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Savor, Bleiziffer & Radic: CONSTRUCTION OF STEEL ARCH BRIDGES

CONSTRUCTION OF STEEL ARCH BRIDGES

Zlatko Savor*, Jelena Bleiziffer** & Jure Radic***

*University of Zagreb, Faculty of Civil EngineeringZagreb, Croatia

**INSTITUT IGH, Zagreb, Croatia

***University of Zagreb, Faculty of Civil Engineering, Zagreb, Croatia &INSTITUT IGH, Zagreb, Croatia

Key words:arch bridge, structural steel, world-record spans, construction methods

Abstract: We arerecently witnessing steel arch bridges revival, most prominently in Chinawith the completion of the Chaotianmen Yangtze River Bridge of 552 m span and the Lu PuBridge of 550 m span, setting new world records. In the last few decades the rediscovery ofsteel arch bridges is also evident in Europe in a wide variety of architectural forms andstructural solutions. They have become very popular and have been built in railway lines,on roads and highways and for footbridges. The main reasons for that are modern steelfabrication, assembly and erection methods, but the influence of architects cannot bedisregarded. The structural advantages of steel arches include their high strength,durability, and smaller weight, hence smaller foundations and lower erection costs. Steelarch bridges are indispensable for railway crossings, because of their inherent stiffness,much larger than that of cable-stayed bridges. Recently built railway steel arch bridges inEurope are predominantly of the through tied type, because of their location across largerivers in low terrain. The other major application is for footbridges, in which advantages ofsteel as structural material may be effectively applied to design unique and aestheticallymost pleasing structures. The mostly applied construction procedure for steel arch bridgesis cantilevering, used in various alternatives since 19th century, with the developmentbasically only in auxiliary structures and erection equipment. Recent European throughtied arches across rivers have predominantly been assembled on the shore and erected by

utilizing floating platforms. Some interesting examples of construction of steel arch bridges,built in the last ninety years, are described in detail in the paper.

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1. INTRODUCTION

The history of metal arch bridges starts in the 18 thcentury with the Ironbridge over the riverSevern near Coalbrookdale, UK. This world famous symbol of industrial revolution had a

far reaching impact on bridge design and on the use of cast iron in building. Cast ironavoided the need for large thicknesses of structural elements, resulting in lighter structuresand thus making possible construction of far longer spans. The Ironbridge, as the first cast-iron arch span which is now the center of a British National Museum, took only threemonths to erect, indicating the huge potential of the material and associated new bridgetechnology. Following is a brief overview of the historic development of long steel archbridges, and discussion of recent practice and developments, focusing on European bridges.

2. HISTORIC BRIDGES

Following the success of the Ironbridge, a number of long iron arches were designed inGreat Britain. The major advantage was the avoidance of the necessity of founding archpiers in rivers. Perhaps the most famous iron arch of the time is the Bonar Bridge, designedby Thomas Telford. This innovatory bridge consists of four arch ribs, each preassembled infive large sections, rather than erected member by member. At the turn of the centuryTelford even proposed a bold design for a single 183 m cast iron arch across the Thames inLondon, which has however never been built [1].The most striking trussed deck steel arch bridge of the 19th century is the Eads Bridgeacross the Mississippi River in USA. James Eads was appointed as the chief engineer, andit was the only bridge he had ever designed and constructed. The bridge consists of three

arch spans (153+158.5+153 m) to provide sufficient navigation clearance. Although majorinnovations are associated with the design of caissons for deep foundation of the piers andabutments (Eads employed two German engineers to help him do the design), the erectionof steel arches supporting a double deck was as great an achievement [2]. This was the firstmajor bridge built in steel. The construction proceeded by cantilevering from the piers andabutments. The bridge was completed in 1874, after seven years of construction (Figure 1).Although steel has been increasingly used in bridge building in the second half of the 19 thcentury due to its advantageous properties, some major bridges of the time were stillconstructed in iron [3, 4].

Figure 1: Construction of Eads Bridge in 19th

century

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Figure 2: Eiffels Garabit Viaduct during construction

No.

No.Year of

completionName, location Type

Hinges

Spans

Ribs

Rib

type

Main span

(m)

1 1884 Garabit, St. Flour, France True 2 1 2 Truss 165

2 1886 Dom Luis I, Porto, Portugal True 2 1 2 Truss 1723 1897

Kaiser Wilhelm, Mngsten,Germany

True 0 1 2 Truss 170

4 1900 Alexandre III, Paris, France True 3 1 15 Solid 1085 1902 Viaur, Carmeaux, France True 3 3 2 Truss 2206 1905 Austerliz, Paris, France Through 3 1 2 Truss 140

7 1908Neckarbrcke, Mannheim,

GermanyTrue 2 1 4 Solid 114

8 1911 La Roche-Bernard, Vilaine, France Through 3 1 2 Truss 1929 1916 Hell Gate, New York, USA Through 2 1 2 Truss 29810 1924 Croton, New York, USA Through 3 1 2 Truss 22811 1931 Bayonne, New York, USA Through 2 1 2 Truss 504

12 1932 Sydney Harbour, Sydney, Australia Through 2 1 2 Truss 50313 1933 Ohio, SAD Through 2 1 2 Truss 24414 1935 Birchenough, Zimbabwe Through 2 1 2 Truss 32915 1935 Mlarsee, Stockholm, Sweden True 0 2 2 Solid 20416 1936 Waal, Nymwegen, Netherlands Through 2 1 2 Truss 24417 1936 Henry Hudson, New York, USA True 0 1 2 Solid 244

