Hølen Viaduct

Hølen Viaduct Hølen viadukt
Coordinates	59°32′20″N 10°44′24″E / 59.539°N 10.740°E / 59.539; 10.740Coordinates: 59°32′20″N 10°44′24″E / 59.539°N 10.740°E / 59.539; 10.740
Carries	Østfold Line
Crosses	Såna
Locale	Hølen, Vestby, Norway
Characteristics
Material	Iron
Total length	130.6 m (428 ft)
Longest span	9.4 m (31 ft)
No. of spans	14
History
Designer	Axel Jacob Petersson
Opened	2 January 1879 (1879-01-02)
Closed	21 September 1996
Replaced by	Hølendalen Bridge
Hølen Viaduct Location in Akershus

The Hølen Viaduct (Norwegian: Hølen viadukt) is a disused iron railway viaduct situated at Hølen in Akershus, Norway. The iron carried a single track of the Østfold Line over the river Såna and the valley where the village of Hølen is located. The viaduct was the first pendulum pillar bridge in the world, and was designed by the principle's inventor, Axel Jacob Petersson. It is 130.6 meters (428 ft) long.

The viaduct was built as part of the Østfold Line and opened on 2 January 1879. It was structurally strengthened through a pillar replacement program in 1914. From 1931 Hobøl Station was situated on its north end. A new section of Østfold Line opened on 21 September 1996, resulting in the viaduct and the old line being closed. Hølen Viaduct is still standing, but not in use.

The Hølen Viaduct is an iron pendulum pillar bridge which crosses Såna. It is 130.6 meters (428 ft) long and consists of fourteen spans supported by thirteen pillars. Two spans measure 8.9 meters (29 ft), while twelve measure 9.4 meters (31 ft). The bridge carried the single-tracked Østfold Line's and was situated 46.90 kilometers (29.14 mi) from Oslo Central Station. The entire viaduct was built on a curve with a curve radius of 470 meters (1,540 ft).

The Østfold Line was the first railway in Norway to use iron as the main construction material for its bridges. This allowed the line to be built with several larger viaducts, the most prominent being the Ljan Viaduct. The design was placed under the construction- and bridgeoffice, which was led by Axel Jacob Petersson. During the design process, he devised the pendulum pillar principle. This method allowed for smaller pillars which could be prefabricated and then mounted easily at the cite, reducing costs significantly. The lower costs allowed for several viaducts to be built, which again allowed for less gradients, as embankments would be prohibitively expensive.

Petersson first designed the Ljan Viaduct and the Sarpsfossen Bridge, neither which used the pendulum pillar process as these were too far into the design process when he reached his breakthrough. Instead it was the later Hølen and Rolfsøsund Viaducts which were designed with it. The Hølen Viaduct is the first structure in the world to be built with the principle. The Østfold Line opened on 2 January 1879.