Behavior and strength prediction of the horizontal joint of prestressed concrete towers for wind turbines under combined compression-bending-torsion loads

Prestressed concrete towers for wind turbines are assembled from precast segments connected by horizontal joints. Due to the limited bond strength of the joints, post-tensioned unbonded prestressing is applied to clamp tower segments together and connect the tower to the foundation. Under extreme combined loads, however, the prestressing force may not be sufficient to maintain tight connections at the joints, leading to joint deformation and altered boundary conditions. Thus, the horizontal joint is the critical region governing the tower’s failure and affecting its overall mechanical behavior, which is a key distinction from conventional structures. It is essential to study the combined compression–bending–torsion behavior and ultimate strength of the horizontal joints of prestressed concrete towers. To this end, this paper presents an analytical study building upon previous experimental research. Finite element models under combined loading were developed and validated, and effects of key parameters on the combined behavior were discussed. Then, the characteristics of three typical failure patterns were analyzed. The corresponding bending-to-torsion ratio ranges distinguishing different failure patterns were identified, and a suggested limit for the axial compression ratio was proposed. By integrating analyses of the stress state of tower segment, contact behavior of horizontal joints, and prestress variation, the full-process combined mechanism of the prestressed concrete towers with horizontal joints was summarized. Subsequently, the correlations between bending and torsional strengths were developed based on strength data within commonly used parameter ranges. Finally, a calculation method for the ultimate combined strength of horizontal joints was proposed, showing good agreement with test and numerical results.