Table 1: List of historic metal arch bridges

The most spectacular are probably trussed true arches Dona Maria Pia Bridge in Porto,Portugal (1877) and Garabit Viaduct (Figure 2) in the south of France (1884), bothdesigned by Gustave Eiffel and also double deck trussed arch Dom Luis I Bridge in Porto,

Portugal, designed by Thophile Seyrig (1866). A new record for steel arch bridges was setin 1898 by Leffert L. Buck's bridge over Niagara Falls spanning 256 m (Upper Arch Bridge

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or Honeymoon Bridge or Falls View Bridge), constructed by the cantilevering method. Thisbridge collapsed in 1938 due to ice pressure crushing the bridge abutments.Further breakthrough came with the construction of a 298 m span half-through truss arch

bridge across the Hell Gate in New York, USA. This engineering masterpiece, carryingfour railway tracks, was designed by Gustav Lindenthal [5] and held the record of theworld's longest arch for 15 years. The rise of the bottom chord is 67.05 m, which gives therise to span ratio of f/l=4.5. The bottom arch truss chord is of parabolic shape and carriesalmost the whole dead load, as the bridge was constructed as three-hinged with a hinge inthe bottom chord at the crown. The truss depth at the crown amounts to 12.258 m and atquarter points of the span 18.3 m. The truss verticals are spaced at 12.933 m. The crosssections of the bottom and top arch truss chords are shown in Figure 3.

1520 cm

1120cm

1326 cm

3156cm

Figure 3: Cross sections of bottom and top arch truss chord of Hell Gate Bridge

The weight of the arch is 9,815 t and the total steel weight of the main bridge amounts to17,130 t. The bridge was erected from both shores by cantilevering, as depicted in Figure 4[6].

Wards Island Long Island

Figure 4: General layout of Hell Gate Bridge construction

The horizontal arch thrust during erection was taken by horizontal steel beams, laid on theground, supported against the bridge abutments. The sequence of construction is shown inFigure 5.

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30. Nov. 1914

31. March 1915

31. May 1915

30. Sept. 1915

15. Oct. 1915

31. Dec. 1915

Figure 5: Construction sequence of Hell Gate Bridge

Only 17 % of the 15,000 t heavy auxiliary steel anchoring was not reused and the rest waslater employed as longitudinal stringers, hangers and plate girders for the approach spans,which clearly exemplifies the economy of the construction. After the arch halves wereconnected at the crown, the deck was suspended from the arch. It should be noted, that theHell Gate bridge carries the largest live loading of all New York bridges, yet itsmaintenance costs are the least, which exemplifies advantages of structures, primarily undercompression (arch bridges) over suspended structures (suspension and cable-stayed bridges)

with respect to maintenance.Major leap forward in steel arch spans was accomplished at the beginning of nineteenthirties, when Bayonne Bridge in New York, USA and Sydney Harbour Bridge in Australiawere opened for traffic within months of each other.The construction of Sydney Harbour Bridge took eight years. The general bridge designwas prepared by Dr J.J.C Bradfield and the detailed design and crucial erection procedurewere undertaken by Ralph Freeman. Two-hinged half-through trussed steel arch spans503 m, while the total length of the bridge including approach spans amounts to 1,149 m.The bridge is 49 m wide and it now carries eight vehicle lanes, two train lines, a walkwayand a cycleway. The steel arch solution was favored to a suspension and cantilever bridges,

regardless of the difficulties associated with the arch bridge construction [7]. Thesuspension bridge alternative was dismissed because of its low stiffness for railway traffic,and the cantilever design was assessed as aesthetically inadequate. With monumentaltowers at the arch springings, the Sydney Harbour Bridge resembles the Hell Gate Bridge.However, the upper chord of the Sydney arch terminates before the towers, thusaccentuating the path in which the loads are carried from the arch into the abutments, whilethe structural role of individual components at the Hell Gate Bridge is somewhat obscuredby the connection of the arch to the towers, designed to further emphasize the overallmassiveness of the structure [8]. The foundations for the four bearings, which carry the fullweight of the main span were dug to a depth of 12.2 m and filled with special reinforced

high-grade concrete laid in hexagonal formation. After the approach spans were erected,work began on the main arch. Two half-arches were built progressively from each shore,each held back by 128 cables anchored underground through U-shaped tunnels (Figure 6).

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Figure 6: Construction of Sydney Harbour Bridge

Steel members were fabricated in the workshops, placed onto barges, towed into positionon the harbor and lifted up by two 580 t electrically operated creeper cranes, which erectedthe half-arches before them as they traveled forward (Figure 7). Behind them moved thefour maintenance cranes, used initially by the riveting and painting teams until they had tobe dismantled to allow the creeper cranes to pass by and be removed in pieces near thepylons. The maintenance cranes were then re-erected on the arch and remained in serviceuntil their removal in 1997. When the arch was closed, the construction of the deck thenproceeded from the middle outwards towards each shore. This procedure was selected to

avoid moving the construction cranes back to the towers.

