Keokuk Municipal Bridge

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Coordinates: 40 ° 23 '28 "  N , 91 ° 22' 24"  W.

Keokuk Municipal Bridge
Keokuk Municipal Bridge
Keokuk Municipal Bridge 1982, looking towards Keokuk
use Railway bridge
Crossing of Mississippi River
place Keokuk , Iowa and Hamilton , Illinois
Entertained by City of Keokuk
construction Truss bridge with swing bridge
overall length 961 m (including driveways)
669 m (main bridge)
Longest span 78 m
opening 1916
planner Ralph Modjeski
location
Keokuk Municipal Bridge (USA)
Keokuk Municipal Bridge

The Keokuk Municipal Bridge, also Keokuk & Hamilton Bridge or Keokuk Rail Bridge, is a combined railroad and former road bridge ( double decker bridge ) over the Mississippi River between Keokuk , Iowa , and Hamilton , Illinois . The truss bridge designed by Ralph Modjeski replaced a railway bridge from 1871 in 1916 and was built on the same bridge piers. In the upper area it led US Highway 136 to the opening of the neighboring Keokuk – Hamilton Bridge in 1985 , underneath it is a track of the Keokuk Junction Railway that is still used today within the truss . The bridge crosses the Mississippi River just downstream behind the barrage Lock and Dam No. 19 . On the Keokuk side, a swing bridge is integrated into the truss bridge at the level of the lock . The adjoining trestle bridge for vehicle traffic was expanded as a viewing platform after its closure, from which the lock process can be observed.

history

The first iron Keokuk & Hamilton Bridge in 1906

The first iron bridge in 1871

The lock on the Mississippi River Lock and Dam No. 19 in 1914, in the background the first Keokuk & Hamilton Bridge (1871)

In the course of the expansion of the railway network in the southwestern United States , the first railroad bridge between Keokuk and Hamilton over the upper reaches of the Mississippi was planned by the Keokuk & Hamilton Bridge Co. in the late 1860s . Its President Andrew Carnegie , who, in addition to local interests, primarily pursued the expansion of his investments in the railroad and iron industry, was the driving force behind the project. The single-track cast and wrought iron bridge was built by Carnegie's Keystone Bridge Company (now the American Bridge Company ) between 1869 and 1871 and could also be used by wagons and pedestrians. Made up of ten Whipple- trusses (named after the father of the iron bridge construction Squire Whipple ) and a swing bridge in the same design on the navigation channel, it rested on eleven current pillars of limestone that were built in the riverbed on rock. The bridge was not entirely perpendicular to the river, which meant that the bridge to the piers placed in the direction of the river also ran at an angle of 17 °.

Behind the Keokuk & Hamilton Bridge Co. were four railway companies as bridge users , which over the years have merged into other companies and no longer exist today. These included the Columbus, Chicago and Indiana Central Railway (later Pittsburgh, Cincinnati, Chicago and St. Louis Railroad ), the Toledo, Wabash and Western Railway (later Wabash Railroad ), the Toledo, Peoria and Warsaw Railway (later Toledo, Peoria and Western Railway ) and the Des Moines Valley Railroad (later Chicago, Rock Island and Pacific Railroad ). In the early 1980s, Keokuk Junction Railway (subsidiary of Pioneer Railcorp ) acquired parts of the line from the latter company in Keokuk and today uses the successor bridge for rail freight transport .

