Abstract: A variable set-up, reusable center frame for the realization of concrete and masonry arches and for restoration applications. The center frame includes a succession of Y-shaped modular rod members. Each branch is provided at its end with a first and second upper hinge joint and a lower hinge joint. The lower hinge joint is provided with a slide rod, and a plate-shaped connection locks the slide rod in place. The upper hinge joints are hingedly connected to supporting saddles extending out of a lower surface of a flexible forming member which is placed in contact with the member being supported. The slide rods are adjustable in position with respect to the lower branch such that the space between the lower branches can be adjusted to achieve different formations in the forming member.