The past, present and future of the Széchenyi Chain Bridge

Due to the commotion about the Széchenyi Chain Bridge’s refurbishment, the bridge has become the subject of political discourse again, so my choice of the topic is not a mere chance. Obviously, this debate is not about the bridge itself, there is a political game going on here. For me, it is the bridge that matters. I don’t care who should have done what and when, rather, I would like to show the future of the bridge in 20-30 years’ time, which is likely to happen regardless of the current refurbishment.

The Széchenyi Chain Bridge has long been more than just a bridge, it has now become a symbol. It is a symbol of an entire country, national progress, development and industrialization. And referring back to my last post, it is also a symbol of Budapest, like the Erasmus Bridge is the symbol of Rotterdam. When they catch sight of the Chain Bridge, everyone knows that they are visiting the Hungarian capital, just like many will recognize the Dutch port city when seeing a white cranked-shaped pylon only.

Almost everyone has some information about Chain Bridge. Most people know when it was built, they have heard about Széchenyi's role and about Adam Clark. Many books detail the structure of the bridge, the history of its construction and reconstructions and the hardships it endured. In the current post, I would like to raise a few interesting questions about the bridge’s past, present, and future.

The Chain Bridge in 1896. Fortepan / Budapest Főváros Levéltára / Photos of György Klösz (https://fortepan.hu/hu/photos/?id=82607)

One of the most fundamental questions is why the bridge is right where it stands. For hundreds of years, only barges, ferries, a medieval boat bridge and then a reaction ferry operated between Pest and Buda.

The crossing was between Vigadó Square - the northern end of the old Pest’s citywall - and Szarvas Square. This crossing not only created a connection between the two cities, but mainly served the long-distance traffic, as the road ran outside the citywall of Pest and continued in Buda under the Castle, in the direction of Vienna, across Tabán.

The location of the crossing at the citywall of Pest in 1684 (http://epa.oszk.hu/02100/02120/00041/pdf/EPA02120_tbm_2016_41_041-104.pdf, page 17).
 
Wilhelm Dillich: Buda and Pest from Margit Island - copper engraving, XVII. century (https://mek.oszk.hu/01800/01885/html/index1430.html).

With the expansion of the city, the downtown road network, which had been formed over many hundreds of years, did not change at all, so today’s Small Boulevard (the then line of the citywall) reached the Danube bank.

The boatbridge between Vigadó Square and Szarvas Square in 1837 (https://mapire.eu/hu/map/budapest-1837).

When placing a permanent bridge, the primary objective of the builders is to have a good road connection, which was given here. However, the Chain Bridge was built hundreds of meters further to the north, which meant that the decision-makers completely ignored the established road network. But why?

As usual, the future of bridges is decided in the political arena. There are topographical features, technical parameters, financial issues, but these can be overruled by politicians at any time. That was true then and this is true now. In fact, the choice of the bridge’s location was not driven by the most complex transport and traffic requirements, what was taken into consideration was the interests of the social layers who financed or influenced the construction. Széchenyi realized that his bridge would not only connect Pest and Buda, but would also symbolically create a connection between the feudal aristocracy in the castle and the emerging industrialists who built palaces in Lipótváros. If we look at the question from this perspective, it is already understandable why the bridge site was not the axis of the boat bridge used by commoners. Of course, this message would have been rather difficult to communicate, therefore the real political bargains were hidden behind technical arguments, such as the fear of possible damage by the drifting ice in the spring. There are few worse locations for a bridge than the current one. It also had many consequences. One of them was that a tunnel had to be drilled under the Castle Hill. Thanks to the tunnel, completed in 1857, it was no longer necessary to bypass the Castle Hill and a straight road could be created to Vienna. Another consequence was that the next bridge could not have been placed too close to the Chain Bridge; thus, today’s Elizabeth bridge had to be built on today’s Ferencziek Square instead of today’s Vigadó Square. In order to build the bridge, which was inaugurated in 1903, a boulevard (now Rákóczi Road) had to be driven through the main square of ancient Pest, thus ripping apart the urban fabric that had formed for hundreds of years. If we take a look at the citymap, it is also apparent that the northern outlet of the Small Boulevard and the bridge at the end of the ringroad are missing. It is clear that a wrong decision was made. It was a similar blunder in the early 1990s to let the ring road network of the Lágymányosi Bridge (now Rákóczi Bridge) be lost and replaced by a radial Szerémi Road to the south. It is interesting to see that, with the exception of the Grand Boulevard, the construction of almost all ring roads in Budapest got stuck somewhere. It is in the nature of politics to always choose the line of least resistance, which would generate negative effects for many hundreds of years. This is particularly true to urban architecture.