Figure 7: Cantilevering the arch of Sydney Harbour Bridge

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The Bayonne Bridge across Kill Van Kull Strait, connecting Newark and Staten Island, wasbuilt in only three years [9]. It was designed by the famous Swiss born engineer OthmarAmmann. This half-through trussed arch is of 503.6 m span with the rise to span ratio

f/L=1/6.3. Although its span is almost equal to that of Sydney Harbour Bridge, he designeda much more slender arch. This was made possible, because Bayonne Bridge wascalculated for only four road traffic lanes, two light rail lines and two walkways with twototal roadway width of 22 m (without walkways), but mostly because of extraordinaryengineering skills of the designer [10, 11]. Additionally, this bridge has no monumentalmasonry abutments, and both chords of the arch continue down below the deck. While thesteel weight for the Sydney Harbour Bridge arch is 39,000 t, the arch of Bayonne Bridgeweighs only 16,500 t. The Bayonne Bridge was constructed by the cantilevering methodwith four auxiliary steel bents and a traveling crane (Figure 8), to keep the Kill van KullStrait, an important shipping channel open at all times.

Figure 8: Bayonne Bridge construction

The arch consists of 40 connected truss segments, each of them fabricated off-site. The archerection could not proceed symmetrically from both shores, because the navigation channelwas positioned closer to the southern shore. The closing segment thereby lies 75.5 m southfrom the arch crown. The difference in the arch thrust due to this non-symmetry had to becorrected by an upward force applied to the three-hinged arch in erection phase andremoved after the third hinge in span was closed and final system of two-hinged archestablished (Figure 9). Sections of the roadway deck were fabricated off-site, transported bybarge, and hoisted into place. Pedestrian walkways were cantilevered sideways from the

primary roadway deck. However, the vertical clearance of the navigation channel is only

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41.3 m, which is not enough for the passing of modern large ships and nowadays there arecalls to either completely replace this masterpiece of engineering or raise the existing span.

H HP

G

H HP

Figure 9: Construction sequence of Bayonne Bridge (left) and correction of arch thrust

(right)

3. MODERN BRIDGES

3.1 Road Bridges

It took almost 50 years before the New River Gorge Bridge in the USA, completed in 1977,extended the world record span of Sydney Harbour and Bayonne bridges. The 518 m truetwo-hinged trussed arch solution was chosen, because the gradient line of the crossing ishigh above the river (eliminating the multi-span truss structure alternative) and asuspension bridge at the location was considered, as too hazardous for air traffic. The rise to

span ratio is f/L=1/4.8, and the ratio of the truss depth at the crown to the span length ish/L=1/50. The bridge structural system, the cross section and main arch chords constructedas steel box sections are shown in Figure 10 [12].The steel material is weathering steel, thusobviating the need for painting. Unfortunately, the weathering steel does not perform well ifexposed to chlorides and hence is not allowed in maritime environment. In the case of NewRiver Gorge Bridge salt was used for de-icing the roadway and consequently steel elementshad to be subsequently painted to prevent corrosion, which was an unforeseen and verycostly measure. The construction of the bridge began with the erection of an auxiliary cableby helicopter to facilitate the construction of the cable-crane. Then column supports for thecable crane, utilized for site transport of large arch truss sections, spandrel columns and the

superstructure, were erected. Steel sections were connected on the site by high strengthfriction bolts. The erection of the arch proceeded by cantilevering from both sides,

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supported by auxiliary stays, anchored in previously constructed approach spans (Figure10).

1473

mm

1029

mm

1067 mm

1029

mm

259.08 m

107.

60

m

276. 83 m

21.

95

m

16.1

5 m

10.

36

m

1097. 3 cm

678.

97cm

548.

64cm

119cm

1118. 9 cm

Figure 10: New River Gorge Bridge: elevation (top left), cross-section (top right) andconstruction scheme (bottom)

The arch closure at the crown is normally executed by inserting jacks in the about 1.0 m

gap between the two arch halves about to meet and extending them until stresses in the archreached design values. The New River Gorge Bridge was the first major bridge to beerected without this jacking procedure, which showed the faith of designers and the clientin the accuracy of fabrication and erection. This seems like a good practice and could be apace setter for future bridges.It took another 25 years before another structure could claim a world record for the longestarch bridge. It was the Lu Pu Bridge in Shanghai, China, completed in 2003, a half-throughtied arch bridge with a main span over the Huangpu River of 550 m. Unlike previous recordholders, the Lu Pu bridge arch rib [13] is solid, of box-type section, 9 m deep and 5 m wide.The half-through tied truss steel arch of the Chaotianmen Yangtze River Bridge in

Chongqing, China, completed in 2008, currently holds a world record for arch bridges, withthe main span of 552 m, 2 m longer than the Lu Pu Bridge [14]. The Chaotianmen Yangtze

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River Bridge carries both road and two tracks of light rail traffic. Other long span steel archbridges in China have been described in [15].

Figure 11: Longest world arch bridges: Lu Pu Bridge (left) and Chaotianmen Bridge (right)

The longest steel arch bridges in Europe are still Zdakov Bridge in the Czech Republic andSilver Jubilee Bridge in the UK.The Zdakov Bridge, constructed from 1957 to 1965, is a two-hinged true solid rib archbridge spanning 330 m. Two arch ribs of box type cross section, spaced at 13 m, areconnected by wind bracing. This bridge was erected by cantilevering, utilizing auxiliarypiers supporting the arch approximately in quarter points of the span [16].The Silver Jubilee Bridge in North West England is a tied through truss two-hinged archbridge with the span of also 330 m, very similar in appearance to the Chaotianmen YangtzeRiver Bridge [17]. This bridge was constructed from 1956 to 1961.

