Torsion in concrete wind turbine towers

Project data

Short description

© Florian Fürll (MB TUD)

The aim of the research project is to develop an analytical model to describe the torsional load-bearing behavior of assembled half-shell segments of prestressed tower constructions with dry joints. The model is to realistically capture the torsional load-bearing capacity in the dry horizontal joint based on the beam theory and taking into account the neighboring segments. In order to consider the influence of the offset neighboring segments in the model, the model assumptions and limits are validated numerically and experimentally. For this purpose, the following hypotheses are formulated for the different observation levels, which are confirmed or rejected within the scope of the project for recording the influences of neighboring segment pairs on the torsional load-bearing behavior:

• The neighboring segments exclusively influence the distribution of the internal forces in the form of shear force and torsion, so that the support conditions of the simplified beam model initially remain unaffected.
• The influence of neighboring horizontal joints decreases as a function of the ratio of outer diameter to segment height, so that the simplified beam model can also be used for a tower geometry with several segments, taking into account the superimposed stress components from the neighboring segments.
• The discontinuous normal stress curve due to restrained cross-sectional warping leads to a shift of the axis of rotation point towards the "compressive stress nests" of the respective half-shell as decompression increases for reasons of equilibrium.
• The horizontal joint bearing capacity depends on the normal stress distribution in the joint, which can be determined in the fully compressed state under global torsional loading on a monolithic tower section with vertical slots.
• The partial section sizes and resulting normal and shear stress components are independent of the geometric boundary conditions, so that a tower section with only three segment levels is sufficient to capture the coupling effects of the neighboring segments.
• Compared to the circular ring section, the restrained warping of the half-shells leads to a considerable reduction of the joint load-bearing capacity as a function of friction coefficient and prestressing force.
• The influence of geometric unevenness of the contact surfaces from the grinding process of the segments on the normal stress distribution due to post-tensioning is considerably lower compared to the circular ring cross-section.
• The superimposed stress states of adjacent half-shell pairs due to obstructed cross-sectional warping can be recorded experimentally by strain measurements.
• The cascade-like twisting out of the individual half-shells can be used within the framework of deformation measurements along the segment joint as a basis for determining the plastic torsional limit load of the horizontal joint load-bearing capacity.