For the refurbishment of the 1545 m long Pians-Quadratsch tunnel system on the Arlberg Schnellstraße S16 in Austria, the fire protection boards were fixed using Multi-Monti screw anchors from Heco. Important factors for the selection of these anchors were structural stability in case of fire, corrosion-resistance, the capability of being unscrewed for inspection and simple mounting.
The works were carried out until the end of 2018 in the course of an extensive safety upgrade of the two twin-bore Pians and Quadratsch tunnels, which are joined by the housed Lattenbach Bridge. Austrian autobahn and expressway operator ASFINAG invested almost 21 million euros in this project with two additional escape routes between the tunnel bores, modern operations and safety systems and improved fire protection in order be able to comply with the requirements of the Austrian road tunnel safety law STSG.
Passive Fire Protection
The improvement of passive fire protection is an important part of the refurbishment concept. For a long time, concrete tubes tunnels were considered indestructible in case of fire. But after various fire catastrophes, this opinion had to be changed. Even small tunnel fires are associated with an enormous development of smoke gas and heat. Within a few minutes, temperatures can rise to 1000 °C and more. Particularly problematic: the combination of damp tunnel atmosphere, high-strength concrete and great heat can tear the concrete. Spalling can be so deep that the reinforcement is exposed and annealed. Fire protection boards in front of the concrete can however protect the wall surface from direct heat and effectively prevent more serious damage.
Mounting of the Fire Protection Boards
One challenge for all the companies involved with the refurbishment of the road tunnels was the tight schedule and the restriction to night-time working. “During the daytime, the tunnel remained open for traffic, with one direction being closed each night from 8 pm to 5 am”, reports Björn Kohl, who coordinated the works together with site manager Tomislav Balja for the specialised civil engineering company Chembau from the Tyrol.
In the first construction section in April and May 2018, 3500 m² of tunnel ceiling were clad with fire protection boards from Fermacell Aestuver. A second construction phase for board mounting followed from August. For reliable compliance with the STSG requirements, 25 mm thick Aestuver Tx fire protection boards and 10 mm backing strips were used. These are cement-bound, glass fibre-reinforced lightweight concrete boards, which have been specially developed for subsequent mounting of tunnel cladding on newbuild and refurbishment projects. The boards can be adapted to variable tunnels sections and flexibly installed without great effort. The works could thus be organised so that daytime traffic was not or only slightly obstructed.
Fixing with Screw Anchors
The fire protection boards were fixed with Multi-Monti screw anchors with self-tapping threads, which are screwed directly into a drilled hole without a plug. The version used – MMS-P 7,5x65/75 – is characterised by a shallow drilled depth of 45 mm and a screw depth of only 40 mm, which reliably avoids hitting the reinforcement in the concrete.
Mobile working platforms were used for mounting on site so no fixed scaffolding had to be erected. The fire protection boards were delivered to the tunnel on pallets with stacks of ten boards each. They were predrilled and already fitted with the necessary backing strips to meet the the fire protection requirements. The holes in the concrete were drilled through the board, which was temporarily fixed on telescopic supports. The anchors were then screwed in with cordless screwdrivers. “This really simple processing played a great parts in our success in meeting the challenging deadlines“, explains construction coordinator Kohl.
The fixing can be completely dismantled at any time. If required, the anchor can be unscrewed and screwed into the same hole again, so a fire protection board can be removed without a great amount of work to inspect the concrete and then remounted. Screw anchors can be used up to ten times according to the approval.
Heco Anchors with DIBt Approval in HCR Steel 1.4529
The precondition for the use of Heco anchors for this application was, in addition to the ETA approval, the national technical approval Z-21.1-1728 from the Deutsches Institut für Bautechnik (DIBt). The design values apply for fire exposure to fire resistance class R120 or according to ZTV-ING Part 5 Tunnelling. For the mounting of the fire protection boards in the Pians-Quadratsch tunnel system, the Multi-Monti screw anchor MMS-P 7,5x65/75 was made as a special production in HCR-Stahl 1.4529. Fixing elements of this steel are particularly resistant to the aggressive atmosphere in tunnels with high humidity, exhaust emissions and chloride action.