Rodrigues and Laím 2018

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Experimental Study, Results, and Discussion

This paper presents results of reinforcement concrete-filled hollow sections with circular, square, rectangular, and elliptical cross section subjected to fire and restrained thermal elongation. Specimens were tested under the standard fire curve for results such as critical time, critical temperature, and buckling mode. The tests were composed of fourteen fire resistance tests which were executed at the Laboratory of Testing Materials and Structures at Coimbra University, Portugal. Longitudinal steel reinforcing was used in the concrete, with a ratio of 2.5% in the circular, square, and rectangular sections, and a 4.2% ratio was used in the elliptical cross sections. All the columns were prepared the same way, with a 450 x 450 x 30 mm steel plate welded to each end in order to connect the columns to the testing frame. The concrete was poured into the upright columns, and the concrete was then cured. A vertical electric furnace is used, with maximum temperature of 1,200°C. A serviceability load was applied to the columns with value of 30% of the design value for the columns at normal temperature prior to the fire exposure, and maintained through the fire portion of the test. Type K thermocouples were placed at five locations along the columns, including at different depths, and linear variable differential transformers were used to measure displacements. The elliptical columns buckled along the minor axis, while the other shapes buckled about both axes. The axial restraining forces are the highest for the elliptical cross sections, and the lowest for both the circular and square cross sections. The concrete provides thermal insulation and prevents local buckling, however local buckling occurred when the depth to thickness ratio exceeds 35. The increase in axial and rotational stiffness led to a 5% decrease of fire resistance. The square exhibited the least fire resistance, whereas the elliptical exhibited the greatest fire resistance.


References

Rodrigues, J., Laím, L.(2018). “Behavior of Concrete-Filled Circular, Square, Rectangular, and Elliptical Hollow Columns Subjected to Fire.” Journal of Structural Engineering, 144 (6), June. doi:10.1061/(ASCE)ST.1943-541X.0002035