爆炸冲击荷载作用下SRC柱等效单自由度模型

爆炸冲击荷载作用下结构构件的反应分析方法常用的是等效单自由度模型，在现有的有关资料中，等效单自由度模型主要用于钢筋混凝土构件和钢构件。等效单自由度模型的关键是确定等效弹性位移、破坏位移和屈服强度。以通用有限元分析软件LS—DYNA为基础，研究了钢骨混凝土（SRC）柱在爆炸冲击荷载作用下的反应特征，确定出了等效单自由度模型的等效弹性位移和破坏位移；以常规SRC柱设计理论为基础，提出了等效单自由度模型的等效屈服强度计算公式。最后用所建立的等效单自由度模型和LS—DYNA软件分别对8根SRC柱共48种爆炸冲击荷载工况进行对比分析，验证了所提出的等效单自由度模型。     

Model validation and parametric study on the blast response of unreinforced brick masonry walls

Numerical simulations are carried out to estimate the response and damage of unreinforced brick masonry walls subjected to explosive blast loading based on the transient dynamic finite element program LS-DYNA. A previously developed dynamic plastic damage model was used for brick and mortar. A new model for strain rate effects of bricks and mortar is included in the numerical analysis. The results obtained from the numerical models are compared with field test data and good agreement can be found. Parametric studies are conducted to evaluate the effect of material strength, boundary conditions, and thickness of the wall on the blast response of unreinforced brick masonry walls. It was found that boundary conditions and wall thickness significantly affect the blast response, while the effect of material strength is relatively small.     

Security risks and probabilistic risk assessment of glazing subject to explosive blast loading

A probabilistic risk assessment (PRA) procedure is developed which can predict risks of explosive blast damage to built infrastructure. The present paper focuses on window glazing since this is a load-capacity system which, when subject to blast loading, has caused significant damage and injury to building occupants. Structural reliability techniques are used to derive fragility and blast reliability curves (BRCs) for annealed and toughened glazing subjected to explosive blast, for a variety of threat scenarios. The probabilistic analyses include the uncertainties associated with blast modelling, glazing response and glazing failure criteria. Damage risks are calculated for an individual window and for windows in the facade of a multi-storey commercial building. If threat probabilities can be estimated then the paper shows illustrative examples of how this information, when combined with risk-based decision-making criteria, can be used to optimise risk mitigation strategies.     

Generation of a pressure–impulse diagram for a temporary soil wall using an analytical rigid-body rotation model

This study aimed to provide a simple and efficient model to calculate a time history of response and construct a pressure–impulse (P–I) iso-damage curve for a free-standing soil-filled HESCO Bastion (HB) concertainer^® wall subjected to blast loading based on the maximum rotation of the wall. An analytical model is formulated for a free-standing HB simple straight wall based on rigid-body rotation. The maximum rotations observed in a full-scale blast testing of free-standing simple straight walls were compared with the maximum rotations calculated using the proposed analytical model and are in good agreement. The model is subsequently used to calculate a P–I curve for the wall, which is a common iso-damage curve used in a blast-resistant design, and represents various combinations of blast pressures and impulses required to damage the wall to a selected failure criterion. The failure criterion was selected as the critical amount of rotation required to completely overturn the wall. The resulting P–I curve was plotted along with the different charge performance curves or the pressures and impulses of different charge sizes. The curves show that the overturning of the HB walls, except for extremely large charge sizes, is governed by the amount of blast impulse and not the blast peak pressures. This indicates that the response of HB walls is impulse dominated. The effect that material density has on P–I curves was studied and found to be relatively insignificant. The P–I curves calculated based on different degrees of rotation as failure criteria were also plotted and compared. The curves showed that the required blast impulse to rotate the wall to 75% of the complete overturning angle and the required blast impulse to completely overturn the wall were very close. This illustrates that the magnitude of rotation becomes increasingly sensitive to blast impulse as blast impulse approaches the critical blast impulse required to completely overturn the wall.     

