In the scenery of innovative composite materials provided by FIDIA S.r.l. - Technical Global Services are available also unidirectional ultra high tensile steel sheets, known with the acronym of SRP (Steel Reinforced Polymer) when impregnated with epoxy resin or SRG (Steel Reinforced Grout) when impregnated with mortars (cement or hydraulic) consisting of steel fibers that have high tensile strength and reduced diameters. The steel filaments are braided into cords of various geometries and strength and then glued on a polypropylene scrim with the only function to ease installation procedures.
The main characteristics of this innovative system can be summarized as follows:

• ultra high tensile strength;
• increase of ductility of the strengthened member, thanks to the twisted geometry of the cords;
• possibility of maintaining unaltered the geometry of the structure ;
• reduced thickness and lightness (70% thinner and 25% lighter than glass fibers);
• hand-manageability and ease of installation;
• simplifies all the problems concerning anchoring the material, making possible using mechanical anchors;
• possibility of pre-stressing the sheets;
• fire resistance in case of mortar matrix;
• resistance to corrosion and durability in the long run.

Steel fiber sheets that have low, medium or high density are applied on masonry structures, in particular on historical patrimonies thanks to the possibility of the material to be impregnated in situ using mortars and guaranteeing a strengthening extremely compatible with the substrate, easy to remove and maintaining excellent mechanical properties.
Medium and high density wires impregnated using epoxy resin are indeed used for strengthening RC and PC structures strenghtening, thanks to their excellent mechanical properties, if compared with the unidirectional carbon and glass fiber sheets one. Moreover, thanks to their strength and their high shear resistance, they may be pre-stressed using special systems of tensioning and anchored through traditional solutions without damaging the fibers.
Similarly, steel materials are commonly used also in retrofitting structures subjected to dynamic loads caused by earthquake shocks, strong winds and/or exposions, since they are able to protect them from impacts generated by flying debris or projectiles.
The mechanical response of composite steel materials is influenced by:

• the strength class of the filament (2400-4000 MPa);
• the diameter of the wire, included between 0.20 and 0.48 mm;
• the cord type depending on the way filaments are twisted. Concerning civil engineering only, different experimentations, carried out in co-operation with the main national (Perugia and Naples) and international (University of Missouri-Rolla, University of Miami) research centres, demonstrated the effectiveness of 3X2 wire, which is better than the effctiveness of other cords type available from the manufacturer;
• the density of the tape, that is represented by the number of cords per unit length (low, medium, high); this parameter allows the use of either mortar or epoxy matrixes, depending on the density chosen and according to the kind of strengthening level desired and substrate to work with.