Numerical Investigation of Rockfall Impact Area Effects on the Dynamic Response of Flexible Hexagonal Nets

Double-twisted hexagonal wire mesh is a common interception structure in low-energy flexible barrier systems. Previous studies focused on its responses under concentrated loads (polyhedral block), but distributed loads received little attention. This study introduced a discrete representation of the mesh panel, and defined a slab to create a distributed load. Parametric tests were designed to quantify the effects of impact area using a calibrated drop weight model. Results showed that braking time ( T b ), braking displacement ( S b ), maximum mesh elongation ( S m ) and maximum supporting cable force ( T m ) decreased with increasing impact area. Bullet effect for the sphere was confirmed because S b and T b increased by 43.8% and 16.7% compared with the large slab. Although a large slab induced the widest deformation zone, S m and T m decreased by 31% and 34% compared with the sphere. Energy analyses indicated that the portion of dashpot energy increased with impact area as more contacts were mobilized. Intermediate cables significantly improved mesh performance in resisting distributed loads due to a favorable load-sharing mechanism. In summary, this work validated the use of concentrated loads as the worst-case scenario in design guidelines and highlighted the need to incorporate distributed loads into net testing from a risk management perspective.