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Grosvenor Bridge

Grosvenor Bridge

A favorite pastime of mine when visiting other countries is to just walk in a direction and get lost. Cities are composed of so many different communities, landmarks, and secrets that you never know what you’ll stumble across on an afternoon stroll. And that’s especially true for London, in part because of how diverse and bustling it is, but also because it’s so huge I get lost constantly. Grosvenor bridge was one such discovery I made after wandering across the Thames, where I found this bridge among a blooming new community.

Structure Information

Grosvenor Bridge is a multi-track railway bridge crossing the River Thames between Abbot’s Manor and Battersea Park, just adjacent to Chelsea Bridge. Initially known as the “Victoria Railway Bridge”, this bridge was designed by engineer John Fowler and opened for the London Brighton and South Coast Railway in 1860 [1]. At the time, the bridge’s scope was much smaller, with only two railways running across it, built at a cost of 84,000 pounds (funded entirely by the railway industry). Since that time, the bridge has undergone many expansions and redesigns – the current crossing is actually a series of ten parallel bridges carrying ten railways across the river. Grosvenor Bridge is the widest bridge on the Thames, and one of the busiest rail bridges in the city, connecting up Victoria Station with the rest of the nation [2].

Historical Significance

At a first glance, this bridge is easy to look past. It lacks fancy decoration and seems simple in form, which doesn’t betray its deep historical impact on the city of London. This bridge was the first rail bridge constructed over the River Thames in London, which was a huge milestone in improving the rail connectivity of the city. The bridge was initially constructed of wrought iron arches, and its designer John Fowler was bound by tight design constraints. The bridge had to have a clearance of 22 feet for shipping traffic by water below. It had to feature 4 spans, with mid-river piers lining up with Chelsea Bridge to the west [3]. By this time, construction with wrought iron was not a new practice – the bridge was built without issue over the course of a year. However, the designer, John Fowler, would go on to be one of the most influential rail engineers in London, growing the early London Metropolitan Railway, developing tunneling technology, and working with Benjamin Baker on the Firth of Forth Bridge in Scotland [4]. This bridge really was a starting point for his revolutionary career with trains!

Additionally, this bridge design was used as a template for further expansions of rail crossings at this spot on the Thames. As capacity increased, additional adjacent river bridges were constructed in similar design, and simply connected via deck to the original. It wasn’t until 1963 that the bridge underwent major renovations, mainly due to increased train loads and deterioration. The bridge continued on with its four-arch design for aesthetics and practicality [5], and kept consistent with history in that the bridge is really designed as 10 separate bridges able to carry 10 tracks. During reconstruction, it was necessary to keep 8 tracks open for use along this high-volume bridge – so each bridge and track was replaced one at a time and added to the expanding new Grosvenor Bridge, which is why the tracks and arches were kept relatively separate.

Cultural Significance

As previously mentioned, this bridge was one of John Fowler’s first landmark projects during his career in bridge design and railway work. As the first bridge in London to allow train passage across the Thames, it truly was a pioneering structure, if not in form than in purpose. By looking at a history of its widening, the history of railway expansion in general comes to light. As rail gained speed in London, so did this bridge gain width. Especially today, this bridge remains busy transporting people around the country – so busy that not even structurally integral construction to renovate the bridge in 1963 could halt its traffic.

Nowadays, the bridge serves a further social purpose to compound on its economic providence to the area. The southern end of the bridge meets with the Battersea Power Station. This region of London is an up-and-coming neighborhood situated around a large power station reaching up along the riverside. This structure was what allured me to the area to begin with – my curiosity of the construction zone led me to finding a hip residential area with plenty of new restaurants and hang-out spots. Grosvenor Bridge’s southern end meets the boundary of this place, and the community has begun to integrate this old bridge into new life. Below the bridge runs the Thames Path, a popular walking route connecting up neighborhoods and parks along the River. This tunnel running beneath has turned into quite the social scene: pop-up restaurants, ping-pong tables, and relaxing residents can all be found here. Grosvenor Bridge is becoming popular part of this new scene, adding to its importance here in London.

Structural Art

Now comes the difficult task of assessing the Grosvenor Bridge and its place as structural art. Based on the current structure of the bridge, I have decided it to be a good example of structural art, especially when examining it as a renovation of previous form.

The 1963 reconstruction of the bridge constructed the arches as steel-box girders connected to an orthotropically stiffened steel deck through slender spandrels [6]. Orthotropic steel decks, a relatively new concept at the time, strengthen the deck against the vehicular loads above by resisting bending. This results in lighter forms allowed in supporting the bridge. Despite efficiency increases in the 100 years between construction and renovation, essentially the same bridge design was used. This could be seen in two lights – one that conserves cost by utilizing existing piers, or one that fails to innovate given an opportunity.

Economically, the bridge’s continual expansion over the years became very costly. The most recent renovation from 1963 to 1967 was long-winded and expensive due to the continued use of railway above. However, the new integration of stiffened steel decks and hollow steel box arch supports required relatively little material to be used. Additionally, the fact that this is 10 separate bridges in essence reduces the material needed to support each segment of the bridge.

