Studying the origin of Kyiv, one can find documentary references to the crossing of the Dnieper in the area of ​​interest. I offer a selection of drawings and photographs confirming the very possibility and actual implementation of such crossings.

Similar structures have been known since ancient times. Herodotus (5th century BC) reports that during a campaign in Scythia, the Persian king Darius (522-486 BC) ordered ships to be placed board to board to cross the Bosphorus and Danube, on top of which wooden flooring. His successor Xerxes (486 - 465 BC), who undertook a campaign against Greece, during the construction of such a crossing across the Bosphorus, ordered to keep the ships from being carried away by the current, to twist a rope and stretch it through the strait.

There were documents about the Kyiv crossings, but first, as always, Rome was noted in history.

The figure shows a diagram of the construction of a simplified pile bridge.

Roman technology is often referred to as synonymous with military technology. The world famous roads leading exclusively to Rome were not built for daily use, they were of military importance. By definition, no "traffic jams" could arise on them. Thanks to the roads, the legions quickly reached their destination and also quickly returned. Roman pontoon bridges served the same purpose.

This is the brainchild of Julius Caesar. In 55 BC. he built a pontoon bridge over the Rhine. The length of the bridge was about 400 meters. The Rhine was traditionally considered by the German tribes as their defense against the Roman invasion. And here's to you.

The bridge was built in just ten days, using only lumber. Caesar wanted to cross the Rhine and he did.

The pontoon bridge was held on the course of the river with cues (poles) driven into the bottom of the Dnieper. It consisted of two parts. One part connected the left bank of the Dnieper with Rybalsky Island, which at that time was longer, the other was thrown across the Pochaina River and connected the island with the right bank.

The diagram shows a log flooring, piles (cues) sticking out of the water, to which boats are tied under the flooring. The draw section is located on the right bank of the Dnieper. To let the ships pass, it was pulled up to the pile, on the scheme more remote from the transportation than the others.

Bridges across the Moscow River. 1476

The presence of many bridges across the Moscow River within the city is confirmed by Ambrogio Contarini, the ambassador of Venice: “The city of Moscow stands on a small hill; the castle and the rest of the city are wooden. The river called Moskva runs through the middle of the city and has many bridges. The city is surrounded by forests. The ambassador was passing through Russia and admired the Moscow bridges from August 1476 to January 1477.

Our artists did not stand aside either. A.M. Vasnetsov, Moscow Kremlin under Ivan III. http://www.bibliotekar.ru/kVasnecovApp/15.files/image001.jpg

This bridge was rebuilt many times, having its own name - Moskvoretsky.

Centuries after Contarini's visit, on May 28, 1987, when the USSR celebrated the next Border Guard Day, 19-year-old German Matthias Rust landed on the modern Moskvoretsky Bridge in a small Cessna-172 sports plane. Rust, without an entry visa, crossed the Soviet border, flew 800 km over the territory of the USSR and landed his plane in the center of Moscow.

The aircraft was making a left turn and descending for landing between the Kremlin's Spasskaya Tower and St. Basil's Cathedral. Rust failed to land the plane directly on Red Square, there were many people on the square. Having made one more U-turn over the hotel "Rossiya", he went down, landed in the middle of the Moskvoretsky bridge and taxied to Vasilyevsky Spusk.

Bridge across the Oka, Nizhny Novgorod.

How wonderful that old postcards are preserved in the family archives.

In the center of the picture on the arrow of the Oka and the Volga, the Alexander Nevsky Cathedral is visible, and on the river there are many ships in front of the pontoon bridge.

Bridge across the Neva, Petersburg, 1727

In total, there were 11 large floating bridges in St. Petersburg in the Neva delta. The first of them is Isaac's. He was brought in 1727 by order of Prince A. D. Menshikov, the actual ruler of Russia at that time. The bridge connected Vasilyevsky Island with the left bank of the Neva a little to the west of the Admiralty - where St. Isaac's Church stood, the bridge got its name from it.

Under the guidance of the ship's foreman, bombardier-lieutenant F. Palchikov, in 1732 the St. Isaac's Bridge was rebuilt. It consisted of a number of baroque ponies, anchored. Runs and flooring were laid on the barges. For the passage of ships, the bridge had draw parts in two places.