Anisotropic dynamic damage and fragmentation of rock materials under explosive loading

This paper describes the development of a constitutive model for predicting dynamic anisotropic damage and fragmentation of rock materials under blast loading. In order to take account of the anisotropy of damage, a second rank symmetric damage tensor is introduced in the present model. Based on the mechanics of microcrack nucleation, growth and coalescence, the evolution of damage is formulated. The model provides a quantitative method to estimate the fragment distribution and fragment size generated by crack coalescence in the dynamic fragmentation process. It takes account of the experimental facts that a brittle rock material does not fail if the applied stress is lower than its static strength and certain time duration is needed for fracture to take place when it is subjected to a stress higher than its static strength. Numerical results are compared with those from independent field tests.     

模拟破片杀伤战斗部空爆冲击波与高速破片群联合作用的等效试验方法

破片杀伤战斗部空爆冲击波与高速破片群联合毁伤作用下目标结构的毁伤特性、防护效能等是当前防护领域的热点和难点,但目前的试验研究手段和方法存在不足,为此,提出采用等效缩比战斗部(其原理为炸药爆炸驱动预制破片分散)来模拟破片杀伤战斗部,可作为进行空爆冲击波与高速破片群对防护结构的联合毁伤作用的实验方法。在确定防御目标战斗部、防御目标弹丸和几何缩尺比的基础上,根据爆炸力学相关经验公式,提出了求解等效缩比战斗部的装药和预制破片的相关参数的等效计算方法。该等效试验方法考虑了多破片侵彻的增强效应以及与爆炸冲击波的联合毁伤增强效应,且等效计算方法参数较少、简单实用。     

Prediction of fragment size and ejection distance of masonry wall under blast load using homogenized masonry material properties

The fragment hazard resulting from a nearby explosion is a major concern in the design of structures which may be subjected to blast loads. This paper presents a predictive method based on the theories of continuum damage mechanics and mechanics of micro-crack development, and numerical simulation to determine the probabilistic fragment size distribution and the launch distances. Theoretical derivations are presented to calculate fragment distribution. The fragmentation process is modeled according to the crack initiation and propagation, which depend on the material damage levels and are estimated using continuum damage mechanics theory. The proposed method involves two steps. First a finite element model is developed to estimate the material damage, fragment distribution and the ejection velocity. Then a simple algorithm is used to predict the fragment trajectory and the launch distance based on the fragment size and the ejection velocity. A masonry wall is used as an example in this study. The wall is modeled with both the distinctive consideration of the brick and mortar material properties and the homogenized masonry material properties. The reliability and efficiency of using the homogenized masonry material model in predicting the masonry wall damage and fragmentation are proven. The program AUTODYN is used in this study to conduct the numerical simulations with the proposed models linked to it as user subroutines. The numerical results indicate that the masonry fragments approximately follow the Weibull distribution, which is consistent with some empirical fragment distributions. The proposed method avoids using erosion technique, which inevitably results in a loss of fragment mass, and avoids discretizing the structure into particles or predefining the failure planes, which may lead to unrealistic prediction of damage propagation and evolution and therefore inaccurate fragmentation process and fragment size distributions.     

核爆冲击波作用下空心砌块墙对主体结构的作用

该文采用显式动力有限元软件LS-DYNA对核爆冲击波作用下高层建筑混凝土小型空心砌块外墙(以下简称砌块墙)的破坏模式进行了数值模拟,计算模型考虑了材料非线性、接触非线性、大应变、大变形等主要特征。在此基础上讨论了砌块墙在破坏飞散过程中传给结构的荷载,得到了不同冲击波超压作用下砌块墙传给结构的荷载时程。计算结果表明:核爆冲击波作用下,砌块墙的破坏模式与冲击波超压的大小有关;其传给结构的荷载时程基本呈三角形分布,荷载峰值随超压的增加而增大,墙体顶部与结构构件之间接触面的允许抗剪强度对荷载峰值时间和持续作用时间起关键作用。     

