The Southwark Bridge

Walking along the Thames River during the Walking Bridge Tour in London, I encountered so many bridges–10 to be exact–that I was slightly overwhelmed. Although I love bridges and I encountered many different types, I choose to research a bridge that is less known and even less used–the Southwark Bridge.

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Figure 1: Southwark Bridge

Structure Information

The Southwark Bridge lies on the Thames River like the many other bridges in London. This bridge can be seen as one of the older ones and even then, another bridge existed before the Southwark Bridge was constructed. The older existing bridge was known as the Iron Bridge and it was constructed to alleviate congestion as London and the existing London Bridge was getting extremely congested. This bridge had its construction commence in 1813 and finish in 1819. It was a toll bridge. Just the mention of a toll bridge made the residents not want to use this bridge and return to using the London Bridge near by. After demolition of this old bridge, the new bridge, now known as the Southwark Bridge, was rebuilt from 1913 to 1921. This new Southwark Bridge, which will be referenced as just the Southwark Bridge, was built to be stronger and wider than its predecessor without the use of tolls later on. It still fulfills the purpose the bridge was originally designed to do: alleviate the traffic and congestion due to growth in the city of London while getting ride of the negative aspects of the old, Iron Bridge. It linked the Upper Thames Street to the other side of the Thames River, or the city part. Specifically, the south end sits near Museums and tourist areas while the north end sits near the Cannon Street Station. The bridge was designed by a combine effort of architects, Ernest George and Alfred Yeates and engineer, Basil Mott. The contractor was Sir William Arrol but the bridge is owned by City Bridge Trust, a charitable trust run by the City of London Corporation.

Historical Significance

The Southwark Bridge was built in place of the old Iron Bridge that was demolished at the time of World War I. Although it does not have many innovative and striking characteristics, it has adapted to attain the best characteristics of the old bridge and has achieved a few standards for its time. The Iron Bridge was made to be the longest spanning cast iron bridge in London with 3 separate arches placed across the river. Innovation can be seen in this old bridge as the material of that time, cast iron, was used to attain an engineering structure that was large and vast. On the other hand, Southwark Bridge was not built along those lines or even as an innovative idea. Steel arches were constructed and steel plate girder ribs were used. It was built to fulfill the purpose of the old bridge and used materials and construction methods that were expected of its time. Nonetheless, 2 facts can be noted. Firstly, in order to assist with the painting process, 1,000 tonnes of expandable abrasives were put on the bridge to attain the original metal framework. Secondly, 13,000 liters of paint was used to maintain the color of the bridge: the yellow and the green that can be seen from far away. This emphasizes the metal work and the importance of it. Again, the emphasis here is the lack of innovation in the engineering design and construction method used as this bridge was added as a replacement of a previously functional bridge.

Contrary to being an example or model for future buildings, the Southwark Building was in competition with the surrounding bridges–one of them being a similar bridge, the Blackfriars Bridge. It was built after this bridge and has a very similar appearance and form. Also, it should be noted that the piers of the Southwark Bridge aligned with those of the Blackfriars Bridge for ships and water vehicles to better flow through. In conclusion, the Southwark Bridge does not stand out as being a breakthrough structural engineered structure for the materials and processes it used but also because it followed other modeled bridges than becoming a model itself.

Southwark Bridge 1829

Figure 2: The old, Iron Bridge

Cultural Significance

There are less details behind the construction process and time of when the bridge was built so there are no facts to state the human cost or the number of deaths both while the bridge was being constructed and after it was built.

At the south end, there is the city of Southwark that is both quiet and not as well-known as some of the other areas. Therefore, there are no historical stories or events that characterize this bridge. However, popular culture has some link to this bridge. Some films have either been filmed at the site or have made referenced to it. For example, Charles Dickens references the Southwark Bridge in Little Dorritt and Our Mutual Friend not once but many times. The bridge has also appeared in films like Harry Potter and The Order of the Phoenix or Mary Poppins. It seems as though the location has been chosen due to the area being connected to London and the lack of population on the streets rather than the actual marvel of the bridge.

The Southwark bridge stands as being the least used bridge along the Thames River. It is not because the bridge is disliked but rather, it was a tolled bridge with narrow and steep lanes that made it inconvenient to use. The residents used the London Bridge that was close by. Also, it should be noted that the bridge runs through a quiet area while the London Bridge ran through a major road within the city. These reasons made the bridge less popular than it was intended to be but it should not be characterized as a bridge that is disliked. Now, the bridge is one of the quietest bridges connecting the two areas at the ends of the Thames River with only one-fortieth of the traffic from the other bridges but still allowing people and cars to cross it.

Structural Art

The decision of the Southwark Bridge being structural art will be made by me using the 3 E criterion.

Firstly, the bridge is efficient to a small extent. The load path can be seen clearly. However, there are some members that are either too heavy-looking or have no structural purpose. I am making reference to parallel ribs where it does seem a bit discontinuous. Less material could have been used to have an as efficient structure but I do realize that indeterminate structures are usually safer and preferred. In conclusion, the bridge is not as efficient due to the complexity that can been seen in the structural members.

Secondly, the cost of the project was about 2.5 million pounds. Other than the process of repainting, no major rehabilitation efforts were put into place. One more point should be noted: even after facing material shortages, the bridge was finished. Therefore, the economy of this structure is reasonable and can be considered an advantage.

Lastly, the elegance of this bridge is more of a personal opinion. I do not think that the bridge is very aesthetically pleasing of this time and generation and has a very heavy-structural feeling associated with it. It could have been considered to be aesthetic and elegant during its time. However, I do not classify this bridge as being elegant in comparison to the other bridges surrounding it.

In conclusion, this bridge does not classify as structural art. Nonetheless, I do not want to undermine its functionality and the purpose it fulfills.Image result for southwark ugly bridge

Figure 3: A very dull image of the bridge

Structural Analysis

Although there is lack of information about both the construction process and structural systems implemented, the Southwark Bridge will be analyzed below using engineering techniques.

Starting at the foundation, there are granite piers and turrets on each side of the arches that sit in the water. The piers can be seen to be slightly heavy and elaborate due to the time they were built: before the start of the War. They were designed by Sir Ernest George. 5 steel arches span over the Thames River: 2 spans of each being either 45 meters or 48 meters rest on the side and the 3 middle spans that are known as the central spans with length of 73 meters. These particular dimensions were designed for the span to match and align with the Blackfriars Bridge and The London Bridge. This would allow vehicular traffic on the waters to flow easily and smoothly. The arch system has specifically 7 arches layered underneath and attached by metal fixtures to make sure it would not bend. Then, each arch has parallel and vertical steel rods to allow for the loads to freely flow.

The bridge has two particularly complex and slightly hidden structural systems other than the ones that can be seen such as the deck, piers, etc listed above. Firstly, it is the layer of 7 arches underneath the deck. They are spaced out so that the inner 5 get the most load through them (based on their rectangular tributary area) while the arches on the outer sides get the least loads due to their smaller tributary area. Secondly, trusses within the system of arches are used for bracing and greater stiffness of the bridge. Although not visible clearly, the arches are connected through these rectangular and crossing sections.

Image result for southwark bridge deckImage result for southwark bridge

 

Figure 4: The 7 arches underneath the deck and the vertical rods

The load flows through the bridge from first the deck where all the loads are typically acted upon. The loads are then transferred to the vertical rods down to the arch. From there, it flows from each side of the arch to the nearest pier. As can be seen in the figure below, half of the loads flow to the left pier and half flow to the right pier. This load then flows into the piers and then into the foundation and the ground. And, that is how a bridge will transfer loads acting upon it into the ground.

Figure 5: Load Path on Southwark Bridge

The middle arch of the Southwark Bridge will be analyzed in the section below. I am looking at just one arch because when looking at the entire bridge, it acts like an indeterminate structure. Also, once one arch is analyzed, the others have a similar behavior.

Figure 6: Arch Free Body Diagram

I assumed that a uniform load of 5 Kilonewtons/millimeter squared or 105 pounds/feet squared was acting uniformly across the bridge deck. This was retrieved from an European engineering website which suggests typical loads on a short-medium span bridge. This value was multiplied by the thickness or in this case, the width of the bridge to get 5880 pound/feet which is the value as can be seen in the figure above (measurement per linear foot). From here, the vertical reactions at the base of the arch were calculated solely from statics. As can be seen from the symmetry of the Arch, the reactions at both points are equal to each other.

Figure 7: Calculations

Now, to calculate the horizontal forces, or the thrust enforced by the Arch, a cut was made at the middle. This cut allows an internal tension force to appear as seen in the figure below.

 Figure 8: FBD of Cut Arch

The horizontal reactions are calculated using a Moment equation.

Figure 9: Calculations of the Arch

Although the values do not reflect this, it can be seen that all the arches are in compression. The vertical forces are carried or held down by the piers while the horizontal forces, or the thrusts are cancelled out by each arch next the one being looked at except the arches at the ends. These arches at the end have their thrust force taken by abutments which are placed at the ends of the bridges. In all, the forces are calculated for the arch to see how it behaves and the overall behavior can be understood too. One more note should be made: to simplify the calculations and the results, a uniform load was considered. However, bridges are acted upon by combinations of dead, live, point, uniform and dynamic loads.

Bridge House Estates operates the City Bridge Trust which was used to build the Southwark Bridge. This Estate as well as all the stakeholders (engineers, architects, construction team, etc.) that were involved in the construction process of the bridge used drawings–newly rendered ones as well as inspiration from the old bridge to communicate the design on the bridge.

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Image result for southwark bridge drawing

Figure 10: The Iron Bridge vs. The Southwark Bridge

Personal Opinion

While standing near the bridge and taking pictures of it, I realized that the bridge does its job extremely well. It links two sides of the Thames River to allow for greater accessibility. Sure, it’s not the most eye-pleasing bridge like the 9 other bridges in its vicinity. Nonetheless, it’s a cool bridge that has peace due to the lack of people walking or driving across it. I would also like to admit that I felt particularly sad or empathetic towards it due to how it is seen by others. We should definitely give credit to this Bridge– after all, it still glows at night!

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Figure 11: The Southwark Bridge at night

 

References:

http://eurocodes.jrc.ec.europa.eu/doc/WS2008/EN1991_8_Calgaro.pdf

https://web.archive.org/web/20131215153238/http://www.southwarkbridge.co.uk/project

https://www.bristol.ac.uk/civilengineering/bridges/Pages/NotableBridges/Southwark.html

http://www.engineering-timelines.com/scripts/engineeringItem.asp?id=667

http://www.southwarkbridge.co.uk/history/old-southwark-bridge.htm

https://historicengland.org.uk/listing/the-list/list-entry/1385913

http://www.towerbridge.org.uk/about/bhe/

 

Cannon Street Railway Bridge

On our bridge tour today, the tour guide pointed out a low slung greenish bridge and began expressing his dislike of its “ugly” appearance. This made me feel like the Cannon Street Railway Bridge deserves some love so I was determined to analyze. The visible brute strength of the thick columns and flat spans caught my attention as it is clearly designed for massive railway loads rather than car or pedestrian passengers like other London bridges.

Figure 1 – Cannon Street Railway Bridge from South Bank

Structure Information

The Cannon Street Railway Bridge was built from 1863-1866 by the South Eastern Railway Company (SERC) and designed by Sir Joh Hawkshaw, a famous English Civil Engineer. The SERC was in control of the rail lines to the London Bridge Station and wanted to expand the lines over the Thames in order to reach the Northern half of London, so they initiated the design for this bridge to the Cannon Street Station [1]. In order to carry a greater capacity of trains, the bridge was widened from 1886-1893 by adding a column on each side for a new total of six (from an original of four) and more decking on top. The bridge was strengthened from 1910-1913 in order to bear heavier trains and strengthened again in 1983 to account for both greater loads and general wear and tear [2].

Historical Significance

The simply supported beam bridge is the oldest and simplest type of bridge, and although the Cannon Street Railway Bridge doesn’t innovate in form it is unique in its massive appearance. With three spans of 45m, numerous thick columns, and 2.6m deep iron girders the bridge clearly looks capable of carrying the 10 rail tracks laid on top of it [2]. It was one of the first rail bridges over the Thames and the only one located in the Eastern part of London and as such a very important connection point in Victorian London as well as today, but it is not a model for modern railway bridges, nor the best example of a period bridge.

