Flexural Behavior of Concrete-Filled Steel Tube CFST Members with Initial Imperfections Due to Steel Tube Notches

Abstract This study experimentally investigates the flexural behavior of concrete-filled steel tube (CFST) beams incorporating artificial notch imperfections. Twelve specimens were tested under four-point bending, including control beams, hollow tubes, and notched CFST members. Notches varied in orientation (vertical/horizontal), location (tension/compression zone), and steel thickness (2.7 mm and 4.7 mm). Results showed that notches in the tension zone critically reduced performance, with SBH-2.7 exhibiting a 30.12% drop in ultimate load and a 76.19% reduction in deflection. In contrast, compression-zone notches had a smaller effect, particularly with thicker tubes. Increasing wall thickness to 4.7 mm improved load capacity and ductility but could not fully counteract notch-induced weaknesses. Compared with hollow sections, CFST beams demonstrated up to a 72.71% strength increase and superior energy dissipation due to concrete confinement. The findings confirm that notch geometry, orientation, and location strongly influence CFST flexural response. The study provides practical guidance for evaluating damage tolerance and improving design provisions for real-world structural applications.