Seismic performance of prestressed concrete piles and pile-pile cap connections

Abstract

The performance, strength and ductility of prestressed concrete piles, and their connection to pile caps, subjected to severe seismic loading are investigated in this thesis. Knowledge of the strength and ductility of the pile within its embedded length in the foundation material is of importance due to the large deformations which can occur during an earthquake, particularly at the interface of hard and soft layers of foundation material. Connection details are of interest since high moments, shears and axial forces need to be transferred to pile caps during earthquake loading. Two series of tests of piles and their connections, and accompanying analyses, were conducted. Design tables and charts were derived. The first test series consisted of six full scale octagonal prestressed concrete piles, confined spirally with either Grade 275 steel or hard drawn (Grade 485) steel wire and having various confinement levels, tested under axial load and cyclic flexure. Results of the theoretical analysis were compared with the experimental data. It was found that properly detailed prestressed concrete piles without additional nonprestressed longitudinal steel can sustain large displacement ductility factors without losing their lateral load carrying capacity significantly if confined according to full ductility. The second test series consisted of six full scale octagonal piles connected to full scale reinforced pile caps. The piles were either fully or partially prestressed. Three types of pile to pile cap connection were investigated, namely the precast embedded type, the stripped pile head type, and the type where steel dowel bars are used as the connection device. Theoretical analyses were used to compare the experimental data. The connection details investigated were found to give satisfactory performance. Finally, tables and charts obtained for the pile properties are presented for design purposes. The design tables are used to assess the enhancement factors of pile cross sections within the length or at the interface of the connection at the pile cap. The design charts are used to calculate the yield curvatures as well as the available curvatures and available curvature ductility factors. Recommendations for future research are proposed to complement the work already done up to this stage.