One more bridge from this time period is also worth mentioning. This is the FehmarnsundBridge, a steel through tied network arch with inclined hangers. According to FernndezTroyano [18] it is a classic among the bridges. Completed in 1963, this bridge connectsGerman mainland and the island of Fehmarn in the Baltic Sea. The bridge carries combinedrail and road traffic. The total bridge width is 21 m and it comprises a 10.8 m wide roadwayand a single-track rail. The two arch ribs are inclined inward and are continuouslyconnected near the crown, while additional connection is provided by large-diametertubular struts at lower levels. The arch spans 248 m and the rise is 45 m, with rise to spanratio of f/L=1/5.5. The construction of the bridge was not easy [19]. An auxiliary steeltower of 80 m height had to be erected at mid-span, and arch segments were supported by

auxiliary ties, anchored into arch abutments. These temporary supports were active duringthe whole arch erection procedure until the erection of the superstructure, because tiedarches obviously cannot take up any loads till the arch thrust is taken over by the tie astensile force. A cable crane was utilized for local transport on site. This bridge was declareda historic monument in 1999.The only recent European bridge spanning more than 300 m is Dunaujvaros Danube Bridgeacross the Danube River at Dunajvros in Hungary [20]. The bridge was completed in2007 and carries the motorway over the river and its flood plains. The total length of thebridge is 1677 m, with access bridges on the east and the west side of 302 m and 1067 m,respectively. The 41 m wide main bridge is a 308 m long steel basket handle shaped

through tied arch structure. The main arches and webs of the stiffening girders are inclinedat 16.5 to the vertical. The rise of circular shaped arches is 48 m. The inside dimensions ofthe arch box cross-sections of S 460 M steel grade are 1960x3720 mm, allowing access for

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erection, supervision and maintenance. Arches are interconnected by eight cross beams ofbox cross section with no bracing.

Figure 12: Dunaujvaros Bridge: assembly at the river bank (top) andfloating of the arch span to its final position (bottom)

The 3.6 m deep structure comprises stiffening girders shaped as parallelogram box sections2400x3100 mm and orthotropic deck with cross beams spaced at 3.8 m, all made of S 355steel grade. Hangers are made of parallel cables, supporting the deck at 11.4 m spacing. Themain criteria influencing the selection of this structural type of main span, was that it couldbe constructed on the river bank and then floated into place when it was finished,

minimizing the disruption to navigation and making it safer and easier for site personnel.Some photos of the bridge construction are shown in Figure 12 [21].The Apollo Bridge in Bratislava in Slovakia was completed in 2005. The bridge with thetotal length of 514.5 m, comprising access bridges and a basket handle through tied centralarch bridge of 231.0 m span, was constructed as an orthotropic steel structure [22]. Thearch is of circular shape with the radius of 211.3 m and the rise of 37.67 m (rise to spanratiof/L=1/6.1). The arch cross section is of box type, 1,860 mm wide and 3000-4000 mmdeep. Thirty-three inclined hangers on each side, made of 12 15.2 mm diameter strands,carry the weight of the superstructure. The 32.0 m wide cross-section of the superstructureconsists of two diamond shaped box type main girders interconnected by the orthotropic

plate. Main girder boxes with 2.20 m depth on the access spans and deeper on the archbridge, reaching about 1.0 m above the orthotropic deck plate are constructed with webs of

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14-25 mm thickness and the bottom flange up to 50 mm thick. The top flange on the arch isexecuted perpendicular to the hangers. The 14 mm thick orthotropic deck plate is stiffenedby trapezoidal stiffeners at 600 mm spacing. Cross beams are curved with the maximum

depth of 3.30 m in the middle, spaced at 6.0 m. Arches and parts of the main girders aremade of S 420 steel grade and the remaining parts of the main girders, the orthotropicroadway deck and footways of S 355 steel grade. The complete steel structure, weighingapproximately 8,000 t, was finished in 15 months and fully welded. The main girders weredivided in 23 segments up to 2 m long. The arch bridge was completed on the left Danubebank in one year. The erection began with three main girder sections at mid-span,positioned on auxiliary columns and welded together. There followed the erection andwelding of the cross beams and one segment behind the erection of the roadway plate. Thissequence of works was repeated towards both arch abutments. The erection of arches beganin the next step on auxiliary columns constructed on the superstructure. Hangers wereinstalled after the closure of the arches and prestressed with the force of 40 kN. The finalstep of the erection was the spectacular rotation by ninety degrees to the final position. Forthis operation the bridge was placed on a sliding track of a box girder 1800x1920 mmdimensions and on a rotation bearing on the left bank pier. Sliding was performed with asliding shoe over longitudinal launching plates. The rotation bearing was a combinedbearing, consisting of a bottom spherical bearing for the bridge rotation, which wasembedded in concrete and thus made fixed after the successful maneuver and the topguided sliding top bearing as permanent bearing, which was fixed during the whole erectionprocess. The other bridge end was placed on a temporary pier with a concrete outstand as asupport for the sliding track. Four interconnected barges were utilized for the rotationmaneuver with a radial sliding track positioned on them. Barges were anchored near the

auxiliary pier and after they were flooded the sliding track was installed on the pieroutstand. The bridge rotation operation took place in three days, during which time riverboat traffic was completely stopped. The 5,000 t bridge structure was pulled onto the bargestracks with strand lifters over Teflon tracks. Hydraulic presses were utilized to keep thebridge structure during the whole operation in horizontal position. The pontoons moved thebridge to the right Danube bank and after docking to the pier and anchoring of the pontoonsthe bridge was pulled onto the pier and placed on permanent bearings, which completed thebridge erection (Figure 13).