底部铰支自复位钢筋混凝土剪力墙设计与性能研究

为克服传统钢筋混凝土剪力墙在遭受较大地震时易发生墙脚压溃形成塑性铰等问题，减小结构残余位移，提出一种底部铰支自复位钢筋混凝土剪力墙。通过将传统剪力墙破坏严重的底部进行替换，上部墙板通过V型连接梁与基础铰接，两侧墙脚位置处布置具有双线性滞回特性的复位支撑，将墙板传递的内力解构，弯矩由复位支撑单独承受，在墙体底部形成弹性旋转约束的方式，实现了剪力墙较大弹性侧移，从而降低墙体损伤和残余位移。数值模拟分析了普通钢筋混凝土剪力墙（SW）和相同截面的自复位钢筋混凝土剪力墙（SC-SW）在低周往复荷载下的承载能力、耗能能力、变形能力及损伤分布。结果表明:SC-SW通过合理设计可达到与SW相同初始刚度和承载力，同时延性提高了26.52%；损伤水平明显小于SW，避免了以墙体塑性受损而吸收能量的耗能方式；残余位移明显减少，复位效果较好。     

Transfer of impulsive loading on cladding panels to the fixing assemblies

The fixing assemblies for prefabricated cladding panels on buildings, are often designed on an empirical basis, to support the dead weight of the panel, wind loads and possibly temporary loads arising during construction. If, subsequently, the design loads are accidentally exceeded but the panel is undamaged; it may be necessary to check the condition of the fixings. A physical check would require costly dismantling and reconstruction of the panel but, as an alternative, this paper presents an analysis of the force transferred to cladding fixing assemblies when the panel is subjected to impulsive loading, using the finite element analysis program, DYNA3D. The results were validated with experimental results from impact tests on a steel plate supported on four steel bars. Having obtained this validation, a finite element analysis was then carried out to determine the response of fixings for panels under different levels of blast loading using two different models for the panel-fixing assemblies. The first model considers only the effect of out-of-plane fixing, whilst in the second model both the out-of-plane fixings and in-plane fixings are considered. It was observed that forces transferred to fixings include an axial force, shear forces, and bending moments and these force components can vary along the length of the fixing. Inspections of cladding panels, after being subjected to impulsive loads, often show that the connection between the fixing and the panel and between the fixing and the support structure are more vulnerable to impulsive loading than the panel itself. The FE analysis has shown that forces in the fixings are related to the dynamic response of the cladding panel; hence damage to the fixings could be deduced from damage to the panel.     

Experimental study on scaling of RC beams under close-in blast loading

Damage effects analysis and assessment of buildings under blast loading is an important problem concerned by the area of explosion accident analysis, blast-resistant design, anti-terrorist and military weapon design.The damage character of RC beam under close-in blast loading is investigated through experiments. The damage modes and damage levels of RC beams are studied under different blast loads. The results show that the spallation area increases with the decrease of the scaled distance. The concrete beams are prone to be damaged in flexure mode with concrete crushed on the front face, concrete spallation on the back surface and concrete flake off on the side surface. The scaling of the dynamic response of reinforced concrete beams subjected to close-in blast loadings is also studied. The test results showed a similar macrostructure damage and fracture in all experiment conditions. But the local damage degree of RC beams with smaller size has been reduced a little as compared with that of beams with larger size. Based on the results, empirical equations of the center deflection to height ratio are proposed to correct scaling model considering size effects.     

