•Rivista GFS n. 14-2010 24-10-2011 12:37 Pagina 93 Friulian Journal of Science 14. 2010, 93-109 The “Ponte di Muro” bridge on a disused railway line at Dogna, Udine, and its recent conversion to cycle use ALESSANDRO COCCOLO* Abstract. This article illustrates the rail-to-trail conversion of a truss bridge known as “Ponte di Muro”, located near the village of Dogna in the Julian Alps. The bridge was part of the disused Pontebbana railway line which has now been converted to accom- modate the new “Alpe Adria” cycle trail. The paper includes a short history of the rail- way line, with particular reference to the bridge, the main technical details of the pro- ject and a description of the different phases of its execution. Key-words. disused railway line, cycle route, metal bridge. 1 The Pontebbana railway line Jesenice-Cˇ eské Budeˇjovice) (AA.VV. 1.1. Historical outline. The line. The 1996, Petronio 1997) and “Südbahn” historians of the railway network (Trieste-Semmering-Vienna) (Ram- which has been crossing the Alpe- pati 2002, AA.VV. 2007), the Ponteb- Adria region for the last hundred and bana railway line between Udine and fifty years have produced over the Pontebba (Bortotto 1979, Roselli decades a large and well-detailed 1979, AA.VV. 2006) deserves an im- body of research, also serving as a portant place in 19th-century railway precious and comprehensive techni- engineering, also by virtue of its spec- cal bibliography. tacular and audaciously-accom- A contemporary of the famous plished crossing, by its 5th section, of Austrian lines “Transalpina” (Trieste- the orographically complex “Canal * CP Ingegneria, via Roma, 274, 33013 Gemona del Friuli (UD), Italy. E-mail: [email protected] 93 •Rivista GFS n. 14-2010 24-10-2011 12:37 Pagina 94 A. Coccolo del Ferro”, the narrow and rugged the life of the population of the valley, valley of the River Fella between the who contributed to the greater part villages of Chiusaforte and Pontebba. of the 3000-strong workforce. The construction of the line was The first train pulled in at Ponteb- approved by Law no. 896 of 30 June ba railway station, by the Austria- 1872, following am agreement signed Italy border, at 3 pm on 12 July 1879, by the Italian Government and Rome while the line was officially opened Banca Generale on the previous 6 on the following 25 July, when regular May. It was designed by engineers Udine to Pontebba services started. Cesare Bermani and Lodovico On the other side of the border, the Richard on the basis of a feasibility construction of the “Rudolphsbahn” study written in 1857 by Alessandro line, linking Pontebba/Pontafel to Cavedalis. The construction phase, Tarvisio and to the Austria-Hungary supervised by engineer Giuseppe Oli- network (24.9 km), started off only in va, took place between 1873 and April 1877. However, due to the 1879 (Marinelli 1894) and was divid- more favourable orographic situation ed in 5 sections: Udine-Gemona, of the Fella valley between Pontebba Gemona-Stazione per la Carnia, and Camporosso, work was complet- Stazione per la Carnia-Resiutta (7900 ed by October 1879. The internation- m), Resiutta-Chiusaforte (8102 m), al line Udine-Pontebba-Tarvisio was Chiusaforte-Pontebba (12058 m of officially dedicated on 30 October which 4311 m curvilinear, with two 1879, and the event was largely re- crossings of the River Fella by daring- ported by the press (Roselli 1979). ly-designed metallic bridges)1. The A crucial turning point in the de- construction of the 4th and 5th sec- velopment of the line was the re- tions, conducted roughly between placement of steam with electric trac- 1877 and 1879, completely changed tion, as part of the electrification plan Figure 1. Workers engaged in the construction of a tunnel (archive Sorgato A. & Brusa- dini S.). 94 •Rivista GFS n. 14-2010 24-10-2011 12:37 Pagina 95 The “Ponte di Muro” bridge on a disused railway line at Dogna of the Italian railway network when it merged with the Pontafel- launched by the Fascist regime in Tarvis line, and the gradient rose in 1932-1933. The first electrically-pow- parts of the line to 2.2%. ered train ran on the line on 16 Sep- Construction costs were of tember 1935, while the official inaugu- 440,000 lire/km for the Italian por- ration ceremony took place on the fol- tion, and of 430,000 lire/km for the lowing 28 October. The estimated cost Austrian portion. However, if we of electrification was of around 1 mil- break down the costs between the lion lire per kilometre. During electri- first three sections of the line (Udine- fication work the line was substantial- Resiutta) and the last two (Resiutta- ly refurbished: the tracks, the metallic Pontebba), it appears that the 4th beams of bridges, the blockage and and 5th sections had a much higher signalling apparatuses were radically cost per kilometre, equal to around modernized (Bortotto 1979). 