Britannia Bridge
Coordinates: 53 ° 12 '57 " N , 4 ° 11' 8" W.
| Britannia Bridge | ||
|---|---|---|
 ( colored ; original in sepia ) |
||
| Official name | Britannia Bridge | |
| use | Railway bridge | |
| Convicted | North Wales Coast Line | |
| Crossing of | Menai Strait | |
| place | at Bangor | |
| construction | wrought iron box girder bridge | |
| overall length | 561 m | |
| Clear width | 70 + 140 + 140 + 70 | |
| start of building | 1846 | |
| completion | 1850 | |
| Status | Partly destroyed by fire | |
| planner | Robert Stephenson et al. a. | |
| closure | 1970 | |
| location | ||
|
||
The Britannia Bridge is a bridge over the Menai Strait near Bangor in north Wales. The Britannia Bridge, built by Robert Stephenson and opened in 1850, was originally a double-track railway bridge made of parallel wrought-iron box girders between high masonry pillars. The girders were destroyed by fire in 1970 and had to be demolished. In their place, steel truss arches were erected and the bridge was converted into a combined rail and road bridge. The first tram was able to cross the bridge again in 1972, the expansion to a road bridge was completed in 1980.
location
The bridge connects the places Penrhos-Garnedd, a suburb of Bangor on the southern side of the deeply incised Menai Strait, and Llanfairpwllgwyngyll on the northern side, i.e. H. on the island of Anglesey . It was not built at the narrowest point of Menai Strait, just 1.5 km away, as the Menai Bridge was already there . In the middle between the two banks is Britannia Rock , a rock that only protrudes from the water at low tide, on which the middle pillar of the bridge named after him could be built.
The first bridge (1850)
description
The first bridge consisted of the three remaining pillars made of stone blocks and the two abutments built far into the bank . The middle pillar on Britannia Rock is just under 60 m (196 ft) above the high water line, slightly higher than the other two towers standing on the bank. Two wrought-iron box girders for one track each ran a short distance apart from one bank to the other bank through two passages in the abutments and pillars. The hollow boxes were only stored in the towers, but otherwise cantilevered. The trains drove through the portals in the abutments and through the hollow boxes as if through a tunnel. The towers are significantly higher than the hollow girders, as Stephenson wanted to keep the possibility open of attaching support chains like a chain bridge even after they were installed, but this turned out to be unnecessary.
The bridge is 561 m (1,841 ft) long at the level of the rails and has a clear height of 31.6 m (103.9 ft) above MHW . The clear width between the pillars is 140 m (just under 460 ft) each, that of the outer openings above the bank slopes is 70 m (230 ft) each. The pillars are made of very hard limestone blocks from a specially constructed quarry at Penmon on the eastern tip of Anglesey, while the inner masonry is made of a softer but easy to work sandstone from Runcorn in Cheshire . The pillars have a rectangular cross-section and a slight suit ; the middle tower measures 18.9 m × 16.9 m at the base and 16.7 m × 13.8 m at the level of the tracks; the pillars on the bank measure 18.9 m × 15.9 m or 16.7 m × 9.75 m at the height of the tracks.
The two hollow boxes of the trains were from abutment to abutment continuous components (after their individual sections had joined in the assembly fixed to a continuous beam with each other). At 461.2 m (1,513 ft) in length and weighing 5,000 tons each, they were the largest pieces of wrought iron ever built and almost twice as heavy as a fully equipped 120-gun ship .
While the floor had to be straight and horizontal for the railway, the roof described a parabolic curve. The height of the box girders fell from 9.14 m (30 ft) in the middle in the Britannia tower to 6.93 m (22 ft 9 ″) in the abutments (external dimensions). The hollow boxes had double floors and roofs, which were divided into six and eight chambers. The inside of the box girders were therefore 1.22 m (4 ft) lower than the outside. Its internal width was 4.26 m (14 ft), but the clearance profile was slightly smaller because of the internal reinforcement profiles . The box girders consisted of wrought iron sheets of different lengths and thicknesses; the longest measured 3.65 × 0.71 m and were up to 2.44 cm thick - the largest and strongest plates that could be rolled at that time. 2 million rivets had to be knocked down to connect all the sheets of the bridge .
