Air Void and Cap Gap Composite Defects of Concrete-Filled Steel-Tube Arch Bridge Transverse Brace

Large-diameter concrete-filled steel tube (CFST) arch bridge transverse braces adopt self-compacting concrete to avoid laitance and air void defects. However, several old CFST arch bridges in China use ordinary concrete, whose fluidity before initial setting produces cap gaps at the top of the transverse brace. Furthermore, harsh environments and concrete dry shrinkage enlarge the gaps, producing composite defects. Hence, using ultrasonic scanning, this study performs a scale-model experiment and finite-element analysis to determine the bearing capacity of a serviced CFST arch bridge transverse brace with cap gap and air void defects in the concrete core column under small eccentric axial compression. Parametric analyses were conducted to investigate the influence of the composite defects on the bearing capacity of the transverse brace. A new ultimate strength index of the brace with composite defects was proposed, including a simplified formula for estimating the effects of cap gap and air void defects on the ultimate strength of the CFST arch bridge transverse brace. Thus, this study can provide a strong foundation for the construction of reliable CFST arch bridges.