3-D FINITE ELEMENT ANALYSIS OF PILE-TO-PILE CAP CONNECTIONS SUBJECTED TO SEISMIC ACTION M. Teguh 1,2) , C.F. Duffield 1) , P. A. Mendis 1) , G.L. Hutchinson 1) 1) University of Melbourne, Melbourne, Victoria 3010, Australia 2) Islamic University of Indonesia, Yogyakarta 55581, Indonesia Abstract Damage in recent earthquakes has resulted in the design of pile foundation systems becoming more conservative, particularly pile-to-pile cap connections. Ground movement has led to plastic hinges forming in the piles near their connection to the pile cap. Application of current international design practice results in pile cap joint details having congested steel reinforcement in the pile cap and this is extremely difficult to construct. This paper reports the results from a three-dimensional finite element model that has been utilised to analyse the nonlinear behaviour of pile-to-pile cap connections. Two models of pile-to-pile cap connections have been developed, namely: plain embedment; and headed embedment and both models have been simulated under monotonically lateral loads. Results indicate that the use of a suitable headed embedment significantly improve the seismic behaviour. Based on the analysis, it is recommended that using 1.2- 1.5 of pile width (or diameter) for embedment length of headed reinforcement produces adequate connections that have reduced stress concentration and crack damage at the interface between pile and pile cap. 1. Introduction Earthquakes that have occurred globally over the last two decades have resulted in an increased expectation of acceptable performance and damage control for different structures during seismic events. Catastrophic failures of piled foundation systems in the recent earthquakes of Loma Prieta, Northridge (Nogami 1987), and Kobe (Building Research Institute 1996) have led to considerable effort being directed towards safer civil infrastructure particularly in the seismic zones. However, repair of damaged piles in high-rise building systems is impractical because of the expensive cost and difficulty associated with ground excavation. This paper reports a study focusing on two types of connections, i. e., plain embedment and headed embedment, to improve the capacity of the connection. In the plain embedment (without treatment), the prestressed concrete pile is simply embedded in the cast-in-place pile cap. In the headed embedment (with treatment), pile strands confined with round reinforcement are exposed and embedded in the cast-in-place pile cap. In this paper, two pile units using plain embedment model which were tested by Harries and Petrou (2001), are reviewed and the validity of their hypotheses is rigorously investigated through comparison of the observed and predicted nonlinear behaviour. Teguh et al. (2004) have shown that numerical predictions for the load-displacement Page 14-1