Specimens S3 and S8 have stiffeners arranged obliquely at two adjacent steel plates.
The smaller spacing of welding constraint points in cross section provided more uniformly distributed lateral confinement for concrete. Meanwhile, the horizontal segments of the battlement-shaped reinforcements directly restrained the out-of-plane deformation of the tubes at welds.
The bucklingwave heights of specimens S3 and S8 were respectively mainly 5–10 mm and 0–5 mm.