Leader: Prof. Claudio di Prisco (Politecnico di Milano)

**Why? **The evaluation of the impact force exerted by granular flows on rigid obstacles is of fundamental importance for the design of sheltering structures. In most of the practical approaches and standard, a pseudo-static approach is employed: the maximum impact force is estimated by using empirical formulas and it is quasi-statically applied to the barrier. Considering the dynamic nature of impacts, the maximum impact force is not sufficient to design protection works and the impulse value should be used in design. For this reason, the study of the time evolution of the impact force is of fundamental importance.

**What? **The main goal is to propose a design approach for the sheltering structures by integrating the formula previously introduced by Calvetti et al 2017 for the maximum impact force with the information about the time evolution of the impact force, necessary to compute the impulse and for dynamic design of sheltering structure.

**How? **The Discrete Element approach is employed to study the evolution with time of the impact force exerted by granular flows on rigid obstacles and to better understand the impact mechanism. The granular mass is initially positioned in front of the wall with an assigned uniform velocity and porosity and the evolution with time of the impact force is evaluated. In particular, the influence of mass initial porosity, velocity, front inclination, lenght and height on the impact force evolution is investigated.

**Results**

- Formula for the maximum impact force exerted by dry granular masses on rigid obstacles
- Mechanical interpretation of the impact mechanism

(Calvetti et al., 2018, submitted)

**On going research**

- Study of the effect of mass initial porosity, velocity, front inclination, lenght and height on the temporal evolution of the impact force
- Definition of a simplified force-time curve to be used in the dynamic design of sheltering structures

### Researchers involved in this project

Francesco Calvetti, Claudio di Prisco, Irene Redaelli