Experiments and numerical analyses of blast and fragment impacts on concrete

Concrete structures are commonly used as protective structures. An important issue is how the blast wave and fragment impacts from an explosion affect the concrete. It is well known that the fragments penetrate or even perforate the structure. Moreover, spalling occurs in the impact zone and scabbing may occur on the reverse side of a wall that receives an impact. However, knowledge of how the blast wave and fragment impacts influence the material properties of concrete is quite limited. Experiments and numerical analyses were carried out to examine the extent to which the concrete, at various distances, is affected by the blast wave and fragment impacts. The fragments, which were spherical, were shot against thick concrete blocks by using the explosives octol or hexotol; the fragment velocity was approximately 1650 m/s. After the concrete blocks were shot, the depths of penetration and spalling were measured. Next, the concrete blocks were cut into halves, and the global macro-cracking could be observed. To study how the material properties of concrete were influenced, uniaxial compressive and splitting tensile tests were carried out on cylinders drilled from selected positions in the block. Furthermore, specimens from the blocks were thin-ground to facilitate analysing the micro-cracking with a microscope. The experiments and numerical analyses presented here showed that the damage in the concrete, from the blast wave and fragment impacts, is localized in the impact zone. The concrete below this zone, at a depth of approximately twice the depth of the maximum penetration, was hardly affected at all by the blast wave and fragment impacts. This indicates that it is possible to distinguish between the global load effects and the local damage effects that are caused by the fragment impacts. Consequently, it may be possible to separate the loads, at the design stage, from a blast wave and fragment impacts.     

The effects of explosive blast load variability on safety hazard and damage risks for monolithic window glazing

Although the modelling of built infrastructure subject to blast loading has been well developed, considerable uncertainty remains with respect to explosive loading parameters and structural response. This paper focuses on facade glazing – as this poses significant safety hazards when affected by explosive blast loads. A structural reliability analysis is used to calculate probabilities of glazing damage and safety hazards conditional on given threat scenarios. The analysis considers the variability of explosive blast loading; in particular, from variations in explosive weight, explosion effects in terms of pressure, stand-off distance, inherent blast load variability and model error. Uncertainties in structural response (including the variability in glazing stress limits, situational geometry, fragment drag coefficients and modelling error) are then considered in the analysis. This allows the prediction of likelihood and extent of damage and casualties. It was found that damage and safety hazard risks are very sensitive to the accuracy of the blast loading prediction model and the inherent variability of blast loading.     

潜艇艇体结构在水下爆炸冲击载荷作用下损伤研究

采用数值计算和试验手段相结合的方法,对潜艇艇体结构在水下爆炸载荷作用下的损伤进行了研究。利用试验手段确定了潜艇艇体用钢的材料动态性能参数和潜艇典型单元结构在爆炸冲击载荷作用下的开裂判据。采用双层壳体建模方案对潜艇结构进行整艇有限元建模,运用MSC.DYTRAN程序对整艇结构进行水下抗爆仿真。分析了三种不同工况下潜艇艇体结构的损伤形式。本文计算方法和仿真结果可供潜艇水下抗爆设计和潜艇结构生命力评估参考。     

战斗部外爆对舰船毁伤快速评估算法

为对舰船在战斗部外爆时破片和冲击波的毁伤进行快速评估,建立快速仿真算法。通过分析目标各部件和战斗部起爆点的相对位置关系,结合经验公式,计算舰船在战斗部外爆加载时的超压分布。模拟仿真战斗部外爆时的破片场,使用射击线方法,计算破片对舰船的侵彻毁伤。使用C++和glut库,实现仿真场景的三维漫游,给出有关的毁伤图像。     

Numerical prediction of concrete slab response to blast loading

In this paper, a dynamic plastic damage model for concrete material has been employed to estimate responses of both an ordinary reinforced concrete slab and a high strength steel fibre concrete slab subjected to blast loading. In the concrete material model, the strength envelope is a damage-based modified piece-wise Drucker–Prager model; the strain rate effect on tension and compression are considered separately; the damage variable is based on Mazars’ damage model, which is a combination of tensile and compressive damage. The equation of state (EOS) is also a combination of the porous and solid EOS of concrete with different forms for tension and compression states. The interaction between the blast wave and the concrete slab is considered in the 3D simulation. In the first stage, the initial detonation and blast wave propagation is modelled in a 2D simulation before the blast wave reaches the concrete slab, then the results obtained from the 2D calculation are remapped to a 3D model. The calculated blast load is compared with that obtained from TM5-1300. The numerical results of the concrete slab response are compared with the explosive tests carried out in the Weapons System Division, Defence Science and Technology Organisation, Department of Defence, Australia. Repetitive applications of blast loading on slabs are also simulated and the results compared with test data.     

