Fiber reinforced polymer (FRP) composites are now widely used for seismic strengthening of the reinforced concrete members as conventional materials pose complications. Although it is cost-effective to use steel plates, the strengthening technique is labor intensive and have many disadvantages. One of the major disadvantages of traditional strengthening techniques is the manipulation of heavy steel and the risk of corrosion. It is also impossible to visually examine the condition of a concrete member following a seismic event.
FRP composites consist of two components: fiber reinforcement and polymer resin matrix. Fillers are used as a secondary component to improve the quality of FRPs in terms of dimensional stability and environment resistance. Additives are also used to customize the properties of the final product. In the past, tt was not easy for the construction industry to utilize advanced composites as there was lack of research and in-practice data.
The purpose of a seismic retrofit is to strengthen and modify a bridge so that it can survive earthquakes that could otherwise cause it to fail. The first thing that structural engineers have to define is what they want their seismic retrofit to accomplish. To be able to effectively design either new bridges or retrofit measures for existing bridges, it is essential to have a clear understanding of potential problem areas. A systematic examination of the damage that has occurred to bridges in the earlier earthquakes can help develop that understanding.
The scope of FRP composites
Attributing to the advantages of high strength, lightweight and incredible workability, FRP sheet has been widely used for repairing and strengthening of RC members in the last couple of decades. One of the techniques is to use FRP sheet to retrofit columns with premature termination of longitudinal reinforcement. FRP sheet is also utilized to reinforce ductility of the columns by jacketing around the plastic hinge in the circumferential direction. Bridge columns are the parts most vulnerable to seismic activities. Following are three FRP seismic retrofitting techniques:
- Column strengthening
- Retrofitting of beam-column joints
- Retrofitting of RC beams
Why FRP composites?
FRP composites are used to considerably increase strength and ductility without increasing stiffness. Therefore, the use of FRPs in seismic retrofit applications can help prevent the need to retrofit other parts of the structure. Following are some of the key metrics of FRP application for seismic retrofitting as compared with steel and other conventional techniques:
- High stiffness and strength-to-weight ratio make advanced composites ideal for strengthening and seismic retrofitting.
- The durability and mechanical characteristics of FRPs can be customized in accordance with the application.
- FRP composites protect the inner reinforcement against rust as they can effectively withstand the harsh environment.
- It is easy to produce, handle, and install FRP wraps without any heavy equipment.
- The reduced maintenance cost and long service life make FRPs economically viable strengthening solution.
Following the new design codes, refined manufacturing processes, and reliable experimental results, it is proven that composite construction materials are highly effective in improving the seismic performance of structurally deficient concrete components.
TUF-BAR, being a leading producer of GFRP fiberglass rebar in North America, strives to manufacture environment-friendly and durable construction materials.