Cultural Significance

The bridge remains a very important railway link over the river Thames and helped bring development to the East side of the city when it was built, as this area was mostly still low income housing with little value. As it is almost entirely used for rail traffic and is not a very beautiful bridge it has never become a cultural symbol or tourist attraction. In fact many citizens of London actively criticize its appearance, and our tour guide today related the story of how it was originally going to be named after Queen Victoria, but she disliked its appearance and had them drop that name. In August 1989 two boats collided right next to the bridge in a tragic accident that caused 51 deaths and led to new lifeboat stations at the sides of the bridge [3]. After expansion and two strengthenings over the last 150 years, the bridge is still used today to transport massive amounts of commuters and tourists around London.

Figure 2: Cannon Street Bridge Looking Eastward to Tower Bridge

Structural Art

The three principles of structural art are: Economy, Efficiency, and Elegance. This bridge is most certainly not elegant as Billington would define it. Although the load paths are as simple as possible and clearly visible (bridge girders to columns to ground), the structure could never be seen as “light” or “graceful”. To me the bridge does not fulfill the category of elegance, even though I personally like the stolid appearance and appreciate the unique appearance of the thick repeated columns. When it comes to being efficient, it is difficult to create a beam bridge with massive railway loads that uses a minimum of material when using iron girders and concrete foundations. An arched bridge could have reduced the material usage and added elegance, so I don’t believe that the Cannon Street Railway Bridge fulfills the principle of efficiency either. For economy however, the materials (concrete and iron) were cheap and easily procurable as well as being inexpensive to build with at the time. The wrought iron girders in the bridge deck are all the same size which made production cheaper, these factors together allow the bridge to fulfill the economic principle of structural art. Overall, by hitting only one of the three principles, the Cannon Street Railway Bridge is certainly not structural art, but that doesn’t mean it is not a useful and functional bridge, and I personally like it a great deal.

(The following paragraph written after doing Structural Analysis, skip ahead then come back so it makes sense…)

After calculating just how massive the loads that each beam and column can take, I’ve reconsidered the efficiency of the bridge. This bridge is so redundant and overengineered that I can no longer think of it as efficient. The only possibility is that its so strong to deal with scour, but even that seems unlikely to me. This bridge is definitely NOT structural art!

Structural Analysis

The major construction materials used are iron in the girders (wrought) and the exterior of the columns (cast), and concrete in both the columns and the beam right above lateral beam right above them. There is also masonry and brickwork as the bottom foundation, and construction was began by digging small caissons to the bedrock under the Thames and building these foundations. The original four concrete columns were then poured to about the water level, where the fluted cast iron exteriors were placed and then filled with concrete. Originally the bridge did not have the tapered concrete rings at the top of the columns, these, along with one column on each side (new total of six) were added in later retrofittings. The long wrought iron girders were then transported to the site (most likely by barge) and lifted by crane onto the supports, then riveted together. Finally decking, railings, and rail lines were added to the top to complete the bridge. The bridge has three major spans of 45m and two approaches of 39.6m, the plate girders are 2.6m deep and thick I-beam shaped. The concrete columns, assuming same river depth as at London Bridge, are about 13m tall, and from visual comparisons with the known 2.6m depth of the girders, are around 3m in diameter.

Figure 3: Looking Up at 18 Iron Girders

The Cannon Street Railway Bridge is a simply supported beam bridge without any fancy arches or trusses, all strength and stiffening are directly from the girders in the deck. Load from self weight and live load from trains is transferred directly from the beams into the huge columns. There are no wind airfoils on the side of the bridge, but it has a small cross section, very stiff deck, and extremely strong supports without a long span so wind load has very little effect on overall design or performance. The bridge faces scour from the Thames, but there are no angled diversion bases around the column bases as they are curved and heavy enough to withstand massive lateral forces. This bridge looks so massive that it would take gigantic live loads to cause collapse, but the three possible sources of failure are: tensile yielding in the girders due to bending in the middle of the spans, bearing stress crumbling at the contact point between deck and columns, and buckling in the columns.

To calculate the max bending stress I first found the volume of a single beam over the longest span (45m) assuming a symmetrical cross section with a flange depth of 0.1m, flange width of 0.5m, and web width of 0.2m. The cross sectional area with these measurements is 0.62m^2, and the total volume per central span per beam is 27.9m^3. Using a density of 7.7g/cm^3 for wrought iron from the internet, the weight of a single girder is 214,830 kg and the self load de to weight is 4,774 kg/m. These are very conservative (high) estimates for the weight per beam. Next I used the formula of stress = My/I, where M is max moment, y is max distance to the edge from the centroid, and I is the moment of inertia. Y is 1.3 meters assuming a symmetric girder, and I calculated the moment of inertia to be 0.386m^4. Then to calculate maximum moment, I know that the max bending moment of a simply supported beam with uniform distributed load is w(L^2)/8. I decided that the max bending moment would be the tensile strength of wrought iron which is 160MPa, so I needed to calculate the max train load that the span could support per beam (of which there are 18). So my equation was: 160MPa = (4,774 + T)*(L^2)/8 using superposition where T is the distributed train load on 1 beam. Using this equation the max train load comes out to be almost exactly 183,000 kg/m which is ludicrously high for passenger trains, and shows the deck to be in no danger of collapse due to bending stress.

Figure 4: Distributed Train Load Calculations and Bending Stress Diagram

To calculate bearing stress I found the surface area of the columns, which have a diameter of approximately 4.5m at contact. This gave a bearing area of 15.9m^2, and as there are 18 beams, approximately three of these would be on each column, and I’ve already estimated the weight of a 45m section of beam to be 214,830kg. This means that each column will need to bear the self weight of the deck of 644,490kg along with additional live load from the trains. T find the max live load of the trains before crumbling I used stress = F/A where stress is the compressive strength of concrete which I found online as 25MPa. This gives the equation: 25*10^6 = (644,490 + T)/15.9 where T is now the total train weight on the tributary area (rather than the distributed train load). This gives a final answer of over 395 million Newtons which is PER COLUMN. That’s actually crazy high and basically unachievable for such a small space (the heaviest train ever was three times the necessary force, but over almost 10km) so the bridge is safe from crumbling.

Figure 5: Load Paths all Channel into Columns

Finally to calculate the critical buckling stress of the columns I used the equation: P= (pi^2)*E*I/(L^2). To calculate E (modulus of elasticity) I used the ACI code formula: E = 4700* sqrt(C) where C is the compressive strength of concrete (I used 25MPa just as before) and found E=23500MPa. I calculated the moment of inertia of the column using D=1.5m (ignoring the upper concrete collar) to find I=3.98m^4 and used the length of 13m as stated before. This gives another comically massive final answer of 8793.8 MegaNewtons/m^2 PER COLUMN!!!!!! No train could fit that into the 45m long tributary area, this bridge is crazy overengineered.

Honestly I have no idea how they pitched such a ridiculously strong bridge to the shareholders, I think they just asked for a permit to build any bridge from Parliament and then Hawkshaw went wild. Crazy stuff, maybe my assumptions of size of members was off, but I’m pretty sure they were close….

Personal Response

The first time I saw the Cannon Street Railway Bridge I just walked past it because it looked so lackluster compared to the other bridges (same for London Bridge to be honest). Once we looked at it on the tour I wanted to give it some love because it seemed so neglected, but now that I have analyzed it my opinion has changed. At first I appreciated the bridge because of its strong and thick appearance, but once I realized just how wasteful it is I no longer appreciate it as much. It seems almost sacrilegious (maybe too strong of a word) to make something so bulky and inefficient when there are structural art options available.

 

References

  1. http://www.engineering-timelines.com/scripts/engineeringItem.asp?id=665
  2. https://www.bristol.ac.uk/civilengineering/bridges/Pages/NotableBridges/CannonStreet.html
  3. http://www.bbc.co.uk/news/uk-england-london-28839099

Lambeth Bridge

Structure Information

The Lambeth Bridge was constructed in 1932 across the Thames River between Westminster and Lambeth. See Figure 1.

Figure 1: Lambeth Bridge Area

This connection was initially necessary because there was a house of the Archbishops of Canterbury at Lambeth that needed to be constantly connected to the King’s palace at Westminster [2]. Initially the Archbishop made the passage across the Thames by barge, then later by ferry. The church bought the ferry so the Archbishop and his goods and servants could travel across freely [2]. The Ferries were taken out during the civil war, so no intruders could pass the Thames this way, but later ferries were returned as a mode of transportation across the Thames [2]. Bridges were proposed as early as 1665. In 1750 the Westminster Bridge was put in very nearby, ending Lambeth Bridge proposals until 1809 [7]. The new Westminster Bridge also ceased the operation of the Archbishop’s Horseferrry, as it was in poor condition and now unnecessary [3]. From the 1809 Lambeth proposal, nothing happened until the Lambeth Bridge Act in 1861, for a toll bridge to be put up [4]. A suspension bridge was eventually selected and opened in 1862 as an 828 foot long, three-span bridge [2]. The old bridge can be seen in Figure 2.

Figure 2: Old Lambeth Bridge

Less than 20 years later, the first Lambeth Bridge was falling apart. The bridge was progressively closed to vehicles and later to people [3]. The current Lambeth Bridge was proposed but delayed by the 1914-1918 war [2]. In 1924, Engineer, Sir George W. Humphreys, and the architects, Sir Reginald Bloomfield and G. Topham Forrest, designed the bridge for King George V and Queen Mary [2&3]. The bridge cost about 80,000 pounds and was fabricated and put up by Dorman Long & Co Ltb in 1932 [4]. See the new bridge in Figure 3.

Figure 3: Lambeth Bridge

Historical Significance

            In 1932, the current Lambeth Bridge was opened, made of steel and pre-stressed concrete [3]. Steel caissons were used to make the piers [4]. This caisson technique along with other details of the construction and design process can be seen in the similar predecessor of the Lambeth Bridge, the Westminster Bridge. The Lambeth Bridge was a common bridge of its time. The bridge itself did not have any major innovations about it and, therefore, was not a model for the future.

In 1965, however, the Lambeth Bridge became the first bridge in London to be tunneled under, making it the first bridge in London that could be walked under [1]. This provided pedestrian access along the embankment, which was not available as it is today. This tunnel and idea of pedestrian use of the embankment sparked the plans for the Albert Embankment to be used as the bustling pedestrian city spot we see today.

 

Cultural significance

Sections of the Lambeth Bridge are painted red to signify the seats in the House of Lords and pylons were added on each end and topped with stone pinecones or pineapples (there is debate over what is represented)[3]. The Bridge Tour guide insisted they were pinecones, a representation of hospitality, but many believe they are pineapples as the Garden Museum is just over the bridge with reference Christopher Columbus whom is known for bringing pineapples to London and presenting them to royalty. To this day, the pineapples/ pinecones cause debate throughout London. Look at Figure 4 and see for yourself!

Figure 4: Pinecones or Pineapple?

Another argument caused by the bridge is less playful. The ferry operators remaining were very opposed to the construction of the bridge. This opposition was to the original Lambeth Bridge, not the one currently standing. The new Lambeth Bridge was well reciprocated because the old bridge was dilapidated and unusable. Luckily, the old bridge caused no injuries or deaths as it was closed before any extreme damage. The new bridge re-opened the pathway across the Thames to cars and pedestrians, helping disperse traffic. Crowds flooded the streets for King George V’s procession, officially opening the new Lambeth Bridge as seen in the video and art piece below [12]. The celebration was so grand it even inspired art, like that in Figure 5.

Figure 5: Grand Opening Inspired Art

Today, the bridge serves the same traffic purposes for cars, busses, bikes, and pedestrians. The increasing traffic, however, has ranked the Lambeth intersections among the top 75 most dangerous in London [11]. A woman on a bike was recently killed in an accident at one of the Lambeth roundabouts. The Lambeth Bridge is soon to be overhauled with safer bike lanes and newly designed intersections [11]. The 12 million pound project is a part of London’s goal to have 80% of people travelling in London to be on foot, bike, or public transit by making the roads safer to travellers [11]. This new project will hopefully make travelling across the bridge a better and safer experience.

The Lambeth Bridge has also been used in a few major films recorded in London. Examples include Harry Potter and the Prisoner of Azkaban, when the Knight bus rescues Harry from a bad holiday with the Dursleys it speeds over the bridge; in Fast and Furious 6, the bridge is used for a view of “Moscow”; and in The Foreigner with Jackie Chan, a bus exploded on the bridge [1]. The Jackie Chan film explosion of a bus caused panic throughout London.