Everyone who used the bridge was charged according to the introduced tariff. From pedestrians - 1 kopeck, from carts - 2 kopecks, from carriages and carriages - 5 kopecks, from 10 small cattle - 2 kopecks, from ships (with a bridge) - 1 ruble. Only palace carriages, palace couriers, participants in ceremonies and fire brigades were allowed to pass free of charge. Tolls were abolished in 1755.

St. Isaac's Bridge was built annually during the summer season for 184 years. On June 11, 1916, from a spark of a tugboat passing along the Neva, the wooden bridge ignited and burned down.

Granite abutments from the side of the Universitetskaya embankment and from the side of the Decembrists' Square are silent witnesses of the St. Isaac's Bridge that once existed here - the first floating bridge across the Neva.

Pontoon bridge in Orsha, 1895

In past centuries in Russia, pontoon bridges connected the coasts not only in the capitals.

In the picture, near the Dnieper, and this is the Orshitsa River.

Source: http://orshagorodmoy.info/forum/24-170-1

Military bridges of Kyiv in 1941

Many bridges knew the Dnieper in different centuries.

During the retreat of the Red Army in 1941, all the handsome bridges across the Dnieper were blown up.

Below are photographs taken by a supposedly German non-commissioned officer, the owner of the album, which was picked up by one of the people of Kiev after the Nazis retreated from Kyiv land. Photo source: http://reibert.livejournal.com/50011.html

The length of the bridge is 110 m, carrying capacity is 20 tons.

The advantage of pontoon bridges is their transportability (both by water and by land in a disassembled state), the speed of installation. The disadvantages include the creation of problems for navigation, low bearing capacity, dependence on wind, waves and water levels, the impossibility of operation during the period of ice drift and freeze-up. If used incorrectly, pontoon bridges can “float away”, as was the case in 2005 in the city of Novokuznetsk with a bridge across the Kondoma River.

One of the famous pontoon bridges of ancient China was the "Scarlet Bird Floating Bridge" (Chinese 朱雀浮航, pinyin: Zhūque fúhang, pall. : zhuque fuhang), about 125 meters long and 15 wide, which led to the central gate of Jiankang across the river Qinhuai(Chinese 秦淮河, pinyin: Qinhuai he).

Story

The first pontoon corps in world history was commanded by the Austrian engineer Carl von Birago, who personally developed the pontoon system, which was soon taken as the basis by all major European armies.

In the 18th century, floating bridges (called pontoons) were built by military teams. The floating supports were flat-bottomed boats, boats or large boats. A flooring was laid on them - a span structure. The bridge was secured with anchors and shore guy lines against the current of the river so that it would not be blown away. To maintain the bridge, a special military team was required, which spent a lot of time and effort.

Pontoon bridges in Russia

The longest pontoon bridge in Russia at that time, about 750 meters long, connected Aspen River (a suburb of Khabarovsk) and Bolshoi Ussuriysky Island. The pontoon bridge connecting the island with the right bank of the Amur channel was built in 2002 and operated from May to October, it was used for the passage of agricultural machinery and vehicles. Before the bridge was built, communication with Bolshoi Ussuriysky Island was provided by a ferry crossing. In winter, the passage to the island was carried out on ice, and during the ice drift and freeze-up, the island remained cut off from the "mainland". In order not to violate the work schedule of Russian and Chinese courts, the pontoon bridge was raised once a day. On October 23, 2013, the capital bridge across the Amur channel was opened, the pontoon bridge was dismantled. The title of the longest pontoon bridge in Russia passed to the newly built bridge across the Tom, 720 m long, in Yurga, Kemerovo region ( 55°44′34″ s. sh. 84°56′29″ E d. /  55.7429° N sh. 84.9415° E d. / 55.7429; 84.9415 (G) (I)).

