Circular Concrete-Filled Tubes for Improved Sustainability and Seismic Resilience

Abstract

Concrete-filled tubes (CFTs) provide an opportunity for more sustainable structural systems through the use of concretes with high volumes of supplementary cementitious materials (SCMs) to replace cement. However, there is concern that the SCM concrete would not be able to sustain the early (construction or dead) loads due to the longer cure time, necessitating stress transfer to the steel tube, possibly leading to tube buckling. Further, these loads are permanent and the long-term response of CFTs with SCM concretes is also unknown. This research evaluates the response of CFTs with conventional and high-volume SCM concretes to immediate compressive, sustained, and extreme loadings. Two large-scale (508 mm diameter) CFT column-to-footing connection specimens, one with a high volume of SCM used to replace portland cement, were tested under long-term compressive and cyclic loadings. Shrinkage and creep were evaluated for both the large-scale CFT and companion cylinders. The total creep strain in the SCM and conventional concretes was found to be much larger in the unsealed cylinders than the CFT specimens. Creep coefficients were found to be similar for the sealed cylinders and the CFT specimens. Drying shrinkage was found to be negligible in the CFTs and the SCM concrete was found to have slightly larger shrinkage than conventional concrete in both sealed and unsealed cylinders. The CFT specimens were subjected to cyclic lateral loading to evaluate their response to extreme loads and the effects of creep loading and the SCM concrete on performance were negligible.