Assessing the impact of horizontal restraints on the seismic rocking of masonry façades including dynamic soil-structure interaction

This study assesses the beneficial impact of horizontal restraints – such as steel tie-rods or catenas – on the seismic out-of-plane rocking behaviour of masonry façades, accounting for the effects of Dynamic Soil-Structure Interaction (DSSI). To this end, the results of preliminary 3D Finite Element Analyses are discussed, where the mechanical behaviour of the masonry façade, the foundation block, and the soil deposit was described by a linear viscoelastic constitutive model assigned to 10-noded tetrahedra elements (cluster), while the façade-foundation contact was reproduced through interface elements allowing for gapping. The entire system was subjected to 1D-seismic inputs applied at the bedrock depth: hence, the contribution of the dynamic soil response was also taken into account in the analyses. The same analysis was performed twice: once with the rigid masonry block free to rock (w/o tie-rod), once with masonry rocking limited by the horizontal restraint atop the block imposed by a steel tie-rod, here reproduced with a horizontal spring with stiffness k. The analysis in the presence of the tie-rod was repeated neglecting the presence of the soil deposit to assess DSSI effects. The comparison between the analyses allows to shed some light on the role played by the horizontal tie-rod and the soil deposit in the rocking of the masonry block.