Composite versatility enables many structures to be strengthened quickly and economically. The most frequently used composite wrapping materials are fabrics made of either carbon or aramid fibre. These materials are not pre-formed and can be delivered to site on a roll accompanied by containers of resin. A significant advantage is the lightness of these materials. This flexible fabric form makes the adaptability of the product almost limitless. Therefore the use of hand applied wet lay-up composites allows the strengthening of a wide variety of more complex shapes.
This type of composite has been used in construction for strengthening a variety of structures including bridge and building support columns, crosshead beams, braces and curved large structures.
Plate bonding provides a cost effective method for strengthening many types of structure. The principle use of the technique has been for flexural strengthening and was originally developed with mild steel plates.
The most commonly used material is carbon fibre. There are several grades of carbon arising from two different manufacturing processes. Principally the variation is in ultimate tensile strength and modulus as well as the different resin systems that can be used to form the plates. This variation allows bespoke design, however suppliers have arrived at a suite of pultruded plate types. Ultra-high modulus carbon fibre is formed into plates by vacuum bag methods and using different resins than the pultruded plates.
To make use of the high strength of the FRP materials, pre-stressing has been developed for pultruded plates and successfully been used to strengthen cast iron beams. The technique is particularly demanding and requires specialist knowledge for installation.