Perea et al. 2013

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Perea et al. conduced an experimental study addressing many aspects of the behavior of concrete-filled steel tubes. The study consisted of eighteen full-scale slender beam-column specimens which were subjected varied loading cases, including concentric axial compression, axial compression plus biaxial bending, and torsion. Also studied was the behavior of the steel tube during pouring of the concrete.

Experimental Study, Results, and Discussion

CFT Beam-Column Specimen in the MAST Laboratory
CFT beam-column specimen in the MAST laboratory

The specimens in the experimental program were both relatively slender in length and in width-to-thickness ratio. In total, eighteen specimens were tested with variations in steel tube shape and size, length, and concrete strength.

The steel tubes were instrumented to during casting of the concrete to investigate the effect of the hydrostatic pressure from the concrete. Stiffeners were used during casting of most of the RCFT specimens to control the initial deformations due to the hydrostatic pressure of wet concrete. During the testing of the RCFTs, adverse effects of not limiting bulging of the steel tube during casting were clear in those specimens that were not stiffened. Steel local buckling was noted to occur earlier and at the location coinciding with the maximum outward deflection of the tube. In contrast, there were very low initial deformations on the plates of those specimens that were stiffened properly, and then the local buckling was developed as expected at the critical section (near the base).

The tests were conducted at the Multi-Axial Sub-Assemblage Testing (MAST) facility at the University of Minnesota. The MAST system consists of a stiff steel crosshead connected to 4 vertical actuators and 2 actuators in both horizontal directions, allowing 6 DOF control of the crosshead. Thick plates were welded to the ends of the specimens. The bottom plate rigidly connected the specimen to the strong floor and the top plate rigidly connected the specimen to the crosshead. Through control of crosshead different end conditions could be simulated, most often a fixed-free (K=2) condition was enforced. The specimens were subjected to a variety of successive load histories.

The first load case subjected the specimens to concentric axial load. All but specimens 1-C5-18-5 and 18-C5-26-12 were held in a fixed-free (K=2) configuration. Specifically, lateral forces and bending moments at the crosshead were force controlled to zero, while the specimen was loaded in axially in displacement control until the critical load was reached. The twist DOF was held in displacement control to zero due to the low torsional stiffness of the specimens. The second load case subjected the specimens to combined axial compression and uniaxial bending. This was achieved with vertical force control at a specified load and displacement control of the lateral DOFs. Again, most specimens were held in a fixed-free (K=2) configuration with bending moments at the crosshead were force controlled to zero. The third load case maintained the same control as the second load case, but subjected the specimen to combined axial compression and biaxial bending. Additional latter load cases were conducted, subjecting the specimens to torsion, combined torsion and compression, or alternate end conditions.

Text Matrix with Nominal Properties

Specimen Steel Section Length (ft) Fy (ksi) f'c (ksi)
1C5-18-5 HSS5.563x0.134 18 42 5
2C12-18-5 HSS12.750x0.250 18 42 5
3C20-18-5 HSS20.000x0.250 18 42 5
4Rw-18-5 HSS20x12x5/16 18 46 5
5Rs-18-5 HSS20x12x5/16 18 46 5
6C12-18-12 HSS12.750x0.250 18 42 12
7C20-18-12 HSS20.000x0.250 18 42 12
8Rw-18-12 HSS20x12x5/16 18 46 12
9Rs-18-12 HSS20x12x5/16 18 46 12
10C12-26-5 HSS12.750x0.250 26 42 5
11C20-26-5 HSS20.000x0.250 26 42 5
12Rw-26-5 HSS20x12x5/16 26 46 5
13Rs-26-5 HSS20x12x5/16 26 46 5
14C12-26-12 HSS12.750x0.250 26 42 12
15C20-26-12 HSS20.000x0.250 26 42 12
16Rw-26-12 HSS20x12x5/16 26 46 12
17Rs-26-12 HSS20x12x5/16 26 46 12
18C5-26-12 HSS5.563x0.134 26 42 12

See Also

References

  • Perea, T. (2010). “Analytical and Experimental Study on Slender Concrete-Filled Steel Tube Columns and Beam-Columns.” Ph.D. Dissertation, School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, Georgia.
  • Perea, T., Leon, R. T., Hajjar, J. F., and Denavit, M. D. (2013). “Full-Scale Tests of Slender Concrete-Filled Tubes: Axial Behavior.” Journal of Structural Engineering, ASCE, 139(7), 1249–1262. doi:10.1061/(ASCE)ST.1943-541X.0000784
  • Perea, T., Leon, R. T., Hajjar, J. F., and Denavit, M. D. (2014). “Full-Scale Tests of Slender Concrete-Filled Tubes: Interaction Behavior.” Journal of Structural Engineering, ASCE, (accepted for publication).