History of Sustainable Bridge Solutions History of Sustainable Bridge Solutions

The chapter is a voice in the discussion concerning sustainable bridge development. Nowadays, the term has rather been abused, and therefore the presented approach refers to these elements of design, construction and maintenance of bridges—with regard to their role in transport and social life—which have been present in bridge construction for a long time and can be easily incorporated into the concept of sustainable bridge construction. Sustainable development, sustainable construction and so on are multidimensional. In the considered bridge construction area, looking at construction processes as interfering with the environment and which could and should be restricted is a new element. Nevertheless, other proven constructional solutions and technologies are characterised by their reliability. Assuming that the constructed bridges are to serve the next two or three generations of users, we can try to extrapolate current technical conditions on the next 30 or 60 years, i.e., up to three generations. We can do it if we know and are able to critically assess the history of bridge construction. Following this reasoning, the history in question is referred to in this paper, although rather subjectively and with the omission of numerous important personalities and technologies as well as instructive failures due to the publishing limitations.


Introduction
Sustainable bridges is a term exemplifying the general idea of sustainable development. The concept is a result of the works of a UN commission-the World Commission on Environment and Development-conducted from December 1983 to December 1987 and concluded with the report Our Common Future. At present, several definitions of the basic concept and its specific component disciplines are in use. One of the general definitions emphasises preservation of natural environment by achieving the developmental objectives in a responsible way: the present generations' responsibility to regenerate, maintain and improve planetary resources for use by future generations. Nowadays, the idea has developed into specific disciplines, such as sustainable engineering, sustainable bridges [1] and sustainable design [2].
In the development of civilisation, an extensive and well-organised transportation system, i.e., roads, railway, bridges, air transport and maritime and inland navigation, safe both for people and environment, is of primary importance. The development and constant modernisation of road and rail infrastructure is connected with significant pollution emissions into the air, soil and water. Investments are accompanied by noise and traffic disruptions. These negative side effects have an equally strong impact both on people and environment. In general, they can result in a temporary or even permanent closing or changing of wildlife corridors, animal herd fragmentation, changing of nesting sites or habitats.
Roads and bridges, despite obvious differences, constitute a technically inseparable set. The name of the first and still functioning technical school, excellent École nationale des ponts et chaussées founded in 1747, is quite symptomatic here. Bridges as such belong to the elite area of civil engineering. This position stems from their civilisational, social, architectural as well as military role.
After the horrible experience of the first World War, the Briand-Kellogg treaty [3], renouncing war as an instrument of national policy, was concluded. History, including the most recent one, shows that military operations are still conducted on a different scale and so it happens that some are aimed at bridges. Figure 1 shows the Hanoi bridge that was destroyed during the Vietnam War. Its crippled form is a dramatic monument to this war. Sustainable bridge construction refers to the minimisation of harmful emissions during bridge construction. It is equally important, however, to design durable bridges, i.e., with minimum serviceability of 100 years as stipulated in the design standards [4]. The bridge longevity results from the structure maintenance therefore its design should take into consideration the ease of its future maintenance.
A design taking into account the future changes of traffic, both in terms of its volume and type, seems to be a great challenge. The existing methods of forecasting traffic changes cover periods from 5 to 10 years. Nobody can foresee what can happen in 50 years, [5]. Bridges have been built for thousands years and that is why it is easy to indicate the ones which have proved reliable according to various criteria. For this reason, they can be seen as sustainable bridges. The history of bridge construction referred to this paper is presented from such a perspective. In many cases, only the name of a bridge is mentioned, which results from its recognisability as well as an easy access to basic encyclopaedic information on the Internet.

Archaic period
The history of bridges can be told in many ways. It will always be a subjective representation, strongly affected by the author's attitude. This is also the case here.
