Explosion resistance performance of reinforced concrete box girder coated with polyurea:Model test and numerical simulation

To study the anti-explosion protection effect of polyurea coating on reinforced concrete box girder,two segmental girder specimens were made at a scale of 1:3,numbered as G(without polyurea coating)and PCG(with polyurea coating).The failure characteristics and dynamic responses of the specimens were compared through conducting explosion tests.The reliability of the numerical simulation using LS-DYNA software was verified by the test results.The effects of different scaled distances,reinforcement ratios,concrete strengths,coating thicknesses and ranges of polyurea were studied.The results show that the polyurea coating can effectively enhance the anti-explosion performance of the girder.The top plate of middle chamber in specimen G forms an elliptical penetrating hole,while that in specimen PCG only shows a very slight local dent.The peak vertical displacement and residual displacement of PCG decrease by 74.8% and 73.7%,respectively,compared with those of specimen G.For the TNT explosion with small equivalent,the polyurea coating has a more significant protective effect on reducing the size of fracture.With the increase of TNT equivalent,the protective effect of polyurea on reducing girder displacement becomes more significant.The optimal reinforcement ratio,concrete strength,thickness and range of polyurea coating were also drawn.

Mechanical Properties of Nano-CaCO_(3) and Basalt Fiber Reinforced Concrete:Experiments and Numerical Simulations

In this study,the compressive,split tensile,and flexural strengths of concrete with nano-CaCO_(3) only were compared with those of concrete with nano-CaCO_(3) and basalt fibers through field experiments,and the underlying mechanisms were analyzed by the Scanning Electron Microscope (SEM) techniques.On the mesoscale,a damage model of concrete was established based on the continuum progressive damage theory,which was used to investigate the influence of different lengths and contents of fibers on the mechanical properties of concrete.Then,the experimental and numerical simulation results were compared and analyzed to verify the feasibility of model.The results show that nano-CaCO_(3) can enhance the compressive strength of the concrete,with an optimal content of 2.0%.Adding basalt fibers into the nano-CaCO_(3) reinforced concrete may further enhance the compressive,split tensile,and flexural strengths of the concrete;however,the higher content of basalt fiber can not lead to higher performance of concrete.The optimal length and content of fiber are 6 mm and 0.20%,respectively.The SEM result shows that the aggregation of basalt fibers is detrimental to the mechanical properties of concrete.The numerical simulation results are in good agreement with the experimental results.

Numerical Simulation on Explosion in Double-Layer Medium of Concrete and Soil

The numerical simulation on explosion in concrete and soil is performed by using the three-dimension finite element code LS-DYNA, into which a continuum damage model which can well describe the fracture of concrete is implemented. As a consequence, wave propagation and attenuation in concrete and on soil-concrete interface are obtained respectively. Moreover, the damage regions of concrete at different thicknesses of soil （TOS） and depths of charge （DOC） are procured. The existent soil reduces damage region of concrete. Numerical results provide reference for design of warhead and protective structure and blasting.

Numerical Simulation on Dynamic Bending Strength of Three-Graded Concrete Beam Based on Meso-Mechanics

To study the bending strength of mass concrete under dynamic loading, the pure bending zone of three-graded concrete beam is considered as a three-phase composite composed of matrix, aggregate and interface between them on meso-level. Dynamic constitutive model considering strain-rate strengthening effect and damage softening effect is adopted to describe the cocrete and meso-element's damage. The failure mechanisms of beam under impact loading, triagle wave load, dynamic load coupling with initial static loading were simulated by using displacement-controlled FEM. Furthermore, stress-strain curve of the specimens and their dynamic bending strength were obtained. The results obtained from numerical simulation agreed well with experimental data.

