FIRE BEHAVIOR OF NOVEL CONNECTIONS TO CFST COLUMNS WITH STEEL CORE

Concrete-filled steel tubular (CFST) columns with embedded bar-bundle steel cores provide high axial capacity, slender geometries, and enhanced fire robustness; however, overall system reliability is often governed by connection detailing as steel softens and bond deteriorates at elevated temperatures. This study develops and assesses two dedicated connection concepts for bar-bundle CFST columns: (1) a recessed slab- to-column punching shear head anchored to the protruding bundle to enlarge the punching perimeter and preserve integrity reinforcement for membrane action in fire, and (2) a prefabricated beam-to-column connection head that transfers compression directly into the core in the fire limit state while minimizing heavy welding. Pre-test numerical simulations are performed in Abaqus using GMNIA under ISO-834 fire exposure, incorporating temperature-dependent steel properties, concrete damage plasticity, and bond degradation. The models reveal hierarchical, ductile mechanisms with load-path migration from the softened tube to the cooler core and head plates, sustained tensile capacity via end-plate and connection components and continuous reinforcement, delayed punching with membrane action, and beneficial semi-rigid rotational restraint without excessive thermal moments. Current work optimizes geometry and loading under fabrication constraints prior to large-scale fire testing and the development of simplified temperature-dependent design models for buildable cored CFST connections.      «

Concrete-filled steel tubular (CFST) columns with embedded bar-bundle steel cores provide high axial capacity, slender geometries, and enhanced fire robustness; however, overall system reliability is often governed by connection detailing as steel softens and bond deteriorates at elevated temperatures. This study develops and assesses two dedicated connection concepts for bar-bundle CFST columns: (1) a recessed slab- to-column punching shear head anchored to the protruding bundle to enla...     »