Title:
Behavior of Earthquake-Resistant Column-Foundation Connections (Prepublished)
Author(s):
U. Neupane, F. Niyonyungu, R. D. Lequesne, A. Lepage, and D. Darwin
Publication:
Structural Journal
Volume:
Issue:
Appears on pages(s):
Keywords:
breakout; deformation capacity; embedment length; foundation longitudinal reinforcement; foundation shear reinforcement; moment transfer; reversed-cyclic loading
DOI:
10.14359/51750613
Date:
7/1/2026
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 with increased foundation longitudinal reinforcement ratio ρ or 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 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 divided between the top and bottom mats. Column longitudinal bars should be extended to the bottom mat of foundation reinforcement because terminating the bars near foundation middepth resulted in earlier breakout and lower deformation capacity.
Related References:
1. ACI Committee 318, “Building Code Requirements for Structural Concrete (ACI 318-19) and Commentary (ACI 318R-19) (Reapproved 2022),” American Concrete Institute, Farmington Hills, MI, 2019, 624 pp.
2. Cheng, M.-Y.; Chen, P.-J.; Chen, C.-H.; Worsfold, B. L.; Parra-Montesinos, G. J.; and Moehle, J. P., “Effect of Reinforcement Detailing on Cyclic Behavior of Reinforced Concrete Column-Footing Connections,” ACI Structural Journal, V. 122, No. 4, July 2025, pp. 19-34. doi: 10.14359/51746671
3. Worsfold, B. L.; Moehle, J. P.; and Silva, J. F., “Moment Transfer at Column-Foundation Connections: Physical Tests,” ACI Structural Journal, V. 119, No. 5, Sept. 2022, pp. 95-110. doi: 10.14359/51734799
4. Mahrenholtz, C.; Akguzel, U.; Eligehausen, R.; and Pampanin, S., “New Design Methodology for Seismic Column-to-Foundation Anchorage Connections,” ACI Structural Journal, V. 111, No. 5, Sept.-Oct. 2014, pp. 1179-1189. doi: 10.14359/51686968
5. ACI Committee 318, “Building Code for Structural Concrete—Code Requirements and Commentary (ACI CODE-318-25),” American Concrete Institute, Farmington Hills, MI, 2025, 702 pp.
6. Herzog, M., “Beitrag zur Vereinheitlichung der Bemessung im Stahlbetonbau und in der Befestigungstechnik (Contribution to the Standardization of Design in Reinforced Concrete Construction and Fastening Technology),” PhD dissertation, University of Stuttgart, Stuttgart, Germany, 2015, 457 pp. (in German)
7. ASTM A706/A706M-22a, “Standard Specification for Deformed and Plain Low-Alloy Steel Bars for Concrete Reinforcement,” ASTM International, West Conshohocken, PA, 2022, 9 pp.
8. Ajaam, A.; Yasso, S.; Darwin, D.; O’Reilly, M.; and Sperry, J., “Anchorage Strength of Closely Spaced Hooked Bars,” ACI Structural Journal, V. 115, No. 4, July-Aug. 2018, pp. 1143-1152. doi: 10.14359/51702065
9. Niyonyungu, F.; Lequesne, R. D.; Lepage, A.; and Darwin, D., “Deformation Capacity of Reinforced Concrete Column-to-Foundation Connections with Anchorage/Breakout Failures,” SM Report No. 161, The University of Kansas Center for Research, Inc., Lawrence, KS, 2024, 182 pp.
10. Neupane, U.; Lequesne, R. D.; Lepage, A.; and Darwin, D., “Behavior of Earthquake-Resistant Reinforced Concrete Column-Foundation Connections,” SM Report No. 162, The University of Kansas Center for Research, Inc., Lawrence, KS, 2024, 250 pp.
11. ASTM A370-23, “Standard Test Methods and Definitions for Mechanical Testing of Steel Products,” ASTM International, West Conshohocken, PA, 2023, 51 pp.
12. ASTM E8/E8M-21, “Standard Test Methods for Tension Testing of Metallic Materials,” ASTM International, West Conshohocken, PA, 2021, 31 pp.
13. Neupane, U.; Niyonyungu, F.; Lequesne, R. D.; Lepage, A.; and Darwin, D., “DATASET: Results from Cyclic Tests of Reinforced Concrete Column-Foundation Connections,” KU ScholarWorks, Lawrence, KS, Jan. 2025, https://hdl.handle.net/1808/35803. (last accessed June 30, 2026)
14. ASTM C39/C39M-23, “Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens,” ASTM International, West Conshohocken, PA, 2023, 8 pp.