The construction of the Aquincum Bridge has been a political and professional issue for decades, but to date no substantial progress has been made. All that has emerged in recent years is conventional solutions that are mediocre and unimaginative. If a good initiative can appeal to the public, sooner or later politics will find it for itself, because getting votes is one of the most important political goals. Since almost everything is decided in the political arena, the fate of this bridge will also be decided by politics. As a bridge designer and university lecturer with a passion for bridge aesthetics, all I can do is offer alternative solutions that I believe best meet the needs of today's society. In this spirit, I would like to come up with a completely new concept.
Everything we build affects our environment, our behaviour and ultimately our choices. Urban pedestrian and cycling infrastructure are significantly cheaper to build than road infrastructure. A more attractive environment encourages walking/cycling, the rising number of pedestrians/cyclists leads to a more intense public life. Social inclusion is also increasingly important because of the sense of security. If people can meet each other and not just sit at home, the life of the city will be more vibrant, and even safer, more sustainable, and healthier. Creating community spaces is a priority. Community spaces can also be created on bridges, of which there are many international examples from Paris to Copenhagen, but unfortunately there are no such bridges in Hungary. Bridges are basically seen as monofunctional facilities, but I am determined that where it is justified, bridges with additional functions could be built. This is already an accepted view abroad in the field of pedestrian and cycle bridges, but there are few good examples of this in the case of road or rail bridges: Kienlesbergbrücke, Paleisbrug, Lentloperbrug.
 |
| Paleisbrug, ’s-Hertogenbosch, The Netherlands, 2015 – Benthem Crouwel Architects |
In this country, however, the idea is still very new and there are therefore many decision-makers who see bridges as mere transportation facilities that no one wants to sit on. The example of the Szabadság Bridge perhaps best illustrates the situation in Hungary. It is a low-traffic road bridge with a beautiful urban panorama looking north. In the middle of the girder bridge that looks like a suspension bridge many students and tourists sit on the girder itself, the upper chord of the truss. From spring to autumn, the bridge is almost full to capacity, showing that there is a real need for community spaces like this. One could go on at length about why the bridge is so popular, but the point is that it is a successful community space.
My concept is a general one, but I will apply it to the Aquincum bridge and take the characteristics of the bridge as a starting point.
First, let us look at the constraints that define the bridge. The proposed bridge would be built on the north side of the Northern Link Rail Bridge. There is no road connection, so there is quite a detour for those wishing to cross to the other side of the Danube. The design of a new bridge is constrained by the almost 700 m long, monotonous, repetitive truss girder structure of the adjacent railway bridge. The new bridge will have to respond to all these constraints, while, at the same time, it also needs to meet traffic demands to the maximum.
The surrounding area of the bridge is almost untouched. Looking north from the bridge, the 600 m wide Danube can be seen, bordered on two sides by woodland and trees, while the peaks of the Börzsöny and Pilis can be seen on the horizon. Looking south, the green spaces of Népsziget, Hajógyári Island and Margaret Island can be seen in the foreground, while the Buda Hills and the well-known buildings of the city centre can be seen in the background.
An urban bridge is not only a transportation facility for transit, but also a unique vantage point and community space that offers unusual perspectives to those crossing the bridge. The length of the bridge is considerably longer than the 150-200 m of the ideal pedestrian bridges in Paris, and therefore requires the installation of attractive features on the bridge deck that will make pedestrians oblivious to the inconvenience that may be caused by the distance.
Secondly, let us look at the bridge structure I have proposed. The bridge is a straight, 10-span girder bridge with a length of nearly 700 m. One bridge pier each will be placed in the middle of the two, 93 m long outermost spans. The bridge piers widen slightly outwards and support the lower chords of the main girders thanks to the V cut-out. The cross-sectional dimensions of the reinforced concrete piers are continuously reduced in the direction of the superstructure.
