Seismic Behavior of Steel Frames with Geopolymer and Conventional Mortars Under Rigid and Flexible Joint Conditions

This work experimentally examines the seismic performance of steel frames with masonry infill walls produced with geopolymer and traditional mortars under both rigid and flexible joint configurations. Four single-span specimens were evaluated on a uniaxial shake table utilizing eleven scaled earthquake records that represent both in-plane and out-of-plane excitations. Flexible joints markedly diminished acceleration requirements and enhanced deformation capacity in comparison to stiff systems. Rigid frames attained maximum accelerations of 1.82 ± 0.21 g, whilst flexible-joint specimens measured 1.15 ± 0.18 g; the associated lateral displacements were 6.8 ± 0.9 mm and 10.5 ± 1.1 mm, respectively. Geopolymer mortar improved interface adhesion and rigidity, elevating dominant frequencies in rigid systems by around 40% and fostering more ductile behavior in flexible structures. Frequency-domain analysis indicated that decreases in dominant frequency correlated with stiffness deterioration. Geopolymer–flexible systems yielded the minimal acceleration responses and displayed only negligible cracking, indicating enhanced seismic performance.