Time-Dependent Behavior of Recycled Aggregate Concrete-Filled Steel Tubular Columns

Recycled aggregate concrete-filled steel tube (RACFSTs) are attracting increasing attention from academics as a solution to use recycled aggregate concrete (RAC) as main load bearing members in multilevel or even high-rise buildings. Despite their promising future for structural use, limited attention has been devoted to investigate the time-dependent behavior of such elements. This paper reports on an investigation of how the incorporation of recycled aggregates (RAs) affects the long-term responses of these composite specimens. To achieve this, 21 RACFST specimens with different aggregate replacement ratios have been prepared for the long-term tests. The accuracy of currently available RAC concrete models in predicting the creep behavior of the RACFST specimens has been investigated based on the related experimental results. Replacing natural coarse aggregates with recycled aggregates can increase the long-term deformation of the composite columns by 22% but barely affects the rate of creep development of the specimens. The observations from the research reported in this paper indicate that it is reasonable to account for such effects by multiplying an amplification factor to the available concrete models for normal composite specimens. Benchmarking analyses have shown that the available amplification factors proposed for RAC members can be used to predict the long-term responses of RACFST specimens by considering a nil exposed perimeter. Parametric analysis has been carried out to evaluate the time effects on the static responses of RACFST specimens. (C) 2015 American Society of Civil Engineers.