A numerical study on the yielding mechanism of RC frame structure with cast-in-place slabs

The “strong columns-weak beams” principle is widely adopted in seismic design for RC frame structures, yet “column hinge” failures remain prevalent in both experimental tests and earthquake damage investigations. Current design methods often underestimate the influence of cast-in-place slabs, typically assuming a uniform effective flange width without accounting for actual boundary constraints. To better understand the yielding mechanism of RC frames under seismic loading, this study employs a multiscale modeling approach. Sensitivity analyses validate the finite element model, while parametric studies reveal that slabs significantly alter the reinforcement yielding sequence in beams and columns. The effective flange width is found to depend on beam geometry, joint position, and beam end rotation. These findings emphasize the need to revisit the yielding mechanism and further investigate spatial effects and flange width in the collapse mechanism of RC frames.