On the dynamic behaviour of a long missile pipe after impact on a rigid target pipe

Two modes of deformation of a long missile pipe following an impact on a rigid target pipe of larger radius are analysed. It is assumed that the missile pipe can form either a ‘nutcracker’ type of mechanism or simply ‘wrap around’ the target pipe. The influence on the dynamic behaviour of the missile pipe of the parameters like the length, kinetic energy and the plastic moment of the missile pipe and the target pipe radius are discussed. A numerical procedure is presented to obtain the maximum force of interaction developed between the two pipes which also takes account of possible transition from a ‘nutcracker’ mode to the ‘wrap-around’ mode.     

Reliability of reinforced concrete structures under fatigue

This paper focuses on time-variant reliability assessment of deteriorating reinforced concrete structures under fatigue conditions. A strategy combining two time scales, namely the micro-scale of instantaneous structural dynamics (or statics) and the macro-scale of structural lifetime, is proposed. Non-linear response of reinforced concrete structures is simulated by means of the finite element method with adequate material model. A phenomenological fatigue damage model of reinforced concrete is developed and calibrated against experimental results available in the literature. Reliability estimates are obtained within the response surface method using the importance/adaptive sampling techniques and the time-integrated approach. The proposed assessment strategy is illustrated by an example of a concrete arch under fatigue loading. The obtained results show a general inapplicability of local and linear fatigue models to system level of structures.     

Crater formation in a plastic target under hypervelocity impact

The analytical models of crater formation in a semi-infinite target under hypervelocity impact have been analyzed. It has been shown by numerical calculations that to approximately calculate the crater size for a narrow range of impact velocities, the model of an ideal plastic body can be used. A new analytical model of crater formation in a plastic target, which describes the experimental data in a wide range of impact conditions, is suggested. The crater formes are analyzed.     

Mechanical behaviour analysis of a buried steel pipeline under ground overload

Ground overload is one of the most important factors that threaten the safe operations of oil and gas pipelines. The mechanical behaviour of a buried pipeline under ground overload was investigated using the finite element method in this paper. The effects of the overload parameters, pipeline parameters and surrounding soil parameters on the stress–strain response of the buried pipeline were discussed. The results show that the maximum von Mises stress appears on the top of the buried pipeline under the loading area when the ground load is small, and the stress distribution is oval. As the ground load increases, the maximum stress increases, and the high stress area extends. The von Mises stress, plastic strain, plastic area size, settlement and ovality of the buried pipeline increase as the ground load and loading area increase. The buckling phenomenon of the no-pressure buried pipeline is more serious than the pressure pipeline. As the internal pressure increases, the high stress area and the maximum plastic strain of the buried pipeline first decrease and then increase, the settlement of the buried pipeline increases, and the ovality decreases. The von Mises stress, maximum plastic strain, settlement and ovality of the buried pipeline decrease with increasing buried depth, the surrounding soil's elasticity modulus, Poisson's ratio and cohesion. The maximum von Mises stress, high stress area, the maximum plastic strain, plastic area and ovality increase as the diameter–thickness ratio increases. The critical diameter–thickness ratio is 60, and the settlement of the buried pipeline first increases and then decreases as the diameter–thickness ratio increases. Finally, a protective device of the buried pipeline is designed for preventing ground overload. It can be repaired in a timely manner without stopping the transmission of oil and gas and widely used in different locations because of its simple structure and convenient installation.     

合成孔径成像中掩埋目标的深度误差分析

在掩埋目标三维成像过程中,沉积层底质的不同与掩埋深度的变化,会使成像结果中目标深度与真实深度出现偏差。针对这一问题,可以利用下视的面阵合成孔径三维成像算法,通过构建水下分层模型与声速剖面模型,对掩埋点目标进行三维成像仿真。通过改变沉积层底质与掩埋深度,从理论分析与仿真结果研究深度误差的变化。研究表明,深度误差随沉积层声速和掩埋深度的增加而不断变大。     

The behaviour of concrete under impact loading: Experimental procedures and method of analysis

The behaviour of concrete beams under impact loading was studied, using an instrumented drop-weight impact apparatus capable of dropping a 345 kg mass from heights of up to 3 m. Both plain and conventionally reinforced beams, with overall dimensions (length x width x depth) of 1,400×100×125 mm, were tested on a 960 mm span, with the impact load applied at mid-span. The load on the instrumented striking tup, and the acceleration of the beam itself, were measured as a function of time; the entire impact events had a duration of 10 to 70 ms. This paper describes the methods used to analyze the impact data, as well as some preliminary results.     

