Project: Mur Nature Observation Tower
Location: Gosdorf, Austria
Overlooking the Mur River along the southern edge of Austria, where military watchtowers once marked the border with Slovenia and the fringe of the Iron Curtain, a different kind of tower now invites day hikers to ascend 168 steps and enjoy the view. This daring landmark, commissioned by the local municipality of Gosdorf, shows off the digital fabrication chops of Terrain:loenhart&mayr, a young architecture and landscape architecture practice based in Munich.
At first glance, the Mur Nature Observation Tower—89 feet tall and 28 feet wide—may resemble an amorphous nest of beams and cables held together like some kind of upright logjam. But the irregularity is an illusion. Repeating components and nodal geometries engineered by Frankfurt’s Office for Structural Design form three primary elements: an external frame of hollow-steel structural members; an internal web of steel cables; and two helical stairways—cantilevered from the outer frame—that meet at the top. Each of the 24 stair segments, except for the top and bottom pair, is identical in length and angle of incline. Interchangeable save for the varying sizes of the steel members, all 21 “knots,” or structural joints, share the same configuration, which helped control manufacturing costs.
Co-principals Klaus Loenhart and Christoph Mayr wanted visitors to feel as though they are climbing into a breezy treetop. The concept, explains Loenhart, was to create “a bodily experience of being part of the landscape, a 360-degree environment.”
The easiest way to understand the arrangement of the steel members is to “unroll” the tower and map it in two dimensions, as the architects did with dozens of paper and digital models. The pieces form an asymmetrical diagrid; half of the diagrid’s quadrangles are bisected by steel braces, while the other half are reinforced by cables stretching across the central void. Thus the Mur Tower combines beams in pure compression with cables in pure tension. Alternating push with pull, it draws on the tensegrity structures developed by R. Buckminster Fuller and the artist Kenneth Snelson during the mid-20th century.
Because the members near the top bear less weight, they are slimmer than those at the bottom. In fact, there are eight thicknesses—four each for the main beams and for the supporting beams—while the depth remains a constant 10 inches. The shift from 18-inch-diameter members at the bottom to 11-inch-diameter ones at the top not only saves material, Loenhart says, it also exaggerates the tower’s apparent height when viewed from below. Another visually driven element is the cladding of anodized aluminum panels that frames the stairways, abstracting them into spiraling prisms.
Truly a machine in a garden, the Mur Tower would be for naught without its surrounding wilderness, part of the European Green Belt nature preserve, where the structure functions as a waypoint along a journey. In Loenhart’s words, “Your wandering through nature is simply verticalized as you pass through.”