Height-dependent nonlinear seismic response of masonry-infilled RC frame buildings with pilotis configurations

Abstract This study investigates the nonlinear seismic response of reinforced concrete (RC) frame buildings with masonry infills, with particular emphasis on pilotis-induced vertical irregularities and height-dependent behaviour. A parametric set of bare, fully infilled, and pilotis configurations ranging from 3 to 12 storeys is analysed using nonlinear time-history simulations. Masonry infills are represented through a macro-modelling approach based on equivalent strut formulations, while RC members are modelled using fibre-based elements. Results indicate that while masonry infill generally enhances global stiffness and reduces inter-storey drift and acceleration amplification, its influence on dynamic response is strongly governed by nonlinear period elongation and its interaction with the frequency content of the input motion. In particular, the presence of pilotis introduces a height-dependent transition in structural behaviour: low- to mid-rise structures exhibit limited sensitivity to ground-storey irregularities, whereas taller systems show increased concentration of deformation and force demand at the base. The study further indicates that commonly adopted simplified assumptions, such as neglecting infill contribution in asymmetric configurations, may lead to conservative or misleading estimates depending on the relationship between structural periods and input spectra. These findings highlight the importance of considering nonlinear dynamic effects and infill–frame interaction mechanisms when assessing irregular RC buildings, and provide insight into the limitations of current code-based simplifications.