Characterisation of Interfacial Properties for SMAT Steel Plating System

Externally-bonded (EB) fibre reinforced polymer (FRP) is currently one of the most popular technologies for the rehabilitation (strengthening/repair/retrofitting) of concrete structures, largely due to its advantages in construction convenience. However, engineers and building authorities could be reluctant to use FRP due to concerns about its material brittleness and temperature sensitivity (including toxic gas emission under fire), along with the difficulties involved in bonding. Recently, the principal investigator (PI) collaborated with a material scientist (Co-I Lu) to successfully develop a strengthening scheme using a new type of nanomaterial – the surface mechanical attrition treated (SMAT) stainless steel sheet. The SMAT sheet is thin (about 1 mm), but has the high strength, lightweight, corrosion resistance and consequent construction convenience advantages of FRP while retaining the ductile nature of steel. It possesses the advantages of both steel and FRP while avoiding their weaknesses, which makes it an ideal material for structural rehabilitation.Because the SMAT sheet is so thin, the normal method of fastening steel plate with bolts is often insufficient, as the bolts can cut the thin sheet, providing insufficient dowel action for interfacial bonding. However, another mechanism – friction – can be used to supplement the interfacial bond in this case. Frictional bonds, such as friction-type steel joint connections, can be very strong. In fact, the PI has developed a highly effective friction dominant bonding system for FRP-concrete interfaces. A similar friction-based bonding technology can be used to enhance the SMAT sheet-concrete interface to provide a strong, robust, yet ductile interfacial connection. Such a connection will be applicable not only to SMAT sheets, but also to general high-strength yet thin and ductile reinforcing materials developed for future use.The main objective of the proposed project is to develop such a bonding system and its associated design methodology. Joint shear tests will first be conducted to identify an effective joint design and obtain test data for bond characteristics. The test results will then be used to develop the joint governing bond-slip relationships. Using the bond-slip relationship, design equations and guidelines for SMAT sheet strengthened RC beams can be derived from existing composite theory. Subsequently, RC beams strengthened with SMAT sheet will be tested to validate the efficiency of the new retrofitting system and accuracy of the developed design theory.