| Movable bridges:
Special typea of bridges are movable bridges. In a separated condition, the bridge does not obstruct the passing ships. St.Petersburg is famous for its movable bridges, where almost all the bridges, with the exception of the Big Obukhovsky Bridge built on Neva are movable.
The special designs of movable bridges:
Bridges, which are separated at the middle portion
o Type 1: the span rises in horizontal position upwards;
o Type 2: the span or spans rise by rotating around one of its hinges
Turning bridges: the middle portion of such bridges is hinge fastened on a support standing in the middle of the river. The bridge gets separated by rotating the middle portion by 90 °, therefore the middle position becomes parallel to the river channel. The Varvarovsky Bridge, situated in the city Nikolaev, in the Ukraine serves as fine example of such a design, whose swing span has a length of 134 m.
The architecture of bridges:
Many bridges are outstanding monuments of architecture and engineering art. In some cities, such as St.Petersburg or Prague, bridges are an integral part of the city architecture.
Many ancient Roman bridges are made in the style of classicism: almost deprived of decor, they nevertheless create a sense of durability and reliability due to their massiveness and expressive architectonics (the bridge Alcantara on the river Tagus, Spain).
In the Middle Ages, bridges with semicircular (or circular) arches and bridges with pointed arches became the two prevailing types. The first type was based on Roman tradition and the second was borrowed from eastern architecture and soon lost popularity as it unjustifiably increased the bridge height. The bridges-streets, which appeared in all large European cities (for example, Ponte Vecchio in Florence) became one more phenomenon in medieval bridge engineering. In the Middle Ages, décor appeared on the bridges (it started at the end of the 14th century): for example, the Karlov bridge, Prague, was built in the Gothic style.
The modernization of bridge engineering technology in the Renaissance Era allowed significantly in increasing the ratio of arch thickness to span height. Owing to this, bridges were built higher and lighter with respect to design. The design modernization of stone bridges is under process: circular and diminished arches (New Bridge, Paris). As a whole, the tendency to imitate ancient architecture is traced. A little later the Baroque period appeared, attracting dynamic compositions and magnificent decor. The Bridge of Sighs in Venice built in the baroque style is extremely popular.
In the 18th century classicism was used with popularity. Bridges constructed in this style distinguished in precise symmetry, attentive relation to the proportions of structures, spans of huge sizes. Classicism was widespread in France (Pont Concorde, Paris) and Russia (Krestovy Bridge in Pushkin).
The main types of metallic bridges appeared by the middle of the 19th century. During this period, truss balcony girders have become quite popular. Considerable development was made in the designs of arch bridges (Refer for example to the Garaby viaduct, built by Gustav Eiffel). At the end of the 19th century suspension bridges gained popularity: The Brooklyn Bridge was built in 1883 in the USA and a little later the Manhattan Bridge. Suspension bridges retained popularity in the 20th (“Golden Gate Bridge”) and 21st century.
Walking is one of the locomotion methods of people and animals; it is carried out as a result of a difficult coordinated activity of the skeletal muscles and limbs.
Overview:
* Walking is a kind of locomotion of people and animals (walking of a person, walking of a horse, walking of a dog);
* Walking is the most natural kind of locomotion (walking, running, jumping, climbing) of a person;
* Figuratively, walking is described as a “controlled landing”. During each step, the person bends forward and begins landing, which is prevented by the outstretched forward foot. As soon as it touches the ground, the entire body weight is transferred onto it and the knee bends, cushioning the landing and straightens returning the body to its initial height.
* Walking is examined from the position of a direct and inverted pendulum, considering segments of limbs and the body as a system of physical pendulums;
* According to the figure of speech of Bernstein, who combined biomechanics and neurophysiology of motor organs into a uniform science of physiology of movements, walking is:
“… Synergies, covering all muscles and entire motional parts from top to bottom”;
“…a cyclic act, i.e. movement, in which one and the same phase is periodically repeated again and again”.
* Walking is a physical action the result of the realization of the physical stereotype, the set of unconditional and conditional reflexes;
* Walking is a physical skill which is a chain of sequentially conditionally reflector physical actions, carried out automatically unconsciously;
* Walking is an automated physical act, carried out as a result of a difficult coordinated activity of the skeletal muscles of the trunk and limbs.
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