The second steel bridge in 1916

Swing bridge of the Keokuk Municipal Bridge 1990 in front of the new lock (1957) of Lock and Dam No. 19, at the very bottom the new Keokuk – Hamilton Bridge (1985), at the top right the old lock and behind it the power station

With the advent of stronger and heavier steam locomotives at the beginning of the 20th century, the bridge's load-bearing capacity was no longer sufficient. Furthermore, the vehicle traffic developed, and the alternating use between trains and carriages and automobiles increasingly represented a bottleneck. At the same time caused to the upper reaches of the Mississippi several barrages to the transport of bulk cargo from the Midwest to the Gulf of Mexico and to facilitate the To regulate the flow rate of the overflow. By 1913, a few hundred meters upstream from the iron bridge, the Lock and Dam No. 19 built, and efforts to integrate a second bridge into the dam posed a threat to the toll revenues of Keokuk & Hamilton Bridge Co. An originally planned reinforcement of the iron bridge was discarded under pressure from the United States Congress and the bridge construction engineer Ralph Modjeski commissioned with the construction of a new bridge on the existing bridge piers. It was decided on a design with two levels one above the other for rail and vehicle traffic and a gradual replacement of the trusses without interrupting the operation of the bridge. This prevented the construction of a second parallel bridge along the dam. Construction work began in the spring of 1915 and was completed at the end of 1916; the swing bridge was replaced during the shutdown of shipping in the winter of 1915/16.

Purchase of the bridge through the city of Keokuk in 1949

In January 1949, the city of Keokuk acquired the bridge and lifted the toll. However, necessary repair work forced the city to raise a toll again from May 1952 onwards. In particular, the pillars, whose inadequate condition Modjeski had pointed out in 1922, needed an overhaul. The pillar of the swing bridge was extensively expanded by the United States Army Corps of Engineers in the course of the new construction of the lock of the barrage by 1957 and expanded to the almost 400 m long lock.

Until the new four-lane Keokuk – Hamilton Bridge was built in 1985, the Keokuk Municipal Bridge led to US Highway 136 on the upper level since the early 1950s . The trestle bridge on the Keokuk side, which is adjoining for vehicle traffic , was expanded as a viewing platform after its closure, from which the lock process can be observed. The track on the lower level is still used today by the Keokuk Junction Railway for freight traffic, which serves Amsted Rail and Roquette America in Keokuk. The inspection and maintenance of the bridge continues to be carried out for the city by Modjeski and Masters of Chicago , the company of the founder and designer of the Keokuk Municipal Bridge, who died in 1940 .

description

Schematic representation of 1916, the main bridge (Main Bridge) of Keokuk Municipal Bridge with Swing Bridge (left) and the following ten trusses and the respective Trestle bridges of access roads (Approach) for the upper pavement area (all lengths in foot )

The bridge is divided into the 669 m long main bridge with an integrated swing bridge and the two access viaducts for vehicle traffic. The main bridge is designed as a truss bridge made mainly of riveted steel and has 12 spans between the 11 river pillars and the abutments , followed by the trestle bridges of the access roads, the superstructures of which are made of solid wall girders . A railway and tram track is routed on the lower level within the truss and the track on the upper level. On the south side, there is an additional footpath on cantilevers at the level of the carriageway.

Carriageway above the truss with a footpath to the side (view from the swing bridge towards Hamilton)
Railway and tram track within the truss

Main bridge

From east to west, the main bridge consists of eight 8.8 m high and 5.1 m wide parallel-chorded stud trusses (Pratt trusses) with spans between 45 and 50 m. This is followed by two stud framework girders with a curved upper flange (Parker framework), a maximum height of 16 m, a width of 6.3 m and a span of 77.6 m. The conclusion is the 115 m long swing bridge , which is now directly behind the lock of Lock and Dam No. 19 lies. Due to the angle of the bridge to its pillars, the trusses form a parallelogram when viewed from above . Since the steel structure has a stronger and higher substructure under the track than the old iron bridge, the stone river pillars were shortened by 1.5 m and provided with a reinforced concrete cover plate to preserve the original track level . The carriageway level is installed 8.9 m above the track level and runs in the area of ​​the smaller truss above the upper chords. The 5.5 m wide carriageway and 1.2 m wide walk were originally implemented by wooden planks, but were in 1956 by gratings replaced made of steel.

