Ductility of Welded Steel Pile to Steel Cap Beam Connections

This paper discusses the seismic behavior of a bridge bent systems that consist of round HSS piles welded to a steel HP section cap beam. Past practice has typically utilized a simple fillet weld with no backer ring to complete the connection between the pile and cap beam. The results of the research indicate that the overall ductility capacity of this system is controlled by the configuration of the welded connection between the piles and cap beam. Due to the lack of prior knowledge concerning this type of connection, six full scale bridge bent tests have been conducted at North Carolina State University's Constructed Facilities Laboratory to evaluate the performance of the system when subjected to incremental simulated seismic loading. The two main goals of the research were to first evaluate the behavior of the system with a fillet weld which mimics the current typical design practice, and secondly to improve performance by investigating alternative weld configurations and connection details. The results indicate that the use of a simple fillet weld led to connection failure at a low ductility level rendering the detail inadequate for even moderate seismic regions. Subsequent tests showed that the use of other weld configurations, such as full joint penetration welds, improved the capabilities of the system but were still inadequate for higher seismic regions. However, promising results were obtained from a connection in which the flexural hinge region was relocated away from the pile to cap beam connection weld. This connection system remained essentially elastic at the pile to cap beam interface, which allowed for a more ductile base metal failure away from the connection.