A quantitative assessment of the risk of rockfall on a local scale is a complex and challenging task since both the randomness of the natural event and the unpredictability of the behaviour of the elements at risk must be considered. From a technical standpoint, the impact of a block against a building is a phenomenon with a lot of variability, because the location of the impact point on the building (e.g. pillar, infill, roof) affects the level of damage and the possibility that the damage will spread throughout the entire structure. Similarly, impact energy can enhance the level of damage. Logic trees (or event trees) can be used to solve such problems in engineering systems. Event trees, in particular, allow a collection of probability outcomes for a given event to be calculated. As a result, if a block collides with a building, one can estimate the likelihood of hitting either a column (essential component of a concrete structure) or an infill wall (nonstructural component). Different scenarios may occur depending on the hit element, all of which can be represented using the event tree. In this technical note, an example of application of the approach is proposed to compute the physical risk on a settlement in a rockfall hazardous area.

Keywords: Event tree analysis, rockfall, building.