Failure analysis of reinforced concrete walls under impact loading using the finite element approach

In this paper, the punching resistance of a reinforced concrete (RC) wall under missile impact loading is evaluated using the finite element approach. The model is analyzed using LS-DYNA, a commercially available software program. The structural components of the RC wall, missile, and their contacts are fully modeled. Included in the analysis is material nonlinearity, which considers damage and failure. Damping effect is also taken into account. The analysis results are then verified with the test results. Parametric studies with a varying number of layers of longitudinal rebar and shear bar spacing are carried out to investigate the punching behavior of RC walls under missile impact. The distance travelled, scabbing area, and failure mode of various RC walls are examined, and efficient designs are recommended thereafter.     

Experiments on concrete under uniaxial impact tensile loading

A problem of practical importance for designing of structural elements is discussed in this paper—the behaviour of concrete subjected to uniaxial impact tensile loading. The “Split Hopkinson Bar” technique was adopted for testing concrete in uniaxial tension at stress rates between 2 and 60 N/mm²/ms. A remarkable increase in tensile strength was observed due to high stress rate. The ratio of impact and static tensile strength varied between 1.33 and 2.34 for various concrete mixes. The influence of maximum aggregate size, water-cement ratio, cement content, cement type and quality, specimen humidity, static compressive strength and loading/casting direction upon the uniaxial impact tensile strength was studied. The high stress rate resulted in an increase of the modulus of elasticity of concrete in uniaxial tension. An explanation for the observed phenomena is suggested.     

AFRP约束混凝土多次冲击试验研究

为研究芳纶纤维增强层复合材料（AFRP）约束条件下混凝土抗多次冲击的动态力学性能,采用Ф100 mmSHPB试验装置和超声无损检测,在相似应变率条件下,对C30,C40,C50三种基体强度等级的1~3层AFRP约束混凝土抗多次冲击动态力学性能和冲击后混凝土试件内部损伤规律进行试验研究。结果表明：各约束层数AFRP约束混凝土动态峰值应力对冲击次数不敏感,上下浮动不超过8%,稳定性良好;随着冲击次数的增加,动态峰值应变增大,内部混凝土损伤增大,损伤因子与冲击次数呈线性关系;AFRP约束混凝土内部损伤在达到普通混凝土极限损伤后仍能保持试件完整,具备对抗下次冲击的能力。     

Numerical simulation of reinforced concrete structures under impact loading

This study presents the performance of a combined finite‐discrete element method for prediction of the structural response of reinforced concrete beams under impact loading. A combination of finite and discrete element methods enables the modelling of the concrete and the reinforcement before the concrete cracking, as well as a discontinuous nature of the concrete caused by fracture and fragmentation under high impact loading. Discretization of the concrete with triangular finite elements is coupled with one‐dimensional reinforcing bars embedded inside the concrete finite elements. The cracking in the concrete activates the joint elements used to simulate the non‐linear behavior of both concrete and reinforcement. Numerical analysis based on experimental test data has been carried out to simulate the main features of the reinforced concrete beams impacted by free‐falling drop‐weights. A high level of accuracy was demonstrated in various comparisons between the experimental tests and the analysis results, including peak displacement, crack pattern, damage level and failure modes of reinforced concrete beams.     

冲击荷载作用下早强EPS混凝土的力学性能

采用&;#61542;100mm分离式霍普金森压杆（split Hopkinson pressure bar,简称SHPB）试验装置,对养护龄期分别为12h、24h和36h的早强聚苯乙烯混凝土（EPS）进行了冲击压缩试验,得到了相应的应力-应变曲线,并与养护龄期为28d的聚苯乙烯混凝土（EPS）的应力-应变曲线进行比较。结果表明：养护龄期为36h、28d的EPS混凝土随着应变率的增加,其冲击压缩强度也相应增加;养护龄期为12h、24h的EPS混凝土随着应变率的增加,其冲击压缩强度变化不明显。另外,还研究了试件动态抗压强度与平均应变率的关系和养护龄期对动态抗压强度的影响,证明了EPS混凝土的抗冲击性能随养护龄期的增长而增加。     