 

Structural Art

            The Lambeth Bridge could hardly be considered structural art. The load path of the bridge is slightly visible through the side panels and from various angles, but is not clear. The Bridge is carried on granite-faced reinforced concrete piers and abutments [4]. The side panels and granite hide the elegance of the structure. Granite facing also adds unnecessary material and requires a stronger structure, taking away from the efficiency of the structure and requiring more expensive structural support. The tall obelisks located at either entrance are solely for aesthetics, adding more to cost. The attention to aesthetics also adds to cost in the metalwork and painting added to the structure. The exposed truss structures that make the light posts, if no small metal decals were attached, could be considered structural art. Overall, the structure does not satisfy any of the 3 E’s and therefore clearly cannot be considered structural art.

In regards to the three S’s of structural art, the Lambeth Bridge presents a bit better. As explained in the cultural significance section, the bridge is clearly very symbolic of its era. The symbolism of the bridge is mostly achieved by aesthetic decals and details added to the structure. The structure itself symbolizes the older designs of its time, so it is not so much structurally symbolic. Scientifically, the Lambeth Bridge does not have any breakthrough innovations. As a “basic” bridge for it’s time, there is no truly scientifically significant details about the bridge itself. Socially, however, the bridge is very influential. From the huge parade and celebration of its opening and connecting two sections of the city and therefore two communities to supporting green transportation, the Lambeth Bridge clearly satisfies the social aspect of structural art. Even though the Lambeth Bridge does better with the three S’s, it still cannot be considered structural art, as it does not satisfy all three S’s.

 

Structural Analysis

Lambeth Bridge is a five span, steel arch structure, carried by reinforced concrete foundations [4]. Steel caissons were used to make the piers [4]. The caissons were dug to the ground and the reinforced concrete foundations were put in place. The steel arches and supports were attached with pin connections, followed by the addition of the reinforced concrete deck and design features. The Lambeth Bridge was constructed very similarly to the Westminster Bridge, which was nearby, and many other bridges of its time.

I will be analyzing the repeating arches and their reactions at the pin connections with live and dead load. The total length of the bridge is 236.5m, with a 50.3m center span, surrounded by two 45.4m spans, and two shore spans of 38.1m [4]. Each span has 9 ribs supporting the reinforced concrete roadway above. See Figure 6.

 

Figure 6: Under the Bridge

The arches are all two-hinged with pin connections. There is a 60’ span on top of the bridge in reinforced concrete. I am assuming the concrete is 12” thick and using a live load of 640lb/ft, that of a truck [9]. By using this live load the bridge reactions will be for worst-case scenario. Reinforced concrete weighs about 150lb/ft^3

Clearance Per Arch in meters [8]

Lambeth 3.1 5.0 6.3 5.0 3.2

 

Load path

The example dead and live loads are observed as a constant force per linear foot. The load is carried from the deck, along the arches into the caissons to the ground. If these were repeating arches of the same height and width, the horizontal loads would cancel except for those on the ends. The horizontal loads do not perfectly cancel in the repeating arches, because they vary in size. This requires abutments to absorb the extra load on the ends. See the load path in Figure 7.

Figure 7: Load Path

Arch Calculations

Tributary Loads, because the beams spread evenly to the edges of the bridge:

Inner: 60’/8 sections

Outer: 60’/(8 sections x2) *because each outer only takes half a section

See the calculations in Figure 8.

Figure 8: Calculations

My calculations show a very simplified version of the calculations necessary to design the foundations and abutments of the bridge. With the reactions at each joint, the load needing support is known and can be designed for.

Design drawings depicted detailed plans for the Lambeth Bridge to the stakeholders and to the construction workers. Calculations were used to show how the load was distributed into the ground via the abutments and piers and caissons. A model for this bridge working was the similar Westminster Bridge adjacent to the Lambeth Bridge. Because of Westminster’s similar design and construction techniques, it acted as standing proof or a full-scale model of the Lambeth Bridge.

 

Personal Response

I never realized how truly necessary having so many bridges was to London. By walking to and across my bridge, I saw the traffic flowing across it and the surrounding bridges. The Lambeth Bridge is a relatively heavily trafficked bridge, and there were cars and pedestrians crossing, on a Bank Holiday at that. Additionally, on the map the bridge seems very distant from Westminster Castle and the Archbishop’s home, however, upon walking, I saw that the bridge arrives just at the Victoria Tower Gardens of Westminster and the Archbishop’s home.

 

References

[1] https://londonist.com/london/history/secrets-of-lambeth-bridge

[2] http://www.british-history.ac.uk/survey-london/vol23/pp118-121

[3] https://www.greatlondonlandmarks.com/place/lambeth-bridge/

[4] https://historicengland.org.uk/listing/the-list/list-entry/1393007

[5] https://www.lambeth.gov.uk/sites/default/files/pl-listed-buildings-beginning-with-l_0.pdf

[6] http://landmark.lambeth.gov.uk/display_page.asp?section=landmark&id=2955

[7] https://vauxhallhistory.org/lambeth-bridge/

[8] http://www.pla.co.uk/Safety/Thames-Bridges-Heights

[9] https://www.inti.gob.ar/cirsoc/pdf/puentes_hormigon/25-Lecture06-Design%20loads.pdf

[10] http://thames.me.uk/s00140.htm

[11] https://www.newcivilengineer.com/tech-excellence/lambeth-bridge-and-waterloo-to-get-37m-overhaul/10021157.article

[12] https://player.bfi.org.uk/free/film/watch-opening-of-the-new-lambeth-bridge-1932-online

[13] https://www.npg.org.uk/collections/search/portrait/mw271297/Opening-of-the-New-Lambeth-Bridge-King-George-V-Queen-Mary-and-others

 

 

Albert Bridge

  1. Structure Information

The Albert Bridge, shown in figure 1,  is located in central London where connects Chelsea and Battersea over the Thames River. It was completed in 1873 but had to undergo repair in 1884 and 1973. The Albert bridge was desperately needed at the time because the existing Battersea Bridge was decaying and the Victoria Bridge that was just up the river was getting too congested. To ease up traffic, Queen Victoria’s husband, Prince albert suggested to build a toll bridge. Rowland Mason Ordish was hired as the architectural engineer for this project as he had an extensive background with other large projects like Crystal Palace and St. Pancras railway station.

Figure 1

  1. Historical Significance

This bridge was so innovative at the time that Ordish patented his design. This bridge was a combination of a suspension bridge and a cable stayed bridge. This actually was not the first time that this design was used. Before Ordish built the Albert Bridge, he built and designed the same bridge in Prague and in his eye, it was a success. So he kept his design and used it for the Albert bridge. This bridge turned out to be and engineering failure. Like what we learned in class today and at the mellinnium bridge the frequency from people crossing the bridge caused it sway so much that load restrictions had to o be set.  There is still a sign before at each end of the bridge that tells troops to break step while crossing the bridge. Walking at different paces helped reduce the movement of the bridge. This bridge did go under reconstruction just a short 9 years later but I will go into more detail about that in the next section.

  1. Cultural Significance

Even though this bridge was needed at the time it caused a lot of trouble for the people in the area.  The owners of the existing bridge, Battersea bridge, did not want the Albert bridge to be built because they thought they were going to start losing money as less people would need to use it. But in 1864 Parliament passed an Act that made the Albert Bridge Company compensate the owners of the Battersea Bridge annually during construction and agreeing to buy the previous bridge once the new one was complete. In order to get enough money to do this Prince Albert came up with the idea to make the new Bridge a toll bridge. Even though this was a viable solution it just never worked, mainly because the engineering failed. Since the bridge was so unstable load restrictions were enforced which limited the amount of people to cross it. With a limited number of users, the bridge was not profitable since most of the money was going towards payment for the older bridge.  Just 6 years after the bridge was completed the Metropolitan Board of Works Purchased the bridge and immediately got rid of the tolls.[1]

Nine years later the Chief Engineer for the Board of Metropolitan Board of Works inspected the bridge and found that the steel cables were already showing signs of wear. He decided to replace the wood deck and replace the steel cables with steel links… little did he know that this design wasn’t any better. This bridge was still causing so much structural issues that there was a plan to demolish the bridge. Fortunately for the bridge, World War I and II caused the demolition of the bridge to be delayed. Once the wars ended there was a campaign to keep the bridge because all of the local people really thought it was one of the beauties of the London river. In 1971-1973 the bridge went the major structural rework. Two addition piers connected by a steel beam that ran through the middle of the deck was added along with all new decking. [2]

Today the bridge is still in use but there is still load restrictions on the bridge. It is still loved by many people today because of its vibrant colors. To increase the visibility of the bridge it was painted pink, blue and green. This bridge was loved so much that it was used as back drops in movies like Absolute Beginners, Maybe Baby, and A Clockwork Orange (Never heard of these movies but still kinda cool that it was used as a backdrop!).

  1. Structural Art

Right off the bat I can say that this Bridge is not structural art. First, it failed from an engineering standpoint and was incredibly unstable to use it efficiently. Second it was extremely expensive. It was originally estimated that it would cost 70,000 GBP and would only take 1 Year to build  but it took 3 years to complete and the total cost was over 200,000 GBP. Thirdly, it had way too much ornamental detail.

  1. Structural Analysis

As stated earlier this bridge was a combination of a suspension bridge and a cable stayed bridge. It is a suspension bridge where the deck is connected by vertical hangers to the steel link chains which run across the two towers. The cable stayed portion of this bridge is a fan design. This can be seen where the stays are connected to the deck and inclined to the top of the towers. This can be seen in the figure 2 below; the suspension hangers are highlighted in red and the diagonal cable stays of the bridge are highlighted in yellow. In figure 3 you can see the suspension of steel chains which were not part of the original design. You can see the cable stays and the vertical hangers in figure 3. For the suspension portion of this bridge the load is transferred from the deck to the suspender cable which are then transferred to the suspension cables and into the towers. For the Stay bridge portion the diagonal cables stransfer the loads from the deck to the towers.

Figure 3

 

Figure 3

 

For the structural analysis portion of this I made a few assumptions to simplify the calculations since it was a combination of 2 bridge types. The first assumption I made was that the suspension portion of the bridge takes a majority of the load so I will neglect the cable stay portion. The next assumption I made was that there is a roller connection in the top of the bridge  towers so that means that the horizontal components in each side of the tower will be the same. For the loads I assumed a live load of 3 tons since the there is a weight limit of 5 tons and I assumed the dead weight of the bridge to be 56 kips/ft. Below are my calculations for the max forces in the cables for the main span and the side spans.

 

 

 

 

  1. Personal Response

Before I went to this bridge I did a little research and found out it was a combination if a suspension bridge and cable stayed bridge. From looking at the pictures I had a real difficult time seeing exactly how it was a combination of the two because of lighting in the pictures. Even when I saw the bridge in person from a distance I still had a difficult time since the cable are going in every direction. But when I walked across the bridge I could see how the suspender cables attached the deck to the suspension cable and then to the tower. The same goes with how the stay system worked. Being there in person definitely helped me understand the load paths.

References

  1. https://www.britainexpress.com/London/albert-bridge.htm
  2. https://historicengland.org.uk/listing/the-list/list-entry/1358138
  3. https://londonist.com/2016/10/secrets-of-albert-bridge

 

 

Queen Elizabeth II Bridge

Structure Information

The Queen Elizabeth II Bridge spans the River Thames and joins Dartford and Thurrock. It is a part of the M25 London Orbital Motorway. In Figure 1, you can see where the bridge is in relation to the city of London.

Figure 1. Location of Queen Elizabeth II Bridge relative to the city of London.

Construction began in 1988, and the bridge was completed in 1991. This bridge was designed to allow for more roadway traffic using the M25, which circles London, to cross the River Thames. It consists of four southbound lanes, and this was important to match the needs of those using the M25. Instead of using the two  preexisting tunnels, southbound traffic moved to the bridge. You can see the four lanes in Figure 2.

