Wei, Luo, Lai, Varma
High-strength short columns were tested in axial compression and compared with 87 previously conducted tests in order to evaluate design specifications provided by codes.
Experimental Study, Results, and Discussions
Concrete-filled tubes have proven to take all the material benefits of steel and concrete to create a viable composite action structural tool. We have already seen widespread applications of them within megacolumns, chord members in long-span arch bridges, bridge piers, and many others. There are primarily two different methods to increase the compressive strength of concrete-filled tubes. The first method is by increasing the cross-section of the CFTs. The caveat to doing this is that it can become quite costly to fabricate such members. The other commonly used method is simply using high-strength concrete and steel which can be a bit more practical. This experiment investigates the effects of changing these two qualities within CFST short columns. The test parameters of this experiment were the diameter-to-thickness ratio, the yield strength of the steel, and the compression strength of the concrete. Changing the D/t ratio was done by keeping the diameters of the concrete constant and increasing the thickness of the surrounding steel tubes. The steel tubes were fabricated by welding stiffened end plates to the end of the tubes. The concrete was cured in a curing room for three days, then steam cured for 4 days and then cured in a curing room for 28 days. The concrete infill was actually filled 15 mm higher than the end of the steel tubes and then ground down to the level of the ends to ensure an even distribution of loads. The tests were conducted at Fuzhou University using a 10000 kN testing machine. Two linear variable transducers and eight pairs of strain gauges were used as well. The tests showed that the overall strength of CFST short columns increased with increasing steel yield strength and concrete compressive strength. The tests also showed that the strength of CFST short columns decreased with increasing diameter over thickness ratio.
Evaluation of current design codes.
There are a host of equations that are outlined in a variety of design codes all over the world. After these tests, the results were compared to the equations used to derive the cross-sectional strength of circular CFST columns in the Eurocode, the Japanese code, and the American code. It was found that the Japanese code had the most accurate estimations based on the data derived from these tests, but the American code seems to have the most conservative estimations.
Reference
Wei, Jiangang, et al. “Experimental behavior and design of high-strength circular concrete-filled steel tube short columns.” Journal of Structural Engineering, vol. 146, no. 1, Jan. 2020, https://doi.org/10.1061/(asce)st.1943-541x.0002474.