 |
The V-shape of the riverbed pier
|
The shape of the bridge is defined by a warren truss girder, which is undulating in the horizontal and the vertical plane. The sideview of the bridge appears as three waves that blend into the surrounding landscape. Thanks to the relatively dense supports (which are in line with the river piers of the railway bridge), the bridge can have a higher dead load. The support of the truss girder is not usual since they are not supported at the endpoints. The truss is supported by two internal compressed diagonals. The wavelength of the trusses is just twice the span, so that they reach halfway to the adjacent spans. Statically, two structural designs alternate on the bridge, resulting in a continuous multi-span bridge. The peaks behave as a classical truss girder bridge, while the troughs can be considered as an extradosed suspended structure. This design may at first seem unfavourable in terms of rigidity, but the plan and loading of the north terrace slab compensates for this effect. The vertical truss girder on the north side is 13 m high, while the south side is 11 m. The width dimensions of the lower truss chords are also different since the horizontal truss is clamped into the lower truss chord of the north truss. The width of the upper chord of the trusses is 2 m and the height is 1 m. The distance between the two main trusses is 18 m. The connection between the lower chords is made by evenly spaced cross beams. The reinforced concrete deck works in conjunction with the cross beams to provide an economical and easy-to-construct composite deck, which is not unimportant for a bridge deck of this size. The width of the curved terraces on the north side varies between 7 and 14 m. The walkway is a cantilevered structure of the horizontal trusses. The use of the triangular areas between the diagonals is the essence of the concept. The triangles can be left empty or can be used to accommodate containers with a higher dead load or can simply be covered. Triangular platforms vary in area from 15 to 50 m², with a thickness of 1 to 2.5 m and a maximum weight of 50 tonnes. Steel platforms with high load-bearing capacity (container or cover) are supported at the three corners and/or along the edges, depending on the load. There are 57 platforms in 10 different sizes on the bridge.
 |
| A warren truss girder, which is undulating in the horizontal and the vertical plane |
 |
The 'empty bridge' - bridge without platforms
|
 |
The cross section of the bridge in the middle
|
 |
Triangular platforms vary in area - different functions of the community space
|
Thirdly, we look at what I mean by the concept. As I mentioned in the introduction, the need is there, so community spaces can also spontaneously emerge (see Szabadság Bridge). The community space can be created in a planned way, especially if it is endowed with unique features that are popular with city dwellers and tourists. 'The Chameleon' is quite long, so it should perhaps have even more attractive features than a shorter downtown bridge. The needs of the target audience may change over time, so a design that was once thought to be a good solution may become boring, outdated, faded, or ruined. To remain relevant, the community space of a bridge needs to be able to renew itself from time to time. The 15 to 50 m² of space between the horizontal diagonals of the trusses can be used to create any number of features for pedestrians, for example:
- grassed areas with flowers, bushes, trees,
- paved areas with benches, deckchairs, swing beds, wide steps,
- mini playground with toys, swings,
- mini garden with ornamental plants,
- splash pool, fountain, waterfall,
- outdoor gym,
- poster stands for exhibits or other structures for temporary exhibitions, events,
- outdoor workstations with WIFI, outdoor sockets.
The choice of name for the bridge is not a coincidence; it should be noted that chameleons do not change their colour to hide, but to communicate, to send messages to each other. The bridge also communicates with the community of bridge users. The functions and colours of the community spaces on the bridge can be freely interchanged or combined, so that each of the three terraces can be given a completely different function. The external appearance of the north side of the bridge can vary from time to time, either seasonally or thematically for different events. The larger platforms (containers) can accommodate sufficient soil, making them ideal for trees. From a structural point of view, only platforms close to the main support can be loaded with soil. For platforms with a greater eccentricity, the dead load should be limited. On such platforms only plants with a shallower root depth should be planted or some form of surface cover should be provided. Covers may be made of solid or perforated steel sheeting, or the platforms may be covered with glass panels. If no platform is placed in the triangular holes, the inner side of the walkway should be fitted with railings. The platforms can be lifted in and out using a mobile crane and loaded onto lorries for transport, so that rearrangement can be carried out quickly, even at night.
