Fire Resistance and Residual Compressive Behavior of FRP–Concrete–Steel Double-Skin Tubular Columns with ECC or FRP Grid–Reinforced ECC Layers

Hybrid fiber-reinforced polymer (FRP)–concrete–steel double-skin tubular members, which consist of an inner steel tube, an outer FRP tube, and a concrete layer in between, offer significant advantages such as high load-carrying capacity and excellent corrosion resistance and have gained extensive research interest. Despite their recent applications in engineering practices (e.g., bridge piers and arch ribs), there remains a notable lack of research on their fire performance. This study aims to address this research gap by experimentally investigating the fire resistance and postfire compressive behavior of hybrid FRP–concrete–steel double-skin tubular columns (DSTCs) with engineered cementitious composite (ECC) or FRP grid–reinforced ECC (GR-ECC) as external layers. For comparative analysis, concrete-filled FRP tubular (CFFT) columns with comparable fire protection schemes were also examined. The results demonstrated the dual beneficial effects of the ECC or GR-ECC layers, which significantly improve both fire resistance and residual compressive behavior in both types of column specimens. Specifically, CFFT specimens retained between 76.0% and 86.0% of their load-carrying capacity, while DSTC specimens exhibited improvements of up to 118.8% after 60 min of fire exposure. These findings highlight the potential of ECC and GR-ECC as effective fire-resistant materials.