Orthotropic Design Meets Cold Weather Challenges An Overview of Orthotropic Steel Deck Bridges in Cold Regions By Alfred R. Mangus, P.E. Transportation Engineer, Civil California Dept. of Transportation (CALTRANS) Sacramento, California Introduction Initially developed by German engineers following World War II, orthotropic bridge design was a creative response to material shortages during the post- war period. Lightweight orthotropic steel bridge decks not only offered excellent structural characteristics, but were also In Norway economical to build (Troitsky 1987). Nordhordland Floating Bridge Moreover, they could be built in cold The Nordhordland Bridge across the climates at any time of the year. Salhus fjord is Norway’s second float- Engineers from around the world utilize ing bridge and the world’s largest float- this practical and economic system for ing bridge (Meaas, Lande, and Vindoy, all types of bridges. While concrete 1994). The bridge was opened for traf- must be at or above 5 degrees Celsius fic in 1994. The total bridge length is to properly cure, it is physically possible Figure 1. Rib designs. 1615 m and consists of a high level to encapsulate and heat the concrete 369 m long cable stayed bridge and a construction process; admittedly, this cover a matrix of rib types, superstruc- 1246 m long floating bridge (Figure 2). adds to construction costs (Mangus ture types and various bridge types. The floating bridge consists of a steel 1988), (Mangus 1991). Russia has developed a mass manu- box girder, which is supported on ten factured panelized orthotropic deck concrete pontoons and connected to Orthotropic steel deck bridges have system and has devised special abutments with transition elements in proven to be durable in cold regions. launching methods for cold regions. forged steel. The main elements are a The orthotropic steel deck integrates Russian engineers prefer the open rib high-level cable stayed bridge provid- the driving surface as part of the design and have industrialized this ing a ship channel and a floating superstructure, and has the lowest system, while most other engineers bridge between the underwater rock total mass of any practicable system. prefer the closed rib. Researchers, as Klauvaskallen and the other side of In Europe, where the advantages of well as the owners of orthotropic steel the fjord. The cable stayed bridge pro- orthotropic design have been deck bridges, continue to monitor the vides a clear ship channel. A 350 m embraced with enthusiasm, there are performance of various rib types long ramp is required to transition from more than 1,000 orthotropic steel deck (Figure 1). the higher bridge deck on the cable bridges. In all of North America, there are fewer than 100 bridges of orthotropic design. This article will give an overview of imaginative steel deck bridges current- ly in operation in Norway, Russia, Sweden, and Ukraine. The examples Figure 2. Nordhordland Floating Bridge across Salhus fjord of Norway. Welding Innovation Vol. XIX, No. 1, 2002 stayed bridge to the bridge deck 11 m in the bulkheads varies from 8 mm to are located one at each edge of the above the waterline. The steel box 50 mm. The box girder is constructed ramp in order to maximize the stiffness girder of the floating bridge forms a in straight elements with lengths vary- about a vertical axis. The steel weight circular arch with a radius of 1,700 m ing from 35 m to 42 m. The elements of the ramp is 1,600 tons. in the horizontal plane. The supporting are welded together with a skew angle pontoons are positioned with a center of 1.2° to 1.3° to accommodate the distance of 113 m and act as elastic arch curvature in the horizontal plane. supports for the girder, which is The cross section dimensions of the designed without internal hinges. The octagonal box girder are constant for bridge follows the tidal variations by the length of the bridge. elastic deformations of the girder. The stress level varies significantly Figure 4. Nordhordland Floating The steel box girder is the main load- over the length of the bridge. In the Bridge. carrying element of the bridge (Figure areas with the highest stresses, steel 3). The octagon girder is 5.5 m high with a yield strength of 540 MPa is Bybrua Bridge and 13 m wide. The free height below used. The Bybrua cable stayed bridge has a the girder down to the waterline is 5.5 main span of 185 m. The 15.5 m wide m and this allows for passage of small roadway superstructure was fabricated boats. The plate thickness varies from Orthotropic bridge design in the shop in 9.0 m sections (Figure 5). 