Long duration blast loading and debris distribution of complex masonry panel structures

即使在最简单的城市环境中，爆炸荷载及其与建筑物的相互作用也是一个复杂的现象。对空气爆炸和耦合结构响应的影响进行建模是一项非常重要的任务。当考虑长持续时间的爆破时，由于动压阶段所赋予的相当大的阻力载荷，增加了难度。这里定义的长时间爆炸加载是指正相持续时间明显超过100毫秒的爆炸事件；常规炸药的正相持续时间小于50毫秒。这些类型的负荷情况最常与化学蒸汽云爆炸有关，例如2005年邦斯菲尔德灾难(相当于150-250吨TNT当量)。在学术文献中，研究者和实践者都对常见的砖石结构或节段结构的长时间爆炸反应知之甚少。现有方法存在知识空白，主要是：(A)我们目前无法计算将阻止紧急服务提供救生援助的瓦砾或碎片堵塞的数量；(B)我们没有准确的工具来预测造成的伤亡或净损失；以及(C)目前的计算方法存在缺陷，无法模拟超出粗略近似的真实结构。为了解决这一关键的知识差距，需要先进计算建模中的最新技术，并结合仪器密集的国家测试设施赞助的实验。从本质上讲，长持续时间的爆炸载荷传递着巨大的冲量，阻力载荷的不可忽视的影响使得与结构物的相互作用变得复杂，本质上比传统的爆炸源更复杂。在模拟结构倒塌时，现成的数值方法(如有限元分析)的可靠性在离散阶段失效，特别是对于易受颗粒破碎影响的脆性系统。在BLAST效果研究中较新的自适应技术，如应用元素法，通过使用连续体解耦技术和碰撞检测算法来克服这些限制。现在有可能对复杂的分段、节理布置进行建模，并确定破碎后可靠的碎屑场分布。初步研究表明，在长持续期情况下，后结构面的压力均衡可以减少净载荷25%-30%。这些效应由于破碎碎片受到的动态压力而变得更加复杂。重要的是，对于长持续时间的爆炸，入射和反射脉冲至少大一个数量级，导致相对较小的结构快速过匹配。这项研究提案将使用先进的计算技术，并结合在英国国防部空中爆炸隧道进行的全面实验试验，得出破碎算法和碎片破碎轮廓。使用质量分布网格、3D激光扫描和高速视频的精确测绘将允许比较分析结果和试验结果。将仔细检查各个面板上的爆破清理和净压力效应的影响。这将形成复杂的相互关联的结构几何分析的参考基准。将破解算法与目前对常规小爆炸物禁区的有限指导联系起来将是一个关键目标。

Blast loading and its interaction with structures is a complex phenomenon even in the simplest of urban settings. Modelling the effect of air blast and coupled structural response is a non-trivial task. The difficulty is increased when considering long duration blast due to the considerable drag loads imparted by the dynamic pressure phase. Long duration blast loading is defined here as an explosive event in which the positive phase duration, clearly exceeds 100msec; conventional explosives have a positive phase duration of less than 50msec. These types of load cases are most commonly associated with chemical vapour cloud detonation, e.g. 2005 Buncefield Disaster (between 150-250 tonnes TNT equivalence). Academic literature presents both researcher and practitioner with little understanding pertaining to the long duration blast response of commonplace masonry or segmental structures. Knowledge gaps exist in the methods available, principally: (a) we cannot currently calculate the amount of rubble or debris blockage that will prevent emergency services providing life saving assistance, (b) we do not have accurate tools to predict resulting casualties or net damage and, (c) current calculation methods are flawed and cannot model real structures beyond crude approximations. To solve this key gap in knowledge, the latest techniques in advanced computational modelling are required coupled with instrumentation intensive national test facility sponsored experiments. By their nature, long duration blast loads transmit large magnitude impulse and the non-negligible effects of drag loads make interactions with structures complex to model; intrinsically more so than a conventional explosive source. When modelling structural collapse, the reliability of readily available numerical methods (e.g. Finite Element Analysis) fail in the discrete phase, particularly for brittle systems susceptible to particulate fragmentation. Newer adaptive techniques in blast effects research such as the Applied Element Method, overcome these limitations through the use of continuum decoupling techniques and collision detection algorithms. It is now possible to model complex segmental, jointed arrangements and determine a reliable debris field distribution following breakage. Preliminary research has shown that pressure equalisation on the rear structural face in the long duration case can reduce net loading by 25-30%. These effects are further complicated by dynamic pressures entraining broken fragments. Importantly for long duration blast, incident and reflected impulses are at least one order of magnitude greater leading to rapid over-matching of comparatively smaller structures. This research proposal will use advanced computational techniques in conjunction with comprehensive experimental trials conducted in the UK, Ministry of Defence Air Blast Tunnel to derive breakage algorithms and debris fragmentation profiles. Precise mapping using mass distribution grids, 3D laser scanning and high speed video will allow the comparison of analytical and trial results. The effects of blast clearing and net pressure effects across individual panels will be examined carefully. This will form the reference benchmark for the analysis of complex interlinked structural geometries. Linking breakage algorithms to the current limited guidance for conventional small explosive exclusion zones will be a key objective.