• Pontoon (village in the Kolpinsky district of St. Petersburg)

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Notes

Construction types By area of ​​application Structural elements

An excerpt characterizing the Pontoon bridge

- BUT! Telyanin! Zdog "ovo! Inflate me all at once" ah! Denisov's voice was heard from another room.
- Who? At Bykov's, at the rat's? ... I knew, - said another thin voice, and after that Lieutenant Telyanin, a small officer of the same squadron, entered the room.
Rostov threw a purse under the pillow and shook the small, damp hand extended to him. Telyanin was transferred from the guard before the campaign for something. He behaved very well in the regiment; but they did not like him, and in particular Rostov could neither overcome nor hide his unreasonable disgust for this officer.
- Well, young cavalryman, how does my Grachik serve you? - he asked. (Grachik was a riding horse, a tack, sold by Telyanin to Rostov.)
The lieutenant never looked into the eyes of the person with whom he spoke; His eyes were constantly moving from one object to another.
- I saw you drove today ...
“Nothing, good horse,” answered Rostov, despite the fact that this horse, bought by him for 700 rubles, was not worth even half of this price. “I began to crouch on the left front ...” he added. - Cracked hoof! It's nothing. I will teach you, show you which rivet to put.
“Yes, please show me,” said Rostov.
- I'll show you, I'll show you, it's not a secret. And thank you for the horse.
“So I order the horse to be brought,” said Rostov, wanting to get rid of Telyanin, and went out to order the horse to be brought.
In the passage, Denisov, with a pipe, crouched on the threshold, sat in front of the sergeant-major, who was reporting something. Seeing Rostov, Denisov frowned and, pointing over his shoulder with his thumb into the room in which Telyanin was sitting, grimaced and shook with disgust.
“Oh, I don’t like the good fellow,” he said, not embarrassed by the presence of the sergeant-major.
Rostov shrugged his shoulders, as if to say: "So do I, but what can I do!" and, having ordered, returned to Telyanin.
Telyanin sat still in the same lazy pose in which Rostov had left him, rubbing his small white hands.
"There are such nasty faces," thought Rostov, entering the room.
“Well, did you order the horse to be brought?” - said Telyanin, getting up and casually looking around.
- Velel.
- Come on, let's go. After all, I only came to ask Denisov about yesterday's order. Got it, Denisov?
- Not yet. Where are you?
“I want to teach a young man how to shoe a horse,” said Telyanin.
They went out onto the porch and into the stables. The lieutenant showed how to make a rivet and went to his room.
When Rostov returned, there was a bottle of vodka and sausage on the table. Denisov sat in front of the table and cracked pen on paper. He looked gloomily into Rostov's face.
“I am writing to her,” he said.
He leaned on the table with a pen in his hand, and, obviously delighted with the opportunity to quickly say in a word everything that he wanted to write, expressed his letter to Rostov.
- You see, dg "ug," he said. "We sleep until we love. We are the children of pg`axa ... but you fell in love - and you are God, you are pure, as on the peg" day of creation ... Who else is this? Send him to the chog "tu. No time!" he shouted at Lavrushka, who, not at all shy, approached him.
- But who should be? They themselves ordered. The sergeant-major came for the money.
Denisov frowned, wanted to shout something and fell silent.
“Squeeg,” but that’s the point, he said to himself. “How much money is left in the wallet?” he asked Rostov.
“Seven new ones and three old ones.
“Ah, skweg,” but! Well, what are you standing, scarecrows, send a wahmistg “a,” Denisov shouted at Lavrushka.
“Please, Denisov, take my money, because I have it,” said Rostov, blushing.
“I don’t like to borrow from my own, I don’t like it,” grumbled Denisov.
“And if you don’t take money from me comradely, you will offend me. Really, I have, - repeated Rostov.
- No.
And Denisov went to the bed to get a wallet from under the pillow.
- Where did you put it, Rostov?
- Under the bottom cushion.
- Yes, no.
Denisov threw both pillows on the floor. There was no wallet.
- That's a miracle!
“Wait, didn’t you drop it?” said Rostov, picking up the pillows one at a time and shaking them out.

A modern floating bridge (for general civil purposes) consists of an approach, a floating (actually floating) and a transitional part (ramps, coastal links) for pairing with the shore.

Vessels of the river fleet (barges, pontoons), pontoons, links of pontoon parks, caissons, rafts, pipes, etc. can be used as a floating structure.

Barges are most preferred, as they are large (length - 60-85 m, width - 12-17 m) and carrying capacity (600-3,000 tons).

Collapsible bridges allow multiple assembly and disassembly.

Transported by road.

For assembly, they do not require the involvement of special equipment (one 16-ton truck crane is enough).

They are indispensable as temporary bridges during the repair and reconstruction of permanent ones, and can also be used in remote hard-to-reach areas during their development before the construction of permanent bridges.

With regard to permanent bridges of this kind, their construction can take several months.

