Foamed Plastic Absorbs Staged Post‐Tensioning Deflections

Staged construction of a long, post‐tensioned, concrete highway bridge faces a falsework designer with the alternatives of a costly overdesign of falsework bents for all but a one‐time, short‐term load or the provision for expensive lowering devices. The problem is solved by using crushable foamed plastic support blocks. The support blocks can be designed to safely support the dead load of the superstructure and to crush when post‐tensioning increases the reaction, thus limiting the reaction. While crushing, the blocks continue to provide the necessary support for the superstructure. Stress and strain graphs for foamed isocyanurate are provided, which demonstrate its suitability for this application and provide the basis for design.