U型试件混凝土冲击寿命的统计分析

采用自行设计的U型混凝土试件,以及自制的落锤冲击实验装置,研究了其抗冲击性能。引入顺序统计量和秩的概念,根据平均秩法的期望估计,计算累积失效概率函数F(N)和生存概率函数R(N)的估计值。利用双参数威布尔(Weibull)分布理论及线性回归理论,分析了在4种不同落锤质量水平下冲击寿命N的分布规律,结果表明,双参数威布尔分布理论可以很好地描述U型试件混凝土冲击寿命N的分布特征。     

Dynamic response of top-down cracked asphalt concrete pavement under a half-sinusoidal impact load

A 3D finite element analysis model of cracked asphalt pavement is established by the FEM software ABAQUS. Based on dynamics mechanics, fracture mechanics and finite element theory, this paper studies the influence of various vehicle speeds, crack location, crack depth, damping ratio etc. on the dynamic response. The results show that the surface deflection, the maximum tensile strain at the bottom of the asphalt layer, and the maximum shear stress of the asphalt layer decreased with the increase in vehicle velocity when there is no crack in the pavement. No matter where the transverse position of the crack is the stress intensity factors increase with the increase in crack depth and decrease exponentially with the increase in longitudinal distance between the vehicle center and the crack. In the case of the crack locating in the center of wheel clearance, the surface deflection increases with the crack depth increasing. But if the crack is at the edge of the wheel track, there will be a critical vehicle velocity where the surface deflection is smaller than the asphalt pavement without crack if the vehicle velocity is above it. The maximum tensile strain at the bottom of the asphalt layer and the maximum shear stress of the asphalt layer are also smaller than the asphalt pavement without crack. The maximum tensile strain and the maximum shear stress decrease with the damping ratio increasing. So the increase in damping ratio can help to alleviate the propagation of cracks.     

Numerical analysis of oblique impact on reinforced concrete

This study proposes a simple but efficient methodology based on the equivalent inclusion method and finite element analysis. Oblique impacting is considered to investigate the residual velocity and ricochet limit of an ogive-nose steel projectile with various impact velocities against a reinforced concrete slab. The computational results are compatible with Tate’s formula for the ricochet limit as a function of the impact velocity. The proposed methodology is useful for designing defense structures, and the ricochet limit is one of the important parameters that govern the performance of a weapon system. The methodology can be further developing for designing the protection of military structures and nuclear power plants against high velocity projectiles.     

Failure analysis of a cracked concrete gravity dam under earthquake

A dynamic contact model for simulating the interaction of two surfaces divided by a dam crack, and a simplified reinforcing steel constitutive model for simulating the effect of earthquake-resistant reinforcement on a cracked dam are developed in this study. After the verification of the dynamic contact model and the reinforcing steel constitutive model by illustrations, the JINANQIAO roller compacted concrete (RCC) gravity dam is investigated with two case scenarios: a straight crack case and a curving crack case scenarios, including their dam–foundation–reservoir interaction, respectively. Emphasis is paid to analysing the failure process of the cracked dam with and without reinforcement. Results show that the cracked dam maintains a large safety margin, and the curving crack is beneficial to the improvement of earthquake resistance. Commonly applied steel reinforcement measures can effectively decrease the sliding displacement and the joint opening of the cracked dam; however, the layout of the reinforcing steel and its quantity to be used needs particular consideration.     

Reliability analysis of reinforced concrete grids with nonlinear material behavior

Reinforced concrete grids are usually used to support large floor slabs. These grids are characterized by a great number of critical cross-sections, where the overall failure is usually sudden. However, nonlinear behavior of concrete leads to the redistribution of internal forces and accurate reliability assessment becomes mandatory. This paper presents a reliability study on reinforced concrete (RC) grids based on coupling Monte Carlo simulations with the response surface techniques. This approach allows us to analyze real RC grids with large number of failure components. The response surface is used to evaluate the structural safety by using first order reliability methods. The application to simple grids shows the interest of the proposed method and the role of moment redistribution in the reliability assessment.     

Experiments on concrete under repeated uniaxial impact tensile loading

The fatigue behaviour of concrete was a new aspect in the experimental program focused on the behaviour of concrete subjected to uniaxial impact tensile loading. The results obtained in repeated impact tensile loading tests (at stress rates of 2–6 N/mm². ms) indicated that the impact fatigue was associated with progressive crack propagation resulting in accumulative damage of concrete. The upper stress limits varied between 1.7 and 0.6 times the static tensile splitting strength and specimen withstood 1 to 6,055 loading cycles respectively. The influence of water-cement ratio, cement content, specimen humidity, loading/casting direction and compressive strength upon the impact fatigue tensile strength of concrete was studied. The phenomena observed are discussed with the aid of fracture mechanics concepts.

