Title: Predicting Strength Capacity of Three-Dimensional Concrete Struts in Pile Caps

Author(s): Ridha Boulifa, Mohamed Laid Samai, Mohamed Tayeb Benhassine, and Abdelhadi Tekkouk

Publication: Structural Journal

Volume: 118

Issue: 2

Appears on pages(s): 111-126

Keywords: confinement cylinder; pile caps; specimens; strength capacity; strut-and-tie model

DOI: 10.14359/51729344

Date: 3/1/2021

Abstract:
The strength predictions of reinforced concrete pile caps are mainly influenced by the cross section and the compressed concrete strut’s inclination. However, for the case of four-pile caps with top-inclined slabs (tapered footings), many authors show that the cracking load decreased as the reinforcement ratio increased. In the present paper, a new experimental study is performed using a vertical penetration of a cylindrical plated bar in a cylindrical confined specimen with a crown-shaped base. The specimens are entirely confined using cylindrical steel tubes. The thickness of the crown and the specimen’s height governs the inclination of the punching failure cone. The present study’s objective is to evaluate three-dimensional pile caps’ strength capacity by developing an analytical relationship taking into consideration the main parameter, which is the shear-span depth ratio. This relationship is based on the determination of the resulting shear in the most solicited vertical plane considering the confinement thanks to longitudinal reinforcement during loading. Thus, the proposed relationship is on the safety side following the failure mode imposed, which is the critical one (by punching). The proposed approach provides more accurate predictions of the strength for the tests performed and existing pile cap’s tests with lower scatter compared to design approaches in the literature and ACI 318 Code.