Figure 2. Looking at Queen Elizabeth II Bridge from above. [2]

The bridge was designed by Dr. Hellmut Homberg, a German engineer, and other companies like Kvaerner Technology Limited helped in the design process. [2] In order to pay for the bridge, a Private Finance Initiative was created through the Dartford-Thurrock Crossing Act of 1988. This allowed for the toll revenue to pay off the debt from building the bridge. The Department for Transport manages the tolls. [1]

 

Historical Significance

When built, this bridge was the largest cable-supported bridge in Europe. Since the Pool of London is very important for large ships to access, this area was new territory for the bridge. Even though a cable-supported bridge did not use any new techniques, the design had to account for a height of 65 meters to allow ships to pass underneath, which is high. It is the only bridge east of the Tower Bridge on the Thames, so it was the first time a bridge was built high enough in this area to allow for large ships to pass through as well as support four lanes of traffic. [2] The cables are made of steel and the bottom piers are made of concrete and the pylons are made of steel, so no new materials were used. This bridge is relatively new, so it hasn’t been a model for future bridges yet, but since most of the other paths around this bridge that cross the Thames are tunnels, more people may start thinking of building more bridges or expanding this one. With the population of the London area growing, there will be more traffic, and the Department of Transport will have to determine how to increase traffic flow. What was cool about constructing the concrete pylons was that they were slip formed. Concrete was continuously powered for 24 hours a day for 10 days for each column. Also, no scaffold was used, so abseilers on ropes patched up holes as necessary. [4]

 

Cultural Significance

In an article I read, Dennis McNally, supervising the construction of the four piers, talked about how the area has become so industrialized since the construction of the bridge. In 1991, he could just see fields all around, but now it has changed significantly. McNally also expressed that there was controversy about what to name the bridge. On the Essex side, people wanted to name the bridge the Tilbury Bridge, not the Dartford Bridge. Its name is the Queen Elizabeth II Bridge because she opened the bridge in 1991, but many still refer to it as the Dartford Bridge. [4] One interesting thing that occurred earlier this year in February was the closure of the bridge for a brief time when a WW II bomb was found nearby. Luckily, it contained no explosives. [3] The present human cost of the bridge is a toll, which is used to help pay for the construction of the bridge and upkeep of the bridge. Today, the bridge is used for four lanes of traffic southbound for the M25.

 

Structural Art

Using Billington’s 3 E’s method to determine if the bridge is structural art, I will first determine if the bridge fulfills the efficiency component, or minimum materials. This type of cable-stayed bridge requires less material than a cantilever bridge and needs less cable than a suspension bridge. I believe that this bridge fulfills the efficiency component of structural art because it uses minimum materials with this design of the bridge considering the central span is 450 meters. Looking at the economy aspect of structural art, the bridge was estimated to be 120 million British pounds (about $160 million). The average cost of a cable stayed bridge is between $4500 to $5000 per square meter. [5] If I assume a width of 14.6 meters (4 lanes) and complete length of 2872 meters, the estimated cost would be about $187 million. The actual cost was less than that and compared to the cost of a suspension bridge ($8000-$9000 per square meter), is considerably less. [6] Therefore, I believe that this bridge fulfills the second requirement, which is economy or minimum cost. The third aspect I will address is elegance. This bridge is stunning and you can see the load path, but there is a disconnect between the piers and the steel pylons and cables. The color is different and the different material for the pylons creates a disjoint. The concrete piers also look bulky compares to the steel pylons and the thin cables. In Figure 3 you can see how it doesn’t look elegant. It’s not continuous. If the structure had been more cohesive, I would have given this bridge a point for elegance. Since this bridge satisfies two out of the three components for structural art, Billington would say it isn’t structural art because you need all three.

Figure 3. Noncontinuous aspects of the bridge. [7]

Structural Analysis

The design process consisted of a highway scheme under the “Department of Transport’s design, finance, build, operate, and transfer (DFBOT) principle.” [8] Once designed, construction took place. The four main pylons are made of steel and rest on top of concrete piers. The deck is made of reinforced concrete over steel. 112 cables support the bridge. Viaduct sections connect both sides of the bridge to the roadway. Construction lasted for only about three years, but like I mentioned before, there were some cool construction techniques used for this bridge. The concrete pylons were slip formed in which concrete was continuously poured. Also, abseilers on ropes checked everything after construction was completed to make the finishing touches because no scaffolding was used. Reinforced concrete caissons were used to support the piers, and these were constructed in the Netherlands. [8] When building the deck, they built the deck away from the pylons, which acted as a cantilever. The cables were installed as the deck was built. The structural system is a cable stayed bridge in which cables are attached to pylons and these cables hold up the deck. The bridge supports its own self weight, a dead load, and a live load from cars moving across. All the cables are in tension and the pylons and piers are in compression. The deck is also in compression. The dead load from the weight of the bridge (I assumed a concrete bridge with a certain cross-section for the box) and the live load from cars and trucks driving across are transferred to the deck and then the piers. This can all be seen in Figure 4.

Figure 4. Depiction of the load path for the QEII Bridge. [11]

Assuming the deck is a hollow box, I made assumptions based on research about the size of the deck’s cross section considering it’s four lanes across. I found the total cross-sectional area of the deck and then divided it by two because each section of the bridge has two adjacent piers, so the load on one pier only covers half the cross-sectional area. Assuming the deck is concrete with a density of 145 lb/ft^3, I found the dead load to be 9177.31 lb/ft. I also used AASHTO’s specifications for H20-44 and HS20-44 trucks (640 lb/ft) to ensure that the maximum load was used for safety. [10] Since traffic is very congested on this bridge, I assumed that the load was applied over the entire bridge. As seen in Figure 5, I calculated the entire load for the bridge.

Figure 5. Calculations for the loads.

Once I found the load I assumed lengths in between each cable. Each pylon had 14 cables on each side. With my distances assumed based on the length of the main span, I calculated the angles of each of the 14 cables. I only needed to do calculations on one side because the cables are symmetrical to the other side of the mast. As seen in Figure 6, I calculated the angles. I labeled cable 1 as the inner cable and cable 14 as the outer cable.

Figure 6. Calculation of cable angles.

Considering that cable 1 includes the area between the pylon and the cable and the half the area in between cable 1 and 2, I found the weight force, tension force, and force in the deck. All of these calculations can be seen in Figure 7.

Figure 7. Calculations for the tension in cable 1 and bridge force.

I found the forces for the other 13 cables, which can be seen in Figure 8.

Figure 8. Calculations for all the cables.

Once I found this for all the cables, I found the force in the mast. Since there are identical cables on the other side of the mast, I multiplied all the weight forces by 2. This can be seen in Figure 9.

Figure 9. Calculation of the mast force.

By finding the tension forces and the force in the mast, designers can determine how large the cables need to be and how large the pylons need to be to support the bridge based on the materials used. To communicate the design to stakeholders, plans were printed so they could follow them. Many supervisors like McNally oversaw different aspects of construction of the bridge. Models weren’t used for this type of bridge, but since it was built close to the end of the twentieth century, plan sets and standards were used to guide builders. Since a Private Finance Initiative was used for this bridge, it was important that engineers were clear with the stakeholders about all aspects during construction of the bridge with plan sheets. Construction of this bridge was relatively quick.

Personal Response

On the way to the Cliffs of Dover, this striking bridge caught my eye. In the main area of London, the height of many bridges is realistic. Sitting on the train, the bridge caught my attention almost immediately because of how tall and different is was. Being there, I never realized how different this bridge was than the other bridges along the Thames west of this bridge. The size and style of the bridge aren’t like any of the bridges down the river. Looking at this bridge shows how far we’ve come in the bridge design process since the other London bridges were built.

 

References

[1] https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_

data/file/604529/59263_Dartford_unnum_cov_and_text_A4_v2.pdf

[2] http://www.transporttrust.com/heritage-sites/heritage-detail/queen-elizabeth-ii-bridge-dartford

[3] http://www.echo-news.co.uk/news/15990727.Dartford_Crossing_bomb_contains_no_explosives/

[4] http://www.bbc.co.uk/news/uk-england-kent-15467112

[5] http://www.partnershipborderstudy.com/pdf/Cable%20Stay%20Bridge_2.pdf

[6] http://www.partnershipborderstudy.com/pdf/Suspension%20Bridge_2.pdf

[7] http://www.geograph.org.uk/photo/1515684

[8] http://www.engineering-timelines.com/scripts/engineeringItem.asp?id=105

[9] https://www.newscientist.com/article/mg13217924-900/

[10] http://www.ce.memphis.edu/3121/notes/notes_06c.pdf

[11] https://www.flickr.com/photos/dgeezer/13179342704

Blackfriars Bridge

The first time I was able to visit this bridge was on my second day in London while our class was on a bike tour. The bridge stood out to me because of its name and certain features. One of the cooler features of the bridge are the small statues of birds on each side of the bridge. These birds represent the saltwater of the sea and freshwater of the river meeting under this bridge. Fresh water birds like swans face west while seabirds like gulls face the east. Regarding its name, the Blackfriars Bridge actually gets its name from a monastery that used to be by the river that had friars that wore black robes. That’s not a very complex background to the name but it still sounds very cool. I think the friars that play for the San Diego Padres need to look into re-branding!

Figure 1, San Diego Padres Baseball Team [1]

Structure Information

In 1756, the Mayor of the City of London received permission from Parliament to build a bridge at Blackfriars, the third bridge to cross the Thames in the London area [2]. The young Scotsmen Robert Mylne was the designer. Construction on this bridge started in 1760 and was opened to traffic in 1769 [2]. A toll was installed to help the British government fund the bridge [2]. It was removed in 1785 [2]. This first bridge lasted for over 100 years [2]. The bridge that you see today was designed by Joseph Cubitt and commenced in 1869 [2]. It was funded in a similar manner as the first, and no longer has a toll on its road as well [2]. The main purpose of this bridge, when it was initially constructed, was to direct more traffic away from the overwhelmed London Bridge [2].

Figure 2, The Old Blackfriars Bridge [3]

Figure 3, Current Blackfriars Bridge [4]

Historical Significance

The design of the current bridge is not an innovative one. The bridge is supported by five arches which was a standard material and design used in 1800’s [5]. However, there is an innovative part to its foundation. The piers themselves are pointed to help direct water flow, and the caissons are made out of iron to prevent scouring [5]. Scouring is the erosion of soil surrounding a bridge foundation. This was the beginning of a period where pointed piers began to be used as a construction technique.

The best existing example of this bridge had been the previous Blackfriars Bridge. Much of the design had not changed but instead updated. The same columns remain along the bridge for people to sit on and look down the river, and the ornamental designs of the original were kept in mind for the second bridge. This bridge is not a model for future bridges as it did not innovate a significant way. The caisson design would be used in future bridges, but the visual component of the bridge did not innovate.

Figure 4, Bridge Scour [6]

Cultural Significance

There was a great bit of drama surrounding the first Blackfriars Bridge. The City of London had not made many civic changes since the Great Fire of 1666, but needed another bridge that led into the city [7]. At the time, London Bridge was overburdened with traffic and was always crowded. The city was against creating a new bridge that would harm the business of the Thames watermen, and buildings would need to be bought and demolished to create a new approach road [7]. However, an engineer, John Smeeton, suggested the creation of a bridge at the western extreme of the city as to not require the demolition of any buildings. The area was also known for being impoverished and was stricken with criminal activity, so the bridge provided the opportunity for improvement. A bridge design competition was held, with a decent amount of propaganda being spread around the final fourteen candidates. 25 year old Robert Mylne won the competition with his elliptical arch design [7]. Mylne had just arrived in London the previous year after excelling in architecture courses at St. Luke’s Academy in Rome.

The bridge was found defective in the 1832, and the city demolished the old bridge in 1865 and finished building the new one in 1869 [5]. The new bridge was not as well received as the first bridge. The new bridge was rotated and moved slightly to make construction easier, to make access to the bridge easier, and to provide pedestrians of the bridge a better view while on it [8]. To do this, several buildings were demolished to create the new approach road [8]. The people that used to live in those buildings were understandably, extremely unhappy. They were so unhappy that when Queen Victoria came for the Royal opening of the bridge, she was booed and hissed at during the ceremony [8]. The fact that she had not been seen in public for over five years also did not help her case.

Figure 5, A Cold Reception for the Queen [9]

The second Blackfriars Bridge is primarily used to provide cars and pedestrians a way to cross the Thames River into London. However, it was used for a more gruesome purpose in 1982. The body of one of Italy’s most prominent bankers Roberto Calvi was found hanging from the bridge with his pockets stuffed with $14,000 and 5 bricks [8]. The Metropolitan police initially treated this as suicide [8]. However, in 2002 evidence arose that Roberto had actually been murdered by the mafia [8].