Organizations building floating bridges face several challenges:

• firstly, the seasonality of work, here it is necessary to take into account the various features of the reservoir - the time and levels of water standing, various hydrological characteristics of the annual water regime
• secondly, depending on the nature of the ice drift, it may be necessary to build backwaters to shelter the bridge after its withdrawal, which makes the construction more expensive (and the cost of the annual standard maintenance of floating bridges and ferry crossings)

The longest floating bridge in the world remains the so-called “Second Bridge” over Lake Washington.

Its total length is 3,839 meters, and the length of the floating part is 2,291 meters. The total cost of its construction was $15 million and it was completed in August 1963 AD.

It is believed that in Russia the longest floating bridge is the road bridge across the Amur channel near the village of Osinovaya (a suburb of Khabarovsk), its length is 746 m (connects Bolshoi Ussuriysky Island with the right bank of the Amur from May to October). The bridge is opened once a day according to the navigation schedule.

There is a floating bridge project between the mainland and Sakhalin Island.

The construction of waterways and hydraulic structures in general is one of the indicators of the level of development of the economy and education in the country.

The exchange of experience in the design and construction of floating bridges is facilitated by the IABSE (International Association for Bridges and Structures)

Under the conditions of year-round operation, short-term interruptions in operation are possible due to the construction of the bridge for the passage of ships, as well as autumn slush and spring ice drift.

Floating bridges can be adjustable; to pass ships, one part of the bridge, the output link (raft) is taken aside.

The time of direct wiring is 5-15 minutes.

Floating bridges, when they are raised to allow ships to pass, have: on the right side of the span - two red lights at the lower and upper corners of the span, and on the left side - two white lights in the same places. In addition, on the withdrawn part of the bridge, at the end protruding into the river from the running side, a fire is set (to the right bank - red, to the left - white).

On the raised floating bridge along its entire length, white lights are installed at a height of at least 2 m above the upper edge of the bridge every 50 m, but not less than three lights.

The lights must be visible on the horizon through 360° at a distance of at least 4 km.

The regulation of the passage of ships through floating bridges is carried out by the owners of the bridges using semaphore signaling (UVVT, art. 19 "a").

The semaphore is installed on the shore when approaching the bridge (upstream and downstream) or on the bridge itself (Fig. 24).

The semaphore consists of a mast and signal figures, which are a cylinder and a cone and are hung on the yardarm.

Signal figures are placed vertically one above the other. The cylinder is painted black, and the cone is painted red. The relative position of the signal figures has the following meaning:

• the cylinder is at the bottom, and the cone is at the top - passage is allowed for ships going up (Fig. a);
• Two cones with their tops pointing upwards one below the other - passage is prohibited both downwards and upwards (Fig. b);
• The cylinder is at the top, and the cone is at the bottom - passage is allowed for ships going down (Fig. c).

At night, instead of signal figures, two vertical located lights rise on the mast. Green fire in its meaning replaces the cylinder, and red - the cone.

At night, the navigable span of the floating bridge is marked with signal lights, which are located at the corners of the protruding parts of the bridge.

At the same time, constant red lights are installed on the right (downstream) side of the navigable span of the bridge, and green lights on the left.

Multi-purpose rafts made of fiberglass and composite material based on rigid polyurethane foam and fiberglass with polyester resin are also used today.

For several generations, wooden structures have been used in the construction of a wide plan. They can rightly be considered the same age as a person. Many years ago, houses built from whole or hewn wood were alien to all Slavs.

The idea of ​​these structures is simple and clear. Supports are being built on the banks, between which a chain of inflatable structures is stretched - pontoons lying on the water. A roadbed is laid on top of the pontoons, along which the water barrier is crossed by motor vehicles and pedestrians. In addition to pontoons, any other floating means, such as rafts or barges, can be used to build floating bridges.

Floating structures usually appear where construction on permanent supports is impossible or extremely expensive, for example, on very wide or deep rivers, in places with an unstable flow of vehicles crossing a water barrier. Floating bridges are not put up for a long time, it is rather a short-term construction, at least in the conditions of the Russian winter, when all the rivers are covered with ice.

This is due to the fact that the floating elements of such a bridge are not held during ice drift. Therefore, in winter, the bridge is dismantled, and in its place, if necessary, an ice crossing is organized. Although there are known cases when such structures withstood a small ice drift. Floating bridges are characterized by short installation times, so they are popular for solving military problems.

