Experimental study of vertical joints in dry-connected assembled wind turbine hybrid towers

The vertical joint interface of dry-connected prestressed concrete hybrid towers utilizes epoxy resin structural adhesive combined with bent bolts that apply prestressing forces. Compared to traditional grouted wet connections using reinforcing bars, this approach significantly improves on-site installation efficiency. To investigate the shear performance of dry-connected vertical joint interfaces, four static tests are conducted using full-scale specimens. This study primarily examines the influence of the presence of bent bolts on the specimen's ultimate load-carrying capacity and the effect of preload magnitude on ultimate load-carrying capacity. Additionally, this study comprehensively analyzes the failure modes, bond-slip curves, and load-carrying capacity calculations of vertical joint interfaces under static shear loading. Finite element simulation results demonstrate good agreement with the experimental findings. Combined experimental research and theoretical analysis reveals that brittle failure occurs at the bonded interface. Bonded interface failure modes can be categorized into concrete tensile failure (Type A) and structural adhesive failure (Type B). For C70 concrete, the bonded interface exhibits a mixed failure mode combining both Type A and Type B characteristics. Concrete strain distribution near the bonded interface shows a pattern of "high at both ends, low in the middle," indicating that during load application, concrete damage progresses from both ends toward the center, suggesting that concrete at the ends is more susceptible to damage leading to structural failure. Implementing bent bolts to apply prestressing force significantly enhances the ultimate shear load-carrying capacity of the bonded interface. From a failure mode perspective, applying prestressing force through bent bolts increases the proportion of Type A failure, indicating that pre-tensioning improves structural adhesive bonding strength. Increased prestressing force enhances the ultimate shear capacity of the bonded interface, demonstrating that within certain limits, increasing the pre-tensioning force applied by bent bolts improves structural shear strength and provides additional safety margins in practical applications. Furthermore, the applicability of existing interface shear calculation formulas is evaluated, providing a theoretical foundation for subsequent calculation methods for ultimate shear capacity of vertical joints in non-grouted dry-connected precast wind turbine hybrid towers.