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Figure 13: Apollo Bridge: assembly at the river bank (left) andfloating of the arch span to its final position (right)

Figure 14: Tangermnde Bridge: assembly at the river bank (left) andbridge launched to its final position (right)

An arch bridge of exactly the same main span (231 m), but providing three navigablechannels, was constructed in 2004 in Russia. The bridge crosses Irtysh River in WesternSiberia. Total length of the bridge amounts to 1,316 m. The most challenging part of theproject was the bridge assembly and erection. The three main steel sections, weighing morethan seven thousand tons in total, were assembled on the river bank. Subsequently, each ofthe three bridge sections was moved with the help of a complex floating system thatinvolved three massive piers and four barges. The whole moving operation to place thebridge into its final position took only twenty-two hours.The bridge across the River Elbe near Tangermnde in Germany was completed in 2001.The total bridge length is 1435 m and comprises three separate structures: 160 m long westapproach bridge, 185 m long main span and 1090 m long east approach bridge [23, 24]. Thelength of the main span was dictated by river navigation requirements, and an arch solutionwas selected over beam and cable-stayed alternatives, after an evaluation consideringcriteria of construction costs, fitting in the landscape, environment protection, aesthetics,serviceability and maintenance. Cable stayed alternatives were eliminated first and in thefinal choice between the beam and arch bridges an arch bridge was chosen, because a beambridge would detract from the surroundings. The steel through tied arch spans 185 m with arise of 28 m (rise to span ratio f/L=1/6.6). The two arches, inclined at an angle of 10inwards, are interconnected by 12 steel pipe cross beams for horizontal rigidity, providing aVierendeel frame type system in the horizontal plane. The arch bridge has a total width of18.6 m between the bearing axes and of approximately 8.0 m at the crown. The arch crosssections are constructed of welded box profiles, 1.2 m wide and of varying depth from1.3 m at the crown to 2.5 m at the arch springings. The 2x14 hangers, made from steel rodsare connected directly to the main girders by plates and provided with up to three dampersat each hanger to prevent vibration due to rain and wind. The 18.3 m wide superstructurecross section comprises typical composite grillage with 3.15 m deep external main girdersand cross beams of 1.8 m depth, spaced at 3.9 m and the 30 cm thick concrete slab rigidlyconnected by shear connectors to the cross beams only. The concrete slab takes up

approximately 40 % of the superimposed dead load and traffic loads and is designed withthe crack width limited to 0.2 mm.

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The steel structure of the arch bridge was assembled on the embankment of the new roadbehind the western abutment in two stages, because the free assembly area was too short forthe assembly of the complete bridge. In the first stage the first half of the bridge was

assembled and then pushed towards the Elbe River on a launching track, thus creatingsufficient space for the assembly of the second bridge half. After the bridge structure wascompleted, it was launched towards the Elbe River utilizing eight heavy load movingplatform vehicles. Four vehicles positioned the rear bridge end on the launching track,while the four front vehicles were rolling onto the 62x23 m pontoons. Powerful hydraulicspushed the pontoons supporting half of the bridge load towards the other river bank underpermanent echo sounding of the river profile. The pontoons were anchored with four 70mm thick steel ropes, two upstream and two downstream. The steel bridge structure reachedits final position after 2 days. The concrete deck slab was subsequently concreted insegments, starting from mid-span. Some photos of the bridge construction are shown inFigure 14.When authorities desire a signature bridge, a future symbol of the city, usually anunconventional design comes forward. One such example is the Pont de l'Europe Bridgeover the River Loire in Orlans, France, designed by Santiago Calatrava, completed in 2000[25]. The through steel arch is located at the downstream side of the bridge, in an inclinedplane of 22 to the vertical. The bridge spans 88.2, 201.6 and 88.2 m, with the two mid-supports designed as tripods consisting of three inclined legs, the two of them positioned inthe visual continuation of the arch and the third one placed perpendicularly to it. The bridgecarries four traffic lanes, two footpaths and two cycle ways, and is of variable width,reaching a maximum of 25.74 m at mid-span. A steel box girder with an orthotropic decksupports the roadway, with outstand on both sides. The 3.25 m deep box girder has a curved

bottom flange in the form of a ships hull. Diaphragms are spaced at 4.2 m, consisting ofK-bracing in span and flat plates at supports. The cross section is a three cell box girder tomake transportable units. The arch lies between the roadway and the footpaths with theinclination chosen so that the resultant of the permanent actions passes through the point ofintersection of the tripod legs to reduce bending moments at that point. The arch is straightup to the first hanger and from there in a parabolic shaped curve. The cross-section of thearch is trapezoidal box girder 1.65 m wide with the depth of 0.55 m and 1.40 m,respectively. The hangers, which restrain and stabilize the arch in a reversed V-form, areclosed cables of 55 mm diameter for the main hangers and 36 mm for the secondaryhangers, placed at 4.20 m spacing. The hanger connections to the arch are classic pin-hole

connections and connections to the bridge deck a specially designed hinge connections.Each leg of the tripod piers is of elliptical cross section, provided with special pot bearingson their tops to assure the connection with the bridge. These bearings can be injected tocompensate for an eventual shortening of one of the legs due to concrete creep andshrinkage. The global stability of the bridge relies primarily on torsion, due to the locationof the arch and highly asymmetrical form of the cross sections, which introduces largedifferences between the center of gravity of the cross section, the center of gravity ofpermanent loads and the shear center, providing a solution usually not recommended inbridge design. The arch inclination also creates bending in a horizontal plane and all theresulting deformations had to be accounted for by appropriate pre-camber. The vertical pre-

camber at mid-span amounted to 60 mm upstream and 300 mm downstream and thehorizontal pre-camber 230 mm, with torsion deformations and the shortening of the bridge

