Evaluation of Pile Cap Dimensions and Reinforcement Using Conventional, Strut and Tie, and Finite Element Methods

Abstract

Pile caps play a critical role in transferring axial forces, bending moments, and shear forces from superstructures to pile groups. This study comparatively evaluates the dimensions, reinforcement requirements, and structural response of pile caps with two, three, four, and five piles using the Conventional Method, Strut-and-Tie Model (STM), and Finite Element Method (FEM). The Conventional Method was used to assess flexural and shear capacity in accordance with ACI 318, while STM represented internal load transfer through compression struts and tension ties. Three-dimensional FEM models were developed in ABAQUS using the Concrete Damage Plasticity approach and were validated against a numerical model before analysis. The results show that pile configuration and analytical method significantly affect pile cap dimensions and reinforcement requirements. The five-pile configuration exhibited the largest differences, with STM producing a 1100 mm thick pile cap and 7,645 mm² reinforcement, compared with 900 mm thickness and 5,888 mm reinforcement from the Conventional Method and FEM. FEM produced maximum concrete stresses of 8.20, 2.41, 3.03, and 2.41 MPa for five-, four-, three-, and two-pile configurations, respectively. Reinforcement stresses were generally closer to Conventional Method results. The findings demonstrate that the three approaches provide complementary information for pile cap design and evaluation.