With reference to the rockfall risk estimation and the planning of rockfall protection devices, one of the most critical and most discussed problems is the correct definition of the design block by taking into account its return period. In this paper, a methodology for the assessment of the design block linked with its return time is proposed and discussed, following a statistical approach. The procedure is based on the survey of the blocks that were already detached from the slope and had accumulated at the foot of the slope in addition to the available historical data.

A finite-element modeling study on the progressive collapse of steel moment-resisting frames under column removal scenarios is presented. Different parameters, such as location of initial local failure, number of story, material strain-rate effects, and column removal time (CRT), are considered. The model structures are analyzed using static- and dynamic-incremental analyses. The former being the well-known pushdown simulations, and the latter performed through dynamic column removal at various gravitational load levels. The progressive collapse potential is mainly related to location of initial failure and size (height) of the models, which determine the affected area after initial local failure. To compare the results, the displacement-based dynamic amplification factor (DAF) is also adopted. It is observed that above a certain gravitational load, the dynamic simulations accounting for material strain rate show displacements smaller than the ones predicted by the static analysis. With the decrease of CRT, the progressive collapse capacity decreases, but DAF tends to be independent from CRT when the systems experience large plastic displacements.