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deck also compensated by pre-camber. The steel bridge deck was launched in plan view ina curve from the southern river bank over temporary steel towers [26].

88.2 m 201.6 m 88.2 m77 m 58.8 m

C0 PC3 P4 PC6P5

Figure 15: Construction sequence of Pont de l'Europe Bridge

Figure 16: Pont de l'Europe Bridge: arch assembly using temporary towers (left) and arch todeck connection (right)

A 20 m long launching nose was utilized to decrease and compensate the cantileverdeflections, with its bottom flange pre-cambered by 1.25 m. The assembly site was 77 mlong, accommodating three 21 m long segments. The erection was carried out by two 120-200 t mobile cranes. The bridge was launched in 17 phases utilizing four hydraulic jacks

with the stroke of 800 mm and a capacity of 75 t each. Both 20-m long arch springingswere erected on the deck before launching. The other arch elements were assembled on site

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into two 55 m long lifting units, weighing 120 t each. These two arch elements were placedon the deck during assembly and launched with it. Finally, after the last deck launchingstage, two 400 t mobile cranes, mounted on the deck, were used to lift the two arch

elements into their final position. These elements were supported by 30-m high temporarysteel tower located in the middle of the river. This support was removed only after the archwas welded to the stubs that connect the steel deck to tripods and 28 principal hangers(hangers in the arch plane) were installed and tensioned to 42 t in each cable. Then, the 28secondary hangers connecting the edge of the footway and the arch were installed withoutpre-tensioning. After this operation was completed the bridge behaved as a real tiedbowstring, with the bridge deck carrying the tension force of 1100 t. Finally, six potbearings could be installed between the six legs of tripods and the steel stubs. They weregrouted simultaneously, and all temporary supports were subsequently removed, whichcaused the transfer of loads to the legs of the tripods. Thus, the arch compression forceswere transferred directly to the foundations.The network tied arch in Wolin, Poland was opened to traffic in 2003, as a part of the newbypass of this historical city [27]. The roadway width between safety barriers is 12 m. Thetheoretical arch span amounts to 165 m and the rise is 24 m, which gives the rise to spanratio of f/L=1/6.9. The inclined arches are of rectangular box type cross section withdimensions b/h=1000/1800 mm, transversely interconnected by seven cross beams, made ofcircular pipes, resulting in a frame type structure. The composite deck serves also as thearch tie. The deck cross section comprises a steel grillage fixed by shear Nelson typeconnectors to the 0.24 m thick concrete deck slab. The deck slab is longitudinallyprestressed by six external tendons, each comprising 37 strands of 15.5 mm diameter, toeliminate the deformations stemming from arch tension forces. The grillage consists of

main edge longitudinal girders, 0.86 m deep, one middle longitudinal girder 0.64 m deepand cross beams of 0.90 m depth. Steel plate thickness in the range from 12 mm to 30 mmwas used. Cross beams extend beyond the concrete deck plate to make room for passiveanchors of the inclined hangers. Inclined hangers are made of 41 mm cables. They lie indifferent planes, so that a direct contact at their junctions does not exist. Arch abutments,utilized for the connection between the deck and arches and for the anchoring of externallongitudinal deck tendons are constructed in reinforced concrete.

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Figure 17: The network tied arch in Wolin construction sequence

Figure 18: The network tied arch in Wolin: arch erection and suspending of the deck

The bridge is supported by double reinforced concrete columns, connected on top by a steelhead. Deep foundations consisting of 43 vertical 1.2 m diameter piles are utilized, with thepile length of 15.0 m for the right bank columns and of 22.0 m for the left bank columns.The sequence of bridge construction is shown in Figures 17 and 18 (Courtesy of DerStahlbau).In the first phase pile foundations and columns were constructed. There followed theconstruction of arch abutments, positioned on pot structural bearings. After that two

auxiliary steel towers with hydraulic lifting devices were erected. Arch segments weretransported to the site on barges. Three segments were connected on site and then theerection of the steel deck grillage began. Deck steel grillage segments were transported on a

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pontoon to a working platform, so that they could be erected together with the inclinedhangers. After positioning of all segments, they were rectified and interconnected bywelding. Only the connections of arches and longitudinal deck girders to arch abutments

were executed by high strength bolts. The external deck tendons were installed prior toconcreting of the deck slab. The last construction phase entailed the casting of the concretedeck slab. The process was divided into segments, whereby the segments at arch abutmentswere concreted first. Forces in external tendons were permanently controlled and increasedduring concreting, so that no tension forces due to the increasing dead weight, could ensuein the fresh concrete.It should be noted that another much larger network arch of 267.8m span across Ohio Riverand the Blennerhassett Island, was completed in the U.S.A, in 2008 [28].

