Strengthening of concrete bridges or structures in the field of structural maintenance is an important task. Increasing the capacity of present operational elements is the main objective of carrying out strengthening. This task is important since the bridges are not considered safe resulting from increased load.
The two methods used in the strengthening of bridges include;
- Using steel plate
- Using Fiber reinforced polymer(Mazzolani, 2013)
- Strengthening using Steel plate
The use of steel plate is one of the commonly used materials during strengthening. It is necessary since it increases the shear and flexural capacity of the reinforced concrete beam. Readily available, high tiredness strength, constant material properties, cheapness and easy to work makes the steel plate popular when strengthening as depicted from the mentioned features. In the year 1960, the investigation concerning the structures strengthened using this method began and this type of method had been applied in strengthening both bridges and buildings in numerous countries such as United Kingdom, Poland, France, Japan, Belgium, South Africa and Switzerland (Reid, 2012).
The most commonly used method of plating is gluing steel plates to the tension faces of beams whereby at this stage, the plate is at its utmost extremity from the area of compression whereas the composite action is at its maximum. However, maintenance of composite action between glue, concrete and the plate will be done until failure. This method efficiency depends on bonding methods between existing beam, preparation of the surface and steel plate, therefore the preparation of the surface of the present beam and steel plate should be carried out efficiently and also roughening of beam surface before placing the plates as explained by Adhikary et al (2011).
The process of roughening is done using a mechanical grinding the laitance is removed then brushing and cleaning the surface scrupulously using acetone. Acetone can also be used to clean steel plates bonding faces after sandblasting. Epoxy adhesive is sited on the surface which is rough after preparation of the surface has been done after which the steel plate is positioned on top (Wipf, 2004).
Strengthening using Fiber reinforced polymer
This is a widely spread material for strengthening concrete structures and is a composite material made of a polymer matrix. The fibers are usually armed, carbon or glass, while the polymer includes vinyl ester or polyester A high strength to weight ratio, makes fiber reinforced polymer (FRP) for strengthening to become an effective method. Compared to steel, the fiber reinforced polymer had physical and mechanical properties superior to them, more so when comparing fatigue and tensile strength (Rodger, 2014). Introduction of fiber reinforced polymer composite materials was first carried out in the year 1940s which made US Air Force and Navy use this material in the various application as a result of its exceptional strength to weight ratio.
The world’s first highway bridge was built using fiber reinforced polymer in 1986 in Germany, pedestrian bridges were built in 1996 and also more sustainable markets have developed as a result of FRP materials in repairing and strengthening of structures made of concrete. Numerous fiber reinforced polymer system are currently available commercially for strengthening of concrete constructions externally (Milne, 2015). The arrangement of FRP is shown in the picture shown below.
Strengthening of reinforced concrete structures is one of the major task linked with concrete structures maintenance and number of materials available in the market and used for strengthening include steel plate, sprayed concrete, fiber reinforced polymer but in general, steel plate and fiber reinforced polymer are the most preferred methods due to their features.
Mazzolani, F., 2013. Refurbishment of Buildings and Bridges. London: Adventure Works Press.
Milne, D., 2015. Strengthening bridges using composite materials. Toledo: Cambridge University Press.
Reid, K., 2012. Steel Bridge Strengthening. Colorado: IEEE.
Rodger, D., 2014. Methods for Increasing Live Load Capacity. Michigan: IEEE.
Shinozuka, M., 2006. Structural Safety and Reliability. New York: China Publishing Company.
Wipf, T., 2004. Cost-effectiveness Practices for Off-system and Local Interest Bridges. s.l.:University of Nairobi press.
Xanthakos, P., 2011. Bridge Strengthening and Rehabilitation. Perth: Wiley and Sons.