Lookout Tower with Treetop Trail on Grünberg near Gmunden, Austria

The lookout tower of the tree-top trail on Grünberg in Gmunden is a striking timber structure in the shape of a barrel with a height of approximately 39 m (128 ft). From the tree-top trail, the tower offers impressive panoramic views of Lake Traunsee, the Traunstein mountain, and the Alpine foothills.

The supporting structure consists of an outer ring with twelve rotationally symmetrical, curved glulam beams (GLT) that form a stable polygonal spatial structure. Barrier-free access is provided by an internal ramp with a maximum gradient of 6%, which leads to the surrounding viewing platform. This is located at the highest point of the tower and is supported by steel cantilever beams. At a height of approx. 28 (92 ft), the ramp was partially widened to create an intermediate platform from which a tunnel slide leads to the central shop building.

Bracing against horizontal loads is provided by a surrounding net of diagonally arranged steel members, which are anchored to the timber columns and thus transfer horizontal forces into the supporting structure. Horizontal ring structures at the anchor points supplement this stabilization.

The vertical loads from the timber columns are transferred to the reinforced concrete foundation via steel beams and safely dissipated into the subsoil. The foundations rest on uniformly supporting ground, thus preventing uneven settlement.