In most structural components, especially offshore wind turbines, the superstructures and the substructures are connected using grouted connections. Offshore wind turbines usually experience different loadings, including wave and wind loads, due to the variation in the marine environmental conditions. Interestingly, the loads can be transferred from the superstructures to the substructures via the grouted connections. Over the past few decades, extensive research has been conducted to understand the behavior of grouting connections under different loadings. For instance, numerical simulations have been widely used to investigate the mechanical behavior of grouted connections with various geometric connections. Research findings demonstrated the practical significance of shear keys and their influence on the performance of the grouted connections.
Besides the arrangement of the shear keys, the load transferring mechanism depends on several other factors such a grout strength, radial stiffness and length-to-diameter ratio. Through these factors, researchers have been able to explore the change in the flexural capacity and the stress behavior of the grouted connections with and without shear keys. These results have enabled the prediction of the ultimate axial and flexural capacity and the development of different optimization and simplification methods. Nevertheless, despite the significant progress, achieving a complete experimental test of the stress in the grouted connections has remained a challenge. This problem can be partly attributed to the increasing capacities of the offshore wind turbines and deeper pile foundations, which require more robust structural connections.
On this account, Professor Chen Tao, Mr. Fang Qi and Mr. Zhang Chihai from Tonji University, in collaboration with Mr. Chen Ke and Mr. Yuan Guokai from China Energy Engineering Group Guangdong Electric Power Design Institute Co., studied in depth the mechanical behavior and load transferring mechanisms of grouted connections through numerical analysis. The authors provided a better understanding of the mechanical performance of the grouted connections. Their work is currently published in the journal, Thin-Walled Structures.
In their approach, a numerical model was proposed based on three critical design parameters: length-to-diameter ratio of the tube, the grouted thickness and the height-to-spacing ratio of the shear key. A parametric study was carried out to explore the effects of these parameters on the mechanical properties of the connections. Two coefficients, the regression function and the amplification coefficient, were used to analyze the contact pressure distribution and non-uniformity of the shear keys, respectively. Finally, the flexural capacity was evaluated and discussed in detail.
Results showed that the shear key represented the portion of the flexural capacity composition, seconded by the contact pressure. The three key design parameters exhibited considerable effects on the mechanical properties of the grouted connections, such as the stress states, stress-strain curves and contact pressure. When the grouted connections attained the ultimate flexural capacity, a variation in the stress correlation from 1.2 to 2.0 was observed under an axial load ratio of 0.1. On the other hand, the oblique angle in the grout was mainly dependent on the variation of the height-to-spacing ratio of the shear keys. Furthermore, the non-uniform coefficient proved useful in predicting the bending moment of individual shear keys, as indicated by the relatively larger amplification coefficient range 1.3 – 2.5.
In summary, a numerical investigation of the mechanical behavior of the grouted connections subjected to bending moments and axial forces was reported by Professor Chen Tao and colleagues. A detailed and comprehensive understanding of the effect of the key parameters on the mechanical properties of the grouted connections was demonstrated. The numerical simulations offered an alternative method for researching grouted connections through the analysis of critical parameters and related variables. In a statement to Advances in Engineering, the authors noted that the study provided an in-depth understanding of the mechanical performance of grouted connections and would pave the way for their applications in various fields.
Chen, T., Fang, Q., Zhang, C. H., Chen, K., & Yuan, G. K. (2020). Mechanical behavior of grouted connections under compression-bending loads. Thin-Walled Structures, 157, 107110.