Loading rate effects on CFRP strengthened steel square hollow sections under lateral impact

Application of fibre reinforced polymer (FRP) composites has steadily gained popularity in rehabilitation of steelwork over the last decade or so. This popularity is based on the inherent advantages of FRP and the considerable amount of research conducted on the response of FRP strengthened steelwork members under static loads. However, over the course of their service life, steel structures can be subjected to impact loads induced by a variety of sources. This necessitates the requirement for a comprehensive study that can shed light on the behaviour of FRP strengthened steelwork under various loading rates. This paper discusses the experimental results of carbon fibre reinforced polymer (CFRP) strengthened square hollow sections (SHS) under different loading rates. The experiments comprised a series of SHS columns tested under two loading rates: quasi-static (0.05 mm/s) and impact (4.43 m/s). Some of these columns were strengthened with different CFRP configurations comprising fibres oriented in the longitudinal direction, transverse direction and in both directions. The effect of co-existing axial compression applied prior and during the application of the transverse load (impact or quasi-static) was also examined. The axial load was introduced in the experimental program to simulate the normal service load that exists on columns in multi-storey frame buildings. Generally, it was found that the effectiveness of CFRP strengthening was increased at a higher loading rate to different degrees depending on the CFRP configuration.