Advancing the state of the art in post-tensioning solutions
Extending the service life of reinforced concrete structures such as bridges has many advantages. For instance, a longer lifespan means less cost to the structure’s owner and increased safety for end users. It can also help reduce carbon emissions by minimising the pollution caused by construction. Of course, achieving these benefits first requires the ability to easily and cost-effectively retrofit the concrete structure. For this, the EU-funded SMArtPlate project has developed an innovative rapid and reliable post-tensioning-based strengthening system. “Practical feasibility and performance reliability are of utmost importance to a successful strengthening solution,” says Esmaeel Esmaeeli, a lecturer in structural engineering at Brunel University London, the project’s lead partner. “Furthermore, the solution must minimise any disruptions that a strengthening initiative could cause to the structure’s use – such as to traffic flow on bridges.”
A speedy advantage
With the support of the Marie Skłodowska-Curie Actions, the project leverages the synergistic advantages of ultra-ductile mortar (UDM) and shape-memory alloys (SMAs). Using these materials, researchers created a prefabricated plate made of UDM reinforced with SMA rebars – a design inspired by the hdl.handle.net/1822/40465 (hybrid composite plate) (HCP) strengthening system that was the main outcome of Esmaeeli’s doctoral thesis. The result of this work is SMArtPlate, an innovative, rapid and reliable post-tensioning system that goes beyond the state of the art of existing solutions. According to Esmaeeli, the prefabricated SMArtPlates are brought to the project site to reduce deflection and increase a bridge’s traffic capacity. “Once attached to the girders’ soffit, the strengthening intervention is done by temporarily increasing the temperature of the SMA rebars and then letting them cool down to the environmental temperature,” explains Esmaeeli. One of SMArtPlate’s key differentiators over conventional systems is its speed of use. “Conventional systems, such as pre-stressed, fibre-reinforced plastic (FRP) laminates, or rods, require setting up mechanical devices and curing the bonding epoxy adhesive. This is a time-consuming process,” adds Esmaeeli. “SMArtPlate, on the other hand, can be quickly installed using mechanical fasteners and, by passing electrical current through the SMA rebars, generate the post-tensioning forces.”
A step change in post-tensioning solutions
According to Esmaeeli, SMArtPlate represents a step change in post-tensioning solutions, providing industry, engineers and researchers an innovative and robust retrofitting solution. “SMArtPlate’s rapid application, along with its high durability and connection reliability, makes it a unique solution for post-tensioning of a variety of reinforced concrete structures, particularly bridges,” he concludes. “Furthermore, by minimising any disruption to the existing structure, it also offers notable socio-economic advantages.” Although the project is now finished, work continues. The team, which included re-fer in Austria and www.empa.ch (Empa) in Switzerland, are currently seeking additional funding to support large-scale tests to comprehensively assess SMArtPlate’s short- and long-term performance. The results of these tests will allow for the development of design guidance – the next step towards the industrial exploitation of the SMArtPlate solution.
Keywords
SMArtPlate, post-tensioning solutions, reinforced concrete structures, bridges, shape-memory alloys