Damage of a large-scale reinforced concrete wall caused by an explosively formed projectile(EFP)

To quickly break through a reinforced concrete wall and meet the damage range requirements of rescuers entering the building,the combined damage characteristics of the reinforced concrete wall caused by EFP penetration and explosion shock wave were studied.Based on LS-DYNA finite element software and RHT model with modified parameters,a 3D large-scale numerical model was established for simulation analysis,and the rationality of the material model parameters and numerical simulation algorithm were verified.On this basis,the combined damage effect of EFP penetration and explosion shock wave on reinforced concrete wall was studied,the effect of steel bars on the penetration of EFP was highlighted,and the effect of impact positions on the damage of the reinforced concrete wall was also examined.The results reveal that the designed shaped charge can form a crater with a large diameter and high depth on the reinforced concrete wall.The average crater diameter is greater than 67 cm(5.58 times of charge diameter),and crater depth is greater than 22 cm(1.83 times of charge diameter).The failure of the reinforced concrete wall is mainly caused by EFP penetration.When only EFP penetration is considered,the average diameter and depth of the crater are 54.0 cm(4.50 times of charge diameter)and 23.7 cm(1.98 times of charge diameter),respectively.The effect of explosion shock wave on crater depth is not significant,resulting in a slight increase in crater depth.The average crater depth is 24.5 cm(2.04 times of charge diameter)when the explosion shock wave is considered.The effect of explosion shock wave on the crater diameter is obvious,which can aggravate the damage range of the crater,and the effect gradually decreases with the increase of standoff distance.Compared with the results for a plain concrete wall,the crater diameter and crater depth of the reinforced concrete wall are reduced by 5.94%and 9.96%,respectively.Compared to the case in which the steel bar is not hit,when the EFP hit one steel bar and the intersection of two steel bars,the crater diameter decreases by 1.36%and 5.45%respectively,the crater depth decreases by 4.92%and 14.02%respectively.The EFP will be split by steel bar during the penetration process,resulting in an irregular trajectory.

Propagation Characteristics of Plane Explosion Wave in Layered Concrete Media

Layered concrete media with different wave impedance materials under one-dimensional strain are studied by numerical simulation. The four typical prototypes are analyzed,including concrete foam,air,steel plate and concrete as the middle layer,and the upper and lower layers are concrete materials. The propagation characteristics of plane blast wave in the concrete structure are illustrated,including the propagation and attenuation of stress wave across the different interlayers,the wave reflection and transmission at layered interfaces,the peak value of stress in the lower concrete and the total energy distribution in various medium layers. The result shows that the role of soft interlayer in concrete structure is mainly due to its low wave impedance,the waveform of incident wave is changed,the stress wavelength is pull wide,the radial diffusion of energy is enhanced,and the stress amplitude of and the energy input into the third layer are reduced. Meanwhile,it has been also proved that the air interlayer is able to reduce the peak value of explosion wave which is obviously different from that of foamed material. As a result,it should be concerned about stress amplitude and energy in order to get the best protective structure.

Numerical Simulation of Concrete Plate Damaged Under Explosive Loading

The grisliness after-effects can be induced by explosion accident with the collapsing of the structures, the demolishing of the equipments and the casualty of the human beings. Isolation belt constructed between the blast point and the construction is one of the useful design schemes for blast resistance. The nonlinear procedure ANSYS/LSDYNA970 is used to simulate the contact detonation and the isolation belt of blast resistance filled with the air or water respectively. The results indicate that the maximal damage can be caused by the contact detonation, and the isolation belt of blast resistent filled with water can reduce the damage greatly.

Peridynamic Modeling and Simulation of Fracture Process in Fiber-Reinforced Concrete

In this study,a peridynamic fiber-reinforced concrete model is developed based on the bond-based peridynamic model with rotation effect(BBPDR).The fibers are modelled by a semi-discrete method and distributed with random locations and angles in the concrete specimen,since the fiber content is low,and its scale is smaller than the concrete matrix.The interactions between fibers and concrete matrix are investigated by the improvement of the bond’s strength and stiffness.Also,the frictional effect between the fibers and the concrete matrix is considered,which is divided into static friction and slip friction.To validate the proposed model,several examples are simulated,including the tensile test and the three-point bending beam test.And the numerical results of the proposed model are compared with the experiments and other numerical models.The comparisons show that the proposed model is capable of simulating the fracture behavior of the fiber-reinforced concrete.After adding the fibers,the tensile strength,bending strength,and toughness of the fiber-reinforced concrete specimens are improved.Besides,the fibers distribution has an impact on the crack path,especially in the three-point bending beam test.

