Fail Fraction: ArcGIS Pro and QGIS tools to calculate the probability of roof collapse under tephra fall loading

The Fail fraction tools (for ArcGIS Pro and QGIS) allow GIS users to calculate the probability of roof collapse under tephra fall loading for different eruption scenarios based on buildings’ roof type and condition properties and typical failure loads. There are versions of the tool for coarse and fine tephra as experimental results show fine tephra can be stable at higher roof pitches and the user must select the one that is most appropriate for the scenario being considered. The output is a map that shows the tephra load as a fraction of the failure load (the Fail fraction, F) and for values of F ≥ 1 the roof is at high risk of collapse.