Avalanche protection is a constant concern in the Austrian Tyrol, but the construction of the screen at Melkstein was not allowed to affect traffic flow on the Zillerstrasse, the only route down the mountain to the valley.
The semi-circular tunnel is 204m long, and it had to adapt to an existing avalanche screen. The formwork system therefore needed to be highly flexible with a cross-section that complied with the existing structure but also gave the clearance profile required by road traffic.
Contractor Gebr Haider chose arch formwork developed by the Austrian company Noe as the most economic solution. The screen has 17, open sections each 12m long with plus three raked supports, and four 17m long closed sections. All have a constant inner profile, although the closed section does not need the cantilevered roof plate.
The arched roof section is erected and supported either by the side formwork or by the articulated section of the cantilevered plate mounted on the mobile falsework.
The supporting element for the formwork cross-section uses Noe's LS 200 heavy duty columns for the first time eliminating the need for timber shuttering and special components. Mounting the circular brace on the cross-member and tensioning the arch formwork by bracing members provides clearance for road traffic. The outer formwork - large area girder formwork with H20 beams, circular braces and plywood facing support braced against inner formwork - is moved by crane.