3.2 Rail Bridges

A substantial number of steel arch railway crossings have been constructed around Europeduring the past decades. They were almost exclusively built on low terrain, crossing someof the major European rivers, and thus the only possible arch type was a through or halfthrough arch. The advantage in comparison with solid beam or truss bridges was theirappearance and in comparison with cable stayed bridges their much higher inherentstiffness and hence much smaller deformations under heavy railway traffic, a conditionespecially important for high speed rails.The longest span and the heaviest rail traffic of all European railroad arch bridges belongsto the Hamm Bridge across the Rhine River at Dsseldorf-Neuss, Germany. This four-tracked railway bridge was completed in 1987 with the main span of 250 m [29, 30]. Such a

long span was called for because of the ever increasing shipping traffic on the Rhine. Theoriginal design of the German Railways proposed a continuous beam with spans of 220 and165 m, weighing 9,500 tons. The bridge was a very rigid three-chord trussed frame of18.2 m height, with two tracks between the main truss girders and the other two tracks oncantilevers, placed on both sides on the outside of main girders. After long deliberationsrailway authorities accepted another solution, comprising a continuous 12.4 m high Warrentype trussed frame over 135 and 250 m spans, with the larger span supported by an archwith the rise of 45.5m (rise to span ratio of f/L=1/5.5). Such a relatively high rise waschosen, so that the visible parts of the arch above the trusses do not seem too flat. The trussweighs 6,800 t, the arch 1,600 t and hangers weigh 100 t, so that the total bridge steel

weight including transverse diaphragms at supports and moving maintenance platformamounts to 9,150 tons. All tracks are ballasted to reduce noise emission and facilitate trackmaintenance. Two tracks are positioned between the main truss girders, but all four trackslie between the arch planes. Both the arches and the main trusses are inclined at 14 degreesto the vertical, positioned on both in mutually parallel planes. This adopted solution is bothaesthetically more pleasing and structurally more advanced with end tangent angles undertraffic 32 % smaller than in the originally proposed design. Hangers are constructed fromflat plates, welded to a cross-shaped cross section. The arch, top truss chords and trussdiagonals are constructed without stiffeners to facilitate the production and assembly. Onlythe bottom chords had to be provided with longitudinal stiffeners to accommodate the loads

during erection. Cross sections of both the arches and the deck trusses are of box type,provided with access openings and facilities for inspection, with dimensions chosen so thatno plate is thicker than 50 mm.

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Neuss Dseldorf

Portal crane

Direction of longitudinal launching

Without deck

Launching devices

Launching bearings and

lowering device

Launching bearings and

lowering device

Abutment Dsseldorf newRiver pier new River pier

south old

Figure 18: Hamm Bridge: launching of the truss deck structure

The top truss chords are connected by bracing, installed mostly to resist by torsion the one-sided traffic. The deck is an orthotropic plate with open longitudinal stiffeners, a standardsolution for railway bridges, passing continuously through the cross beams, spaced at thirdsof the distance between two truss joints, i.e. at 4.17 m. The construction depth, i.e. thedistance between the top edge of the rails and the bottom edge of the structure is 3.25 m, sothat the bottom box type truss chords are 2.55 m deep, which made possible the erection bylongitudinal launching. The 25 m long erection segments, weighing up to 110 t were

transported to the assembly site by rail. Two gantry cranes, of lifting capacity 60 t each,were utilized for unloading and assembly. The truss deck structure was erected bylongitudinal launching (Figure 18). The stiff bottom truss chords were utilized as alaunching nose, with truss diagonals and top chords on the first 25 m left out and withoutinstalling the orthotropic deck on first 88 m of the cantilever. The erection time for thetrussed frame was about 14 months, with 25 m of the bridge completed in 4 week cycles.The launching was executed from the special launching table with a hydraulic system,capable of applying a force of 300 t. After the trussed frame reached its final position, itwas lowered onto the final bearings and the missing parts of the orthotropic deck plate wereinstalled. The arch was assembled in two halves at a lower level above the trussed frame

top chords with two gantry cranes and then jacked up to its final position. This wasaccomplished by inserting auxiliary hinges approximately at the level of the trussed frametop chords. The erection proceeded from these hinges so that the arch crown at first lay atthat level (Figure 19).

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Erection of arch segments

and cross beams

Lifting of both arch halves

Closing of arch connections at the

auxiliary hinges and at the crown

Auxiliary erection hinge

Sequence of hanger erection

Auxiliary pierLifting support

4 23 1 2 5 5 1 2 36

78

67

8

Figure 19: Hamm Bridge: arch erection procedure

The arch was then raised by specially designed jacking devices to the level about 1 m aboveits final position. The closure segment at the crown was inserted after the lowering of thearch to its final position. The erection was completed by placing in the hangers in a strictlypredetermined order. All hangers were installed in a stress-free state, which was madepossible by lifting the trussed frame for the installation of first four hangers and then bysequential lowering on the auxiliary pier to allow stress-free erection of further hanger pairs.Similar examples of steel arch railway bridges include Wittenberg Bridge of156.8 m main span completed in 2000 in Germany [31], Dintelhaven Bridge of 170 m main

span completed in 1999 in the Netherlands and 117 m long Louvain High-Speed Rail ArchBridge completed in 2002 in Belgium [32]. One should also mention Rhine crossingbetween Ludwigshafen and Mannheim in Germany, completed in 2000, with its uniquethree polygonal arches, each spanning a distance of 91.3 m.

