A concrete fillable steel joist includes a generally U-shaped member and a top chord. The generally U-shaped member has spaced apart webs and a bottom chord. The top chord is operably attached to the U-shaped member. The top chord has a plurality of spaced apart top chord holes. The U-shaped member and the top chord define a volume that is fillable with concrete when opposed ends of the U-shaped member have joist ends operably attached thereto. The joist ends may be a pair of end plates. Alternatively, the joist ends may be structural members. A concrete fillable steel joist system includes a plurality of spaced apart concrete fillable steel joists, and metal decking. The metal decking is operably attached between the spaced apart steel joists. The concrete fillable steel joist and the metal decking are configured to receive concrete.