 |
Possible functions (e.g. outdoor gym) of the community space in span of Pest
|
 |
Possible functions (e.g. wide steps to sit down) of the community space in the middle span
|
 |
| Possible functions (e.g. outdoor workstations) of the community space in span of Buda |
The terraces are separated from the carriageway by vertical wave-shaped trusses. To reduce the noise impact, noise barriers will be installed in the triangles of the vertical truss brackets on the north side. Noise from traffic will be compensated by the sound of splashing water and waterfalls which pour into the Danube, and which are fed in a continuous flow. The north side of the truss will be covered with nets for plants (i.e. ivy), creating a living, green, lush bridge.
|
| A flight of stairs on the upper chord of the central truss leads up to the top |
The three terraces could have three completely different functions, which will further increase the interest in exploring the bridge. The terraces are between 100 and 150 m long, with 100 m spans in between. From these intermediate sections, a flight of stairs on the upper chord of the central truss leads up to the rooftop viewing platform, from which the panoramic view of the city centre is revealed to the south. The uninterrupted panorama from the observation point is unprecedented, there is no other bridge in Budapest with similar features.
 |
| The rooftop viewing platform |
Finally, let us look at how the bridge can be adapted to current traffic needs. As already mentioned in the previous post, traffic needs can vary considerably depending on whether only local traffic or even many long-distance commuters need to cross the bridge. The width of the bridge deck allows for a 2x2 lane configuration, but this does not necessarily mean that it has to be designed. If local traffic is the initial priority, 2x1 lanes and a separated bicycle lane between the two main girders may be sufficient. Bridges are designed to last 100 years, so no one knows today what the future needs will be. For a future renovation of the Árpád Bridge, it would also be important to know whether there is a bridge nearby where traffic can be redirected. If higher traffic demands are to be met, the 2x2 traffic lanes would be placed between the two main girders, while the cycle lane would be retrofitted on the outside of the south girder. The 3.6 m wide 2x1 lane cycle track would be laid on evenly spaced 4 m long cantilevers and would be embedded in the lower chord of the south trusses. Of course, there is also the possibility to have the northern sidewalk of the railway bridge serve the cyclist traffic.
 |
The south side of the bridge with the 2x1 lanes arrangement
|
 |
The bicycle lanes on the south with 2x2 lanes arrangement (from the same point of view)
|
 |
The inner bicycle lanes in the case of 2x1 lanes configuration
|
 |
| The 2x2 lanes configuration (from the same point of view) |
In conclusion, I would like to summarise why I see great potential for urban bridges with a freely reconfigurable pedestrian walkway and a carriageway that can be adapted to changing traffic needs. Nowadays, many different fashionable adjectives are used for different objects and buildings. 'Environmentally conscious', 'energy-conscious', 'smart', 'minimal ecological footprint', 'sustainable' are all adjectives or signifiers that express a sense of responsibility and commitment towards our environment. However, except for small-span pedestrian bridges made of wood, stone, or concrete, it is not realistic to expect multi-lane road bridge structures to be built with a minimum carbon footprint.
 |
| Striatus Bridge, Venice, Italy, 2021 – Zaha Hadid Architects, Block Research Group |
In the case of bridges, environmental performance is measured by whether the bridge meets current traffic demands at all times. If a bridge structure has to be demolished prematurely because it was built with too few lanes or if lanes are empty because traffic capacities were wrongly estimated, then we failed to properly address environmental issues. The adjective 'smart' is applied to bridges that have a monitoring system. In this case, we have continuous feedback on how the environment and the traffic impact the structure. The sensors of the bridge collect structural measurements such as strain, rotation, load, displacement, vibration, and could measure environmental factors such as air quality, temperature, and wind speed. The bridge can be equipped with solar panels that generate the energy needed to operate the bridge (LED lighting, sockets for outdoor workplaces, possible water pumps etc.), which can earn it the 'energy-conscious' label. A permanent, vibrant, renewable community space can only be created if the bridge users are fully satisfied with the additional features. The functions of the triangular platforms of the free-form pedestrian walkway could be determined by the community of bridge users, in partnership with the city administration, and could therefore also be labelled 'democratic'.
 |
The 'green bridge' version
|
'The Chameleon' will hopefully provide an active community space where people can gather, enjoy themselves or simply contemplate the river landscape through a carefully selected mix of features, open and intimate in design, and of varying scales.
Megjegyzések
Megjegyzés küldése