A multiphase mesostructure mechanics approach to the study of the fracture-damage behavior of concrete

A multiphase mesostructure mechanical model is proposed to study the deformation and failure process of concrete considering its heterogeneity at the meso scopic level.Herein,concrete is taken as a type of three-component composite material composed of mortar matrix,aggregates and interfaces on the meso-scale.First,an efficient approach to the disposition of aggregates of concrete and a state matrix method to generate mesh coordinates for aggregates are proposed.Secondly,based on the nonlinear continuum damage mechanics,a meso-scale finite element model is presented with damage softening stress-strain relationship for describing the mechanical behavior of different components of concrete.In this method,heterogeneities of each component in the concrete are considered by assuming the material properties of three components conform to the Weibull distribution law.Finally,based on this multiphase meso-mechanics model,a simulation analysis of fracture behavior of a rock-fill concrete(RFC) beam is accomplished.The study includes experimental tests for determining basic mechanical parameters of three components of RFC and four-point flexural beam tests for verification of the model.It is preliminarily shown that the numerical model is applicable to studying failure mechanisms and process of concrete type material.

Numerical simulation of drop weight impact sensitivity evaluation criteria for pressed PBXs

A thorough understanding of drop-weight impacted responses for polymer-bonded explosives(PBXs)is significant to evaluate their impact sensitivity.The characteristics of the drop-weight impacted pressed PBXs including deforming,fracturing,forming a local high-temperature region and igniting,were simulated using a coupled mechanical-thermo-chemical model integrating micro-defects evolution.A novel evaluation method for impact sensitivity is established using the relation between the input kinetic energy and the output energy due to deformation,crushing energy,local hot spot energy and ignition.The effects of impact velocity on sensitivity were analyzed and the critical local ignition impact velocity is determined as 4.0-4.5 m/s.The simulated results show that shear-crack friction heating is the dominant ignition mechanism.The region along the boundary of PBXs sample is the most hazardous regions where ignition first occur.The propagation of stress wave in PBXs causes shear-crack hotspot and bulk temperature exhibiting an approximate 45°direction evolution path,which is the main reason that dominated damage-ignition region transits from the boundary to the central of sample.

Experiments and Numerical Simulation of Small-scale Slapper Driven by Electrical Explosion

Based on the low inductance technology and parallel-plate transmission principle,an experimental apparatus of small-scale slapper initiating primary high explosives driven by electrical explosion is designed and established.The problem of instantaneously and continuously measuring the velocity of the small-scale slapper is successfully solved by using the technique of laser interference.Compared with the results published on the literatures at home and abroad,data of the experimental and the numerical simulation shown in this paper are more proper to reflect the physical process of electrical explosion driving slapper.One-dimensional numerical simulation of electrical explosion driving slapper is done using the hydrodynamic code.The experimental results are consistent with the computed ones by introducing a power correction factor.In the end,the introduced power correction factor is discussed.

Numerical Analysis of Effect of Water on Explosive Wave Propagation in Tunnels and Surrounding Rock

Based on the application of practical engineering,propagation processes of explosive waves in rock with water well and tunnel are simulated by ANSYS/LS-DYNA software. The evolution of damage in rock is presented. The effect of water on the damage of the concrete slab in a tunnel is compared with damage inflicted without water. The numerical simulation illustrates that water plays an important role in the evolution of damage of the concrete slab in a mine tunnel. In the presence of water in the rock the concrete slab is damaged more severely than without water in rock. The effect of water location in the rock is also considered. It is found that the concrete slab in the tunnel shows various degrees of damage as a function of the different locations of water. Attenuation laws of stress waves over time-space in rock with water are also obtained. Numerical results indicate that,under blast loading,there are three zones in the rock: a crushed zone nearby the explosive charge,a damaged zone and an elastic zone. The conclusions of numerical analysis may provide references for blasting designs and structure protection.