Does the bridge have any original structural elements? The bridge was inaugurated in 1849. Tierney Clark, the bridge engineer, originally designed the bridge for a distributed load of 250 kg/m².

The Chain Bridge in 1894. Fortepan / Budapest Főváros Levéltára / Photos of László Kiss (https://fortepan.hu/hu/photos/?id=93392).
 
The Chain Bridge in 1894. Fortepan / Budapest Főváros Levéltára / Photos of László Kiss (https://fortepan.hu/hu/photos/?id=93391).

By the early 1900s, the bridge deck had already become quite worn, the deck could easily swing, the cast iron structures were broken in many places, the wooden elements were rotting.

 

The bridge did not have a real bracing system, only the braced handrails (constructed in timber and iron brackets) on either side of the chains stiffened the bridge. During the refurbishment (rebuilding) in 1913-1915, practically the entire cast iron structure was replaced except the piers. The old chains could not have held the weight of the new steel deck, so they were also replaced. The new chains had twice the cross-sectional area and the chain-plates became taller and thicker. The bridge also received steel trusses to stiffen the deck, these are the structural elements that make it practically impossible to see the Danube if we drive across the bridge.

The bracing trusses in 1939. Fortepan / Photos of Gali (https://fortepan.hu/hu/photos/?id=128957).

The load-bearing capacity of the new structure withstood a distributed load of 400 kg/m². During the second rebuilding in 1947-1949 after the World War II, 76% of the chains were reused and the bridge received a completely new steel-concrete composite deck with bracing trusses.

The reconstruction of the bridge in 1949. Fortepan / Photos of UVATERV (https://fortepan.hu/hu/photos/?id=5360).

The load test of the bridge in 1949. Fortepan / Photos of UVATERV (https://fortepan.hu/hu/photos/?id=79982).

The reconstruction of the bridge in 1949. Fortepan / Photos of UVATERV (https://fortepan.hu/hu/photos/?id=79857).

The triumphal arches were shaped with tapers on all sides. The gate was widened by 1 m almost imperceptibly, so now the originally vertical inner walls became parallel to the outer sides of the towers. The bridge is nearly 170 years old, but every element except the towers is newer. Three-quarters of the chains are around 100 years old, while the steel-concrete composite deck is “only” 70 years old.

What is the current condition of the bridge? The bridge will not collapse, neither now nor in the near future. The condition of the deck’s reinforced concrete slab is poor, because the Hungarian construction industry of the 1950s was not famous for quality work. The water insulation of the deck has been ruined, the corroded rebars cast off the concrete cover. Under heavy loads, the slab can crack easily. One of the chain bearings is stuck due to corrosion, not moving. The chains were last examined in the 1980s. The worst conditioned chain-plates are in the tunnel of chains, between the chain chamber and the surface.

Longitudinal section of the shewing tunnel for chains (http://www.bpestchainbridgearchive.com/fb/fb.php?pdf_file=PLate%2023.pdf ).