Swing bridge

The roller ring bearing of the swing bridge with gear drive
Trestle bridge for access to the carriageway level on the Hamilton side

The equal-armed swing bridge has two cantilever girders around 54 m long on a central truss tower 6.3 m in length and width and 14.6 m in height. In the upper area they are fastened with eye rods that are only subjected to tensile loads , whereby the lower chords run through the entire length of the swing bridge and are mounted under the central tower on a 1.6 m high drum with a diameter of 8.8 m. This rests on a roller ring bearing with 40 rollers, which have a length and diameter of 46 cm. Due to the construction of the swing bridge as a parallelogram , the cantilever girders have different lengths on their outer sides (53.4 m or 55.3 m) and the opening is therefore only possible in an anti-clockwise direction. The rotating mechanism is driven by a 26- kW - AC motor on two opposite toothed gear on the drum, which are connected to the outer ring of the bearing on the bridge piers. A locking system ensures the vertical and horizontal alignment of the bridge and the track when closed. To operate and control the bridge, a multi-story house is attached to the central truss segment on the south side, with access to the carriageway level for the operating personnel.

Driveways

Since the carriageway and the footpath are almost nine meters above the level of the platform, additional trestle bridges (scaffolding pillar viaducts) had to be built as accesses when the bridge was rebuilt. On the west side the driveway has a length of 183 m and leads to the higher situated town Keokuk without inclination, at the end there is the former toll station. On the west side, the access towards Hamilton has a gradient of 6% and a length of 110 m. Both trestle bridges have eleven piers each. Where the track and carriageway are separated behind the main bridge, these are sometimes wider than the superstructure to span the track .

literature

Web links

Commons : Keokuk Municipal Bridge  - Collection of pictures, videos and audio files

Individual evidence

  1. ^ A b Martha H. Bowers, Hans Muessig: Keokuk & Hamilton Bridge, Keokuk, Lee County, Iowa. Historic American Engineering Record, HAER No. IA-3, Denver 1982, pp. 13-17.
  2. ^ A b Reconstruction of the Keokuk Bridge. In: Railway Age Gazette. Vol. 61, No. 3, 1916, pp. 97-100.
  3. ↑ Keokuk Junction Railway Company KJRY # 365th Customers: Short Line Railroads Profiles DK, Union Pacific Corporation . Retrieved November 25, 2017.
  4. ^ A b Reconstruction of the Mississippi River Bridge at Keokuk. In: Engineering News. Vol. 75, No. 15, 1916, pp. 690-693.
  5. ^ Martha H. Bowers, Hans Muessig: Keokuk & Hamilton Bridge, Keokuk, Lee County, Iowa. Historic American Engineering Record, HAER No. IA-3, Denver 1982, pp. 19-22.
  6. ^ Martha H. Bowers, Hans Muessig: Keokuk & Hamilton Bridge, Keokuk, Lee County, Iowa. Historic American Engineering Record, HAER No. IA-3, Denver 1982, pp. 22-24.
  7. ↑ Bridge Observation Deck. Keokuk Area Convention and Tourism Bureau. Retrieved November 19, 2017.
  8. ↑ Steve Dunn: Railroad bridge Reacts to offer. Daily Gate City, March 12, 2010. Retrieved November 22, 2017.
  9. ↑ Keokuk Swing Bridge Inspection and Rating. ( Memento from December 1, 2017 in the Internet Archive ) Modjeski and Masters, Railroad Services.
  10. ↑ GENERAL ELEVATION AND PLAN - Keokuk & Hamilton Bridge, Spanning Mississippi River, Keokuk, Lee County, IA. (HAER IOWA, 56-KEOK, 1--72) Library of Congress Prints and Photographs Division.
  11. ^ A b c Martha H. Bowers, Hans Muessig: Keokuk & Hamilton Bridge, Keokuk, Lee County, Iowa. Historic American Engineering Record, HAER No. IA-3, Denver 1982, pp. 5-11.
  12. ^ Reconstruction of the Mississippi River Bridge at Keokuk. In: Engineering News. Vol. 74, No. 6, 1915, pp. 60-62.
This article was added to the list of articles worth reading on December 6, 2017 in this version .