Solutions to Reinforce: Concrete Bridges and Barrier Wallsfrom Dritan Topuzi
Bridges and barrier walls are often constructed of reinforced concrete, a material where the low tensile strength of concrete is compensated by the high tensile strength of steel. Steel rebar is commonly used within the concrete, however, certain properties of steel, such as electrical conductivity, magnetism, thermal conductivity, and most importantly, low resistance to corrosion, may negatively affect the performance of a reinforced concrete bridge.
Depending on the application and conditions of the structure these properties of steel can affect the performance of bridges. Corrosion control is crucial in reinforced concrete bridges, especially when exposed to de-icing salts. Corrosion of steel reinforcement in bridges causes increased maintenance cost, and if not properly maintained, it affects aesthetics and can lead to structural collapse.
These corroded bridges are found practically everywhere. The Gardiner Expressway in Toronto is a prime example of steel rebar corrosion, and was best described in an article by Dr. Paul Gauvreau on The Globe and Mail, “Toronto’s crumbling Gardiner: Bring on the engineering innovation.”
“…Gardiner was built with materials and structural details that make it prone to deterioration and difficult to maintain…”
Solutions to avoid corrosion in bridges and barrier walls
Epoxy coated steel and stainless steel have been widely used as corrosion resistant reinforcement. Yet, epoxy coated steel has not performed as expected, and corrosion occurs. This corrosion is evident and the reason many owners have now banned the use of epoxy coated steel rebar.
Stainless steel is an alternative option which performs well, yet comes at a much higher expense. Fiber Reinforced Polymers, with Glass Fiber Reinforced Polymers (GFRP) providing a higher value in terms of the ratio of cost to mechanical properties, is a highly performing corrosion resistant reinforcement.
Compared to steel, GRFP is a relatively new material and there is skepticism within the engineering community, with concerns typically related to the low stiffness, creep, and reduced properties and geometrical limitations of bent bars.
Being aware of these concerns, Schoeck has been continuously researching and innovating.
Stiffness of GFRP Rebar
Schoeck introduced the high grade ComBAR® GFRP with a modulus of elasticity of 60GPa into a market which also includes a low grade of 40GPa. Schoeck has been supporting the use of high grade GFRP which brings a better structural performance. With continuous research, Schoeck is further increasing the stiffness of 60GPa.
Creep of GFRP
GFRP provides a high short-term strength of up to 1,500MPa depending on the bar size. However, under sustained loading, this strength decreases and codes typically limit design strength at 30% of the ultimate tensile strength. Schoeck ComBAR® GFRP provides a long-term strength at the 50% range. Although the design codes are to be followed, a higher strength increases the confidence of the engineer.
GFRP bent bars have reduced mechanical properties compared to the straight bars because of the fiber orientation at the bent portion as well as of a different manufacturing process. For this reason Schoeck introduced headed bars to eliminate the use of hooks where a bent bar would be necessary for anchorage only.
Bent bars however are still necessary as stirrups etc. and Schoeck has recently developed bent bars of the highest stiffness and strength on the market.
With regard to typical geometrical limitations, with the new technique Schoeck has practically no such limitations. Bent bars bent in two directions at any angle and closed stirrups are manufactured as part of the standard manufacturing process.
Thousands of tests have been carried out at various research institutions across the world. The specimens range from single GFRP bars to full-scale applications like the crash test of a TL-5/PL-3 barrier wall, by the Texas Transportation Institute. As it may be seen in the following video, the performance of the ComBAR GFRP reinforced barrier wall exceeded all requirements.
Crash test video
Schoeck is not only a manufacturer and supplier, but also provides the necessary engineering services to provide the best value to the client. These include from preliminary ideas or concept design to shop drawings for an awarded project, followed by on-site support during construction.
ComBAR® GFRP on the Canal Bridge, ON, installation in 2012
If you have a project that may be a candidate for Schöck ComBAR® GFRP or if you need additional information about our products, please contact us at 855.572.4625 or firstname.lastname@example.org.