formwork for erecting a crown on a top end of a structural concrete column of a highway bridge is supported by a pair of vertically positioned elongated jack - screws . lower ends of these jack - screws are threaded respectively into adjusting nuts seated on outer ends of respective horizontal arms of a pair of brackets . each bracket includes an upright support member . these members are attached respectively to opposite sides of the column . the vertical location of the formwork attached to an upper end of a jack - screw may be adjusted up or down by selective rotation of the adjusting nut into which that jackscrew is assembled .