This study investigates the design of fire resistant concrete using combined fibers. The effect of the combined fiber technique on the level of spalling protection was experimentally confirmed by applying to large columns. Four different size of large columns were prepared for proving the effectiveness of the combined fiber technique. In addition, the authors presented the detailed procedure of the optimum fiber design for spalling protection of concrete in fire. In this design, critical parameters of fiber length, fiber diameter and the total number of fibers per unit volume were quantitatively established, so that the fiber addition can be reduced over 50% for the single type of fibers and can be further reduced for the combined type of fibers.

Keywords: Fire resistant concrete, Combined fibers, Spalling, Column