Kilpatrick and Rangan 1997

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Tests were conducted on circular high strength CFTs under eccentrically applied axial load. In addition, the authors described a deformation control method of analysis to estimate the strength and load-deformation response of the test specimens. The analytical and experimental results were compared.

Experimental Study Results and Discussions

The main parameter of the experimental study was the amount of eccentricity in the applied axial load. The measured yield strength of the steel tubes was 59.47 ksi. The specimens filled with high strength concrete having a measured compressive strength of 13.92 ksi. The L/D and D/t ratios were 21.43 and 42.29, respectively.

The columns were tested both in double curvature and single curvature. The eccentricity at the bottom and top of the specimens were different in most of the cases. The ends of the columns were clamped to hardened knife-edge assemblages. The required eccentricity was provided by moving the column ends laterally from the loading axis.

Analytical Study

The experimental results were compared to analytical results using a classic Newmark iteration scheme based on use of moment-curvature-thrust relations. In general, the calculated strength and force-deflection response of the specimens matched with the experimental results quite accurately. However, the response of the specimens under single curvature showed better correlation than the specimens tested under double curvature. Analytically generated strength envelopes for equal eccentricity at the top and bottom showed a greater rate of increase and a higher concentric axial load capacity in the case of double curvature.

The authors also investigated the effect of variation in eccentricity on the column strength. For this purpose, columns in double curvature having equal magnitude of eccentricities at the bottom and at the top were analyzed with ±0.0394 in. error. In the first case, the eccentricity at the top and bottom was increased by 0.0394 in. In the second case, the eccentricity at the top decreased by 0.0394 in. while the eccentricity at the bottom was increased by 0.0394 in. It was found that the strength decreased most severely in the latter condition, with the amount of reduction being up to 25%. This was attributed to the change in the deformed shape as it was not perfectly asymmetrical any more.

References

Kilpatrick, A. and Rangan, B. V. (1997). “Behaviour of High-Strength Composite Columns,” Composite Construction—Conventional and Innovative, Proceedings of the International Conference, Innsbruck, Austria, September 16-18, 1997, International Association of Bridge and Structural Engineers, Lausanne, Switzerland, pp. 789-794.