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Deformation Capacity of Reinforced Concrete Column-to-Foundation Connections with Anchorage/Breakout Failures
Lepage, Andrés
Lepage, Andrés
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Abstract
Recent tests of column-foundation connections showed that these types of connections are prone to fail by concrete breakout at low deformation demands when subjected to cyclic loading. This report describes tests of four large-scale reinforced concrete column-foundation connections that were designed to investigate how foundation reinforcement details affect deformation capacity. Primary variables were the amount of foundation flexural reinforcement (spaced at 5.5 in., 9 in., or 12 in. in two directions), whether foundation transverse reinforcement was provided around the column, and foundation depth (18 in. or 30 in.). All specimens had the same column nominal dimensions, column reinforcement, concrete compressive strength (6000 psi), and nominal reinforcing bar yield stress (60 ksi). Lateral loads were applied to the column, while the foundations had vertical simple supports located 10 ft apart and a horizontal support 9 in. from the top of the foundation. The foundations were designed for the shear and flexural demands associated with the expected flexural strength of the column.
All specimens exhibited similar strengths, which were limited by column flexural yielding, and failed by breakout within the foundation that limited the deformation capacity. The results show that deformation capacity of column-foundation connections is sensitive to the amount of foundation longitudinal reinforcement, and that adding longitudinal bars or small quantities of foundation shear reinforcement delays breakout in specimens like those tested. Conversely, increasing the foundation depth without also increasing column bar embedment length led to somewhat earlier breakout and reduced deformation capacity. Strain measurements suggested that initiation of breakout is linked to bond strength decay along the straight portion of the column hooked bars, which in turn may be linked to the magnitude of strains in the top mat of foundation longitudinal reinforcement. Strains in the top mat of foundation longitudinal bars were larger than in the bottom mat and larger than expected based on strength calculations, suggesting that the top mat was more active in resisting transfer moment than the bottom mat.
Description
Results from these tests can be found at this reference:
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, January 2025. https://hdl.handle.net/1808/35803
Date
2024-09-11
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University of Kansas Center for Research, Inc.
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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, September, 2024, 182 pp.