The thermal expansion of the hollow boxes was calculated to be a maximum of 30 cm. They have therefore been fixed in the central tower, in the other towers and the abutments but on cast iron rolls stored . Rail extension devices were located at both ends .
The entrances to the bridge are decorated with large stone lions. From a distance they look rather modest next to the large bridge, but in fact they are around 4 m high and 7.6 m long and each weigh around 30 t. They are still in their original place next to the train tracks. Therefore, they cannot be seen from the new overpass built over the tracks.
history
planning phase
The Chester and Holyhead Railway , founded in 1844, had commissioned Robert Stephenson with the construction of the railway line, which included the crossing of the Menai Strait and the River Conwy, both tidal waters. The more than 300 m long Britannia Bridge naturally posed the greatest challenges, even if it was supported with a pillar on Britannia Rock in the middle of Menai Strait. At that time only suspension bridges could span such widths, but because of their flexibility they were considered unsuitable for railway bridges. Robert Stephenson initially thought of a cast iron bridge with two 134 m wide arches and a clearance height of 30 m, which should be erected in a cantilever so as not to disrupt ship traffic. There were concerns about the feasibility of such large arches made of cast iron, but the deciding factor was the Admiralty , who demanded a clearance not only in the center but also close to the pillars. Ultimately, this only allowed a bridge with a kind of flat beam, a design completely unknown for this size at the time.
Stephenson initially only had a vague idea of a bridge with two large round or oval tubes made of wrought iron sheets through which the trains should run and which would have to be held by chains like a chain bridge. In 1845 he turned to William Fairbairn , who should advise him on the feasibility and the method of construction of such a bridge. For reasons of principle, Fairbairn was against combining an inherently flexible structure such as a suspension bridge with a structure designed for rigidity such as a bridge made of riveted iron sheets, since the two systems would only damage each other. With the consent of the client, models were made from December 1845 onwards, numerous experiments and investigations with round, elliptical and rectangular cross-sections were carried out and various solutions of various details were discussed. Eaton Hodgkinson was called in, who developed a series of calculations for the load-bearing capacity of the structures. The experiments showed for the first time and to the surprise of the experts that wrought iron, unlike cast iron, does not withstand as much pressure, but withstands greater tensile stresses than was expected at the time. In any case, a box girder with a rectangular cross-section turned out to be the best solution. Apparently the experts were by no means always in agreement. Fairbairn finally resigned and claimed in his detailed publication that the box girder without chains was due to him alone, which met with astonished opposition. Hodgkinson seems to have advocated the use of chains to the last. In order not to take any risks, Stephenson decided to have the towers built so high that, if necessary, chains could still be inserted after the hollow girders had been assembled.
Construction phase
In May 1846 - long before the design of the box girders was finally finalized - the preparatory work and in September the construction of the foundations on Britannia Rock began. Since sheet pile walls were not used, work could initially only be carried out for a few hours at low tide until the rising tide at up to 4 knots washed over the work that had begun. 26 cable cranes powered by three steam engines were used for the work. In total, the masonry work took 2 years and 9 months. During this time, valuable experience could be gained on the Conwy Railway Bridge, which was built from 1846 to 1848 and planned by Stephenson according to the same system but was much smaller .
The box girders were made in individual sections that corresponded to the openings of the bridge. The shorter box girders over the bank slopes were built on site on falsework. They were still longer than any railway bridge at the time, with the exception of the Conwy bridge. The falsework, which in some places was up to 30 m high, represented considerable structures as such. The great fire hazard caused by handling the red-hot rivets was countered with extensive extinguishing devices. In fact, there were three small fires that could be extinguished quickly and easily.
The four box girders for the two main openings of the bridge each measured 144 m (472 ft) and were thus 4 m (12 ft) longer than the clear width between the piers. This length was made clear to contemporaries by means of a comparison: If the boxes were placed vertically next to St Paul's Cathedral , they would tower over the cross on the dome by 33 m. Three cast iron frames were built into the ends of the long box girders. The outermost one was supposed to stabilize the box when it was rested on two ibexes after manufacture, the other two were used to fasten the chains with which the boxes were lifted into their final position in the bridge. In total, each of the long boxes weighed around 1,800 t.
The hollow girders were built on wooden platforms on the bank, which were arranged between two ibexes and curved upwards in a slightly concave manner . After a box was completed, the platform was knocked out from under him so that his ends could lie freely on the ibexes. The box bent so far under its own weight that its bottom formed a flat surface.