The first large-scale bridge, recorded by Herodotus, was a structure for crossing the Dardanelles (Hellespont in the ancient times, the area of Çanakkale in Turkey at present), constructed by Greek constructor Mandrocles of Samos in 513 B.C. It was a ship pontoon bridge. Soon after, in 480 B.C., two other pontoon bridges were constructed by Xerxes' army, see History of Herodotus [6]. At the point of the bridge crossings, the Strait of the Dardanelles is 1.4 km wide. It should be noted that Herodotus' description of the bridges gives rise to doubts; therefore it can only be assessed in terms of likelihood.
In 55-53 B.C., during the wars with the Germanic peoples, Julius Caesar commissioned the construction of two wooden bridges over the river Rhine. At least two reconstructions of these bridges exist [7]. Another large-scale bridge was constructed during Emperor Trajan's war against Dacia in 105 A.D. by Greek architect Apollodorus of Damascus. Its remains, in the form of stone pillars, are to be found in a place with a poetic name: Turnu Severin. It was a wooden arch structure based on 20 massive supports where the Roman pozzolana cement was used. The bridge was immortalised in a relief on Trajan's column in the Foro di Traiano in Rome. All of the aforementioned bridges do not exist anymore, but in Peloponnesus there are still two stone bridges constructed with so-called Cyclopean boulders to be found, known as Mycenaean Bridges. The period of the Mycenaean culture falls in the mid-Bronze Era from approx. 3000 B.C. to 1000 B.C. Hence, it can be inferred that the bridges are at least 3000 years old and for that reason are considered the oldest existing bridges in the world. Given their age, they are in a superb technical condition. They are not large-scale objects-the width of the light of the flow opening is approx. 1.5 m, its height approx. 2 m, Figure 2.
It should be highlighted that Mycenaean bridges were elements of the road system, which today is known as Mycenaean Highways [8] -which may be a slightly exaggerated name. The term was first introduced by A. Jansen, the author of one of the chapters of this book.
Mycenaean bridges are very interesting from the point of view of structural mechanics and construction technology. At the first glance, they seem to be arch structures. But if so, one must admit that these arches are rather accidental. The arrangements of boulders of which the arches are made demonstrate the lack of knowledge with regard to the essence of the arch behaviour. As a matter of fact, they are corbel structures which-as a result of seismic earthquakes-have been degraded to the present shape. Hence, the currently observed cyclopean boulder arches are a result of the transformation of the corbel system into a possible mixed arch-corbel static system. The effort and stability of Mycenaean bridges were analysed in the paper [9]. Identification of the technology of Mycenaean bridges is a great challenge, Figure 2. The cantilever slab technology enables construction without scaffolding. If indeed it was so, Mycenaean bridges were a major constructional achievement. Despite the fact that Mycenaean bridges constitute a part of the heritage of mankind, they have not been sufficiently studied. Paradoxically, apart from taking external measures, their ultra-historical character makes it impossible to conduct standard research.

Times of the Roman Empire
The period of the Roman Empire saw an overwhelming abundance of stone, brick and stonebrick arch bridges-apart from military bridge structures, naturally. This period can also be equated with Roman roads. The system and quality of roads enabled movements of the Roman legions and also served civil purposes.
Before we start discussing Roman bridges, however, we need to look at a much older and historically very important road, namely, the Persian Royal Road [10]. It crossed the Persian Empire from Susa or from Persepolis to Smyrna (present-day Izmir). Depending on historical sources, the total length of the road amounted to 2600-3000 km. The road was built by the Persian king of kings, Darius I (c. 550-486 B.C.) and was used as a postal route. It took from 7 to 10 days for the system of courier stations and teams to cover the distance. The road was used by Alexander the Great, and then by the Romans. It was in service for more than 3000 years and coincided with the Silk Road to a considerable degree.