850,000 lire/km. In its original version (Udine-Pon- tebba) the Pontebbana rail line had a Main features. If on one hand the length of around 68.3 km with a max- Pontebbana line was, on the whole, imum gradient of 1.6%, and was clas- characterized by a relatively modest sified as a 2nd-grade, single-track transport capacity, as is to be expect- line, with a capacity of 60 axes. ed by a mountain railway, on the oth- The length of the line became of er its individual structures (bridges, 93.2 km at the end of World War I viaducts, tunnels, retaining walls, Figure 2. The longitudinal profile of the Udine-Tarvisio line (Roselli 1979). The gradient is indicated in the bottom row, the top row shows the progressive distance measured from Udine station. 95 •Rivista GFS n. 14-2010 24-10-2011 12:37 Pagina 96 A. Coccolo Table 1. Types of structures in the original Udine-Pontebba line (Roselli 1979). Type of structure number total length [m] Bored tunnels 28 5,673 Artificial tunnels 5 565 Masonry bridges and viaducts 16 1,551 Steel bridges and viaducts 11 820 Retaining walls over the structure 12,592 Retaining walls under the structure 3,180 bank protection structures, all of Udine-Pontebba or Pontafel-Tarvisio which were abundantly represented lines. In the former case, they are in the mountainous portion of the built in a typically northern-Italian line) were, and still are, a remarkable style with a small eaves overhang and engineering feat. have an altogether more anonymous Table 1 summarizes the many dif- appearance; in the latter case, they ferent structures comprised in the are very Alpine-looking and charac- original Udine-Pontebba line and terized by a large use of exposed which were mostly concentrated in its stone (Bortotto 1979). Metallic 3rd, 4th and 5th sections. bridge designs, on the other hand, Stations and crossing keeper’s cot- following the extensive moderniza- tages display very different architec- tion work carried out on the line in tural features depending on whether the first half of the twentieth century, they originally belonged to the precisely correspond to the rigorous Figure 3. Examples of some of the original structures of the line (AA.VV. 2010). Top right, the bridge on the River Fella at Chiusaforte, top left the bridge over the Rio Potocco. Bottom, the spectacular viaduct over the River Dogna, which tragically collapsed in 1968. As shown by the photographs, the same truss design was used with all struc- tures. In the 1930s when the line was electrified and struc- turally reinforced, existing beams were replaced and stan- dard Italian Railway designs were adopted depending on span lengths. 96 •Rivista GFS n. 14-2010 24-10-2011 12:37 Pagina 97 The “Ponte di Muro” bridge on a disused railway line at Dogna Figure 4. Examples of metallic bridges on the Pontebbana rail line (years 2007-2008). Top left, the small bridge over Rio Confine with twinned girders (on the municipal border be- tween the villages of Dogna and Pontebba). Top right, the bridge on Rio Pontuz with plate girders (Dogna). Bottom left, the pony truss bridge “Ponte Peraria”. Bottom right, the through truss bridge “Ponte della Chiusa” (Chiusa- forte). standardization which had been im- bridge) situated a few miles more to posed at the time by the Italian na- the north (prog. dist. 63 km + 868 m tional railway company, Ferrovie dello from Udine). Stato. Accordingly, four bridge de- The Dogna bridge collapsed a few signs were used on the line, depend- years before its one hundredth an- ing on the length of the span: niversary on 16 September 1968, when – girder bridges with twinned gird- the river overflowed with disastrous ers, for modest spans; results. It was replaced by a much – plate girder bridges, for longer more anonymous structure in pre- spans; stressed concrete with five spans in- – truss bridges with the deck sitting stead of the original four (Bortotto on top or at the bottom of the 1979). A description of that tragic truss, and unconnected sides event lies beyond the scope of this ar- (pony trusses), for very long span; ticle; in fact, an adequate discussion of – truss bridges with the deck sitting the history of the Dogna bridge would on top (deck truss) or at the bot- call for a separate treatise, also in con- tom (through truss) of a box truss, sideration of the structural damage also for very long span. that it suffered from allied bombing It is not easy to single out an indi- raids in 1944-1945 (D’Aronco 2008) vidual structure as the symbol of the and from an act of sabotage by the re- Udine-Pontebba line.