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Résumé Un aspect nouveau dans la recherche du comportement du béton soumis en traction uniaxiale à des charges de choc est le comportement à la fatigue. Ce problème de fatigue a une grande importance pour des pieux de fondation. On a obtenu 89 résultats en faisant des essais répétitifs de choc en traction où la vitesse de mise en tension variait entre 2 et 6 N/mm². ms. Les limites des contraintes ont varié entre des valeurs égales à la résistance du choc en traction uniaxiale (1,7 f_b,r) et 0,6 fois la résistance statique à la traction par fendage. Les éprouvettes ont résisté à des variations de charge de 1 à 6 055. Les résultats montrent que la fatigue au choc allait de pair avec une augmentation progressive de la fissuration provoquée par la dégradation accumulative du béton. Il a été constaté que la résistance du béton à un effort de chocs repétés en traction augmente quand la valeur du facteur eau-ciment et la teneur en ciment augmentent. L'humidité des éprouvettes n'influence pas la résistance à la traction par chocs répétés. La résistance déterminée sur des éprouvettes chargées perpendiculairement à la direction du bétonnage était plus élevée que la résistance mesurée dans un essai où la direction de chargement et du bétonnage étaient parallèles. En général un béton de qualité inférieure a une meilleure résistance aux chocs répétés. On propose des explications des phénomènes observés par les théories de la mécanique de la rupture.

     

路旁地下光缆受冲击压路机振动影响的数值分析

冲击压路机施工振动对路旁地下光缆有何影响,尚没有明确的实验及理论定论,制约了冲击压实技术在埋设地下光缆路段的应用。为了解决这个问题,基于实际工程参数,根据有关假设,模拟冲击压实施工多周期加载模式,建立三维有限元模型,利用ANSYS软件对路面附近不同埋深的光缆在冲击压路机施工时受到的振动影响进行数值分析,结果表明冲击压实施工对埋深60cm的光缆影响不大,当光缆的埋设位置由原来位置向路面板方向靠近时,冲击压实施工对光缆产生的影响逐渐变大,在基层底部向上0.1m处和基层底部向上0.14m处Z方向压应力和X方向拉应力分别达到允许值,对光缆造成破坏     

Mixed-mode fracture performance of fibre reinforced concrete under impact loading

A test procedure developed to determine the mixed-mode impact resistance of fibre reinforced concrete materials is described. Results are presented from a series of experiments using a repeated drop-weight impact apparatus for the impact resistance of both polypropylene and steel fibre reinforced concrete. The behaviour of the mixed-mode specimen geometry was investigated under impact loading condition. The effect of the fibre types and contents on the impact fracture energy of the specimens was investigated. A close investigation was made of the positions and formations of the crack patterns. The fracture performance of the plain and fibre reinforced concrete was investigated with the proposed geometry using 1.0, 2.0 and 3.0% by weight in the case of steel fibre, and 0.1, 0.2 and 0.3% by weight in the case of polypropylene fibre.

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Resume Aux charges statiques auxquelles les structures en béton sont soumises s'ajoutent souvent des charges dynamiques, parfois significatives, qu'il convient de prendre en compte dans le calcul. Cet article décrit un mode opératoire visant à déterminer la résistance au choc en mode mixte de béton renforcé de fibres (FRC). On y présente les résultats d'une série d'essais utilisant une machine d'essai au choc à répétition (mouton) pour évaluer la résistance de béton renforcé de fibres d'acier et de fibres de polypropylène. On a mis au point une géométrie d'éprouvettes en mode mixte qu'on a soumises à des essais au choc, et on a étudié l'effet des types et des pourcentages de fibres sur la résistance des éprouvettes à la rupture par choc. On s'est aussi livré à une étude précise des emplacements et de la formation des fissures. On a examiné la résistance à la rupture de béton ordinaire et de béton de fibres dans la géométrie proposée avec des pourcentages de 1, 2 et 3% en poids de fibres d'acier, et de 0,1, 0,2 et 0,3% pour les fibres de polypropylène.