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Carbon, aramid and glass FRP systems for civil engineering

FRP systems in the concrete repair industry are used to strengthen existing structures. Structures may need strengthening due to:

• deterioration;
• design/construction errors;
• change in use or loading;
• seismic upgrade.

FRP essentially works as reinforcement in concrete and provides strength where concrete is weakest in tension.

FRP may be used on beam or slab soffits to provide additional flexural strength, on the sides of beams to provide additional shear strength, or wrapped around columns to provide confinement and additional ductility (a primary concern in seismic upgrades).

Among many other applications, concrete and masonry walls may be strengthened to better resist seismic and wind loads, concrete pipes may be lined with FRP to resist higher internal pressures, and silos and tanks may be strengthened to resist higher pressures.

Applications where existing FRP systems may not be useful include correcting punching shear problems in slabs or footings, correcting vibration problems, and providing greater compression strength to walls.

In cases where FRP is useful, it should be recognized that there are reasonable limits to the additional strength afforded with FRP.

Typically, increases in strength up to 50% are reasonable.

In selecting the type of fiber to be used for an application, there are a few things to consider: Glass (GFRP) and aramid (AFRP) are excellent for seismic upgrades where the seismic loads only temporarily engage the FRP.

In cases where stresses are sustained in the FRP (such as in bending and shear strengthening), GFRP should be avoided (or service stresses maintained at a minimum level) because of creep rupture effects.

Carbon is much more suitable in these applications. Similarly in exterior applications, Carbon (CFRP) will be much more durable.