Structural failure analysis of assembled spread foundation for onshore wind turbine tower

This paper presents an experimental investigation into the failure behavior of a large-scale assembled spread foundation for wind turbines, subjected to combined loading of bending moment, shear force, and vertical force. Seven load cases are established to explore the failure mode, cracking pattern, and nonlinearity development of the test model. The results indicate that, under the ultimate limit state (ULS), failure of the test model is governed by soil damage, directly leading to a decline in the structural load-bearing capacity. The cantilever root in the uplift region is the main cracking area for the joints, and the tilt rate of the foundation far exceeds the code requirements under ULS. Notably, through innovative calculation of local internal forces at the joints, the specific areas with higher stress levels are identified, accounting for the observed primary joint cracking areas and facilitating reasonable joint design to prevent failure. Besides, it is found that the lower limit of tension control stress as per the code is insufficient to meet the crack width limits, thereby highlighting the significance of adequate prestress in crack control. Furthermore, a linear decreasing trend of maximum crack widths at key load-bearing joints with an increase in the foundation’s axial load ratio is also disclosed. Finally, a prediction formula for nonlinear critical loads resulting from soil-structure interaction is established to prevent soil degradation under cyclic loading.