Description
Kleine Emme bridge was a truss bridge built in 1998 for pedestrians and bicycles with a span of 46.8 m in the city of Lucerne - Central Switzerland. The bridge structure was a space truss made of steel pipes in composite action with a reinforced concrete deck. The bottom chord consisted of a steel tube that was post-tensioned with 2 parallel-wire CFRP cables inside the channel, a world premiere 25 year ago. Each cable consisted of 91 pultruded CFRP wires of 5 mm diameter which were prestressed to 1'350 MPa each, corresponding to 45% of the CFRP design tensile strength. The CFRP cable anchorages were obtained by casting the CFRP wire ends in steel sleeves with a special epoxy grout, a gradient stiffness load transfer media patented by Prof. Urs Meier of Empa in 1998. In spring 2016 the bridge was dismantled due to a new concept for flooding protection for the city of Lucerne which made it obsolete. 8.7 km of CFRP pultruded wires (market value 45'000 Euro) came back to Empa after decommissioning of the bridge. The 47.8 m long CFRP cables were stored outdoors for 7 years while Empa was looking for re-use options of these valuable materials, their residual tensile strength was assessed to be more than 90% after 25 years. This paper presents the development of a new filament wound CFRP sleeve and resin grout at Carbo-Link and Empa for the efficient anchorage of the 25 years old re-used CFRP wires. The new anchorage and cables were tested to tensile capacity (1.833 MN) in two full scale instrumented experiments using distributed fiber optic sensors, laser and strain gauges before two new 28.4-32.4 m long post-tensioning cables were produced by Carbo-Link with each 37 of the regained CFRP wires. Both CFRP parallel wire cables were finally successfully prestressed to 1 MN (55% of their UTS) in order to strengthen an existing bridge in the Swiss Alps over the river Ilfis in summer 2023. This strengthening project is thoroughly described: The re-use of valuable CFRP pultrusions for post-tensioning confirms the durability and shows the sustainability potential for CFRP.