负压条件对T2/Q235爆炸焊接复合板界面的影响

为了探究负压条件对T2/Q235爆炸焊接复合板界面的影响,选用硅藻土敏化的低爆速粉状乳化炸药作为焊接专用药,T2为覆板,Q235为基板分别在100、60、20kPa环境压力下进行爆炸焊接试验;采用金相分析等方法研究了复合界面的形貌特征和元素组分,采用数值模拟进一步揭示了负压爆炸焊接机理。结果表明,负压条件会增大粉状乳化炸药的装药密度,但爆速变化不大,20kPa条件下猛度比常压条件下提高8.4%;随着环境压力的降低,复合板界面波高和波长逐渐增大,20kPa条件下波高比常压下增加了49%,波长增加了23%;负压条件下T2/Q235结合面氧元素含量低于常压环境;数值模拟结果表明,T2/Q235界面波随着炸药的装药密度变大而增大,与实验结果一致。在爆炸焊接时密度为0.8g/cm^(3)(20kPa)比0.711g/cm^(3)(常压)炸药碰撞速度提高了16.3%,碰撞压力提高了66.3%。研究表明,负压相比于常压条件提高了爆炸焊接的炸药能量利用率。

基于拉压杆模型的装配式混凝土挡墙结构设计方法

为了研究装配式混凝土箱体挡墙结构在水压力和土压力共同作用下的受力机理,提出了一种基于拉压杆模型的装配式混凝土挡墙结构设计方法.以体积和应变能为优化目标,采用Tosca软件对数值模拟得到的主要受力骨架进行拓扑优化.构建拉压杆模型,结合箱体挡墙结构的破坏机理,分析并推导出侧墙受压、临水面挡墙和集束连接受拉3种主要破坏模式的承载力公式.实际工程对比分析结果表明:进行900次模型优化后,优化形态和应变能基本保持不变;基于拉压杆模型的装配式混凝土箱体挡墙结构的承载能力低于规范值和有限元模拟值,但误差均保持在16%范围内,从而验证了该方法的合理性.

爆炸荷载下预制节段拼装双层钢管混凝土墩柱的动力响应数值模拟

为提升装配式公路桥梁的抗爆防护能力,提出了一种新型预制节段拼装双层钢管混凝土(PS-CFDST)组合墩柱.基于非线性显式动力分析程序LS-DYNA建立了新型PS-CFDST墩柱在爆炸荷载作用下动力响应分析的精细有限元模型,并通过已有试验结果验证了模型的准确性.对爆炸荷载作用下PS-CFDST墩柱的动力响应进行数值模拟分析,研究了PS-CFDST墩柱在爆炸荷载作用下的破坏过程、损伤机理和耗能机制.运用参数化分析方法,研究了爆炸距离、节段数量和预应力水平等关键参数对PS-CFDST墩柱动力响应的影响,并在此基础上提出了PS-CFDST墩柱的抗爆设计建议.结果表明:PS-CFDST墩柱除通过材料塑性损伤耗能之外,节段接缝界面滑移耗能机制对耗能贡献可达40%以上;增大墩柱可接近距离是提升墩柱抗爆安全性的有效手段,增大预应力有利于减小柱中最大水平位移和墩底剪切滑移,从而提升PS-CFDST墩柱的抗爆性能.

基于修正力磁模型的混凝土结构压磁疲劳模拟

为了通过混凝土梁内钢筋在力磁效应下的磁信号来定量分析混凝土梁的疲劳状态,整合几种力磁模型的优缺点和适用范围,提出了适用于铁磁性材料弹塑性阶段的力磁本构模型,并通过ANSYS定量模拟分析了混凝土梁在弹性和弹塑性阶段的磁化特征;对混凝土结构在拟动力和疲劳加载过程中的力磁效应进行了有限元模拟,得到了测点处磁感应强度的时变曲线,并与试验和隐式微分模型所得结果进行对比。结果表明:修正后的力磁模型在弹性阶段的应用能够准确反映试验观察到的3个阶段变化规律,即梁开裂前的平直段、开裂后的迅速磁化段和加载后期的磁化饱和段;该模型的磁场模拟结果还能反映箍筋、纵筋的相对位置和梁的受载情况;在疲劳阶段,模拟结果与试验观察的规律一致,精度较高,并与试验结果在同一数量级;该修正力磁模型不仅具有应力与磁学属性的直观映射关系,而且相较于隐式微分模型更易于应用,可作为力磁效应的定量化研究工具。