In the town of Diyarbakir (Kurdish: Amed) in south-eastern Anatolia, a bridge called Ten Eye Bridge has been in use till this day, Figure 3. It was constructed in the eleventh century, although its dating is connected with the conducted reconstruction. Some historical sources connect this place with the Royal Road and if this were to be the case, it would be one of the oldest bridge crossings in the world. Assuming that 1065 A.D. is a trustworthy date of the reconstruction, the bridge on the river Tiger (Dicle -tr.) comes from the Roman period. Here, the dating of the Roman Empire should be highlighted. In most part of Europe, it covers the period until the fall of the Empire in 476 A.D. In the Mediterranean, it is seen as connected with the fall of Constantinople on 29 May 1453. There is a difference of almost one millennium. In these circumstances, Roman bridges in Turkey and Arab countries may be much younger than Roman bridges in Spain.
One of the first bridges on the river Tiber built in 62 B.C. is certainly Roman-according to the both modes of historical dating, Figure 4. There is a funny story connected with the bridge: when it was constructed, the payment for work was refused unless it was proved that the structure was durable. The photograph in Figure 4 was taken in 2008. Nevertheless, the ordering party's anxiety is easier to understand if we take a look at other, even later, Roman bridges, as shown in Figure 5. The bridge is located on a Roman road bearing a Spanish name: Via de La Plata. It is over 700 m long. Its elements include processed granite arches. There are 60 arches based on massive pillars. They are heavy, reliable structures.
The Pons Fabricius marked the beginning of a new way of looking at bridges that, aesthetically, are relatively light and this trend has survived in Rome till this day. With the exception of the Ponte Pietro Nenni that carries an underground line, all the bridges in Rome have arches. Among them, one finds the first reinforced concrete bridge in the world, the Risorgimento of 100 m span, constructed in 1912 by F. Hennebique. Also, in 2011, a beautiful pedestrian steel footbridge with shallow arches was built-the Ponte dela Musica. In the Roman period, bridges known as aqueducts were also built, slender and beautiful in their monumentality. The only load they carried was the dead load with an insignificant addition of flowing water, Figure 6. It should be mentioned that during the Roman Empire, but 200 years later, tower aqueducts were constructed. Water flew in a leak-proof pipe located on relatively short arcades. The level differences were solved on the basis of the principle of communicating vessels according to, surprisingly, Pascal's theorem, see Figure 7.

Bridges in the middle ages
During the European Middle Ages, stone arch bridges were continued to be built, although their variety was limited. Also, the road development slowed down. Bridges usually had a defensive character. Figure 8 shows two bridges leading to the medieval capital of Spain, Toledo, which are a good example of the role and technique of the medieval bridge construction. In this period in Turkey, a bridge construction canon was developed. Nowadays, such structures are sometimes called Turkish. The bridges in question were still arch bridges, usually made of light colour stones. They have a main span and, possibly, additional spans that serve as flood relief channels in case of high water. It should be born in mind that in the case of the arch bridge, only the arch is the carrying element. The extended walls in arch bridges act only as a façade, very often hiding empty spaces. These spaces were frequently used as utility rooms by bridge guards and sometimes even as guest rooms for travellers. This was the case of the bridge on the river Batman in Turkey, twelfth century, Figure 9. A twin object, built by Mimar Hayruddin in sixteenth century, can be found in Mostara on the river Neretva. The stem of the name of the town, which is an adjective, comes from the word most, i.e., bridge. The popularity of arch bridges results from the arch mechanics. To offer an insight into the issue, we can refer to an exercise solved by students in the structural mechanics class. It is about a parabolic three-hinged arch, evenly loaded. Performing basic transform calculations we find that the bending moment at any point of the arch equals nought. It means that, in fact, the arch is not three-hinged but it is a sequence of hinges. Similarly, in the case of a shearing force we find that it equals naught at all the points. It is not a classical approach, but consequently reasoning we can conclude that the arch is a sequence of hinges functioning of which is based on a shear force. Another conclusion is that the only non-zero internal force in the arch is the force normal with regard to its cross-section, and, what is more, it is a compressive force. In practice, we can shape the sides of stone blocks in such a way that, geometrically, they form a parabolic arch. This arch is going to be a durable and efficient structure-on one condition. In arches, the outward-directed horizontal reaction, called thrust, is of primary importance. It has a significant impact and, more often than not, the lack of the proper ground resistance results in the destruction of the arch as a whole or its substantial weakening as a superstructure-at best. The discussed case of a parabolic arch equally loaded is a theoretical one, however, in the case of a real structure we can imagine a set of material points of the highest bearing capacity and that will be an illustration of such an arch. Figure 10 shows two viaducts on a mountain path near Konya, made with processed stone blocks assembled without mortar.