Structural Art

There are three components that are used to determine if a structure can qualify as structural art. They are efficiency, economy, and elegance. The ultimate goal of each of these three is to be found in a structure. This means that the structure minimizes the amount of materials used to make it, does not provide unnecessary costs and expenses, and provides the maximum amount of aesthetics as possible.

Looking at this bridge initially, the first thing a person can see is the very simple design of the bridge and its arches. This paints a very clear picture as to what is going on in terms of its load path. If we were to not go any closer to the bridge, it would pass on this aspect. However, when you approach the bridge on foot, you can see all the extra ornamental decorations that the bridge contains. There are small architectural flairs all along the bridge, a requirement by the City of London [7]. There are also large columns along the outside of the bridge that serve no structural purpose. They only exist to give people a place to sit while walking and to provide more opportunities for ornamental design. Taking in the sum of all its components, I would argue that the bridge does not check the efficiency box.

Figure 6, Example of Ornamentation

From an economy perspective, the bridge actually was not too strenuous on the City of London. The bridge only needed a toll to help pay for expenses for less than 10 years each time it had been built. The social gain that citizens were provided was also a tremendous boon. The area started as a place of thieves and low class people, but the bridge provided economic growth and improvement to the area. Today it is the scene of many large businesses and serves as a business powerhouse in the City of London. In terms of economy, I would say that this bridge did in fact meet and exceed this standard.

Finally looking at elegance, this bridge appears to be balancing between a light and gaudy form. The arches are very simplistic and tasteful, but the columns that are placed along the bridge break up the light form. There are also very complex lattice structures that break the flow of the load paths on the bridge. This bridge took a solid design base and added extra things for no reason. It actually reminds me of my brother and his teeth brushing habits when he was a kid. Instead of doing the simple act of brushing his teeth for a minute, he would close and lock all the bathroom doors, run the water and put some in his mouth to act like he brushed, squeeze some toothpaste out into a tissue… well you get the idea. Instead of keeping it simple, he tried to do all these complicated things in attempt to give the appearance of clean teeth. But in reality, they were not. This bridge could have kept the beautiful and simple arch design but chose to do complicated things for no reason. Well, the government telling them to is the reason. But this is a great example of why the engineer is the most capable of creating structural art.

Basing my opinion on the three aspects that were discussed, I would argue that this bridge is not structural art. It comes very close but the ornamentation adorning the bridge takes it away from structural art. However, the basis for a simplistic and elegant design is hiding under the surface.

Structural Analysis

Because there is little information on the bridge’s method of construction, assumptions have to be made regarding this part of the bridge. There are a few pictures that shed some light on the construction process. Figure 7 shows men in diving gear. The piers would be the first part of the bridge to be constructed and the caissons that were sunk into the river would need workers in the water to help with that process. Figure 8 shows workers fabricating metal on site. In doing so, the material did not need to be transported very far. This saved time and money for the project. While the arches are different sizes, they are close enough for the on-site fabrication to be feasible. This would also be consistent with the type of material the bridge’s arches are made of.

Figure 7, Bridge Workers [10]

Figure 8, Making of the Material [10]

The main feature of the Blackfriars Bridge is its five wrought iron arches [5]. These arches sit on piers that have granite stonework [5]. The central arch of the bridge is 56.4m long [5]. The next two arches are 53.3m and 47.25m respectively. The bridge’s total length is 281m [5]. The width of the bridge was originally 22.9m, but it was widened by 9m on the west side to accommodate tramways [5]. The arch is 3.3m high [5]. The main structural system employed for this bridge is the arch form.

The system carries load using its arch form to its benefit. The bridge experiences loads on top of it in various forms. There is the dead load of the bridge itself, live load of people walking across it, live load of cars driving over it, and possible rain/snow live loads. Arches are fantastic at managing compression forces, which is exactly what this bridge does. All of the loads mentioned are transferred through the arch down to its connections at the bases where it connects to either an abutment or a wall that has another arch on the other side. That is important because the thrust forces of two arches next to each other will cancel out. This is why repeated arch forms are so efficient.

Figure 9, Load Path

Figure 10, Repeated Arch Form

Now that the load path of the structure is understood, we can do an analysis of it to see what kind of forces this bridge is withstanding. The main loads were mentioned above, but some math is needed to get numbers to those. We will assume the worst possible scenario which would mean maximum traffic, maximum people, maximum amount of rain, and the weight of the bridge itself. Below is a very simplified version of the arch.

Figure 11, Simplified Arch

Figure 11 is a symmetric arch with linear loads going across it. We can solve for the reactions at the ends using the following math.

Figure 12, Solving for Reactions & Maximum Force on Abutment

The design drawings were able to communicate the idea of the bridge to the government very well. There was little in the way of disagreement amongst them, but the drawings were changed slightly. The government wanted more architectural flairs than what the original design called for, so the giant non-load bearing columns and ornamental designs were added to make the bridge ‘more appealing’.

Personal Response

After studying and researching the Blackfriars Bridge, I think it is a very important and historic bridge that could use a little less ornamentation. I enjoyed being able to bike across it so the expansion for the top of the bridge greatly enhanced my first experience with it. My first impression of it was that this was a very pretty bridge, but after having studied it I can now see the more unnecessary parts of it that I can do without. While the Blackfriars Bridge may not be the most famous bridge in London, it certainly stands out as one of its most important bridges.

References:

  1. http://www.peoplequiz.com/trivia-quizzes-5536-San_Diego_Padres_Baseball_History__Facts.html
  2. http://www.british-history.ac.uk/survey-london/vol22/pp115-121
  3. https://londonhistorians.wordpress.com/tag/blackfriars-bridge/
  4. https://www.mrsmithworldphotography.com/photograph-of-Blackfriars-Bridge-5-London-England/WOF_G043_0033
  5. http://www.engineering-timelines.com/scripts/engineeringItem.asp?id=693
  6. https://blogs.scientificamerican.com/but-not-simpler/scour-why-most-bridges-fail/
  7. http://www.thehistoryoflondon.co.uk/the-original-blackfriars-bridge/
  8. https://lookup.london/the-old-blackfriars-bridge/
  9. https://www.gettyimages.co.uk/detail/news-photo/queen-victoria-opening-blackfriars-bridge-london-1869-news-photo/463951667
  10. https://www.theguardian.com/cities/gallery/2016/aug/02/how-london-was-built-tower-bridge-southbank-in-pictures
  11. https://www.quora.com/How-much-does-an-average-car-weigh
  12. https://www.ag.ndsu.edu/archive/dickinso/research/2004/range04c.htm
  13. https://hypertextbook.com/facts/2004/KarenSutherland.shtml

Southwark Bridge

Structure Information

Southwark Bridge in London crosses over the River Thames and was built in 1921.

Figure 1. Southwark Bridge

The Southwark Bridge was constructed to provide an additional Thames River crossing with the goal of alleviating traffic on the London and Blackfriars Bridges [1]. The bridge that stands today was the second bridge to be built over this span. The 1921 bridge was designed to reduce the effects of tidal scour and cross currents [2]. This bridge was designed by architect Sir Ernest George with Basil Mott of Mott, Hay, and Anderson (now known as Mott MacDonald) as the engineer [3]. Sir William Arrol and Co. were the contractors [3]. It is owned by Bridge House Estates [2].

Historical Significance

Basil Mott worked with Benjamin Baker, designer of the Forth Rail Bridge in Edinburgh [4]. Besides the architect, this same group of engineers constructed the Forth Rail Bridge. While I haven’t found any thing stating Southwark Bridge is innovative or a model for future structures, the fact that it was designed by engineers who designed other remarkable bridges makes it noteworthy. Southwark Bridge is similar in appearance to Blackfriars Railway Bridge, Blackfriars Bridge, Westminster Bridge, Vauxhall Bridge, and Grosvenor Bridge, just to name a few. All of these bridges cross the Thames and were completed within the 50 years prior to the design of the Southwark Bridge.

As mentioned earlier, this is not the first bridge to be called the Southwark Bridge. The original bridge was completed in 1819 and designed by architect John Rennie [1]. It was a three span arch bridge made of cast iron and masonry [3]. It ended up being the longest cast-iron arch span ever built [5]. The original bridge was innovative because its centers were formed, reducing the disruption to the river during construction [3]. This was a new and unique way to construct bridges at the time.

Figure 2. Old Southwark Bridge Construction [3]

The Old Southwark Bridge form was also innovative because the cast-iron was formed into ribbed arches made up of blocks of iron, similar to how a stone arch would work [1]. This can be seen in Figure 2. This eliminated the need for bolts and the blocks were, instead, tied together [1].

In 1856, the old London Bridge was removed, changing the currents that flowed around the Southwark Bridge [3]. This increase in current caused the bridge to be subject to scour as seen in Figure 3 [3]. Scour is the erosion of the parts of the structure around the waterline due to rapid currents. To reduce this problem, the new Southwark Bridge had five arches that aligned with the piers of the Blackfriars and London Bridges [3]. It also has thinner piers to allow water to flow more easily around the structure. This was a method developed in the earlier similar bridges mentioned previously.

Figure X. Scour along the Thames

Cultural Significance

The Southwark Bridge was built into old steps that had been used by watermen waiting for customers [6]. Because of its low traffic volume, it is a popular spot for filming. The bridge was used in the broomstick flight scene in Harry Potter and the Order of the Phoenix [7]. The bridge was mentioned in Mary Poppins when the Banks family thinks that Mr. Banks had jumped off the bridge after losing his job at the bank [8]. In real life, a pleasure boat collided with a barge near Southwark Bridge and killed 51 people in 1989 [9].

Figure 4. Scene from Harry Potter featuring the Southwark Bridge [10]

The Southwark Bridge was built as another crossing over the Thames to alleviate traffic on the London and Blackfriars Bridges. Several factors resulted in the bridge being unsuccessful in relieving traffic. The Old Southwark Bridge charged a toll, unlike its neighboring bridges, causing people to avoid using the bridge [1]. A major problem was the bridge’s connection to the other roads on the North and South sides. The Old Southwark Bridge was also steep and narrow, qualities that made drivers feel less safe. Because of its lack of use and the fact that some coach drivers park their cars on it, some people refer to it as the “car park bridge” [11]. Today, it is said that if you’re on the bridge, you are either lost or will be lost soon. It is often used as a way to get around the traffic of its neighboring bridges, but even then its traffic is minimal as it is the least used bridge over the Thames.

In 2009, the bridge underwent restoration that included repainting the bridge in its original green and yellow colors [2]. The reason for the green and yellow coloring is unknown, but I think most people would agree that it is aesthetically pleasing.

Structural Art

The structure is comprised of 5 steel arches with 4 stone piers [2]. The steel members are relatively thin. It is easy to see how the load transfers from the deck to the vertical steel members to the large steel arches. There are 7 arches in each span that are connected by truss members. This contributes to the transparency of the structure. Especially when compared to other London bridges like the Vauxhall Bridge, the Southwark Bridge has little ornamentation, unlike Vauxhall’s large statues atop each pier. However, Southwark has some components that are nonstructural. The towers on each pier were originally designed to provide a space for sculptures on the bridges. It was later decided to not include sculptures so now the extra height of the towers serve no use. However, these towers are not much taller compared to the overall structure. Another nonstructural element is the lampposts. There are 30 lampposts on the bridge that each have 3 lamps. This is clearly an architectural choice. Looking back at the structure, the extensive truss stiffening of the arches makes the structure less efficient and requires more material, making it less economical. While the overall arch structure is aesthetic, the addition of material in the trusses and the towers make the structure less elegant. Overall, I would say that while the bridge has some successful components and was designed by engineers who have been involved in structural art, the Southwark Bridge is not structural art.

Structural Analysis

When designing Southwark Bridge, the engineers were very aware of the damage that scour was causing to the bridges over the Thames as mentioned previously. Scour ending up being a major design factor in this bridge. The bridge features a 5 arch span, very similar to the nearby Blackfriars Bridge. This was done to allow for a smoother flow of currents and boats through the bridge [2]. The arches of the bridge are made out of steel and are supported by stone piers [2].

