RenewWrap Strand Sheets® are unidirectional reinforcement sheets consisting of an assembly of pre-cured carbon fiber micro bars. They are available in various stiffnesses and may be used to strengthen existing concrete or steel structures by external bonding. Strand Sheets combine the best features of traditional wet lay-up fabric and pre-cured plate FRP system. 

This material was inspired by Japanese bamboo blinds — it consists of hundreds of pre-cured carbon fiber micro-rods assembled into a sheet bonded to a structure with epoxy resin.  The resin allows the strand sheet to be uniformly bonded to an existing structure.  The material can be spliced in the field by overlapping, like a wet lay-up system, and the quality of the bond line is visible by uniformity and complete coverage of carbon fiber strands. 

The rehabilitation of the 1,090-foot-long Honjo Truss Bridge was one of the first Strand Sheet® applications to a steel structure. This steel truss superstructure was weakened from the corrosion of truss members — where the diagonal members penetrated the concrete deck — and the sufficient section loss required strengthening. The deck was removed around the truss members and the carbon strand sheets bonded to the webs and flanges of the W-beams comprising the diagonal members. Thirty-six diagonal members were strengthened with strand sheets, and the area of the bridge was painted after the sheets were finished curing.

Applications

  • Retrofit and strengthen concrete, steel and masonry structures

  • Repairs a variety of deficiencies in steel structures caused by corrosion-related deterioration or increased loads

  • Restore section loss of tension and compression

  • Restore steel members such as flanges, bracing, webbing, truss chords, and girder ends

  • Increases member stiffness or localized stiffness

  • Repairs stresses in existing steel members to improve fatigue behavior

  • Steel bridge girders, beams, column repairs

  • Precast bridge deck panel repairs

  • Concrete poles and marine pilings

  • Un-bonded Post Tensioning of Precast Members

  • Replacement of Corroded Steel Tendons

Benefits

  • Prevents CFRP debonding 

  • Walk-in mobilizations—no ordering steel, shipping steel, crane lifting steel; no welding

  • High-elongation polyurea elastic putty suppresses debonding, and allows sheets to follow significant deformations

  • Applicable to tensile, compression, and shear members

  • Compliant with the repair and reinforcement procedures for steel structures, and applicable not only to tensile members but also to compressive and shear members

  • Suppresses corrosion progression, using only textiles and resins that do not rust

  • Heat resistance corresponding to steel structure substrate

  • Simple workability—minimal training requirements

  • Materials used are light, heavy machinery is unnecessary, and can be installed only with hand tools 

Features

  • Open construction of strand sheet facilitates bond to substrate allowing paste adhesive to encapsulate each micro bar

  • Unlike solid carbon fiber plates, adhesive bond line can be visually inspected for consistency

  • Unlike solid carbon fiber plates, can be spliced by overlapping

  • Easy to slit to desired width

  • High modulus versions ideally suited for strengthening steel structures

  • Can be used to retrofit steel structures where welding is dangerous or not allowed

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