Title:
Behavior Of Earthquake-Resistant Column-Foundation Connections (Prepublished)
Author(s):
Utsav Neupane, Ferdinand Niyonyungu, Rémy D. Lequesne, Andrés Lepage, and David Darwin
Publication:
Materials Journal
Volume:
Issue:
Appears on pages(s):
Keywords:
breakout; column-foundation connection; deformation capacity; embedment length; foundation longitudinal reinforcement; foundation shear reinforcement; moment transfer; reversed-cyclic loading
DOI:
10.14359/51750613
Date:
3/25/2026
Abstract:
Six large-scale reinforced concrete column-foundation connections, designed to represent interior connections of a continuous foundation slab, were subjected to reversed-cyclic displacements to investigate the effects of foundation longitudinal reinforcement ratio (ρ), foundation thickness (h), column hooked-bar embedment length (le), and foundation shear reinforcement on connection deformation capacity. The specimens were designed to be nominally similar to a specimen from an earlier study, except for the variables of interest. In all specimens, strength was limited by column bar yielding, and deformation capacity was governed by concrete breakout, even though the embedment length was adequate to yield the column bars. ACI CODE-318-25 was published late in the course of this study, so specimens did not satisfy ACI CODE-318-25 Section 25.4.11 requirements for anchorage of bar groups in tension. Test results indicate that improved drift ratio capacity can be achieved by either: a) delaying column-bar yield strain penetration into the foundation by increasing the foundation longitudinal reinforcement ratio ρ or the column longitudinal bar embedment length le, or b) increasing concrete breakout resistance with longer le or foundation shear reinforcement that has a shear strength exceeding the shear demand associated with 40% of the transfer moment based on the eccentric shear stress model assuming vc=0. The concept of transfer width (based on em>le instead of h) is useful for designing foundations to resist column moment transfer, but foundation flexural reinforcement for moment transfer should be placed near the top of the foundation instead of being divided between the top and bottom mats. Column longitudinal bars should be extended to the bottom mat of foundation reinforcement, since terminating the bars near the foundation mid-depth resulted in earlier breakout and lower deformation capacity.