The floating method had been tested on a model on which the distribution of the numerous lines, winches and rope brakes was determined in order to allow the pontoons with the box girders to slowly float with the tidal current to their place between the pillars. Stephenson had hired an experienced captain and some sailors to swim in. A total of around 650 men were involved, including 386 seafarers from Liverpool.
First, the floor under the finished boxes was removed so that eight pontoons could be pushed under each box. The large valves of the pontoons were opened so that the water of the rising tide could run into the pontoons and they would not create buoyancy. At the last ebb before swimming in, the pontoon valves were closed again. The rising tide then lifted the pontoons including the box girder until he could swim freely over the ibex. The actual swim-in started 1 ½ hours before high tide. The pontoons were pulled into the current, which was still running at 1.6 knots (almost 3 km / h), and brought to the intended place between the pier walls. The control of the unusual watercraft with ropes and winches went from time to time more routine after initial incidents. At the height of the tide, 15 minutes were available to position the box girders exactly between the pillars until they could be set down exactly on two protrusions at the foot of the pillars when the tide began.
Continuous niches were provided in the pillar walls from foot to tip that were wide enough to allow the hollow boxes to be guided in them during the lifting process. Hydraulic presses were installed on the pillars, lifting the box girders with several parallel chains made of 2 m long eye poles. Similar to a strand jack, the jacks lifted the eye rods by almost 2 m each. The eye sticks were then held in place with clamps while the grippers of the presses were lowered to start a new lifting process. During the lifting process, beams were continuously inserted into the niches and the niches were then filled with masonry. The hollow box could therefore only fall a few centimeters if the lifting device failed, which happened during the first lifting process when the cylinder of a press broke.
After the hollow girders were lifted into place and the smaller ones above the banks were completed, their ends, which were not always at the same height, were adjusted and connected in a complex process, so that the bridge finally consists of two long hollow girders with a length of 461.2 m (1513 ft) each weighing 5000 t.
The first rivet for the box girders was struck on August 10, 1847. In June 1849 the first box girder was floated in. The lifting process, which had been interrupted by repair work, was ended in October 1849. The second box girder was lifted in December 1849 without major incidents and was in its final place on January 7, 1850.
On March 5, 1850, Stephenson and his team drove three locomotives over the bridge for the first time. On the same day, a 503-ton train made up of three locomotives, 45 coal wagons and wagons with 700 people drove across the bridge. After further tests by the government inspector, the still single-track bridge was opened to public traffic on March 18, 1850.
The third box girder was floated in on June 10th and lifted into position the next day. The fourth and last box girder followed on June 25, 1850. The final opening took place in October 1850.
The bridge was equipped with temperature and expansion measuring devices, which continuously recorded the measurement data, which at the time revealed unexpected differences between the temperatures outside and inside the box girder and the metal itself, and showed the different expansion behavior when the sun came from one side or from above or even did not seem on the bridge. The deflections caused by storms were significantly smaller than expected.
1,500 workers were employed on the bridge, 700 of them masonry and 800 ironwork. At the construction site there was a camp for 500 workers with their families, which was equipped with shops and a school, and in which a pastor and paramedic took care of the well-being of the people. There were seven fatal accidents in the four years, a number that was considered very small at the time. The dead were buried in the nearby Llanfairpwllgwyngyll cemetery. An inscription plaque commemorates them there.
Stephenson's box girder system was only used once on the Pont Victoria in Montreal . After that, it was replaced by other construction methods such as the lattice girder and the truss girder bridge as too expensive .
Monument protection
In 1966 Stephenson's Britannia Bridge was listed as a Grade II building .
Destruction 1970
On the evening of May 23, 1970, two young people went about 10 meters into one of the railway tubes out of curiosity. In order to see more in the dark, they set a piece of paper on fire on the ground. Its flame set the tar paint on the sleepers and the metal construction on fire, the slight draft in the tube fanned the fire so that both tubes and the roofed space were quickly set on fire. The fire brigade did not succeed in extinguishing the fire. The hollow box construction had to be broken off due to enormous deflections. The stone pillars remained intact and were reused for the new Britannia Bridge.
