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