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

爆炸荷载及其与建筑物的相互作用即使在最简单的城市环境中也是一个复杂的现象。模拟空气爆炸的影响和耦合的结构响应是一个不平凡的任务。当考虑长时间爆破时，由于动压阶段产生的相当大的阻力载荷，困难增加。长持续时间爆炸载荷在这里被定义为爆炸事件，其中正相持续时间明显超过100毫秒;常规炸药的正相持续时间小于50毫秒。这些类型的载荷情况通常与化学蒸气云爆炸有关，例如2005年的邦斯菲尔德灾难（150-250吨TNT当量）。学术文献提出了研究人员和从业人员很少了解有关的普通砌体或节段结构的长时间爆炸反应。现有方法存在知识差距，主要是：（a）我们目前无法计算阻碍提供救生援助的紧急服务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，（c）目前的计算方法有缺陷，除了粗略的近似值外，无法模拟真实的结构。为了解决这一关键的知识差距，需要先进的计算建模的最新技术，再加上仪器密集的国家测试设施赞助的实验。就其性质而言，长时间爆炸载荷传递大幅度的脉冲，并且拖曳载荷的不可忽略的影响使得与结构的相互作用建模复杂;本质上比传统爆炸源更复杂。在对结构倒塌进行建模时，现有数值方法（例如有限元分析）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。爆炸效应研究中较新的自适应技术，如应用单元法，通过使用连续解耦技术和碰撞检测算法克服了这些局限性。现在可以模拟复杂的分段、连接排列，并确定破碎后可靠的碎片场分布。初步研究表明，在长持续时间的情况下，后部结构面上的压力均衡可以减少25- 30%的净载荷。这些影响因动压夹带破碎碎片而进一步复杂化。重要的是，对于长时间爆炸，入射脉冲和反射脉冲至少大一个数量级，导致相对较小的结构的快速过匹配。这项研究建议将利用先进的计算技术，结合在联合王国国防部空气爆炸隧道进行的综合实验，得出破碎算法和碎片碎裂轮廓。使用质量分布网格、3D激光扫描和高速视频进行精确绘图，将允许对分析结果和试验结果进行比较。将仔细检查单个面板上的冲击波清除效应和净压力效应。这将成为分析复杂互连结构几何形状的参考基准。将断裂算法与目前对常规小型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.