Elegance is where the bridge seems to lack the most. The bridge doesn’t come across as a complete structure, and in reality, it isn’t – this is a crossing consisting of 10 bridges joined at the same piers. Additionally, despite being a fairly modern bridge, it doesn’t look it. The bridge relies on the same design as the original back in 1860, failing to show off too much new in the ways of bridge forms. However, the simplicity of design and openness of the structure really do shine.

Structural Analysis

This structure is interesting to analyze because the deck is disconnected in a way such that each individual track is supported by an individual bridge structure yet also connected by the same concrete piers. Each of the 10 possible tracks is kept separate, rather than acting as one individual structure. This really simplifies analysis on the bridge, since only one live load can exist on each structure at any time, and each structure is essentially a copy of the next. Also fortunate is that dimensions of the truss structure itself are known, and other loads such as that of the deck and trains can be reasonably assumed.

As stated before, the structure is composed of 4 arches spanning over the river, connected to concrete piers above. Each rail bridge is connected to two arch spans supporting it on the sides. These arches are hollow steel box girders measuring 1.13 (3.7 ft) meters tall by 0.61 (2 ft) meters wide, approximately 0.1 feet thick, pin connected to the concrete piers and supporting the orthotropically stiffened steel deck above via tubular steel spandrels (which appear to be approximately 0.5 ft in diameter). The arches each have the same clear span between piers of 50 (164 ft) meters. Each arch connects to the bridge deck with eight slender spandrel columns symmetrically spaced and at the apex of each arch. The rise of each arch is 5.4 (17.6 ft) meters. Each rail bridge deck segment is approximately 5.4 (17.7 ft) meters wide, and plan views show the deck thickness to be 5/8″ ft. These measures give a good idea as to the dimensions and can help determine forces felt in arch members under load.

This bridge acts essentially the same way any arch bridge would: the dead load of the bridge deck and live load from crossing trains is transferred downward via the steel spandrels and center connection to the arch tube. Each spandrel is designed to transfer load from its individual tributary area and does so through compression forces. These loads are transferred to the arch through compression forces, moving down to the ends of the arch and finally into the concrete piers supporting the bridges. There are two arches, so the overall load to be carried is split in half.

Idealizing the bridge as a distributed load including deck weight  and both arches acting as support, the bridge can be described as below:

Because of even areas, the load distributed to each arch is similar. For the center three concrete piers, the horizontal forces of the archways cancel out, resulting in only a vertical resultant force. The end piers do have to support horizontal loads produced by the arches. When a live load (train) is introduced on the deck, more horizontal loading occurs. I will be analyzing the reaction and member forces in one arch span. Construction documents specify the deck to be of mild steel, which has a density of 0.284 lb/cu. in, or 490.75 lb/cu. ft. Using a single span length this results in the deck weight being 890,343 lb. Assume a passenger train load weight of 200,000 lb, resulting in a total vertical load of 1,090,343 lb. Due to symmetry, the vertical reactions on each side of the arch are the same, so each end has a vertical reaction force of 545,172 lb. To find the horizontal reactions at each end, cut at the arch center and take the moment about the center of the arch. (Distributed load [-6648.43lb/ft]*82ft*41ft) + (Vertical reaction [545,172lb]*82ft) + (Horizontal reaction *17.6ft) = 0. This equation results in the horizontal force being 1,270,003 lb, acting inward towards the arch. This exists on both sides. The force in the steel box member then would be 1,382,071 lb, or since in the actual bridge there are two arches supporting each deck, a member force of 691,035 lb. Further, the member stress can be calculated by dividing this force by its area (found to be 0.56 square feet), which gives the result of 8,569 psi.

Personal Response

Along the River Thames, communities are growing, and Grosvenor Bridge has not been left out. Below the bridge, families take walks and friends play ping-pong. Above the bridge, trains cross the river carrying passengers away. This structure plays a large role integrating into the community today, and it holds great importance in the history of London as the city’s first rail bridge to cross the Thames. There is more to Grosvenor bridge than meets the eye as I discovered through my research. Even its simple form goes further than surface level, being truly one bridge composed of 10, increasing the efficiency of its design and paying homage to its long history of expansion and heavy use. When first approaching this bridge I did not expect it to be significant. It felt basic from a distance. Only when examining it closer did I come to appreciate this simple arch bridge more for what it was and is.

References

[1] http://thames.me.uk/s00160.htm

[2] https://londonist.com/london/transport/9-secrets-of-the-grosvenor-railway-bridge

[3] http://www.semgonline.com/structures/struct_34.html

[4] https://www.britannica.com/biography/Sir-John-Fowler-1st-Baronet

[5] http://www.engineering-timelines.com/scripts/engineeringItem.asp?id=697

[6] http://happypontist.blogspot.co.uk/2011/06/london-bridges-8-grosvenor-railway.html

Comments

  1. slowentritt3 says

    It’s so interesting that this bridge went from 2 tracks to 10 tracks and that the original design was kept up. I like that you were able to find out that the bridges are pretty much separate except for at the foundation. I also like how you found the stress in the members in your analysis.