While information about construction of the current Southwark Bridge could not be found, I was able to find information on the Old Southwark Bridge construction and on similar construction projects in the early 1900s. The construction of the Old Southwark Bridge began with the foundations, using a cofferdam for the necessary excavation [5]. The central arch was made of segments of iron connected by dovetails and sockets to form the 8 ribs that made up the arch [5]. The formwork used to construct the arch can be seen back in Figure 3. Like the Old Southwark Bridge, the construction for the new Southwark Bridge would have started with the piers. In the 1900s, it was common for caissons to be used for foundation work, so it is likely that the current bridge used caissons instead of cofferdams. In 1903 when the proposed concrete Vauxhall Bridge was being constructed, it was found that the clay soil would not be able to withstand the weight of the concrete [12]. After realizing this, the design was changed to steel [12]. While their relation is unknown, it is possible that the problems of Vauxhall may have affected the engineer’s decision to use thin steel members for the Southwark Bridge.

The structural system of Southwark Bridge is a three-hinged arch made up of six smaller arches connected by trusses for stiffening. Each arch is supported by pier towers.

Figure 5. Loads on the arches

Figure 6. Load Path of the arch

The deck and vertical members transfer traffic and dead loads to the arch. The arch then transfers the load to the supporting piers. The truss members that connect the arches together and connect the deck to the arches are primarily there for stiffening of the structure.

The following assumptions can be made to analyze this system: the arch is pin connected to the piers, the road paving has a density of 145 pcf with a 3 inch thickness, steel with a density of 489 pcf and a 6 inch thickness, and a live traffic load of 200 psf [13]. The resulting distributed load is 480.75 psf. This is then multiplied by the width of the bridge, 55 feet, to get the load over one arch. The linear distributed load is 26.4 k/ft. The length of each arch is approximately 160 feet [3]. Because the load is uniformly distributed, the vertical reactions would be equivalent to half of the distributed load. After summing the vertical forces, the vertical reactions are (26.4 k/ft)*(160 ft)*(0.5) = 2,112 kips. The horizontal reactions from the piers can be found by taking the moment about either end. The distance between the top and bottom of the arch is assumed to be 50 feet. The horizontal reactions, which are equivalent by sum of the horizontal forces, is 3,368 kips. Figure 7 shows the math behind this.

Figure 7. Calculations

The internal force of the arch can be found by using Pythagorean Theorem with the reactions. The internal force is found to be 3975 kips. As the resultant of the reactions, the force would be acting towards the center of the arch making the arch in compression, as it should be.

To communicate to the stakeholders, the Bridge House Estates, renderings such as the one in Figure 8 were developed. The Bridge House Estates also owns nearby Blackfriars Bridge which has a similar design and was built earlier. Since Southwark Bridge has a simple and common style, it was probably easier for the engineers to communicate with the stakeholders about the bridge because the design wasn’t innovative; there was no need to prove that the bridge would work.

Figure 8. Rendering of Southwark Bridge

Personal Response

After visiting this bridge, I can definitely say it is the bridge less traveled. The reduced traffic on the bridge was an interesting change of pace in a city as busy as London. I found it to be the calm in the middle of a city in addition to providing a good view of the city’s skyscrapers. Seeing the bridge in person gave me a better idea of the many components that make up the truss system under the bridge. But when looking at the bridge from a distance in person, it is hard to see just how many members make up the structure.

Figure 9. Underneath Southwark Bridge

References

  1. http://www.southwarkbridge.co.uk/history/old-southwark-bridge.htm
  2. http://www.engineering-timelines.com/scripts/engineeringItem.asp?id=668
  3. http://www.thames.me.uk/s00070.htm
  4. https://www.gracesguide.co.uk/Basil_Mott
  5. https://www.icevirtuallibrary.com/doi/full/10.1680/ehah.2011.164.3.163
  6. https://web.archive.org/web/20131215153238/http://www.southwarkbridge.co.uk/project
  7. http://www.the-magician.co.uk/harry-potter-locations.htm
  8. https://www.revolvy.com/main/index.php?s=Southwark%20Bridge
  9. http://www.thepeoplehistory.com/1989.html
  10. https://aclbradio.blogs.lincoln.ac.uk/2016/02/12/walk-in-the-footsteps-of-the-stars/
  11. https://www.greatlondonlandmarks.com/place/southwark-bridge/
  12. https://www.revolvy.com/main/index.php?s=Vauxhall%20Bridge
  13. https://www2.iccsafe.org/states/Florida2001/FL_Building1/PDFs/Chapter%2016_Structural%20Loads.pdf

Chelsea Bridge

Of the 30-some odd bridges that cross the River Thames, many people, including me are probably wondering why the Chelsea Bridge is at all different or special. Most of the bridges have been there a long time and some look similar. There haven’t been any huge scandals involving the bridge since it was the original bridge that stood in the same place a long time ago. However, this bridge is unique, at least to the structural engineers out there. It’s especially unique to the structural engineering Brits, as the Chelsea Bridge was the first of its kind in the U.K. and still is one of the only ones in the country like this.

As someone new to the country and only being here for a short while, I don’t have any fun anecdotes to share about the Chelsea Bridge; pity. But, I think the Chelsea Bridge speaks for itself and anyone who cares about bridges would be interested in this bridge’s history and I don’t know about you, but looking at any bridge I can’t help but ask myself: “how the hell does it stand up like that?” I guess we’re going to find out.

 

Structure Information

 

Name: Chelsea Bridge

Location: London, United Kingdom

Figure 1: The Chelsea Bridge at Night [1]

Figure 2: Satellite Image of Bridge Location

Construction Start Date: 1935

Bridge Opening Date: May 6, 1937

Main Span: 352’

Side Span (2 of them): 173’

Width: 64’

Total Length: 698’

Budget: £365,000 (approximately $486,300 with 1937 conversion rate)

Budget (2017 equivalent): £ 22.4 million (approximately $29.8 million with 2017 conversion rate)

Designers: E.J. Buckton and H.J. Fereday of Rendel, Palmer & Tritton

General Contractor: Holloway Brothers

Steelwork Subcontractor: Furness Shipbuilding

Cables Subcontractor: Wright’s Ropes Ltd.

Fun fact (maybe not fun, but relevant): The construction finished 5 months ahead of schedule

[3]

 

Structural Elements and Materials

  • Towers – steel
    • Sit on rocker bearings

Figure 3: Chelsea Bridge Pylons

  • Cables – steel
    • Comprised of 37 strands of high tensile strength wires
    • Each wire has an 1 7/8 ” diameter
    • Hexagonal
    • Self-Anchored

Figure 4: Cables and Self-Anchors

  • Foundations – steel sheets
    • Cofferdams

Figure 5: Rocker Bearings Under Piers

 

  • Piers – concrete encased in granite

The Chelsea Bridge I am discussing in this blog is actually the second of the Chelsea Bridges. The first one was built to connect the densely populated north side of River Thames to the new (at the time) open green space, Battersea Park. The current bridge replaced that bridge to deal with the high traffic volumes that doubled in the time from the beginning of the 1900s to 1929.

 

Historical Significance

The Chelsea Bridge was the most significant suspension bridge built in Great Britain in between World War I and II. Being the first ever self-anchored suspension bridge (meaning it balances itself) in the country, its erection signified a new era of British bridge engineering. Despite the U.S. having already achieved this bridge form multiple times, Britain was recovering from the Great War and by this time had fallen a bit behind other engineering world leaders. Nonetheless, this type of bridge was perfect for its location because soil in London is more of a clay, and not very easy to stabilize a bridge with. As a self-anchoring suspension bridge, the cables anchored to the deck, rather than the clay which made the whole structure more stable and strong while also being innovative. Even cooler, the old Chelsea Bridge’s abutments were left and strengthened when the rest of the bridge was demolished, and the new bridge rests upon them bringing the past into the future (sorry for the cheesiness but, come on. That’s cool.) However, it is important to note that while the abutments were the major stabilizing and strengthening support for the Old Chelsea Bridge, they are entirely secondary to the new.

 

Despite being innovative in its location and in its time, only one other bridge in the U.K., built in 2011 is a self-anchored suspension bridge. Chelsea Bridge may have been significant in regards to the past, but historically it did not serve as a trendsetter when looking ahead all the way into 2018. Furthermore, the United States had already started mastering the form of self-anchoring by the time the Chelsea Bridge was built, so the Chelsea Bridge may be the best example of its kind in the country, it is not in the world. Perhaps this is due to the difficulty in constructing self-anchored suspension bridges because normally the suspenders would be able to serve as temporary supports for the deck during assembly. Since the cables have to connect to the deck, this method doesn’t work, meaning a lot more money must be spent on constructing temporary falsework until the system can work as a whole.

 

Cultural Significance

 

The Chelsea Bridge holds massive amounts of cultural significance. The original bridge was meant to connect Battersea to the rest of London, but also serve as a bridge for the lower class to connect to the upper classes. But, the bridge’s history predates even the original bridge: during construction in the mid-1850’s, many Roman artifacts were unearthed (literally). Researchers now believe that Julius Caesar crossed River Thames at this same point in 54BC. A Celtic Battersea Shield, one of their most famous and coveted pieces of military equipment was also found at the site. To be honest, I don’t know much about either of these things and I might be nerdy, but not so much for history. But, crossing over the River Thames at the exact same place Julius Caesar once did is almost unfathomable to me; I honestly can’t describe what that even represents, so I’m not even going to try and describe it. I will just move on and let that sit.

 

Much more recently (of course relatively) Queen Victoria opened the Victoria bridge in her name and walked across it for the first time in 1858. Of course, once the bridge started showing significant failures and people worried it might collapse, she ordered for the name to be changed to Chelsea Bridge so as not to associate any negative connotation to her name. I mean, she named the bridge after herself and then un-named it because she wanted to only be seen as perfect. I am legitimately rolling my eyes right now. Anyway, the original Bridge was taken down. Adding even more to controversy, the bridge was meant to better connect the lower and upper classes, but crossers had to pay tolls to pass over it. Finally, along with all the other bridges in London, the tolls were removed by an act of Parliament and people started using the bridge again.

 

Moving forward to the new bridge, the current Chelsea Bridge, many cultural events demonstrated not only its local significance but also its national and international importance. The bridge opening was in the news (you can watch the original news reel below attached below) and the Prime Minister of Canada was the one who cut the ribbon ceremonially to cross over the bridge with King George VI. The bridge is made of materials all sourced from within the U.K., or at least its territories, to stimulate the economy.

The bridge, though originally hated for its tolls and basic inadequacy (it couldn’t even be crossed once the sun went down because it didn’t have any street lamps), Chelsea Bridge is well received today. It still stands as a road and pedestrian bridge. Chelsea Bridge has also passed with no drama since the original bridge – Queen Elizabeth II hasn’t tried to name it after herself since its success – and has represented positive engineering progress, especially in the time during the two World Wars when London clung to everything that could be positively symbolic.

 

Structural Art

 

When considering the 3 E’s, efficiency, economy, and elegance, we have to consider both what the bridge serves as and stands for now and in the past, but also what the bridge was meant to represent when in the design and construction phases. However, since we are now into the 20th century, we are moving more towards company collaborations between architect and structural artist, and the exact intentions become more obscure in all the data provided for these bridges. Chelsea Bridge is decades old, but when comparing to bridges built a century or two ago, even when comparing to some of the other bridges crossing River Thames, Chelsea Bridge is young. Consequently, not as much time or analysis has been done in regards to its building or its overall impact. Whereas I can say Roebling was known for the Brooklyn Bridge and his cables as well as his overall understanding of structures as an art, or Telford cared immensely for all the E’s, not enough has been unearthed about the intentions or techniques of the specific designer, but rather to the technology as a whole. As a result, I will analyze and compare this bridge as structural art from my own lens, looking at what it is and represents now that it is built. This is valid analysis because thinking back to the Amann and the George Washington Bridge, the final product of the Iron Skeleton that the bridge is notorious for now was never the intention of Amann in the first place, yet the bridge still stands as one of the most beautiful and ideal examples of structural art in my opinion. So, with that in my mind, and being the perfectionist (or so I like to think) that I am, I have provided a pros and cons list to really simplify my analysis as much as possible, despite my realizing that it just takes me one step further on the nerd scale.

 

Efficiency

Pros:

Chelsea Bridge as a self-anchoring suspension bridge saved material and effort.

  • By not trying to tear down or restoring the old abutments that were used unsuccessfully for the first Chelsea Bridge, but rather letting the deck rest on them as an added precaution, material and effort was saved.
  • Workers did not have to demolish the old abutments and then start from scratch and use extra material to stabilize the bridge in the unstable clay soil.
  • A brand new bridge was made with less hassle and was innovative in its design so that it could essentially hold itself up.