The advantages of arches in bridge structures make this solution commonly used until this day. The photograph below shows an arch bridge destroyed to such a degree that the arch structure is plainly visible, Figure 11.

Renaissance: Leonardo bridge over Golden Horn
Renaissance is strongly associated with an outstanding personality of this period, Leonardo Da Vinci. This genius had a brief albeit challenging bridge episode, Figure 12.
Through diplomatic channels he was asked to design a project of and construct a bridge over the Golden Horn (Haliç -tr.), an inlet of the Bosphorus in Istanbul. In 1502, an ambassador of Sultan Bayezid II came to Rome. It is probably then, from 1502 to 1503, that Leonardo made the sketch of the bridge that now can be found in the manuscript commonly known as Paris Manuscript L [11]. The manuscript pages are rather small, 7 × 10 cm, and the drawing itself is quite simple. Despite the fact that the drawing does not contain any dimensions, it is assumed that the bridge was supposed to be 240 m long and 23 m wide with the arch curvature of 40  [12], which was a reference to Leonardo da Vinci's concept. However-in the author's subjective view-it is only partially successful, both in the aesthetic sense and as an incorporation of the Renaissance genius' idea. Looking at the drawing in the manuscript, it is difficult to decide about the bridge structure. Sand's footbridge seems to be one of many possible interpretations.

Wooden simple bridge
Wooden bridges have always been built. For this reason, a technology was developed which took into account the characteristics of wood as a material of relatively low strength, but at the same time commonly available and easy to handle. The strength of wooden bridges has always been low. It was good if the serviceability period amounted to 20 years. A wooden bridge is also the result of a skilful application of structural mechanics. For the above reasons, usually simple, mechanically pure solutions were chosen. Let us consider the most common wooden bridge, Figure 13. Abutments are meant to transfer two kinds of impacts. The first one refers to vertical reactions caused by loads on the carrying deck. For this reason, a row of poles was constructed under each girder. The other impact refers to active ground pressure behind an abutment. Here, the second row of poles was used-outer poles were put behind so-called planking. As a result, a retaining wall was obtained which was also additionally supported by its anchoring in the ground (deadman). The bridge wings were slanting, of variable heights.
An interesting solution is a saddle which enables reduction of support spans and the values of bending moments under the supports. In the case illustrated in Figure 13, the bridge beam is single but wooden bolster composite bridge beams were also used. The composition was not complete-from the modern perspective it should rather be called partial integration. The construction of wooden bridges was at least as complex as the modern bridge technology. The dimensions of a saddle are determined on the basis of a simple differential calculus assuming extreme curvatures of the beam and the saddle at the local point of contact. Paradoxically, the best work about wooden bridges is a book [13] written 100 years ago. The technology of wooden bridges is still in use in the case of temporary bridges. Additionally, there is a new option available which is connected with the ecofriendly recycled plastic technology, see [14]. Instead of natural or sawn wood, recycled plastic logs or panels are used which contributes to the minimisation of deforestation. Figure 13. The scheme of a wooden bridge: carrying elements.

Iron bridges
The industrial revolution in England was a turning point in bridge construction. In 1779 an arch bridge, known as the Coalbrookdale Bridge or Iron Bridge [15], was constructed by Abraham Darby III with cast iron from his ironworks located in Shrewsbury, Figure 14a.
One hundred years later, bridges of spans reaching 160 m were built with wrought iron. Figure 14b shows a photograph of the bridge on the river Duro in Porto. It was constructed by T. Seyrig, Gustave Eiffel's associate. At present, the bridge has no utilitarian function, but it is one of the highlights of the city of Porto.

