Investigating the influence of masonry infill walls on the seismic response of reinforced concrete frame structures in Uganda

Abstract

This study investigates the influence of masonry infill walls on the seismic response of Reinforced Concrete frame structures in Uganda, where current seismic design codes lack explicit provisions for infill wall and RC frame interactions. The study develops a site-specific design response spectrum for Uganda’s highest seismic zone. Finite element modelling in ABAQUS was employed to simulate the detailed nonlinear in-plane behaviour of infilled and bare RC frames. For broader parametric studies across varying building heights and infill types, like, clay bricks and solid concrete blocks, the equivalent diagonal strut method was implemented in ETABS. Model validation was conducted against established experimental results from pseudo-dynamic tests, ensuring accuracy in displacement, drift, and base shear predictions. Nonlinear static pushover analyses were performed to evaluate seismic performance indicators, including lateral displacement, storey drift, base shear capacity, and stiffness contribution. Results indicate that concrete block infills, owing to their higher compressive strength, provide greater initial stiffness and higher base shear capacity than clay brick infills. However, stiffness contribution decreases with increasing building height, reducing the relative benefit of infills in taller frames. Infill walls significantly reduced displacement and storey drift across all configurations, while Base shear was increased. Displacement was reduced by 80% for the concrete infill in the 2-storey structure and by 73 % for the clay infill. However, the stiffness contribution decreased as building height increased. This is observed by concrete infill reducing displacement by 79.7% in a 2-storey structure, but reducing it by 50% in a 10-storey structure. This research, therefore, provides region-specific evidence for the inclusion of masonry infill effects in seismic design.