The chains are rusting away and their cross-sectional area is decreasing continuously. The deficit was 10% then, by the 2000s it had continued to grow, by now it may have reached 15-20%. The chain-plates in the tunnel of chains cannot be accessed, repaired, or even inspected. So, the load-bearing capacity of the bridge must be reduced from time to time.

What kind of traffic load is allowed on the bridge right now? The distributed load of the deck is still 400 kg / m². The global load-bearing capacity is adequate under vehicular and distributed loads, but due to the poor condition of the reinforced concrete slab, it can easily crack under a wheel, so buses and trucks are currently banned from the bridge. The load of pedestrian bridges is 500 kg / m², that is higher than the current one, so the reclassification of the Chain Bridge as a pedestrian bridge is not possible.

What is the condition of the old English chain bridges? Nearly a hundred chain bridges were built around the world, but most of them have been destroyed. There are currently only 4-5 bridges under road traffic. The most notable are Menai Suspension Bridge (1826), Marlow Suspension Bridge (1832), Clifton Suspension Bridge (1864) and Hammersmith Bridge (1887).

The cross section of the bridge deck of the most notable bridges (http://www.bpestchainbridgearchive.com/fb/fb.php?pdf_file=T14_34_IV_33_001.pdf).

Almost all of the superstructures have been demolished and rebuilt from durable steel. However, the rebuilt bridges are also at least 100 years old, so they need to be closed down from time to time and their whole structure must be thoroughly checked like in the case of Hammersmith Bridge a few months ago.

What does the future have in store for the bridge? There is a decision to replace the old reinforced concrete deck with a new orthotropic steel deck next year (the chains and the steel trusses will remain), so most of the visible problems will disappear. Everyone leans back confidently, the political storm subsides and the problem is frozen for 20-30 years. But in fact, the chains continue to corrode. The load-bearing capacity of the bridge will be constantly decreasing and no one will know at what rate.

From my point of view, there are three solutions to save the bridge. In the first two cases, the Chain Bridge would become a pedestrian bridge, and in the third case, the current traffic load would remain. The first solution is a regulation to limit the load, the second is to reduce the area available to traffic, and the third is to strengthen critical chain-links.
The standard loads of pedestrian bridges are greater than the current load of the Chain Bridge that is the reason why it cannot be directly reclassified as a pedestrian bridge. The Gordian knot can be cut through by limiting the number of people allowed on the bridge at the same time. If access is restricted by an access system, the load on the bridge can be controlled. The road could be used by pedestrians, public transport vehicles and emergency vehicles. However, pedestrians walking on the roadway can’t see the river from behind the steel trusses. There was no visual obstacle on the bridge in 1849, so the elimination of the steel trusses could also be viewed as authentic restoration if a new and suitable bridge deck would be built. Even though this is a possible solution, the current tender documents contain different bridge deck arrangement.

In the second case, also without the steel trusses, the available area of traffic should be reduced with street furniture and other landscaping solutions, etc. intensive / extensive green roof surfaces, similar to New York's High Line Park.

The third, long-lasting solution would be to reinforce the chain-plates in the tunnel of chains. The plates cannot be accessed in the tunnel, so it must be exposed from above and widened from the side. This operation would involve the demolition of the roadway, but would be located inside the building site, so it would not cause any further traffic restrictions. The chain links are connected by means of a steel pin. Both ends of the pin are closed with a giant nut.

After removing the nuts, the outer 17 mm thick chain-plates must be replaced with newer and thicker chain-plates, that have a larger cross-sectional area. The steel pins have sufficient length, so additional chain-plates can be placed next to the existing 12-13 pieces of 29 mm thick plates. The increased cross-sectional area would extend the life of the bridge by several decades, or even a century, under the current traffic conditions.

Each of the three solutions is significantly simpler, cheaper, and faster than a complete replacement of the chains. I admit that everyone is accustomed to the stiffening steel trusses, built in 1915, but without them the sidewalk could be wider, the massive visual barrier would disappear, and finally, we would get back the look the bridge had 170 years ago.

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