Design-Oriented Testing and Modeling of Reinforced Concrete Pile Caps

A new perspective in the design of reinforced-concrete pile caps is proposed in this paper, where the conventional approach leading to a reinforcing mesh is replaced by modelling the cap as a strut-and-tie system, in agreement with the strut-and-tie model, STM proposed by several design codes, ACI 318 included. Twelve RC pile-cap specimens were designed and manufactured. In the first group of 4 specimens the caps rest on two piles (Group A, axis-to-axis distance 300 mm), while in the second and third groups the piles are three and four, respectively (Groups B and C, axis-to-axis distance 400 mm). In each group, the first and third specimens were designed according to the traditional sectional method (reference specimens, with constant depth and lateral shoulders), while the design of the second and fourth specimens was based on the strut-and-tie method (no lateral shoulders; no corners opposite to the piles). Needless to say, the nominal design load was the same within each group. The tests clearly show that cap design based on strut-and-tie systems brings in a sizable reduction in terms of reinforcement amount and cost, accompanied by a less pronounced but still sizable extra bearing capacity.