The Europe Bridge, Austria

From
Building with Steel
May 1960

Most visitors to Austria know Innsbruck, the Capital of Tirol, with its statue of King Arthur in the Hofkirche. It is the junction of the three great alpine roads, Arlberg, Brenner and Mittenwald. The Brenner Pass is the lowest of all the passes crossing the Alpine watershed and the first mention of it is in 13 B.C. when Augustus crossed it to subdue the tribes of the Tirol. In A.D. 452 Atilla and his Huns went southwards over the same road to destroy the Roman Empire of the West.

Today the scene is different; the Brenner carries such a tremendous volume of traffic that a new Motorway is being constructed from Kufstein via Innsbruck to Brenner and on the ascent from Inns­bruck the road crosses the valley of the River Sill three times. The first crossing – between the villages of Patsch and Schonberg – necessitates a remarkable bridge, now in course of construction. The importance of this bridge is such that it was named ‘The Europe Bridge’ on the occasion of the formal commencement of site work on 25 April, 1959. The principal dimen­sions are worth noting – the scheme envisaged a bridge with a total length of about 2,725 ft. and a maximum height above the valley floor of nearly 600 ft.; the bridge deck is on a gradient of 1 in 19.

The Tirol Government prepared a scheme for the bridge upon which tenders were invited and at the same time promoted a competition, since bids were permitted for alternative proposals. Tenderers were provided with geological and surveying details and were required to conform to the requirements of the Austrian Standards for Class 1 Bridges for design and execution, modified by certain supplementary con­ditions. Any alternative scheme was required to main­tain the same roadway line and gradient and to adhere very closely to the length of the official scheme. Special conditions were also made on account of the magnitude of the scheme and the layout of the bridge in relation to the surrounding landscape since the greatest importance was attached to the blending of the bridge with its surroundings. It was therefore stated in the competition conditions that special con­sideration would be given to schemes having a good appearance.

Tenderers also had to keep in mind, when siting the piers for their proposals, the existence of the Brenner railway tunnel and the existing main road.

The official scheme comprised six approach spans of 116 ft. 6 in. each of plate girders supporting con­crete decks and twin warren trusses for the three con­tinuous main spans of 531 ft. 6 in., 738 ft. and 531 ft. 6 in. respectively. These also carried a concrete deck on cross girders cantilevered out at top boom level. The main spans were to be carried by slender rein­forced concrete columns. The total width of the deck between parapet railings was 65 ft. 6 in. including twin carriage ways each 26 ft. 5 in. wide.

The magnitude of the work resulted in tenders from Germany as well as Austria which presented many new features and original ideas with wide variations in the resulting prices. The analysis of the tenders which were finally considered for acceptance is of much interest as it demonstrates most clearly the economy of steel bridgework where large spans are desired. These bids, arranged in ascending order of price are briefly detailed below.

It is worth noting that the five lowest tenders are based upon the use of a steel superstructure.

1. Twin continuous warren girders with an orthotropic steel plate deck over the middle span and a reinforced con­crete deck over the side spans of the rtlain bridge; pre­stressed reinforced concrete beams over three small ap­proach spans. Spans of the main bridge are 236 ft., 443 ft., 834 ft. 6 in., 443 ft. and 236 ft.
   £1,123,742
2. A scheme identical to the above except that the deck of the five main spans was of orthotropic steel plate construc­tion.
   £1,177,681
3. Twin lattice girders with spans nearly identical to those of the official scheme with an orthotropic plate deck over the main bridge and prestressed concrete beams over the approach spans.
   £1,184,309
4. Lowest tender for the official scheme.
   £1,211,090
5. Steel solid web box girder with an orthotropic deck over the main spans. This scheme, slightly modified, was chosen for execution and is dealt with later in this article.
   £1,212,225
6. Reinforced concrete arch bridge of three spans 423 ft., 886 ft. and 476 ft.
   £1,219,323
7. Reinforced concrete beam bridge of seven spans ranging from 164 ft. to 426 ft. 6 in.
   £1,301,905
8. Reinforced concrete arch of 886 ft. span flanked by eight spans of prestressed concrete beams ranging from 180 ft. to 235 ft.
   £1,304,410
9. Steel arch bridge of 1,312 ft. 6 in. span composed of twin circular sections carrying an orthotropic plate deck, with approach spans of 135 ft. to 153 ft.
   £1,376,768
10. Reinforced concrete arch of 918 ft. for the main span and prestressed precast beams for the side spans.
    £1,481,443
11. Box girder bridge with perforated walls in prestressed concrete.
    £1,900,329

The original tenders in Austrian Schillings, have been converted at the rate of As 72.52 to £1 sterling.

Scheme 5 was selected for execution after careful consideration of the design and aesthetic considera­tions. Preference was given to this design for its appearance and also since pier displacement, due to earthquakes to which this district is subject, produces minimum stresses by virtue of the lateral and tor­sional stiffness of the bridge. The boldness of the design is accentuated by the slenderness of the centre span (span/depth ratio 25.7/1) and the height of the piers. The bridge, 2,456 ft. long, carries the motor­way on a gradient of 1 in 19 at a height of 590 feet above the river bed. It has been designed as a con­tinuous bridge of 2,155 ft. 9 in. length between end bearings and is carried on five intermediate piers in spans of 265 ft. 9 in., 354 ft. 3 in., 650 ft., 3-:54 ft. 3 in., 265 ft. 9 in. and 236 ft. 3 in. The width between parapets is 70 ft. 10 in.

The steel superstructure is a closed torsionally stiff box section girder 32 ft. 10 in. wide, the depth of which tapers uniformly from 25 ft. 3 in. at the centre to 16 ft. 5 in. at the ends of the bridge. The roadway deck is cantilevered out 19 ft. on each side and acts as the top flange of the girder. There is a 1½ in. asphalt surfacing to the roadway. This noteworthy design was prepared jointly by the Austrian firms YOEST of Linz and WAAGNER-BIRO of Vienna who are fabricating and erecting the steelwork.

The piers are each composed of hollow concrete sections. The tallest is 466 ft. in height, 39 ft. 3 in. by 75 ft. 6 in. at the base tapering to 16 ft. 6 in. by 52 ft. 6 in. at the top.

The technical data for this article has been extracted from an article by Oberbaurat Dipl.Ing. Josef Gruber of Innsbruck entitled “Europabrücke” which appeared in Stahlbau Rundschau, No. 2/1959, the official journal of the Austrian Steelwork Fabricators Association. The concluding words of this article are “one ought to comment with the utmost gratification that, with the Europe Bridge, Austrian bridge builders have found in their own land a project of truly great stature”. Readers will, we feel, wholeheartedly support this.