Axial Performance of Reinforced Concrete Columns with Lap Splices and Flash-Butt Welded Splices under Concentric Compression

This study presents an extensive experimental investigation into the axial behavior of reinforced‑concrete columns containing different splice types, transverse reinforcement configurations, and cross‑sectional geometries. A total of six groups of circular and square columns were tested under concentric compression to evaluate the structural performance of lap splices and flash‑butt (forging) splices in combination with various confinement systems, including individual ties, circular hoops, and spirals with different pitches. Mechanical and electrical strain gauges, displacement transducers, and load cells were employed to monitor stresses in longitudinal and transverse reinforcement as well as concrete strains at multiple heights, enabling a detailed assessment of stiffness degradation, crack initiation, ductility, and failure mechanisms. The results demonstrate that the measured peak axial loads ranged from ۳۷۱.۵۲ kN for the plain-concrete reference specimen to ۹۵۸.۴۸ kN for specimen FB. The pre-peak secant stiffness at ۴۰% of peak load, K۰.۴, ranged from ۲۳.۷۳ to ۱۲۹.۲۵ kN/mm, whereas the normalized energy-absorption ratio ranged from ۰.۴۵ to ۱.۱۰. Specimen FB, which contained a bottom flash-butt-forged splice and individual hoops, achieved the highest peak load, stiffness, and energy-absorption ratio. However, no consistent overall superiority of either lap splices or forged splices was observed; the response depended on the interaction among splice type, splice location, confinement, concrete strength, and specimen-specific construction quality. Specimens without transverse reinforcement in the splice region generally exhibited earlier cracking, wider cracks, and less stable deformation. The maximum crack width, ۳.۰ mm, was recorded for specimen LSM. Reducing the spiral pitch from ۹۵ mm to ۵۰ mm generally improved cracking resistance and deformation stability, although the magnitude of improvement varied among specimens. The results demonstrate that adequate transverse confinement and reliable construction quality are essential for stable axial performance of columns containing either lap splices or flash-butt-forged splices.

کلیدواژه ها:

Reinforced-concrete columns ، Lap splice ، Flash-butt-forged splice ، Axial compression ، Secant stiffness ، Energy absorption