Experimental Investigation of Ultrahigh-Performance Concrete for Capacity-Protected Pile Shafts Connecting with Precast Columns

The use of ultrahigh-performance concrete (UHPC) in pile shafts offers a promising solution for addressing challenges in the seismic design of connections between pile shafts and precast concrete columns. In particular, UHPC’s exceptional tensile properties enable the design of pile shafts that maintain capacity protection without requiring excessively large foundation or heavy reinforcement. This study experimentally examines the lateral load behavior of three 1/3-scale precast column-to-pile shaft assemblies, with variations in pile shaft material (normal concrete and UHPC), diameter, and transverse reinforcement spacing. The specimens were subjected to combined axial load and reversed cyclic lateral load. All specimens demonstrated similar lateral stiffness and strength and ultimately failed with maximum drift ratios reaching 8.53% due to flexure-induced damage at the column base. The normal concrete pile shaft showed moderate prying action–induced damage, whereas UHPC pile shafts, irrespective of diameter or reinforcement levels, remained uncracked throughout the tests. The use of UHPC allowed for a 13.3% reduction in pile shaft diameter and a 25% increase in transverse reinforcement spacing while maintaining capacity-protected performance, testifying to its efficiency for seismic connections in precast bridge pier systems.