Experimental study on motion and sling-tension responses of a steel-concrete five-bucket foundation during submerged lowering

Experimental data on motion responses and sling tensions of steel-concrete five-bucket foundations during suspended lowering remain limited. This study investigates a steel-concrete five-bucket foundation (SCFBF) under wave action through a 1:50 physical model test. The lowering process was represented by four depths: 5, 15, 25, and 35 m. Pitch, longitudinal and vertical accelerations, and sling tensions were measured under regular and irregular waves. Responses varied non-monotonically with lowering depth. Under regular waves, pitch was more pronounced at 15 and 25 m after complete submergence. For the 25 m lowering-depth case under a regular wave with a period of 11 s, the pitch amplitude was approximately 4.7°. With identical initial pretension, the peak tension in the wave-facing inclined sling was approximately three times that in the lee-side sling for the 15 m lowering-depth case under a regular wave with a period of 10 s. At 35 m, motion and sling-tension fluctuations were reduced. Under irregular waves, response extrema were more readily affected by local fluctuations in the random wave train. The results describe the submerged-lowering characteristics of the present structural configuration, sling arrangement, and test wave conditions, and provide experimental data for response analysis under comparable conditions.