Title: Design of Deep Pile Caps by Strut-and-Tie Models
Author(s): Perry Adebar and Luke (Zongyu) Zhou
Publication: Structural Journal
Appears on pages(s): 437-448
Keywords: building codes; caps (supports); deep beams; footings; piles;
reinforced concrete; shear strength; structural design; strut-and-tie
Comparisons with results from 48 pile cap tests demonstrate that the one-way shear design provisions of the present ACI Building Code are excessively conservative for deep pile caps, and that the traditional flexural design procedures for beams and two-way slabs are unconservative for pile caps. Flexural design can best be accomplished using a simple strut-and-tie model, and test results demonstrate that the longitudinal reinforcement should be concentrated over the piles as suggested by strut-and-tie models. A simple shear design procedure is proposed in which maximum bearing stress is considered the best indicator of shear strength for deep pile caps. The maximum bearing stress that can be applied without causing splitting of compression struts within pile caps depends on the amount of confinement, as well as the aspect ratio (height-to-width) of compression struts. The influence of confinement is more gradual than suggested by the ACI Code bearing strength provisions.