Mechanical response of CFRP-reinforced hollow ultra-high strength steel circular tubes under axial impact loads: Experimental and numerical investigations

This study investigates the mechanical behaviour of CFRP reinforced ultra-high strength steel (UHSS) circular hollow section (CHS) columns subjected to axial impact loading. With the growing demand for high-performance materials, UHSS has become increasingly popular in civil engineering due to its exceptional strength and resilience, making it well-suited for building structures subjected to extreme events such as collisions, and explosions. To further enhance the structural capacity of such members under impact loading, CFRP, known for its high strength-to-weight ratio and excellent energy absorption capacity, was applied externally as a confining layer. Axial impact tests were performed on bare and CFRP-reinforced CHS columns made of three different grades of steel, including mild steel (MS) grade 350, UHSS grades 800, and 1200. Strain evolutions, and failure modes were captured using a digital image correlation (DIC) system. Key energy-based performance metrics, such as energy absorption ( EA ), mean crush load ( P mean ), crush force efficiency ( CFE ), and kinematic coefficient of restitution were evaluated to assess the crush performance of each specimen. In addition, nonlinear finite element (FE) models were also developed and validated against experimental results. The findings demonstrate that CFRP confinement is an effective strengthening strategy for improving the impact resilience of CHS structural elements, offering valuable guidance on the combined effects of CFRP reinforcement and steel grade in enhancing the dynamic response of CHS columns.