3.3 Footbridges

Many steel arch footbridges have been built recently in Europe, ranging in spans from30-230 m, because of their beauty and ease of construction, but the construction of just thelongest of them, the Three Countries Bridge across the Rhine River between the cities ofWeil in Germany and Huningue in France, completed in 2007, shall be presented in the

paper. The open design competition for the design of this bridge was won by Austrian bornarchitect Othmar Feichtinger, working in Paris. The basic conceptual idea of spanning the

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Rhine River with an extremely slim asymmetric arch structure symbolizes the strongconnection between Germany and France.The arch shape was developed on the basis of the following considerations:

- The long span with the rise as small as possible gives the shape greatest elegance.- The arch height is minimized by lowering it to the water level.- The lightness of the structure is continued over the river banks. Instead of the

standard bridge piers, which would obstruct the view, additional structures areutilized as natural continuations of the arch.

This resulted in an extraordinary slender structure, whose lightness can be actually felt.This 229 m long asymmetrical steel arch bridge is unique in its design, as the northern archstands vertical and the southern arch leans against it with an inclination of 18. The archrise to span ratio is onlyf/L=1/13. The arch cross sections are very different, chosen so thatthe asymmetry is also mirrored in them [33].The southern arch and the longitudinal girders were constructed from as small as possiblesteel pipes. The southern arch cross section was built from a 609 mm steel pipe with thewall thickness of 36 mm and the southern longitudinal girder cross section of 325 mmsteel pipe 25 mm thick. The northern arch and longitudinal girders are in sharp contrastwith much stiffer rectangular and double hexagon profiles and take up all the main loads.The northern arch cross section comprised two hexagonal boxes with dimensionsb/h=600/900 mm and the southern longitudinal girder a hexagonal box section ofb/h=434/600 mm. The width of the deck is variable from 5.0 m at mid-span to 5.5 m at archabutments, as dictated by geometrical conditions. The steel deck plate spanning betweenthe main girders is an asymmetric orthotropic plate.

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Figure 19: Some photos of Three Countries Bridge construction

The structural bridge system is extremely flexible and fixed connections in plan werenecessary at abutments to take up the governing wind loading. Yet, the temperature changedid not allow a standard solution with both arch abutments fixed for longitudinalmovements, but a special triangular torsionally stiff and longitudinally movable structurehad to be constructed on the German bank. The torsionally stiff fixed bearing system of theFrench bank consisted of two movable spherical bearings for the northern arch (three forthe southern arch), each on a different radius, but all of them turning about the same focalpoint. The pre-camber was a complex space shape, because of the cross section asymmetryand had to be calculated by a procedure similar to the analysis of suspension bridges. Thewhole bridge structure was pre-assembled at a convenient location on the French side, firstthe deck and then the arches. The steel segments were transported to the site utilizingbarges and welded together. The transverse launching onto the pontoons was executed byheavy vehicles. On the next day cable winches pulled the bridge to the final location, withthe shipping river traffic closed. The last erection phase was most demanding. Underpermanent control of wind speeds, the bridge structure of almost 1000 tons weight wasrotated and positioned on auxiliary jacks, by slowly filling the pontoons with water. Duringthe bridge lowering, the bolt connections at both bridge ends were fixed. The structuralbearings were fixed to the substructure, only after careful surveying and controls of jackforces were performed. Some photos of the bridge construction are shown in Figure 19.

4. CONCLUSION

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An overview of historic development clearly shows that the construction of long steel archbridges has been almost abandoned since the appearance of cable-stayed bridges. Thisstagnation lasted over half a century, but recently we are witnessing steel arch bridges

revival, most prominently in China with the completion of the Chaotianmen Yangtze RiverBridge of 552 m span and the Lu Pu Bridge of 550 m span, setting new world records. Inthe last few decades the rediscovery of steel arch bridges is also evident in Europe in a widevariety of architectural forms and structural solutions. They have become very popular andhave been built in railway lines, on roads and highways and for footbridges. The mainreasons for that are modern steel fabrication, assembly and erection methods and theintroduction of high strength steels, but also the dissatisfaction with the performance ofconcrete structures in service. The influence of architects, who can better express their ideasin steel than in concrete, cannot be disregarded. The structural advantages of steel archesinclude their high strength, durability, and smaller weight, hence smaller foundations andlower erection costs. Steel arch bridges are indispensable for railway crossings, because oftheir inherent stiffness, much larger than that of cable-stayed bridges. Recently builtrailway steel arch bridges in Europe are predominantly of the through tied type, because oftheir location across large rivers in low terrain. The other major application is forfootbridges, in which advantages of steel as structural material may be effectively appliedto design unique and aesthetically most pleasing structures. The maintenance costs for steelarches primarily under compression are much smaller than for suspension and cable stayedbridges, mainly carrying loads by tension, as exemplified by the example of Hell GateBridge.The mostly applied construction procedure for steel arch bridges is cantilevering, used invarious alternatives since 19th century, with the development basically only in auxiliary

structures and erection equipment. Recent European through tied arches across rivers havepredominantly been assembled on the shore and erected by utilizing floating platforms.Some interesting examples of construction of steel arch bridges, built in the last ninetyyears, are described in detail in the paper.

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