More powerful turbines and offshore use: tower segments for wind turbines are becoming heavier and heavier. The lever lugs developed in earlier years are no longer strong enough; only three fastening screws are not sufficient for a proven load-bearing capacity. Lifting lugs with four or more individual holes have to be specially adapted to each individual hole pattern, and the handling of these structural steel solutions can only be done with the help of a crane.
The new Tower Attachment Point (TAP) has been newly developed for tower segments weighing up to 100 t with the usual hole circles of 2.5 – 4.2 m. The new TAP is designed to be used in conjunction with a crane. Each individual TAP stirrup has a load capacity of 25 t with a maximum permissible angle of inclination of the slings of 30°.
The TAP stirrups are drop-forged and made of high-quality tempered steel. Due to the high-strength material, the dead weight remains at a maximum of 30 kg and manual assembly by two persons is possible without any problems.
On the load side, a commercially available, high-strength shackle of nominal size 25 t is threaded into the TAP shackle. The connection of round slings or ropes, which are available everywhere, is easily handled on this. Load securing has also been thought of: several lash hooks can be hooked into the TAP shackle together.
On the tower side, the tower attachment point is mounted with 2 x 2 screws grade 8.8 in sizes M36, M42 up to max. M 48. The two slotted holes are slightly bent according to the tower radius (DBP applied for). This allows mounting on almost any tower segment with diameters between max. 4.2 m and min. 2.5 m.
Every technician knows: Two slotted holes in one direction does not work, because the fitting could slip abruptly under full load.
This is where the second patent of the AXZION-GKS development team comes into play: Each slotted hole has two slants running in opposite directions. The screws are screwed onto these inclines with wedge-shaped shims. In the case of lateral tension, the load on the screw is increased in the direction of tension, the contact pressure is increased and lateral slippage is no longer possible.
Safety is a top priority.
AXZION-GKS is the specialist for load handling attachments in the globally active SpanSet Group. Safety is a top priority here. The forged TAP stirrups were tested with 125 t, i.e. 5 times the nominal load capacity, on the company’s own test rig.
The requirements of DIN EN 13155 “Load handling attachments” are thus considerably exceeded, and the proven 5-fold safety even permits use in the USA. And not only the stirrups are tested, also the assembly with screws from M36, 8.8 is fully proven.
Further research is being carried out in partnership with well-known manufacturers of wind turbines. Thus, additional tests are still taking place. The nominal load of the TAP stirrup will be extended to 35 t at SF 1:5 and the high-strength fittings will also be used for erecting the tower segments in the future.
SpanSet Axzion GmbH
40764 Langenfeld, Germany
Phone: +49 (0) 2173 208920