Study on Pile Cap Design

Abstract

Piles are used to transfer the loads from the superstructure down to the soil stratum. where the required resistance is available. Unless a single pile is used, a pile cap is necessary to spread the vertical and horizontal loads and any overturning moment to all the piles in the group. Unlike footing the base reaction of pile cap Consists of a number of concentrated load. Different methods of designing pile caps are in practice. Those are Broadly classified as ACI Building Code and strut-and-lie model (STM). In this project the cost incurred by different design approaches are compared. The cost of pile caps according to different approaches is compared considering 4 pile -cap with constant pile diameter and column size but with varying pile spacing. The comparison reveals that the pile cap designed by STM costs 5% to 20% lower than AC Building Code for pile spacing 2 to 3 times pile diameter within a range of 75 to 625 kip of column load. The experimental ultimate strength of the pile caps is compared with that obtained by different design approaches. The behavior of pile cap at loading stage is also observed and is seen to agree with other investigators. It is seen that the experimental strength of pile caps is higher than the strength predicted by the STM in comparison to ACI Building Code. Within the limitation of pile spacing up to 3 times pile diameter, modified STM is more rational than ACI Building Code in terms of cost and integrity.