14 mm to 20 mm. The plate stiffeners There is a combined pedestrian plus are in the traditional trapezoidal shape was a creative response bicycles area on each side of the three and they span in the longitudinal direc- to material shortages traffic lanes. The cross section of the tion of the girder. The stiffeners are main span has a deck-plate 12 mm supported by cross-frames with center during the postwar period thick, but this increases to 16 and 20 distance of maximum 4.5 m. At the mm at the cable anchorage. The bot- supports on the pontoons, bulkheads tom plate varies between 8 mm and are used instead of cross-frames. This In the remainder of the bridge (in the 10 mm thickness, and the webs is done because the loads in these cross-frames and bulkheads) normal- between 12 mm and 20 mm. At sections are significantly larger than in ized steel with yield strength of 355 intervals of 3.0 m there are frames the cross-frames. The plate thickness MPa is used. The total steel weight of supporting the longitudinal stiffening the box girder is 12,500 tons, of which system. In the bridge deck this is approximately 3,000 tons are high made up of standard trapezoidal ribs strength steel. The elevated ramp is approximately 350 m long and has a grade of 5.7 percent (Figure 4). The elevated ramp is constructed with an orthotropic plate deck 12 mm thick and has 8 mm and 10 mm thick trape- zoidal ribs 800 mm deep. T-shaped crossbeams support the ribs with a Figure 3. Nordhordland Floating maximum center distance of 4.5 m. Bridge. The main 1,200 mm deep box girders Figure 5. Bybrua Bridge. Welding Innovation Vol. XIX, No. 1, 2002 from the German steel company of Norway fabricated the Bomla Oka Bridge Krupp, and in the bottom flange box Bridge’s steel approach superstruc- The four-lane orthotropic twin box section of bulb flats open ribs were uti- ture, which was launched out over the girder bridge crossing the Oka River lized (Aune and Holand 1981). In the tops of the columns from the shore. on the bypass freeway around the city longitudinal direction the deck was The steel components for the main of Gorki, Russia, was opened to traffic divided into six fabricated sections, span superstructure of the Storda in 1991 (Figure 7). The 966 m long two of which were welded to the web Bridge were prefabricated in the superstructure consists of 2 spans x sections. The box bottom was fabricat- Netherlands (Figure 6) and the main 84 m + 5 spans x 126 m + 2 spans x ed as three sections. The total steel span superstructure of the Bomla 84 m (Design Institute Giprotransmost weight is about 1,100 tons. All ele- Bridge was prefabricated in Italy. The 1991). This bridge is a single continu- ments prefabricated in the shop were orthotropic ribs for the Storda Bridge ous superstructure with a fixed bearing welded, as were the field splices in the were prefabricated in France. The 420 m away from one of the abut- deck, whereas “Huck” high tensile orthotropic sections were transported ments. The total bridge width (29.5 m bolts were used in all other field joints. to the site by barge, and were lifted including steel traffic barriers) provides All field joints were calculated as fric- into position by a crane. two sidewalks 1.5 m wide each, four tion connections. The whole steel traffic lanes, four safety shoulders and structure is metallized with zinc and a center median. The total weight of painted according to the specifications steel for the superstructure is 10,635 of the Norwegian Public Roads tons, or 373 kg/m2. The orthotropic Administration. The superstructure steel superstructure comprises five received the maximum live load basic elements (Figure 7). There are stresses during the erection of the two main box girders assembled from bridge. The wearing surface of the two L-shaped sections for the bottom bridge deck is the same as that devel- face and sides. The intermediate oped by the Danish State Road orthotropic plate sections were used Laboratories for the Lillebelt Bridge of for the top flange of the two box gird- Denmark. Figure 6. Storda Bridge. ers, as well as the majority of the deck. The end sections of the Storda and Bomla Bridges orthotropic plate were panelized with The “Triangle Link” project connects tapered ends, because only sidewalk three islands off the Norwegian coast In Russia loading is required. The transverse south of Belgen to the mainland with Russian engineers have standardized diaphragms are steel trusses between three bridges (Larson and Valen their orthotropic deck plates using the box girders. The diaphragms open or flat plate ribs as shown in required extra steel beams at the bot- Figure 1. They have several launching tom flange of the box girder above the solutions or standardized methods for bearings.