INDUS T RI AL PH D capacity of the construction”, explains Jacob Wittrup Schmidt. However, the problem is that while carbon fibre features appreciable tensile strength longitudinally—i.e. in the direction of the cable (the direction of the fibres), its compressive strength is very low in a latitudinal direction. This means that it is easy to crush by applying latitudinal force. For this reason, it is not possible to use the same anchoring systems that are used for steel cables. If a carbon fibre rod is screwed in place using a traditional system, the pressure will crush it. A patented sleeve anchor system In his industrial PhD study, Jacob Wittrup Schmidt worked to come up with a solution for securing carbon fibre rods in place without crushing them, and he succeeded in developing what is known as a ‘sleeve anchor’ system. A ‘sleeve’ is the industry term Slit Gap Carbon 10 for a metal cover or casing. Jacob Wittrup’s sleeve anchor is around 105 mm long and shaped like a cone that encompasses the ends of the carbon fibre rod. The unique aspect of this new and patented sleeve is that it can be tightened firmly around the carbon fibre rod without damaging it. LOTTE KR ULL >> Sleeve wedge Barrel Integrated sleeve 21 30 95 105 93,1° 93,0° Illust rat ion Jacob Witt rup Schmidt The illustration of the patented sleeve anchor shows how the three wedges are integrated in the sleeve. This ensures that the pressure is distributed better in the carbon fibre rod, which is thus not crushed when the sleeve is tightened around the pole. COWI helped the Land Transport Authority of Singapore reinforce a number of bridges. Carbon fibre as reinforcement In recent decades, attempts have been made to replace steel with carbon fibre when a material with a very high tensile strength was needed. Carbon fibre is a very light material with high tensile strength in the fibre direction. However, it has very little strength across the fibres and is therefore easily affected by transverse loads. This has challenged engineers worldwide when having to apply carbon fibre in practice. Carbon fibre can be used both in the form of bars or long, wide ribbons. It can be attached to the existing structure, e.g. a concrete bridge deck, either by gluing it to the outside or in grooves cut into the structure. It can also be adhered in mechanical and adhesive sleeve anchors (adhesion is the cohesive force between the two bodies in contact with each other, ed.). Carbon fibre can be used for reinforcing bridges, silos and similar structures on land and offshore. The material can also be used in new structures such as pre-stressed concrete bridges or cables and rods in cable-borne structures such as suspension bridges and cable-stayed bridges. 30 Technical University of Denmark photo COWI
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