Abstract: “The purpose of this study was to determine the behavior of castella beams reinforced with concrete due to cyclic loading, so that the beam can be used as a structural element for receiving seismic load. Test beam consists of beam castella fabricated from normal beam (CB), castella beams with concrete filler between the flange (CCB) and normal beam (NB) as a comparison. Results showed castella beam (CB) has the advantage to increase the flexural capacity and energy absorption respectively 100.5% and 74.3%. Besides advantages, castella beam has the disadvantage that lowering partial ductility and full ductility respectively 12.6 % and 18.1%, decrease resistance ratio 29.5 % and accelerate the degradation rate of stiffness ratio 31.4%. By the concrete filler between the beam flange to improve the ability of castella beam, then the beam castella have the ability to increase the flexural capacity of 184.78 %, 217.1% increase energy absorption, increase ductility partial and full ductility r”

Keywords: steel, castella ,column beams, cyclic load