Reinforced concrete
Another turning point in bridge construction was the invention of Portland cement and, as a result, using concrete based on it as well as reinforced concrete. The first concrete bridge was a small park object in the botanic garden in Grenoble, Figure 15, constructed by Louis Vicat and his son. Vicat was also one on the inventors of cement.  Chronologically, between Vicat's bridge and Lambot's boat there is only an interval of 3 years, but the bridge in Chazelet was built 20 years later. It can be assumed then that the popularisation and implementation of the new technology lasted a similar amount of time.
Even a reinforced concrete bridge had to be invented by someone. Again, there are numerous candidates to the title of the inventor: T. Hyatt (1877), F. Coignet (1861), P. Christophe (1902). It seems, however, that François Hennebique can be indicated as one, Figure 16a. He was an author of several patents and, apart from conclusions from the author's bibliographic research, he is named as the reinforced concrete pioneer in various studies, e.g., [17].
Hennebique created a global company (Figure 16b) which employed the best engineers and architects building reinforced concrete structures including bridges, Figure 16. He offered ready-to-use projects, technology and very often materials as well. From the very beginning Hennebique developed a network of contractors. In practice, the company was known as Le Système Hennebique or Béton Armé Hennebique. The sale of structural and technological solutions was connected with intensive training and supervision provided by Hennebique.
An essential tool of Hennebique's success in building his company was the technical magazine Le Béton Armé [18], published from 1898 to 1939, Figure 16c. Apart from purely technical texts in the area of the theory of reinforced concrete as well as the practice, i.e., descriptions of the construction of reinforced concrete structures, one could find information about the network of the company's representatives and contractors. The magazine was richly illustrated with technical drawings, photographs of various construction stages and finished structures as well as advertisements of companies, products and technologies.
Thanks to a happy coincidence, in the city of Lublin in Poland there are two Hennebique beam bridges constructed by Polish engineer Marian Lutoslawski in 1908 and 1909, respectively. One of them has been renovated. After it was put into service, the city's cultural circles took it over and it has been called the Bride of Culture since, Figure 17. The bridges in Lublin are examples of a successful transformation of the bridge technology using wood into the one of reinforced concrete, a new material at the beginning of the twentieth century, see [19].

Suspension bridges
The carrying elements of a suspension bridge is a set of pylons and a rope in its natural catenary shape. It is assumed that the origins of suspension bridges are hidden in remote history. The tradition of the construction of narrow footpaths in Asia, especially in Tibet, is widespread. The first modern chain suspension bridge was built over the Menai Strait in 1826, connecting the Welsh island of Anglesey to the mainland. Its maker was brilliant bridge constructor Thomas Telford (1757-1834), see [20].   Actually, it was a mixed system which nowadays is called the hybrid suspension and cable stayed bridge. In a manner of speaking Roebling repeated the above-mentioned bridge in New York in  Modjeski (1861Modjeski ( -1940. The longest span is 910 m, see [22]. The most famous American suspension bridge is naturally the Golden Gate Bridge, constructed in 1937. Its total length amounts to 2737 m, while the main span 1280 m, Figure 20. At present, the Akashi Kaikyō Bridge (Japan) has the longest central span of all suspension bridges-it is 1991 m long.
All the above-mentioned bridges have truss platforms. It is a proven and reliable solution.
Simultaneously, suspension bridges with plate girder deck were constructed such as the Tacoma Narrows Bridge, for instance. The length of its main span amounts to 853 m. The bridge was opened for traffic on 1 July 1940. On 7 November 1940, the catastrophe stuck-and was filmed. The cause of it was the so-called aeroelastic flutter effect. For this reason, the bridge is unofficially known as Galloping Gertie. The studies and analyses conducted at that time showed that truss load-bearing structures should be used [23]. Nowadays, when the advanced finite element method (FEM) procedures are available, it is easy to demonstrate by means of numerical analyses that the causes of the catastrophe were correctly identified.