Cons:

  • The concrete, was covered in granite for aesthetic effect, which was entirely unnecessary to the structure.
  • Construction required more materials and effort including an independent pedestrian bridge to allow crossing during construction.

Considering all factors in terms of efficiency, the overall finished product of Chelsea Bridge is efficient, the construction was not necessarily. I am deciding this because even though Granite is used inefficiently, the load path is still clear to the viewer and there are very few ornamental elements besides some lamp posts that are there for architectural rather than structural purpose. To learn more about the old bridge and the construction of the new, see the newsreel by News in a Nutshell on the topic:

Economy

Pros:

  • The bridge has had no failures since its erection, meaning relatively low maintenance costs.
  • Saved money by not completely erasing the old bridge and starting from scratch.
  • Only used materials from within the commonwealth of Great Britain.
  • Generated work within the commonwealth during the time in between the wars.

Cons:

  • An entire temporary bridge was built to accommodate the construction of the Chelsea Bridge.
  • Granite cost was unnecessary.
  • Since the bridge is toll-free, it doesn’t generate any revenue itself.

When weighing the pros and cons, I conclude that since economy is inherently tied into efficiency, and since the bridge has lasted so long without significant damages or issues, the Chelsea Bridge is economical. Furthermore, the bridge helped Britain’s economy in general by only using materials from within its jurisdiction, which sort of counterweighs the negative effect of additional material and lack of direct revenue generation.

Elegance

Pros:

  • Small pylons
  • Self-anchored allows for no large abutments
  • Clear load path
  • Relatively few ornamental and unnecessary flourishes

Cons:

  • Painted to represent national pride, but in my opinion takes away from the look of the steel (again, I love the GW Bridge so I’m a bit biased).
  • Granite obscures the steel piers above the water line
  • Lamp posts are ornamental in their composition and take away from the sight of the bridge as a system

Overall, the new Chelsea Bridge in my opinion achieves the label of structural art. I cannot say much about the intentions, but I believe the bridge is in fact elegant when compared especially with some of the other bridges across River Thames such as Tower Bridge which is mainly ornamental. This bridge stands for the purpose of standing while also fulfilling social and symbolic missions such as connection the classes in the neighborhoods surrounding the bridge and aiming for elegance, efficiency, and economy.

Structural Analysis

As previously stated, though probably not adeptly explained, Chelsea Bridge is a self-anchored suspension bridge constructed of steel. It has two towers, each containing two pylons, that transfer the load from the cables to the foundations. The cables connect the main span of the bridge to the deck of the side spans, right above the abutments from the last bridge. This means that the deck counteracts the tensile forces of the cables that point towards the center of the bridge rather than the abutments. The load path and free body diagrams are shown below in figures 5 and 6 respectively.

Figure 6: Load Path

Figure 7: Simplified Free Body Diagram of Entire Structure

 

Load calculations:

Material weights:

Steel: 490 lb/ft^3

Reinforced Concrete: 150 lb/ft^3

Assume Live Load factor is .8: LL = .8*DL

Structural Element Weights:

Pylons (x4):

Hp= 69.2’

Assume square cross section with side length of pylons, Sp = 1.5’

So, weight of pylons, Wp=4*((1.5ft)^2)*69.2ft*.490k/ft^3=305.2kips

Cables:

Based on common values for high tensile strength cable properties, WC =3.97 kips/698’ = .006k/ft

Deck:

L = 698’

wD = 68’

Assume cross sectional area AD=.75’*68’=61sqft.

WD = 150lb/ft^3*51ft^2/1000lb=7.65k/ft

DL = ((7.65+.006)k/ft * 698’ + 305.2k)/698’ = 8.09k/ft

Therefore, the total load W = DL + .8DL = 14.57k/ft

Using equilibrium to solve for the reactions we can take the following steps:

Figure 8: Solving for Vertical Reactions

Figure 9: Continue Calculations

Figure 10: Calculations Continued

Now try and picture this: if you make a new cut and look at the bridge from one of the piers to the anchor on its respective side, then you find that Ax = Cx =Bx = Dx = 17325.16kip. Otherwise, the pylons and anchors would not be in equilibrium and everyone would be watching the pylons tumble down all dramatically.

Figure 11: Continued Calculations

To find the maximum and minimum tensile forces in the main and side spans, we can use Pythagorean theorem and sum of moments:

Tmain,max= sqrt(“(8662.58kip)^2 + (2564.32 kips)^2) = 9034 kips”

Tside,max = sqrt(“(8662.58kip)^2 + (5142.26 kip)^2) “=10074 kips

Figure 12: Final Calculations

Unfortunately, there is not much information on the original drawings and plans of the Chelsea Bridge or how they were disseminated to the public to increase engagement. My guess would be that the public did not have access to the bridge plans, but that they were passed around among the team, which was quite large. Similarly, since there is not much information on the funder of the bridge, it’s unclear whether or not they would’ve been able to understand and use the drawings to inform their decisions. However, considering there were so many subcontractors and parties involved, the drawings would have to be pretty legible and easy to read, otherwise everyone would’ve have fought and there is no way (I mean seriously, imagine if they couldn’t communicate because of bad handwriting) Chelsea Bridge could have been finished 5 months ahead of schedule. I mean, when my family tries to do a group gift at Hanukkah time, we have trouble communicating and that’s just looking at emails and different sites, never mind that my older siblings complain that I text in “hip” lingo that they can’t understand. So, imagine that on a huge scale with absolutely no room for error; I’d say the drawings were both made and utilized pretty successfully.

Personal Response

At first glance, the Chelsea Bridge didn’t seem all that special to me. However, the history of it, the fact that while self-anchored bridges are uncommon in the area attracted me to it. Plus, I can’t help but laugh about the fact that the Queen changed the name of the bridge so she wouldn’t have any negative connotations. Like, I’m pretty sure that the British Monarchy has been battling many haters, especially Queen Victoria who was surrounded by scandal. And yet, an unsuccessful bridge can’t be associated with the royal family. Anyway, the colors catch my eye and the idea that the bridge balances itself really amazes me.

References

  1. http://www.job32v8.com/_2/?p=293
  2. https://londonist.com/london/features/secrets-of-chelsea-bridge
  3. https://historicengland.org.uk/listing/the-list/list-entry/1393009
  4. https://www.greatlondonlandmarks.com/place/chelsea-bridge/
  5. http://web.engr.uky.edu/~gebland/CE%20382/CE%20382%20Four%20Slides%20per%20Page/L2%20-%20%20Loads.pdf
  6. https://www.youtube.com/watch?v=uHEtLvHeaOE
  7. https://www.youtube.com/watch?v=mmAo9Ft8xHw
  8. https://www.britishpathe.com/video/chelsea-bridge-news-in-a-nutshell/query/Bridge
  9. https://www.bristol.ac.uk/civilengineering/bridges/Pages/NotableBridges/Chelsea.html
  10. http://www.engineering-timelines.com/scripts/engineeringItem.asp?id=53

 

Go Arsenal! (Emirates Stadium)

Figure 1: Me in front of Emirates Stadium

Structure Information

Emirates Stadium was completed in 2006 and is located in Ashburton Grove, London [1]. The stadium is used for the Arsenal Football team’s home games. The structural engineer for the project was Buro Happold [2]. Funding for the stadium came from loans from many banks given to Arsenal Holdings plc, Granada, Nike, and sales from the land that was not needed for the stadium. Additionally, Emirates Airline paid £100 million for a 15 year sponsorship of the stadium as well as an 8 year sponsorship of team uniforms [1].


Historical Significance

A newer technique for creating steel parts was used by the steel contractor to insure the accuracy of the parts. The method included creating three-dimensional models of sections from individual X-Steel models to be used in manufacturing of the steel. The three-dimensional models could be rotated and moved in order to create the most accurate version of the parts for the stadium.  [2]

Other than this, the stadium was built as a typical football stadium, with the roof allowing sunlight to hit the field while also keep the sun or rain off of the spectators. Since the roof is not connected to the seating, there is also airflow to keep the stadium cooler without the need for air condition. What sets Emirates Stadium apart is that the stadium is an ellipse shape, rather than a rectangle, which is more common for football stadiums. [1]


Figure 2: Development at Past Stadium for Arsenal [2]

Cultural Significance

The stadium is situated inside of a 7.8 acre park, which is open to the public. Additionally, Arsenal built houses and other buildings around the stadium for the surround communities. The location of the stadium allows for access from the London Underground and helped push for improvements at the Holloway Road station and promotes politicians to obtain funding for improvements at two other stations. Arsenal also sponsored the conversion of their past stadium into apartments, student housing, a garden, and health centers. [1]

 

 


Structural Art

When looking at the roof of Emirates Stadium from inside, outside, and especially from Google Earth, the stadium, this structure displays structural art very well. The arched trusses that hold up the roof and the connection points of the roof to the elements holding the roof up are all visible and easy to find. The load paths are visible, and the structure looks light. Additionally, efficiency and economy were highly considered in the structure. Steel tubes were specifically chosen for the cost and efficiency, as well as the constructability.


Structural Analysis

The roof of Emirates Stadium is made up of polycarbonate and steel tubes [1]. Steel tubes were chosen for cost and weight purposes, as well as constructability since less surface area means less detail in the steel manufacturing process. The girders were built off-site in pieces and assembled on-site. Temporary structures were used until all of the trusses were put into place with cranes so that there was no deflection from the self-weight of the trusses. [2]

The roof consists of the polycarbonate covering and many trusses, varying in size. There is a circular truss around the perimeter, truss beams, and truss girders. Additionally, there are 8 tripod columns to stabilize and take loads. All of these parts work together to create a stadium roof that does not touch the seating area and draws the viewer’s eye to the pitch, rather than the roof [1].

The load path goes from the roof up to the smaller, triangular truss beams, up to the larger truss girders. The two secondary girders transfer the load to the two primary girders. The primary girders then transfer the load to tripod columns. A circular truss around the perimeter of the roof is attached to the roof and provides support for the beams. It also transfers load to the tripod columns, seen in Figure 3. There are also 64 props around the stadium to help transfer the load down [3]. All of the beams and girders can be seen in Figure 4, a bird’s eye view of the stadium. From the inside of the stadium, the load paths from the secondary and primary girders, as well as the columns can be seen (Figure 5). From the outside, the tripod columns can be seen connecting to the roof (Figure 6).

Figure 3: Load Path from Top View [6]

Figure 4: Tripod Column from Inside Stadium

 

 

 

 

 

 

 

 

 

 

Figure 5: Load Path from Inside Stadium

Figure 6: Load Path from Outside of Stadium

The primary girders span 204 m and the secondary girders span 100 m, with the 32 beams varying in size. The girders cross section is 15 m deep and 10 m wide. [2] The polycarbonate roof covers 27,200 m2 [4]. All of the steel on the roof weighs 3,000 tons [1]. The total weight of the roof is about 41,510,000 N [5]. This means that the average area load of the roof is 1,526 N/m2.

To idealize the roof, we can say that each beam takes the same amount of load. Figure shows the idealization schematic. The force from the roof that each beam takes is calculated by multiplying the area load by the area divided by 32. The load for each beam is:

The loads of 6 of the beams go to each secondary girder, meaning each secondary beam has 6 point loads and reactions the ends from the primary load. Due to symmetry, the reactions are equal and there are no forces in the x-dimension. Figure shows the free body diagram. The reactions are:

The loads from two reactions of the secondary girders and the loads from 10 beams are on the primary girders, seen in Figure . As with the secondary girders, there are no forces in the x-dimension and the reactions are equal. The reactions on the primary girder are:

The maximum moment in the primary girder is in the center, while the maximum shear force is right next to the reaction. Assuming the distance between the beams are all equal to 16 feet and the distance between the secondary girder and perimeter is 30 feet, the maximum moment is:

This very large maximum moment is one of the many reasons why a triangular truss in the shape of a moment diagram was chosen for the primary girders.

The design of the stadium included a huge development of the area around the stadium in addition to the stadium. Because of this, the elliptical shape was chosen since it meant that the closest residential building was over 100 meters from the stadium. Models of all of the initial designs were presented to stakeholders, and once a shape was chosen, a full model including the neighborhood was presented. [3]


Personal Response

I really enjoyed visiting Emirates Stadium. Researching it more and going into the structure was very interesting. The stadium is so massive! I didn’t even really realize at first that the roof wasn’t resting on the seating area, but when I did, I was so amazed at the structural engineering.