Others
In Westminster Abbey is located in the north aisle of the choir a glass window with a medallion of Stephenson's Britannia Bridge.
The construction of the bridge (1971)
| Britannia Bridge (1971) | |
|---|---|
 |
|
| use | Railway + road bridge |
| construction | Steel arch bridge |
| start of building | 1971 |
| completion | 1971/1980 |
| planner | Husband & Partners |
In 1971 the Britannia Bridge was built with a new concept based on plans by Husband & Partners . Renewed by Cleveland Bridge & Engineering Co. The two main openings received a steel arch construction with a framework reminiscent of the Victoria Falls Bridge over the three load-bearing arched ribs, which are supported on concrete reinforcements of the original pillar foundations. The outer openings over the bank slopes were designed as a girder bridge with solid wall girders . The first train was able to cross the bridge again in 1971. As an additional innovation, a second bridge deck was built over the tracks, on which the A55 North Wales Expressway runs over the bridge with two lanes. This second bridge deck was completed in 1980.
literature
- A Resident Assistant: General description of the Britannia and Conway tubular bridges on the Chester & Holyhead Railway. Chapman & Hall, London 1849 ( digitized on Google Books )
- Edwin Clark: The Britannia and Conway tubular bridges, ... Volume 1, Day and Son, London 1850 ( digitized on Google Books )
- Edwin Clark: The Britannia and Conway tubular bridges, ... Volume 2, Day and Son, London 1850 ( digitized on Google Books )
- William Fairbairn: An Account of the Construction of the Britannia and Conway Tubular Bridges. John Weale, London 1849 ( digitized on Google Books )
- Francis Bond Head: High-Ways and Dry-Ways; or, the Britannia and Conway Tubular Bridges. John Murray, London 1849 ( digitized on Google Books )
- George Drysdale Dempsey: Tubular and Other Iron Girder Bridges: Particularly Describing the Britannia and Conway tubular bridges . 3rd ed., Virtue Brothers, London 1865 ( digitized on Google Books )
Web links
- Britannia Bridge. In: arch INFORM .
- Railways of North Wales 1975-1983: Britannia Bridge (English)
- Project Menai - celebrating the bridges over the Menai Strait (English)
- iCivilEngineer: Britannia Railway Bridge (English)
- Video of the fire
Individual evidence
- ↑ The information in this article is based, unless otherwise stated, on the description of a Resident Assistant: General description of the Britannia and Conway tubular bridges on the Chester & Holyhead Railway.
- ^ Karl-Eugen Kurrer : The Britannia Bridge (1846-1850). In: The History of the Theory of Structures. Searching for Equilibrium . Ernst & Sohn , Berlin 2018, pp. 70–73, ISBN 978-3-433-03229-9 .
- ↑ John August Roebling built the Niagara Falls Suspension Bridge, the first suspension bridge for rail traffic , from 1851 to 1855 .
- ↑ General Description, p. 10
- ^ Fairbairn: An Account of the Construction ... , p. 2
- ^ Fairbairn: An Account of the Construction ... , p. 3
- ↑ Fairbairn: An Account of the Construction ...
- ↑ See High-Ways and Dry-Ways
- ↑ Mr. Stephenson's report to the Directors of the Chester and Holyhead Railway . In: William Fairbairn: An Account of the Construction of the Britannia and Conway Tubular Bridges. P. 33
- ↑ The information in this section is based on the detailed description of the construction process in: Edwin Clark: The Britannia and Conway tubular bridges, ... Volume 2, p. 663 ff.
- ↑ Britannia Tubular Bridge, Pentir and Britannia Tubular Bridge (part in Llanfairpwllgwyngyll Community), Cwm Cadnant
- ↑ Eryl Crump: Moments that shocked North Wales: Britannia Bridge Fire - More than 40 years since teenagers accidentally set the bridge alight . Daily Post report of May 4, 2013
- ↑ Official fire report (English)
- ↑ Robert Stephenson . At Westminster-Abbey.org
- ↑ RW Husband: The Britannia Rail and Road Bridge in North Wales (United Kingdom)
- ^ Britannia Bridge on the website of Cleveland Bridge UK Ltd.
- ^ Samuel Halkett: Dictionary of Anonymous and Pseudonymous English Literature . Volume 3, Haskell House, New York 1926–1934, p. 38 ( digitized on Google Books )
