Effect of embedded steel stirrups on fire behavior of square steel tubular columns filled with recycled lump concrete

Abstract Steel tubular columns filled with recycled lump concrete (RLC) made of demolished concrete lumps (DCLs) and fresh concrete (FC) have been shown to have good mechanical properties at room temperature, but the fire performance of such columns has remained poorly understood. This study presents an experimental investigation on the fire behavior of seven full-scale square steel tubular columns filled with RLC or with FC alone. The parameters considered in the fire tests included the replacement ratio of DCLs, the steel stirrups inside steel tube and their arrangement, and the clear distance between the tube and steel stirrups. The columns with stirrups have the same total amount of steel as the control column without stirrups. The test results show that: (1) including DCLs up to a replacement ratio of 25% has little effect on a column’s fire resistance; (2) compared with a columns without steel stirrups, columns with embedded stirrups have significantly enhanced fire resistance (by up to 178%) without increasing the total steel usage, due to the confining effect of the temperature-shielded steel stirrups on the inner concrete core; and (3) fire resistance exceeding 180 min can be achieved in some cases without any external fire retardant coating. The simple calculation method specified in EN 1994-1-2:2005 is extended to predict the fire resistance of columns with embedded stirrups.