Preflex beams: Structural optimization and analysis of economic advantages

This paper deals with Preflex beams which are a very particular kind of composite structures, including a precasted concrete bottom flange, which is prestressed by means of pre-deflection of the steel beam. An important variant of this technology, adding prestressing with pre-strained cables to predeflection (Flexstress), is also considered. The concrete bottom flange increases significantly the stiffness with respect to instantaneous loads and it allows very slender designs. The case of a small span rail bridge is taken into account and the beam geometry as well as the material choice are optimized. These innovative solutions are then compared to a traditional composite design with the same slenderness ratio and with an existing rail bridge deck. Relevant cost savings seem to be possible, especially in the Flexstress case.