Numerical Macro- and Micro-Modeling of Confined Masonry Walls with Emphasis on Seismic Forces in Tie-Columns

A recently developed confined masonry (CM) system, constructed from vertically perforated clay blocks and polyurethane (PU) glue, has demonstrated promising performance in recent tests, largely due to the confinement provided by 25 × 25 cm reinforced concrete (RC) tie-columns. However, current design codes treat tie-columns as prescriptively detailed elements, providing only dimensional and reinforcement limits. As a result, the actual internal seismic force demands in tie-columns are typically neither calculated nor verified. To address this gap, the present study investigates internal forces in tie-columns using different numerical models. The in-plane seismic response of CM walls was simulated in OpenSees using two macro-modeling strategies based on equivalent strut models (ESMs): single- and multi-strut models with different constitutive laws. The seismic response and internal forces in tie-columns were compared with an experimentally validated three-dimensional micro-model in Abaqus/Explicit. The single-strut model captured the global response reasonably well but could not reproduce the tie-column force demands. In contrast, the multi-strut model provided reliable estimates for axial forces, shear forces, and bending moments. This presents a step towards the development of a design which considers the contribution of RC tie-columns in modern CM buildings.