References

1 https://www.designbuild-network.com/projects/ashburton/

2 https://www.steelconstruction.org/design-awards/2006/commendation/the-emirates-stadium-arsenal-football-club/

3 https://issuu.com/jmurphy93/docs/dissertation_final-_emiratesstadium

4 https://www.independent.co.uk/student/magazines/emirates-stadium-new-goal-for-the-gunners-5331573.html

5 http://www-civ.eng.cam.ac.uk/cjb/schools/stadium/silcock_files/S2%20Emirates%20structural%20analysis%20Teachers%20Notes.doc

6 Google Earth

The London Bridge (the real one)

I think I can speak for everyone when I say that the current London Bridge is a big disappointment to whoever sees it. It does not appear to be special and looks awfully plain. No one would imagine that this is the bridge whose name conjures images of beauty and wonder and who, for most of my childhood, embodied the idea of London. I was disappointed, I will not lie, but through this blog, I will try to capture the magic surrounding this structure and show that this unassuming piece of concrete may deserve its fame.

 

1.  Structure Information

The London Bridge is very different from the Tower Bridge contrary to what Google seems to think. I have provided a picture of London Bridge in Figure 2 so that we may all be on the same page. I promise you, figure 2 really is the London Bridge.

Image result for london bridge

Figure 1: Tower Bridge, NOT LONDON BRIDGE

 

 

 

 

 

 

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Figure 2: London Bridge (yeah I know :/)

 

 

 

 

 

 

The current London Bridge is actually the 3rd bridge officially of that name. It is referred to as the Modern London Bridge (1). It is located over the Thames River, between the city of London and Southwark and located between 2 other bridges that cross the Thames River: Cannon Street Railway Bridge and the famous Tower Bridge (see figure 1).

Construction for the bridge began in 1968 and ended in 1972 (1). The Modern London Bridge was opened in 1973. It was inaugurated by Queen Elizabeth II on March 17th of the same year (5).

The purpose of the Modern London Bridge was to replace the New London Bridge which had begun to sag. The bridge was sinking at a rate of an inch every eight years starting in 1896. By 1962, the problem was so prominent that the bridge had to be replaced (6); it was struggling to adapt to the higher traffic volumes of the 20th and upcoming 21st century.

The Modern London Bridge was designed by architect Lord Holdford, the engineers were Mott, Hay, and Anderson. The contractor was John Mowlem and Co (7). It cost £4 million at the time which equals to about £51.9million today (There was crazy inflation!). The costs were covered by the Bridge House Estate Charity.

Figure 3: London Bridge

 

2. Historical Significance

By the time the Modern London Bridge was constructed and opened to the public in 1973, many innovations had already been made in bridge design, especially in prestressed concrete. This bridge sadly did not contribute to any and this bridge did not serve as a model for any other bridges. The innovative part of this bridge is found during its construction. The bride was constructed using the cantilever method (1). They completed the span of the bridge by placing a concrete beam between the two cantilevered parts of the bridge. It represented a major innovation in bridge engineering post World War II. Yet this was not the first time someone had used this method. David P Billington himself said that the bridge itself is not of great historical significance(1). It mainly used existing innovative construction methods. It also used the hollow box girder previously developed by Maillard. The best existing example for that would be the Salginatoble bridge of 1929 and prestressing concrete, an innovation inspired by Freyssinet’s work.

 

3. Cultural Significance

The London Bridge has a long history. In fact, London Bridge is the name of any bridge that was constructed in the area. The first bridge had been built by the Romans around 55 AD. The majority of the first London bridges were made of wood. It was not until 1176 that the first stone London’s construction started thanks to the work of a priest of St Mary’s of Colechurch (1). This bridge, referred to as the Old London Bridge opened in 1209 and was the site of calamities.

It became an important commercial site and over time it also became a business and residential area (It still amazes me how they were able to fit houses on this bridge). Anyway, there were shops, houses on the shops (138 premises were recorded in 1358), walkways and rooms extending about everywhere. It got so bad that the bridge started to resemble a tunnel. At some point, watermills were added to the mix (in the 1580s) (1). The roadway was narrowed down to 12ft – this was used by carriages, travelers, merchants, and commuters. Somehow this chaos survived one fire in 1212 that killed 3000people (1), the collapse of 5 of its arches in 1282 and it wasn’t until 1762 that plans were made to remodel this bridge. This is the bridge that inspired the nursery rhyme ” London Bridge”.

Old London Bridge, lithograph after a manuscript illumination of c. 1500 in the British Library (Royal M.S.S.16.F.ii.XV.) .

Figure 4: Old London Bridge

By 1722, all the houses were removed to and the city decided to try and improve the bridge. This proved to be too much of a burden and they commisioned a renowned engineer, John Rennie to construct a new structure a few feet upstream (1).  The old one was demolished in 1831 after 622 years of use (Holy Moly!). It had seen most of London’s historic events and occupied an important place in the city of London. The new design would be known as the New London Bridge. The new London Bridge only lasted 140 years. The most interesting fact about this bridge is that is was dismantled and shipped to the United States Lake Havasu City in Arizona for a tourist attraction. It was sold to the millionnaire Robert McCulloch for 2.460 million dollars. He spent an additional seven million to build it (10). The Modern London Bridge was the site of a terrorist attack that injured 48 people and killing three on June 3rd, 2017. Three terrorists used a rented van to run over pedestrians on the bridge.

 

4. Structural Art

In order to determine if this is structural art, I will be looking at the three E’s economy, efficiency, and elegance and applying them to the structure.

This structure is elegant enough in its shape.  It is aesthetically pleasing and easily integrates itself with the surrounding environment. The concrete works well with the Thames River and it easily merges with the other buildings. Looking at it, it is hard to distinguish where exactly it begins and where it ends. The design is light and fluid, the deck is very thin and the arches are very wide. The abutments too are very narrow and integrate themselves well in the design  Nothing looks excessively bulky or out of place in this bridge; it is rather plain for my taste but I must admit that the elements work well together. The main issue with this bridge is that it is not exciting and does not inspire awe because of how plain it is, however, this bridge does have elegance.

The bridge cost £4 million at the time which equals to about £51.9million today with inflation. Comparing it with the Waterloo bridge that has a somewhat similar style, that cost around 1.3million in 1877 which equals to about 145 million today(8), we can conclude that the bridge’s price was reasonable. It was built using methods to reduce the price: hollow box girder, prestressed concrete, and thin overall bridge to reduce material.

The Modern London Bridge is a very efficient bridge. It was built with efficiency in mind to some extent. It does not have any superfluous unnecessary elements such as excessive decorations or facades and was built to be as slender and simple as possible. The main criterion for this bridge was for it to be simple and functional. They were looking for something to replace the old bridge and did not care much for anything else besides functionality. The bridge is very thin, due to its wide span arches as well as the use of a hollow box girder. The abutments are very thin and long, allowing for less use of material than if the arches were to continue all the way down. The bridge is made out of concrete which is a relatively cheap material, and it is prestressed allowing for the use of even less material.

I will qualify this bridge as structural art. It is very efficient, it possesses some elegance and was constructed at a reasonable price.  The three E’s are met.

 

5. Structural Analysis

The London Bridge is made of three prestressed-concrete box girders. It is 882.5ft long and 105ft wide. It has a minimum vertical clearance of 26.9ft. The bridge was constructed using the cantilever method. Construction started on both sides. Starting from the piers, segments were built and connect to the previous using high strength steel tendons. The two halves of the bridge were connected by a beam of concrete. The bridge had a very interesting construction process. The old bridge was used partly throughout the construction of the new one. They built the new bridge next to the old one and demolished the old one as they were constructing the new one. Construction began with workers excavating giant shafts under the existing bridge. At that point, the balustrades of the old bridge were taken down and a truss structure was built no the side of the bridge.  On this structure were assembled twin celled precast concrete box units (11). This was repeated on the other side of the bridge. The system is illustrated in Figure 5.  The old bridge was then demolished with spandrel and infills removed first. The gantry truss was used for the final two girder boxes on the new design.

 

Figure 5: Construction of twin-celled precast concrete box units over the river

 

The weight of the bridge, as well as the live loads acting on the bridge, are supported by the arches. The load travels down the arches and into the abutments then the foundation and then into the ground as can be seen in figure 4. It is important to note that arches generate thrust forces due to the tendency of arches to want to spread. This design has three repeating arches which cancel the thrust forces with the bridge. the remaining thrust forces are carried horizontally into the ground at the point where the bridge deck connects with the ground.

 

Figure 4: Load Paths

In order to analyze this bridge, we will be only using the dead weight of the bridge and we will be assuming an area load of 480lb/ft^2 (11). We will base our calculations on the central arch which has the largest span.  We will also be using the density of concrete: 150lb/ft^3. The span of the central arch is 109 ft and vertical clearance is 29.6ft (ref fig.5) and a width of 105ft. We will calculate the maximum force on the abutment at A.

Figure 6: Simplified load distribution

 

I was not able to find the thickness of the hollow box girder so I will be assuming a thickness of 1 foot.

w = (150lb/ft3 * 1ft+480lb/ft2) *105ft =66,150lb/ft

Sum of the forces in Y direction = 0

RAy = RBy = w*109/2 = 7,210.4k/2=3,605.2k

Sum of the forces in the y-direction

Make a cut at the center where h is max

Figure 7: Cut at the middle where h is max

 

Resultant = d*w= w*109/2 = 7,210.4k/2=3,605.2k

Sum of the moments about O = 0

0= RAy (109/2) – RAx(26.9) – Res (109/4)

0= 3605.2k(54.5) – RAx(26.9) – 3605.2k(27.25)

RAx = 3,652.1k = RBx

Force A = (3652.1^2 + 3605.2^2)^1/2 = 5,131.8k

By finding the maximum force on A we now know the maximum load that the abutments can take and help prevent the collapse of the arch. It is important to determine the maximum force as it will also allow to determine the maximum weight of trucks crossing the bridge.

 

The design of the bridge was chosen by a competition. The judges were mainly looking for a simple, functional bridge that was easy to maintain and that did not cost too much. The designers communicated their design to the judges by sending the schematics and plans. Upon examining these schematics, here is what some of the judges said: “The designers selected concrete for its low- maintenance characteristics and visual sympathy to its surroundings” (7) and “the bridge is a testament to both careful design and construction”(7). They appreciated the simplicity of the design.

Figure 5: Schematic of London Bridge Design [8]

6. Personal Response

Looking at the London Bridge for the first time can be a bit ( a lot) of a disappointment. It is beyond simple with its monochromatic facade, its lack of decoration and plain arches. It is all GREY. I believe that says it all. We have been blessed by so many marvelous pieces of structural art, that we sometimes fail to appreciate the simplicity of certain designs. The London Bridge may not be the prettiest (by far) or the most intricate design for a bridge but it carries its beauty in its history. With such an amazing background. it does not need much pump or circumstances to be important. Its importance goes much deeper then its aesthetics and if people took the time to learn more about it, I think they would be impressed. When you see a billionaire walking across the street, you will not see him in colorful, boisterous clothing with shiny and obviously expensive watches. He or she will easily blend in the crowd, he or she might even seem underdressed because they have reached a point where they have nothing more to prove. They are rich beyond comprehension and do not approval from anyone to know that they have achieved something wonderful in life.  I believe the London Bridge is making the same statement. Seeing it was very anticlimactic, but the more I researched it the more I realized that it did not need much to be fantastic.

 

References

[1] https://www.britannica.com/topic/Old-London-Bridge

[2] https://www.londonpass.com/attractions-london-bridge.html

[3] http://www.geograph.org.uk/photo/2630157

[4] http://projectbritain.com/london/bridges.ht

[5] https://uk.news.yahoo.com/on-this-day-queen-elizabeth-ii-opens-london-bridge-1973-121915868.html?guccounter=1

[6] https://www.citylab.com/design/2013/10/how-original-london-bridge-ended-arizona/7200/

[7] https://web.archive.org/web/20120420230132/http://www.buildingtalk.com/news/cyl/cyl123.html

[8] http://happypontist.blogspot.co.uk/2013/09/

[9] https://www.officialdata.org/1877-GBP-in-2018?amount=1300000

[10] https://www.citylab.com/design/2013/10/how-original-london-bridge-ended-arizona/7200/

[11] https://www.inti.gob.ar/cirsoc/pdf/puentes_hormigon/25-Lecture06-Design%20loads.pdf