A hybrid rigid body rotation model for predicting a response of a temporary soil-filled wall subjected to blast loading

This study is aimed to provide an efficient analytical model to calculate a time history of response for a free-standing soil-filled HESCO Bastion concertainer^® wall subjected to air blast loading. The model is formulated based on the observations of the wall response to air blast loading in the experiments and on the deformation of a finite element model. This hybrid rigid body rotation model combines both a reverse Winkler foundation to model the distribution of pressure at the base of the wall and perfectly plastic shear resistance to model the shear deformation at the corner. The time histories of horizontal and vertical displacements calculated from the proposed analytical model are validated with displacements from both full-scale blast testing of free-standing simple straight walls and calculations using a finite element model.     

近场爆炸时斜拉索抗爆性能分析

In order to study dynamic response of a stay cable of cable-stayed bridges under blast loading, based on the basic blast theory, the anti-explosion performance of the cable under near field blast loading was analyzed.Stress and damage of the cable were analyzed, and further the parametric analyses for different scaled distances were performed.Results showed that under near field blast load, fracture does not appear on the cable, and its failure mode presents a failure caused by its stress exceeding yield one;its weakest position is the cable-girder anchorage zone where the stress of the cable is larger than that of the cable near explosion point due to reflection of blast wave; the safe scaled distance to keep the cable from failure is 0.287 m/kg1/3,if the scaled distance is larger than this critical scaled distance, the cable can’t fail.     

The influence of different pre-formed holes on the dynamic response of square plates under air-blast loading

Studying the blast response of plates with pre-formed holes under blast loading serves as a significant method to decouple dynamic response of plates with pre-formed holes under combined blast and fragment loading. Based on material test system (MTS) and Split Hopkinson tension bar (SHTB), the mechanical properties of experimental steel under different strain rates were obtained. Then, the experiments on the responses of plates with square, diamond and circular holes under air-blast loading were carried out and the failure modes of plates with diamond holes were derived. Later, the deformation curves of target plate were obtained by laser reverse forming technique. Next, a constitutive model program considering strain rate, stress status and temperature effect was adopted to carry out numerical simulation calculation, which verified the accuracy of this numerical simulation. Finally, discussions were carried out on the damage level at places where cracks might form, the dynamic stress concentration coefficient and stress status change, and then the influence which pre-formed holes have on the failure mode was analyzed. The results of this study show that: (1) A fortran vectorized user-material subroutine (VUMAT) program considering strain rate, stress status and temperature effect can effectively predict the dynamic response of metallic materials; (2) the shape of pre-formed holes affects the damage level, dynamic stress concentration coefficient and stress status. Besides, failure occurs more easily in plates with diamond pre-formed holes; (3) pre-formed holes have an obvious influence on the failure modes of plates under different blast distance.     

Damage prediction of concrete gravity dams subjected to underwater explosion shock loading

The damage prediction of concrete gravity dams under blast loads has gained importance in recent years due to the great number of accidental events and terrorist bombing attacks that affected engineering safety. It has long been known that an underwater explosion can cause significantly more damage to the targets in water than the same amount of explosive in air. While the physical processes during an underwater explosion and the subsequent response of structures are extremely complex, which involve lots of complex issues such as the explosion, shock wave propagation, shock wave-structure interaction and structural response. Hence a sophisticated numerical model for the loading and material responses would be required to enable more realistic reproduction of the underlying physical processes. In this paper, a fully coupled numerical approach with combined Lagrangian and Eulerian methods, incorporating the explosion processes, is performed. The RHT (Riedel–Hiermaier–Thoma) model including the strain rate effect is employed to model the concrete material behavior subjected to blast loading. Detailed numerical simulation and analysis of a typical concrete gravity dam subjected to underwater explosion are presented in this study. In terms of different TNT charge weights, the structural response and damage characteristics of the dam at different standoff distances are investigated. Based on the numerical results, critical curves related to different damage levels are derived.