Post-tensioned CFRP strap elements for civil engineering applications

Two applications of post-tensioned CFRP strap elements recently developed at the Composite Construction Laboratory (CCLab) of the Swiss Federal Institute of Technology Lausanne (EPFL) are presented. The first application concerns post-tensioned non-laminated CFRP straps used for the strengthening of existing concrete flat slabs against punching shear. Four strap elements are installed crosswise around the column in predrilled openings and are anchored and post-tensioned from the bottom side of the slab. Laboratory experiments on eight full-scale flat slabs showed that, although CFRP is a brittle material, the strap post-tensioning assured a ductile system behavior. A punching shear resistance increase of more than 100% was obtained. The second application concerns post-tensioned laminated CFRP straps used for permanent ground and rock anchors. They consist of a CFRP tendon with a two-strap end on the ground side, embedded in a prefabricated high-strength grout cylinder. The ground anchor is posttensioned to 60% of the 1000 kN design load, which was obtained from pull-out experiments.