Experimental and numerical analyses of the effect of fibre content on the close-in blast performance of a UHPFRC beam

Limited research has been conducted on the influences of fiber content on close-in blasting characteristics for ultrahigh-performance fiber-reinforced concrete(UHPFRC)beams.This paper aims to address this knowledge gap through experimental and mesoscale numerical methods.Experiments were conducted on ten UHPFRC beams built with varying steel fiber volumetric fractions subjected to close-in explosive conditions.Additionally,this study considered other parameters,such as the longitudinal reinforcement type and ratio.In the case of UHPFRC beams featuring normal-strength longitudinal reinforcement of diametersΦ12,Φ16,andΦ20,a reduction in maximum displacement by magnitudes of19.6%,19.5%,and 17.4%was observed,respectively,as the volumetric fractions of fiber increased from1.0%to 2.5%.In addition,increasing the longitudinal reinforcement ratio and using high-strength steel longitudinal reinforcement both significantly reduced the deformation characteristics and increase the blasting resistances of UHPFRC beams.However,the effects on the local crushing and spalling damage were not significant.A mesoscale finite element model,which considers the impacts of fiber parameters on UHPFRC beam behaviors,was also established and well correlated with the test findings.Nevertheless,parametric analyses were further conducted to examine the impacts of the steel fiber content and length and the hybrid effects of various types of microfibers and steel fibers on the blasting performance of UHPFRC beams.

Modification of SDOF model for reinforced concrete beams under close-in explosion

In this paper,a modified single-degree-of-freedom(SDOF)model of reinforced concrete(RC)beams under close-in explosion is proposed by developing the specific impulse equivalent method and flexural resistance calculation method.The equivalent uniform specific impulse was obtained based on the local conservation of momentum and global conservation of kinetic energy.Additionally,the influence of load uniformity,boundary condition and complex material behaviors(e.g.strain rate effect,hardening/softening and hoop-confined effect)was considered in the resistance calculation process by establishing a novel relationship between external force,bending moment,curvature and deflection successively.The accuracy of the proposed model was verified by carrying out field explosion tests on four RC beams with the scaled distances of 0.5 m/kg~(1/3)and 0.75 m/kg~(1/3).The test data in other literatures were also used for validation.As a result,the equivalent load implies that the blast load near the mid-span of beams would contribute more to the maximum displacement,which was also observed in the tests.Moreover,both the resistance model and test results declare that when the blast load becomes more concentrated,the ultimate resistance would become lower,and the compressive concrete would be more prone to softening and crushing.Finally,based on the modified SDOF model,the calculated maximum displacements agreed well with the test data in this paper and other literatures.This work fully proves the rationality of the modified SDOF method,which will contribute to a more accurate damage assessment of RC structures under close-in explosion.

Experimental investigation of p-section concrete beams under contact explosion and close-in explosion conditions

This paper presents the results of an experimental investigation on explosive breaching of p-section concrete beams. Twenty three p-section concrete beams with a 100 cm length were tested. TNT charges were placed at three positions: contact detonation in the center, contact detonation above the web and close-in detonation in the center. The external and internal breach parameters of the panels were evaluated by measuring the diameter of the ejection crater, spalling crater and breach hole created by the charge detonation. The experimental results were compared to predict values obtained by the analytical models proposed by McVay, Morishita and Remennikov. A modified breach with crater limit line and breach without crater limit line were put forward based on the experimental results. The maximum cross-sectional destruction area ratio(MCDAR) values were used to evaluate the damage degree. The maximum value of MCDAR reached 0.331 corresponding to the C5 experimental condition, of which explosion occurred above the web.

Dynamic responses of reinforced concrete beams under double-endinitiated close-in explosion

The reinforced concrete(RC) structural component might suffer a great damage under close-in explosion.Different from distant explosions, blast loads generated by the close-in explosion are non-uniformly distributed on the structural component and may cause both local and structural failure. In this study,an experimental study was conducted to investigate the dynamic responses of RC beams under doubleend-initiated close-in explosions. The experimental results show that the distribution of blast loads generated by the double-end-initiated explosion is much more non-uniform than those generated by single-point detonation, which is caused by the self-Mach-reflection effects. A 3 D finite element model was developed and validated in LS-DYNA by employing the modified K&C model. Intensive numerical calculations were conducted to study the influences of the initiation way, scaled distance and longitudinal reinforcement ratio on the dynamic responses and failure modes of RC beams. Numerical results show that the RC beam suffers greater damage as the cylindrical explosive is detonated at its double ends than the scenario in which the cylindrical explosive is detonated at its central point. RC beams mainly suffer flexural failure and flexure-shear failure under the double-end close-in explosion, and the failure modes of RC beams change from the flexural damage to flexure-shear damage as the scaled distance or the longitudinal reinforcement ratio decreases. The direct shear failure mode is not usually observed in the double-end-initiated explosion, since the intense blast loads is basically concentrated in the midspan of RC beam, which is due to self-Mach-reflection enhancement.

