Mears Memorial Bridge
Coordinates: 64 ° 34 '2 " N , 149 ° 4' 43" W.
| Mears Memorial Bridge | ||
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| use | Railway bridge | |
| Crossing of | Tanana River | |
| place | Nenana ( Alaska ) | |
| Entertained by | Alaska Railroad | |
| construction | Truss bridge | |
| overall length | 397 m | |
| width | 12 m | |
| Longest span | 213 m | |
| Construction height | 29 m | |
| Clear height | 14 m ( MHW ) | |
| building-costs | US $ 1.29 million | |
| opening | 1923 | |
| planner | Modjeski & Angier | |
| location | ||
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The Mears Memorial Bridge is a single-track railway bridge over the Tanana River near Nenana in the state of Alaska . The truss bridge was built by the Alaska Railroad until 1923 as part of the connection from Seward on the Pacific coast to Fairbanks inland. At 213 meters, it has one of the world's longest simple truss between two supports and, since its completion, the longest span in Alaska. The bridge is named after Colonel Frederick Mears , chief engineer of the Alaskan Engineering Commission that later became the Alaska Railroad .
history
At the beginning of the 20th century, the Alaska Central Railway (later Alaska Northern Railway ) and the Tanana Valley Railroad were the first railroad companies in Alaska . In 1914, the state-owned Alaskan Engineering Commission was founded, which acquired the lines of the two railway companies totaling around 200 kilometers and, under the direction of chief engineer Colonel Frederick Mears, expanded them to over 750 kilometers from Seward on the Pacific coast north to Fairbanks in the interior by 1923 . Upon completion, the state railroad company was given its current name, Alaska Railroad .
As part of the route, a bridge was planned over the Tanana at Nenana in the early 1920s . An originally planned route west of Nenana at the confluence of the Nenana River with the Tanana River was later discarded because the effort for the necessary river piers was classified as too high due to the massive ice drift prevailing here in spring and the long-term safety of the piers was questioned - The road bridge of the George Parks Highway has been running at the position of this alternative route since 1967 .
The Alaskan Engineering Commission commissioned the bridge construction engineer Ralph Modjeski with the construction of a bridge without river piers further east, where the Tanana is only about 200 m wide. In collaboration with Walter E. Angier (Modjeski & Angier) he designed a truss bridge with a 213 m long central girder. With the 220 m long girders constructed by Modjeski for the Metropolis Bridge (1917), these were the world's longest simple truss girders between two supports ( single-span girders ); Spans of this size in truss bridges were mostly only realized with Gerber girders or continuous girders . Angier inspected the location of the bridge in the spring of 1920 and again with the start of construction of the bridge piers in June 1922. The trusses were manufactured by the American Bridge Company and erected under the direction of Frederick Mears in the winter of 1922/23. The first train crossed the bridge on February 9, 1923.
description
The central element of the bridge is a 213.4 m long lattice girder with a curved top chord and track below, designed as a Pennsylvania truss with the typical additional cross bracing in the lower area. This type of construction was developed by the Pennsylvania Railroad , was more material-saving in design than older truss constructions for higher loads and was used until the 1930s. The construction height is 29 m and the width about 12 m, with the up to 1.2 m wide belts of the steel trusses having a distance of 11 m between their central axes. The structural elements, which are only subjected to tensile loads, are made up of eye rods and are connected to each other and to the remaining rods and belts with bolts (English pins ), mostly 30 cm in diameter (marked with small circles in the drawing below); the remaining connections are riveted . A total of around 2,160 tons of steel were used for the truss, with the heaviest processed parts of the belts weighing up to 24 tons.
The truss rests on reinforced concrete pillars (between 11 and 12) with a height of about 18 m from the lower edge of the foundation. All pillars on the south side in the direction of Nenana (route to Seward ) are anchored by pile foundations in the clay subsoil that predominates here , the northern pillar (12) is built directly on mica slate . On the north side (route to Fairbanks ) a 19.1 m long girder bridge follows the abutment (13) . In the south to Nenana there is a small parallel - belted lattice girder with an overhead track of 36.6 m length (between 10 and 11), which is followed by a 128.0 m long trestle bridge with solid wall girders . Since the south access on the Nenana side is slightly uphill, the Trestle Bridge has a gradient of 10 ‰ and the following small truss is still 5 ‰. The total length of the Mears Memorial Bridge is 397.0 m.
The truss bridge after its completion in 1923, remains of the scaffolding still in the river bed
Schematic drawing from 1923: central lattice girder over the Tanana with a length of 213 m and a height of 29 m, Trestle bridge of the south approach not shown in full; Figures in feet (′) and inches (″)
Alaska Railroad train on the bridge 2010
See also
literature
- Frederick Mears: Bridging the Tanana River on the Alaska Railroad. In: Engineering News-Record. Vol. 90, No. 11, 1923, pp. 476-482.
Web links
- Alaska - Mears Memorial Bridge. Bridgehunter.com
Individual evidence
- ↑ a b c d Frederick Mears: Bridging the Tanana River on the Alaska Railroad. In: Engineering News-Record. Vol. 90, No. 11, 1923, pp. 476-482.
- ^ Ralph Modjeski: The Metropolis Bridge Over the Ohio River at Metropolis, Ill. In: Journal of the Western Society of Engineers. Vol. 24, No. 2, 1919, pp. 59-82.
- ↑ James Gordon Steese: The Alaska Railroad. In: The Michigan Technic. Vol. 37, No. 1, November 1923, pp. 5-8, here p. 8.
- ^ Ray Bonnell: Mears Memorial Bridge: The connecting link in the Alaska Railroad. ( June 18, 2016 memento on the Internet Archive ) Fairbanks Daily News-Miner, May 21, 2016.
- ^ Glenn A. Knoblock: Historic Iron and Steel Bridges in Maine, New Hampshire and Vermont. McFarland, Jefferson 2012, ISBN 978-0-7864-4843-2 , pp. 33-37.