It briefly introduced the geometric characteristics and material constitutive model of an existing two-layer and three-span frame subway station. Then three cases of different explosive charges were consid-ered to analyze the dynamic responses of the structure. Finally, the maximum principal stress, dis-placement and velocity of the columns in the three cases were obtained and discussed. It con-cluded that the responses of the columns are sensitive to the charge of explosive and the distance from the detonation. It’s also found that the stairs between the two layers have significant effects on the distribution of the maximum principal stress of the columns in the upper layer. The explicit dynamic nonlinear finite element software——ANSYS/LS-DYNA was used in this study.