In 1966, the bridge over the Severn Bay near Beachley in Scotland was built. It is a low profile box carrying deck structure. The middle span is 988 m long. An unusual feature of the suspension cables carrying the deck is that they are not vertical, but arranged in a zigzag pattern. The diagonal arrangement of hangers-as compared to vertical ones-increase the dynamic stiffness that is additionally supported by tuned mass damper-harmonic absorbers.
The deck is an orthotropic steel box of the aerofoil shape. The bridge was tested and approved by the designers Freeman, Fox and Partners following wind tunnel tests.
The First Bosphorus Bridge constructed in Istanbul in 1973 is a replica of this bridge. The main span-the distance between the towers-is 1074 m, Figure 21. When opened, it was the second bridge crossing between Europe and Asia constructed since 480 B.C.

Cable-stayed bridges
A cable-stayed bridge has one or more towers, from which straight cables carry the bridge deck as elastic supports. There is a clear analogy between the behaviour of backstays and cablestayed bridges. The first known analysis of this problem comes from 1823 and was performed by C.L. Navier, see [24]. Diagonal rods in Bollman trusses also bring to one's mind cable-stayed bridges. In 1873 in London, the Albert Bridge, designed by Ordish and Bazalgette, was constructed. The first modern cable-stayed bridge is the Strömsund Bridge in Sweden, designed by Franz Dischinger (1956), Figure 22a.
Considering the development of the cable-stayed structure, one can specify the German period connected with German engineers F. Dischinger, U. Finsterwalder , F. Leonhardt, H. Homberg, H. Wittfoht, E. Jux and others. Naturally, cable-stayed bridges have been constructed everywhere. Figure 22b shows one on the most beautiful bridges of this kind, namely, the Bridge of the Slovak National Uprising in Bratislava, constructed in 1972. Another spectacular cablestayed bridge is the bridge located at the outlet of Lake Maracaibo, designed by R. Morandi and built in 1962, see [26].   Cable-stayed bridges are aesthetically challenging. To highlight their attractiveness appropriate lighting is required, Figure 24a. Figure 24b shows a bridge in the mountainous part of Gran Canaria where an austere structure matches an equally austere mountainous landscape. The whiteness of the bridge contrasts with the surroundings. The backstays are clearly visibleparadoxically, thanks to cloudy weather. Very often backstays are not discernible at all and for this reason, at night special illumination is used.
In the family of cable-stayed bridges, a special group can be distinguished on constructional grounds, namely, extradosed bridges, Figure 25b. In this case, the inclination of cables measured from the deck level to the cables is significantly lower than Π/4. Projecting the normal force acting in the cable N onto horizontal and vertical directions we arrive at N H , N V components and, additionally, we obtain N H > N V . As a result there occurs a significant compression in the carrying-deck which in the extreme degree is manifested near the tower. The horizontal force can be used in the design as the force pre-stressing the deck longitudinally. During the design works and the construction of the Golden Horn Metro Bridge in Istanbul, there was an on-going global discussion about limiting the architectural dominance of a constructed bridge, see [27]. Despite the fact that the pylons demonstrated Ottoman features it was suggested that, with regard to the global cultural and architectural heritage of the area in the vicinity of Golden Horn, the bridge would constitute an extraneous dominant. The bridge was completed without any changes in 2015, see Figure 24a.
Short distances between bridges in cities contribute to amusing and sometimes even grotesque situations. Two gorgeous bridges in Sevilla can serve as an example. The Puente de la Barqueta is a tied-arch bridge designed by J. Arenas and J. Pantalerón. The other bridge is the cablestayed Puente del Alamillo designed by S. Calatrava. The construction of the both bridges was completed in 1992. They are located on a straight strip of the oxbow lake of the river Guadalquivir, 1 km apart. Their views overlap, which can be rather irritating.
It is quite a common case in highly urbanised areas and, actually, it occurs in every city on a big river. Figure 25 shows two frames of a movie that is, so to speak, created in the head of a passer-by walking on the Roman Bridge over the Guadiana River in Badajoz. Depending on the spectator's mood and perception it can appear as chaos or an interesting coincidence.
