Pre- and post-heating behavior of concrete-filled steel tube stub columns containing steel fiber and tire rubber

Concrete-filled steel tube (CFST) columns are increasingly used in different structures owing to their excellent load carrying capacity provided by the interaction between the concrete core and steel tube. However, there is lack of information on the design and prediction of the behavior of CFST columns with rubberized concrete core when they are exposed to elevated temperature. This paper presents a study on the axial compressive behavior of short CFST columns containing steel fiber and tire rubber particles exposed to elevated temperatures. To this effect, steel fibers were added at two volume fractions of 1% and 1.5% and tire rubber particles were added as fine aggregate at two replacement ratios of 5% and 10% to the concrete core. CFST columns were exposed to four temperatures of 20 (as control), 250, 500 and 750 degrees C, and then axial compression tests were conducted on them. The experimental test results show that an increase in the exposure temperature to 500 degrees C does not have a significant influence on the compressive strength of CFST columns, whereas an increased temperature to 750 degrees C results in a significant decrease (34%) in the compressive strength of the columns. It is also found that an increase in the exposure temperature, steel fiber volume fraction and rubber replacement ratio lead to an increase in the axial and lateral strain corresponding to the compressive strength of CFST columns. It is shown that the predictions of the compressive strength and axial stress-strain relationship by the proposed model are in good agreement with the tests results of both unheated and post-heated CFSTs.