燃气爆炸荷载作用下钢筋混凝土板抗爆性能数值模拟

为了研究不同燃气爆炸荷载下混凝土板的动态响应特点,本文通过已有文献中的钢筋混凝土板抗爆试验,利用LS-DYNA有限元软件建立数值模型并验证其可靠性。然后,在混凝土板面施加不同峰值的简化三角燃气荷载,研究混凝土板在燃气荷载作用下的位移、速度、加速度等。结果表明:试验用钢筋混凝土板的最大位移和振动都出现在板跨中位置,且随着荷载峰值的增大而增大;当荷载峰值超过20 kPa时,随着作用在混凝土板上荷载量值的增加,结构的刚度受到削弱,在受迫振动阶段结构振动加速度的特性会发生变化,出现高频振荡;高频振荡开始时间随着燃气爆炸荷载峰值的提高而提前;当荷载结束后,混凝土板进入自由振动阶段,板的振动周期受残余刚度的影响,随着荷载峰值的提高而增大。

6.4级漾濞地震某RC框架及其非结构部件震害分析

2021年云南漾濞6.4级地震造成了较大范围的建筑破坏,在漾濞县城记录到的地震加速峰值(PGA)高达720.2 gal。在强震作用下,大量土木结构的民居发生了破坏,而约束砌体和钢筋混凝土(RC)结构的震害则相对较轻。现场震害调查发现,部分框架结构的震害明显重于同一区域的其他同类型结构,呈现明显、多样的非结构部件破坏特征。因此,该文对某震害较重的框架进行详细调查,分类分析结构及其非结构部件地震破坏细节;依据图纸及现场考察信息建立精细有限元分析模型,对此次地震的地震动破坏力特征以及该框架结构及其非结构部件的地震破坏机理进行了量化分析。分析结果表明:带填充墙框架仿真模型的分析结果与实际震害现象更接近;框架结构局部大空间、框架底部的约束形式和填充墙的布置形式的综合作用导致结构产生局部过大变形与各类非结构部件的严重破坏。在考虑填充墙对框架结构的作用效应后,结构的不规则性大幅增加,导致结构薄弱层的最大层间位移角相较纯框架模型增加127%,并且明显加剧非结构部件的震害。该文对该建筑震害现象的详细调查与仿真分析,可为结构抗震设计与应急救援决策提供参考。

RDX炸药热烤(Cook-off)实验及数值模拟

对一种改性的RDX炸药进行了热烤实验。应用热传导理论对实验中炸药的热作用过程进行了分析,并通过软件PHOENICS3.3对RDX在热烤过程中的热响应情况进行了模拟。结果表明,在环境温度较低时,RDX受热发生分解,所放出的热量可以及时地散失到环境中,从而不发生爆炸。环境温度较高时,药柱的边沿受热形成局部高温,导致热点火,使药剂发生爆炸。

基于陶粒纤维混凝土的衬砌渠道抗冻胀性能研究

为改善北方寒区预制混凝土衬砌渠道存在衬砌板件自重大、尺寸小、装配效率低等问题,探讨将陶粒纤维混凝土用于衬砌渠道。基于正交试验法开展9组陶粒纤维混凝土和1组C35普通混凝土冻融前后力学性能试验,并结合冻胀数值模拟分析衬砌渠道抗冻胀性能变化。结果表明:陶粒纤维混凝土抗压强度因素影响次序为页岩陶粒体积取代率>聚丙烯纤维(PP)掺量>陶粒预湿时间,抗拉强度因素影响次序为PP掺量>页岩陶粒体积取代率>陶粒预湿时间,冻融后陶粒纤维混凝土抗压、抗拉强度损失率低于普通混凝土;衬砌渠道数值模拟的抗冻胀性能变化与材料性能变化趋势一致,陶粒纤维混凝土衬砌渠道抗冻胀性能损失小于普通混凝土衬砌渠道,最优抗冻胀性能损失减小4.68%,同时衬砌板重量减小18.47%;陶粒纤维混凝土作为渠道衬砌材料具有明显质轻的装配化优势。