Fracture and stability analysis of knee-braced column footings under eccentric loading using finite element modelling

Abstract

In conventional structural design, columns are typically placed at the center of footings to ensure symmetrical load distribution and structural stability. However, architectural constraints often require eccentric placement along the edge mid-length, mid-breadth, or corner resulting in biaxial loading and non-uniform stress distribution. This study investigates the seismic behavior of a G + 7 framed structure (an eight-storey reinforced concrete frame comprising ground plus seven floors) simulated in ABAQUS, analyzing 250 mm × 250 mm columns positioned on 900 mm × 900 mm footings in four locations. Inclined knee bracings at 0°, 30°, 45°, and 60° were implemented to enhance lateral and rotational resistance. The number of bracings varied by column position: four for centrally placed columns, three for edge-mid, and two for corner placements. Fracture mechanics methods stress intensity factor and fatigue life analysis were used to evaluate crack propagation and failure modes. While central columns demonstrated better uniaxial load performance, inclined bracing significantly enhanced the seismic resilience of eccentric layouts, increasing critical rocking angles by up to 12%. Nonlinear dynamic analyses and fragility curves quantified the probability of exceedance, offering probabilistic insights into the vulnerability of 16 column–footing configurations.