Title:
Capacity Estimations for Three-Pile Caps with Size and Reinforcement Variations
Author(s):
S. Mogili, S.-J. Hwang, K.-Y. Liu, T. Ichinose, L. Laughery, and K. Kasai
Publication:
Structural Journal
Volume:
122
Issue:
1
Appears on pages(s):
63-76
Keywords:
pile caps; punching; reinforced concrete; scaled testing; shear strength; size effect; softened strut-and-tie model; two-way shear
DOI:
10.14359/51743292
Date:
1/1/2025
Abstract:
Past investigations showed that the one-way shear strength of
reinforced concrete members exhibits “size effect,” a phenomenon
whereby shear strength does not increase in direct proportion to
member size. However, it is unclear if the reduction in the two-way
shear strength of reinforced concrete members due to size effect
applies in the same magnitude as one-way shear strength. To investigate size effect in two-way shear, 12 three-pile caps were tested in three size groups: small, medium, and large. Specimens were doubly scaled from small to medium and medium to large groups, with all other key nondimensional structural parameters such as span-depth ratio, reinforcement ratio, and so on kept constant. The test results supported the existence of size effect in deep pile cap members, although the observed rate of unit shear strength reduction with depth was less severe than that predicted by size effect provisions in American and Japanese design codes. Capacity estimations made using sectional and strut-and-tie approaches prescribed by design codes, as well as the proposed analytical procedure using the softened strut-and-tie model, are presented. The proposed method produced reasonably accurate estimations at all size ranges, capturing the effect of reinforcement more efficiently resulting in an overall mean test-to-calculated capacity ratio of 1.15 with a low coefficient of variation of 11%.
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