Flexural Behavior Characteristics of Steel Tubes Filled with SFRCCs Incorporating Recycled Materials

This study deals with the effect of fly ash and recycled sand on the flexural behavior of SFRCCs (steel fiber-reinforced cementitious composites)-filled steel tubes. As a result of the compressive test, the elastic modulus was reduced by the addition of micro steel fiber, and the fly ash and recycled sand replacement decreased the elastic modulus and increased the Poisson's ratio. As a result of the bending and direct tensile tests, strength enhancement by the incorporation of micro steel fibers was observed, and a smooth descending curve was confirmed after initial cracking. As a result of the flexural test on the FRCC-filled steel tube, the peak load of all specimens was similar, and the applicability of the equation presented by AISC was high. The deformation capacity of the steel tube filled with SFRCCs was slightly improved. As the elastic modulus of the FRCC material lowered and the Poisson's ratio increased, the denting depth of the test specimen deepened. This is believed to be due to the large deformation of the cementitious composite material under local pressure due to the low elastic modulus. From the results of the deformation capacities of the FRCC-filled steel tubes, it was confirmed that the contribution of indentation to the energy dissipation capacity of steel tubes filled with SFRCCs was high. From the comparison of the strain values of the steel tubes, in the steel tube filled with SFRCC incorporating recycled materials, the damage was properly distributed between the loading point and both ends through crack dispersion, and consequently, rapid curvature changes did not occur at both ends.

Automated summary

This study investigates the influence of fly ash and recycled sand on the flexural behavior of SFRCC-filled steel tubes. The addition of micro steel fiber reduces the elastic modulus, while the replacement of fly ash and recycled sand decreases the elastic modulus and increases the Poisson's ratio. The incorporation of micro steel fibers enhances the strength and results in a smooth descending curve after initial cracking. The flexural tests on the FRCC-filled steel tubes show similar peak loads and high applicability of the equation proposed by AISC. The deformation capacity of the SFRCC-filled steel tubes is slightly improved, but the denting depth increases due to the low elastic modulus.