Close-in weapon system planning based on multi-living agent theory

The close-in weapon system(CIWS)is a combat system that faces a complex environment full of dynamic and unknown challenges,whose construction and planning require a systematic design method.Multiliving agent(MLA)theory is a methodology for the combat system design,which uses the livelihood degree to evaluate the multi-dimensional long-term operational effectiveness of the system;whereas,there is still no uniform quantization framework for the livelihood degree,and the adjustment methods of livelihood degree need to be further improved.In this paper,we propose the uniform quantization framework for the livelihood degree and detailed discuss the methods of livelihood adjustment.Based on the MLA theory,the multi-dimensional operational effectiveness of the missile-gun integrated weapon system(MGIWS)is analyzed,and the long-term combat effectiveness against the saturation attack is assessed.Furthermore,the planning problem of the equipment deployment and configuration is investigated.Two objectives,including the overall livelihood degree and cost-effectiveness(CE),are proposed,and the optimization method based on genetic algorithm(GA)is studied for the planning problem.

Numerical study on local failures of reinforced concrete slabs against underwater close-in explosions

Reinforced concrete(RC)slabs are the primary load-carrying member of underwater facilities.They can suffer severe local failures such as cratering,spalling,or breaching as a result of underwater close-in(UWCI)explosions.In this study,we established a fully validated high-fidelity finite element analysis approach to precisely reproduce the local failures of RC slabs after a UWCI explosion.A recently proposed dynamic constitutive model is used to describe wet concrete.The effects of free water content on the material properties,including the tensile/compressive strength,elastic modulus,strain rate effect,failure strength surface,and equation of state,are comprehensively calibrated based on existing test data.The calibrated material parameters are then verified by a single-element test.A high-fidelity finite element analysis(FEA)approach of an RC slab subjected to a UWCI explosion is established using an arbitrary Lagrangian-Eulerian(ALE)algorithm.Simulating previous UWCI explosion tests on RC orifice targets and underwater contact explosion tests on saturated concrete slabs showed that the established FEA approach could accurately reproduce the pressure-time history in water and damage patterns,including the cracking,cratering,and spalling,of the RC orifice target and saturated concrete slab.Furthermore,parametric studies conducted by simulating an RC slab subjected to a UWCI explosion showed that:(i)the local failure of an RC slab enlarges with increased charge weight,reduced standoff distance,and reduced structural thickness;(ii)compared to a water-backed RC slab,an air-backed RC slab exhibits much more obvious local and structural failure.Lastly,to aid the anti-explosion design of relevant underwater facilities,based on over 90 simulation cases empirical formulae are summarized to predict local failure modes,i.e.,no spall,spall,and breach,of water-and air-backed RC slabs subjected to a UWCI explosion.

A review on close-in blast performance of RC bridge columns

In recent decades,the increase in terrorist attacks highlights the necessity and importance of understanding of structural performance under accidental and intentionally malicious blast loads.As an important part of transportation infrastructure,bridges would inevitably suffer explosion hazards especially close-in explosion.Reinforced concrete(RC)bridge column is the most critical components of bridge structures,which is more prone to severe local damage under the action of close-in blast loading and can lead to progressive collapse with catastrophic consequences in most cases.Therefore,the blast performance of RC bridge columns under close-in explosions is of particular concern.Towards a better RC bridge column protection against close-in blast loadings,efforts have been mainly devoted to understanding dynamic response predictions of RC columns,numerical simulation techniques of close-in explosion and damage assessment of blast-damaged RC columns.This article presents a state-of-the-art review of the research status of RC columns subjected to close-in blast loads.The blast loading,experimental study and failure mode,uncoupled and coupled simulation method,damage assessment based on residual axial capacity,vulnerability analysis and machine learning are considered and reviewed.The merits and defects of the existing approaches are discussed,and some suggestions for possible improvement are proposed.Further investigation into the future development of this topic has also been identified.