There are special units in the Russian army that specialize in the rapid deployment of such crossings. We have always been one of the first in solving this military issue, therefore, in 1973, it was with the use of Soviet systems that the Egyptian army crossed the Suez Canal.

It turns out that pontoons have been used for military purposes for a very long time. In historical chronicles there are references to the construction of bridges of this type in the 5th century BC during the war between the Persians and the Scythians. Their glorious history continued both in Tsarist Russia and during the Great Patriotic War. Today in Russia pontoon floating bridges is a means of peaceful application. They allow the construction of crossings over large rivers in rural areas and in the development of new territories.

What are the benefits for builders? The first is the high pointing speed. No matter how simple the construction on rigid supports, in any case, the floating crossing will be built much faster. During construction, it is not necessary to focus on the depth of the reservoir and the nature of the bottom, as is the case with the construction of bridges on rigid supports.

This allows the use of low-skilled workers. The cost of building a bridge of this type is extremely low, since the construction time is minimal, the floating facilities are quite mobile and can be used repeatedly. For the passage of small vessels, the design provides for a navigable channel, which, if necessary, opens.

To complete the picture, it is necessary to note the shortcomings. Such a bridge requires a permanent maintenance team, as it is necessary to monitor the integrity of the structure, pass ships floating on the water and repair the supports. There are restrictions for building floating bridges on rivers with strong currents. From 2.5 m/s it is already dangerous and threatens to overturn the bridge, from 3.5 m/s it is almost impossible.

Under load, floating bridges deform, so the speed of vehicles on them is low, for cars it is from 10 to 30 km/h. There are certain difficulties with a significant change in the level of rivers. It is usually understood that pontoon bridge withstands water level fluctuations of 2.5-3 meters, with large values, redevelopment of coastal supports is necessary.

However, despite all the shortcomings, there will always be a need for floating bridges, because this is an excellent option both for solving emergency problems and for organizing a relatively permanent crossing in the absence of other options.

Floating bridges, depending on their floating supports, can be raft, pontoon and pontoon. Raft bridges are now very rare due to their low carrying capacity. Pontoon floating bridges, the supports of which are hollow closed boxes (pontoons) made of wood or metal, are inconvenient in operation due to the complexity of their inspection and repair. The most common are pontoon bridges with a large carrying capacity on floating supports in the form of barges or pontoons.

A feature of floating bridges is the seasonality of work. With the onset of freeze-up, they are removed to the backwaters or to the shore, protected from ice drift and floods, and if they are exploited during the winter, then they are taken to backwaters for the period of spring ice drift. Floating bridges require large expenses for the maintenance and repair of the floating part. The main element of a floating bridge is its floating part in the form of floating supports and superstructures (buildings) resting on them. The floating part usually covers the main part of the width of the river, on which, at the lowest water level, a margin of 50 cm is provided from the bottom of the river to the bottom of the support when passing vehicles over the bridge. The floating part of the bridge is usually formed from separate links having one or more floating supports with a lining, and is fixed with anchors against drift by water and wind. For the passage of ships, a drawbridge span is arranged, consisting of one or more links. The coastal part of the bridge is a flyover of the simplest design in sections of the river where the depth is insufficient for the construction of floating 262 pores. Usually the coastal part adjoins the exits to the shore. The floating and coastal parts are connected by an ice drift, which changes its level depending on fluctuations in the water level in the watercourse.

Although the construction of floating bridges is simpler and cheaper than permanent bridges, their operation is more complicated and involves significant materials and especially labor costs. Floating bridges require round-the-clock duty of a team of workers to ensure traffic safety and timely elimination of all defects, damages and malfunctions, as well as to ensure normal navigation on the river. Constant supervision is needed for all elements of the bridge - floating supports, anchoring devices, lining, span structures of transitional coastal parts and approaches to the bridge.

The main attention in the maintenance of floating bridges should be given to floating supports. By daily inspection of the supports from the inside and outside, the condition of the support and the amount of water inside are checked. The normal amount of water in the support should not exceed half the height of the diggings. Excess water must be pumped out in a timely manner. In case of damage to the supports and the appearance of a leak, the causes must be determined and eliminated.

In wooden floating supports, defective places (slots or holes) are repaired with caulking or wooden plugs made of non-penetrating wood. If the defective places are not immersed in water, they are caulked from the outside from a boat or other floating craft. Slots and holes in the skin, located below the water level, can be sealed from the inside.

