Marson and Bruneau 2004
The maximum strength and ductility of four concrete-filled circular steel piers joined to a foundation detail proposed to develop the full composite strength at the column bases was investigated. The study was focused on the effectiveness of these columns as piers in seismic regions of North America.
Experimental Study, Results and Discussions
Four CFT specimens were tested with D/t ratios of 2.008, 1.339, 2.517, and 1.654 in. and with diameters of 12.752, 12.752, 16.16, and 16.16 in. respectively. Average compressive concrete strengths of 5.076, 5.801, 5.366, and 5.076 ksi and yield strengths of the steel tubes of 60.190, 65.122, 73.244, and 86.614 ksi were measured. In order to accurately reflect real world design requirements, 1,296 bridges were designed using a suite of different configurations, geometries, and parameters likely to be encountered in highway bridges situated in North America. Specimen parameters were selected from the resulting pier size data to be representative of real prototypes. Restrictions with the test setup limited maximum column height to 86.614 ksi.
The proposed foundation detail was constructed as follows: The bottom of the steel tube was welded to a 30 mm thick bottom plate. Two C channels with their flanges pointing away from the tube were welded to the bottom plate. A 10 mm thick top plate with a hole cut for the tube was slipped over the tube and welded to both the top flange of the channel and the tube. The foundation was attached to a strong floor using four high strength bolts.
A horizontal loading beam, connected to the column by two existing spacers, was used to transfer the vertical axial load from the actuators to the column. The vertical load actuators had to sit on top of the foundation due to setup limitations. For this reason, the concrete foundation was subjected to uplifting tension forces. Specimens were first subjected to an axial load, which was held constant throughout the test. A horizontal displacement history using the ATC-24 procedure was then followed for all tests. P-∆ effects on the specimens were significant and were taken into consideration during analysis.
Overall, specimens exhibited good ductility and showed favorable hysteretic curves. The authors conclude that the tests showed good energy dissipation for the columns and that the foundation detail worked well, ensuring that full moment resistance capacity of the concrete-filled steel column could be developed during testing. As such, they could provide a viable alternative for bridge piers in seismic regions of North America. A brief investigation of the bond in the concrete filled tubing was made with the conclusion that no significant bond was detected between the steel tube and concrete core after testing had been completed. The authors clarify that this investigation was very limited.
Reference
- Marson, J., and Bruneau, M. (2004). “Cyclic Testing of Concrete-Filled Circular Steel Bridge Piers having Encased Fixed-Based Detail.” Journal of Bridge Engineering, ASCE, 9(1), 14–23. doi:10.1061/(ASCE)1084-0702(2004)9:1(14)