Cable-stayed bridges are efficient in terms of bridge structure mechanics when placed between cantilever and suspension bridges. On this position, they also prove to be economic solutions. It means that they can be used in the area of small architecture, even if beam or plate bridges are cheaper and better, in a sense. Above all, the pylon, as an interesting dominant, contributes significantly to the attractiveness of a local landscape, see Figure 26.   The cable-stayed technology has been used as a temporary support for arch bridge scaffolding for many years. These are transitional arrangements and images but ones that are truly charming thanks to the additional spaciousness they create. Sometimes, as shown in Figure 27, an austere surrealist image is obtained. This short-lived aesthetic form refers directly to the art of performance as it disappears the moment the arch is built. A separate place in architecture and structural engineering belongs to Santiago Calatrava, although in this paper he is mentioned only briefly. Calatrava, in the architectural millieu's opinion, is a creator of gigantic forms-spatial sculptures which enhance the landscapes of various cities around the world. As a bridge constructor, he broke a mental barrier existing in the area of bridge design where bridges were designed for bending as a dominant mechanical state. In the case of pedestrian footbridges he constructed bridges where carrying elements are screwed together. Due to this, the mental barrier has been broken.
Examples of gigantic sculptures in urban areas include the following bridges: the Puente del Alamillo in Sevilla, 1992, the Puente De La Mujer in Buenos Aires, 2001 and the Sundial near Redding, California, 2004. The Jerusalem Chords Bridge, however similar, is new concept. These bridges are purely white, the pylons are inclined by approx. 50° and they resemble each other, as images, to a high degree. However, the structural engineering of each of the bridges is different. The Alamino is a road bridge with a beam load-bearing structure identical to the one of the arch bridge Puente Lusitania in Mérida. The rest are pedestrian footbridges with screwed load-bearing structures. The Puente de la Mujer is a moveable bridge with a rotary movement about the vertical axis on the support with a pylon. The Sundial has a truss loadcarrying structure. As demonstrated, each of these bridges is different and only for architects their images are identical.
In the author's opinion, the most interesting is the Katehaki Footbridge in Athens, 2004, Figure 28. The footbridge is never entirely visible and therefore mysterious-making one yearn for more. The pylon is slightly bent as a result of which it loses the original but at the same time primitive form of an opened set square and becomes similar to boats crossing the Mediterranean Sea. The footbridge is literally squeezed between uninteresting street buildings of Athens. A crossing passer-by who reaches one of its ends can look into the windows of the buildings located only 10 m away. The footbridge is in the middle of street traffic. The lack of space and the constant flow of passing vehicles contribute to the dynamics of the structure which, thanks to its white and slender elegance, floats above crowded streets of Athens.
The Millennium Bridge in London is a hybrid of two static schemes. There are deck segments supported by cables (vide the ribbon scheme) and at the same time the deck is suspended on the same cables as in the case of the suspension bridge. Figure 29. The history of the bridge opening is a typical English story, i.e., starting from a total failure and ending in full glory, see, e.g., [28]. The bridge was conceived as an interesting design, quite innovative.
The opening day had been expected for a long time. Finally, on 10 June 2000, thousands (ca. 5000) of people were waiting to enter the bridge and walk to other side. At this moment, the new bridge entered into a state of unpleasant complex horizontal and vertical vibrations. It turned out that despite the use of advanced computational techniques and the designers' experience, the bridge demonstrated dynamical over-sensitiveness. The new bridge was closed on 12 June of the second millennium. Soon after, a diagnosing research was conducted which pinpointed the cause of the dynamic instability of the bridge. On its basis, it was decided to install a system of dampers which changed the dynamic response of the bridge. Two years later, the Millennium Footbridge was reopened and has been working properly ever since.

Instead of a summary
There are many bridges, constructors and technologies that should be and are described and discussed in various papers and monographs. From the wide range of existing bridge structures, one conclusion can certainly be drawn: every bridge is important.