Local infill-frame interaction under seismic loads: Investigation through refined micro-modeling

The paper investigates the complex local interaction occurring between masonry infills and reinforced concrete (RC) frames subject to seismic loads, and its impact on the actual distribution of internal forces in frame members. A high-fidelity damage mechanics-based micro-modeling approach is adopted for the analysis. The modeling framework provides distinct physical modeling of masonry components (units and mortar) and of the reinforced concrete members as continuum 2D nonlinear elements. The STKO software platform for OpenSees is used to implement the modeling framework. Experimental validations are carried out with four infilled frame specimens arranged with different masonry typologies, including calcarenite unit, hollow clay unit, solid clay brick, and hollow clay brick masonries. The actual distribution of internal forces within the frame members is revealed via numerical integration of the nodal forces at different cross-sections. A comprehensive parametric study further investigates the key role of masonry design parameters on the distribution of shear demand and the expected damage mechanism, providing relevant insights about the design as well as the assessment of infilled frames.