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

火山爆发后火山灰落下所产生的荷载会对建筑物的结构完整性造成严重问题。火山灰对建筑物的破坏经常被报道，但研究很少。这在很大程度上是因为需要在火山爆发后尽快收集损害数据，然后才能进行清理和修复，或被风雨侵蚀。这涉及进入有进一步爆发危险的地区，而且当地社区、科学机构和灾害应急管理人员往往很敏感。因此，有必要对火山灰对建筑物的影响进行集中的实验研究，鉴于目前估计有8亿多人居住在活火山附近，评估建筑物对火山灰的脆弱性对减少灾害风险也至关重要。屋顶坍塌是火山灰引起的荷载相互作用的结果，结构的设计和状况以及天气。因此，该项目有三个主要目标。1.定义灰的“特征”量2.确定火山灰的相关季节属性3.评估建筑物的脆弱性和所造成的危害。项目目标将通过案头、实验室和实地工作相结合的方式实现。试图在全球范围内实现这些目标是不可能的，因此本项目将使用Ascension岛作为案例研究。Ascension岛是一个偏远的火山岛，位于约。南大西洋大西洋中脊以东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、Ascension和特里斯坦-达库尼亚的一部分，人口约800人，包括英国皇家空军和美国空军。该岛火山活跃，最近的研究表明，最年轻的熔岩流只有几百年的历史。过去在Ascension岛上的火山活动主要是镁铁质熔岩流和长英质火山碎屑沉积物和火山渣。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100万年中，至少有74次产生浮石的喷发被确定。

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.