An enhanced close-in phase noise LC-VCO using parasitic V-NPN transistors in a CMOS process

A differential LC voltage controlled oscillator （VCO） employing parasitic vertical-NPN （V-NPN） transistors as a negative gm-cell is presented to improve the close-in phase noise. The V-NPN transistors have lower flicker noise compared to MOS transistors. DC and AC characteristics of the V-NPN transistors are measured to facilitate the VCO design. The proposed VCO is implemented in a 0.18 μm CMOS RF/mixed signal process, and the measurement results show the close-in phase noise is improved by 3.5-9.1 dB from 100 Hz to 10 kHz offset compared to that of a similar CMOS VCO. The proposed VCO consumes only 0.41 mA from a 1.5 V power supply.

基于开/闭环交替的GNSS/INS一致性欺骗检测技术

GNSS与惯性导航系统(inertial navigation system,INS)在车辆、无人机等领域广泛应用,但GNSS接收机容易受到欺骗信号影响,因此本文提出一种利用INS观测量的一致性欺骗检测技术.惯性器件有着不易受欺骗信号干扰和易产生累计误差的特性,通过开/闭环交替反馈估计误差来构建GNSS/INS组合导航,在开环期间设置欺骗检测窗口,将惯性器件和GNSS得到的加速度、角速度统计检测量进行一致性检测,判断是否存在欺骗.实验结果证明:当窗口时间为70 s时,检测概率达到99.2%,虚警概率为5.2%.

模糊模式识别在导航系统性能综合评价中的应用研究

就导航系统抗干扰性能评价问题指标的多层次性,根据模糊模式识别的原理,对现有的模糊模式识别方法进行改进,提出了一种新方法。该方法首先将系统分为3个等级,并把它们看作3个模糊模式,根据试验所测得的数据构造各模式的隶属函数,然后采用反向递推的方法从指标体系的最底层出发依次计算待评系统与各模式的加权贴近度,最后由模糊模式识别的择近原则得出待评系统所属的等级。最后应用此方法对某一导航系统进行评价,给出此系统所属的等级。

关闭煤矿的资源开发利用与地质保障

在关闭煤矿中除煤炭剩余外,还赋存丰富的煤层气、矿井水、地下空间、地热等资源,具有巨大的二次开发潜力。依据全国煤层气、矿井水、地热等资源赋存现状,梳理部分重点关闭煤矿资源的绿色开发与清洁高效利用发展趋势;通过系统介绍集钻探、物探、遥感、计算机等勘查技术于一体的综合勘探体系,总结了其在关闭煤矿资源有效开发利用的地质保障作用,并从资源、环境、技术体系及数据库等七个方面提出关闭煤矿资源开发利用地质保障工作建议。

供电企业线损“四分”的闭环管理

线损“四分”管理是供电企业降低线损的一项重要手段，其本质是将各环节各部分的线损都能分析清楚。采取闭环管理才能保障线损“四分”能够真正为降低线损起到指导作用。本文通过供电企业涉及线损主要业务环节、部门在“四分”管理中的职责，论述了线损“四分”的闭环管理的意义，并详细介绍了线损“四分”的闭环管理的具体实施措施，规范了涉及线损管理的各部门职责，保障了线损“四分”管理的实施，有效地提高了供电企业的降损效果。

动态环境下基于移动通信的闭环供应链超网络模型

在动态环境下建立了一个基于移动通信的闭环供应链超网络模型.在该模型中,各层决策者可以通过两种手段进行交易,一种是传统意义上的交易方式,另一种则是借助移动通信手段进行交易.在所描述的网络模型中,价格敏感度和时间是影响需求市场需求的两个重要因素.同时,还借助一个简单的周期函数来描述需求市场对商品的季节性需求.以各层决策者寻求利益和风险的均衡点作为优化目标,并通过变分不等式理论对该模型进行求解.利用具体的算例验证了该模型的正确性和合理性.

一种基于实时物理闭环校正的空中动基座对准方法

提出了一种基于实时物理闭环校正的平台惯导空中动基座对准方法。该方法利用卡尔曼滤波实现惯导误差的实时估计,根据最优二次型准则设计反馈控制进行惯导平台的实时闭环物理校正,有效保证了对准精度。经机载试验,平台惯导空中动基座对准后,导航精度大幅提高。

碳排放权约束下风险规避型闭环供应链网络均衡决策

运用均衡理论和变分不等式刻画闭环供应链网络各层均衡条件，建立了碳排放权约束下风险规避型闭环供应链网络均衡决策模型，探讨网络成员的最优均衡策略。研究表明：当政府放宽对高排放企业的管制时，企业可通过增加产能、提高销量获利，但政府这一举措会导致网络总碳排放量增加。当提高低碳排放企业碳配额分配时，若同时调整碳配额出售价格，则低碳排放企业可获利；否则，收益受损。随着企业的风险偏好的增强，企业的产量、交易量会下降，这使得网络经济绩效与环境绩效相一致。