Assessing the risk of roof collapse in response to loading from volcanic ash with relevance to Ascension Island

火山喷发后火山灰落下所产生的负荷可能会对建筑物的结构完整性造成严重问题。火山灰坠落对建筑物造成的损害经常被报道，但研究很少。这在很大程度上是因为在火山喷发或被风雨侵蚀之前，需要尽快收集破坏数据，然后进行清理和修复。这涉及到进入有进一步喷发危险的地区，而且往往与当地社区、科学机构和灾害应急管理人员有敏感关系。因此，有必要对火山灰负荷对建筑物的影响进行重点实验研究，鉴于目前估计有超过8亿人居住在活火山附近，评估建筑物对火山灰负荷的脆弱性对于减少灾害风险也是至关重要的。屋顶坍塌是火山灰负荷、结构设计和状况以及天气等复杂交互作用的结果。因此，这个项目有三个主要目标。1.界定火山灰的“特征”量2.界定火山灰的相关季节特性3.评估建筑物的脆弱性和可能造成的危险。项目目标将通过案头工作、实验室工作和实地工作相结合来实现。试图在全球范围内实现这些目标是不可能的，因此该项目将使用阿森松岛作为案例研究。阿森松岛是一个偏远的火山岛，位于南大西洋中大西洋海脊以东约90公里处(图2)。它从海底上升4公里，海拔859米，面积约91平方公里。它是英国海外领土圣赫勒拿、阿森松和特里斯坦-达库尼亚的一部分，包括英国皇家空军和美国空军在内，人口约为800人。该岛火山活动活跃，最近的研究表明，最年轻的熔岩流只有几百年的历史。阿森松岛过去的火山活动以镁铁质熔岩流为主，带有长英质火山碎屑沉积和火山渣。爆炸性喷发的历史仅限于该岛中部山区的喷口，最近的研究表明，在过去的1年里，至少发现了74次产生浮石的喷发。

The loading that results from ash fall following volcanic eruptions can pose a significant problem to the structural integrity of buildings. Damage to buildings due to volcanic ash fall is frequently reported yet poorly studied. This is largely because damage data needs to be collected as soon after an eruption as possible before clean-up and repair, or erosion by wind and rain. This involves entering areas where there is a danger of further eruptions, and there are often sensitivities with local communities, science agencies and disaster emergency managers. As a result, there is a need for focused experimental studies on the impacts of ash loading on buildings and given that over 800 million people are now estimated to live near active volcanoes, the evaluation of the vulnerability of buildings to ash loading is also essential for disaster risk reduction.Roof collapse is the result of a complex interaction involving the loading caused by the ash, the design and condition of the structure and the weather. As such there are three main objectives in this project. 1. Defining a "characteristic" amount of ash 2. Defining the relevant seasonal properties of the ash 3. Evaluating the vulnerability of buildings and the hazard posed.The project objectives will be achieved through a combination of desk-, laboratory- and field-work. Attempting to undertake these objectives on a global scale is not possible, so this project will be using Ascension Island as a case study. Ascension Island is a remote volcanic island that lies ca. 90 km east of the Mid Atlantic Ridge in the South Atlantic (Figure 2). It rises 4 km from the seafloor to a height of 859 m above sea level (a.s.l.), and has an area of approximately 91 km2. It forms part of the UK Overseas Territory of St Helena, Ascension and Tristan da Cunha, and has a population of approximately 800 including the UK Royal Air Force and US Air Force. The island is volcanically active, with recent research revealing that the youngest lava flows are just a few hundred years old. Past volcanic activity on Ascension Island was dominated by mafic lava flows with felsic pyroclastic deposits and scoria. The explosive eruptive history is confined to vents on the central mountainous region of the island and recent research has revealed at least 74 pumice-producing eruptions were identified within the last 1 Myr.