To protect the floating supports from decay or rusting, it is necessary to ensure ventilation of their internal cavity, eliminating hatches in the pontoons. All longitudinal trusses, frames, transom frames, as well as load-bearing elements of the internal structure, must be inspected daily, checking the density of interfaces and connections, and any defects found should be immediately eliminated. When rot appears, the affected wood is removed and replaced with healthy, impregnated with an oily or water-soluble antiseptic that is difficult to wash out.

Strict requirements for the maintenance of floating supports force the operation service to keep on the shore or on the water, not far from the floating bridge, spare floating supports, and, if possible, individual links of the floating bridge.

To ensure the necessary position of the floating part of the floating bridge (from drift or wind) during operation, the floating supports are fixed with ropes or cables for ghouls, anchors, pile bushes or trees on the shore. Usually floating supports are fixed on the upper side to prevent them from being carried away by the current. With a weak current of the river, where the demolition of the floating part from the wind in the direction opposite to the current is possible, it is also fixed from the downstream side. Floating supports, located not far from the shore, are fixed to large tree trunks or bushes of piles driven on the shore, and the rest of the supports are anchored. On small rivers, it is sometimes possible to fix the floating part without the use of anchors.

The anchoring ropes must have an angle to the direction of the water flow of no more than 35°. The distance from the anchor to the floating support (Fig. 156) should be 10 times the maximum water depth in the river. Ropes are used, as a rule, steel, hemp due to a very short service life - only in exceptional cases. The ropes are fixed to the anchor and the winch installed on the floating support.

If the anchor is pulled off its bridge, then the floating part of the floating bridge is bent. With a slight pulling of the anchor, the rope is pulled up with a winch, and with a significant one, it must be thrown back into the design position. In the case of a systematic change in the position of the anchors, their number has to be increased or replaced with heavier ones.

The work on the maintenance of the transitional parts includes the constant provision of a smooth entry and exit from the floating bridge. With an amplitude of fluctuations in the water level in the river up to 1.5 m, the transitional part, as a rule, consists of one span structure, hinged at one end to the extreme coastal trestle part, and the other end to the floating part of the bridge. The transitional part in this case is a simple beam system with a span of up to 6-8 m. The ends of the runs usually rest on the extreme floating support, causing it to be overloaded and significant draft. Therefore, the extreme floating support (pontoon or pontoon) should have a greater carrying capacity than the rest.

Rice. 156. Scheme of fixing a floating bridge on a wide river

Often, floating bridges are built across large high-water rivers, where the oscillation amplitude can exceed 5 m. In these cases, it is necessary to arrange transitional spans with through farms or rely on special pile supports (Fig. 157), equipped with lifting devices (hoists or jacks). With the help of these devices, by raising and lowering the transition parts, they provide a smooth entry and exit from the bridge.

The operation service regularly monitors the junctions of transitional spans with floating and permanent supports. In the event of a change in the water level, the lifting beams are respectively raised or lowered with hoists or jacks, giving the transition part an external slope (not more than 80 ° / oo) - The greatest difficulties in maintaining the transition parts of floating bridges arise in the spring when ice drift passes. Before the ice drift, the floating part and the spans of the transitional parts are removed to a safe place, while the tower supports of the transitional spans remain and are protected from ice drift. There are three known options for the preservation of the supports of the transitional spans. With a relatively weak ice drift, the tower supports are protected by ice cutters, and with a strong one they are arranged collapsible. In the latter case, before the passage of ice drift, the upper part of the supports is dismantled and, together with lifting devices, removed to a safe place. The remaining part of the support must be such that it is not damaged by the lowest ice drift.

Sometimes the transition parts are arranged with two independent entrances with a difference in height of about 1.5 m. The arrangement of several entrances makes it possible to reduce the length of the transition part to one span and simplify its design.

Rice. 157. Schemes of the multi-span transitional part of the floating bridge and the profile of water level fluctuations.
A - amplitude of level fluctuation

Moving the entire floating part from one entrance to another when the water level changes does not present any particular difficulties - the entire floating part is pulled upstream or downstream. If the floating support is a floating support or a pontoon, then the height of the dry side, i.e. the height from the water level to the top of the floating support, must be at least 50 cm. Therefore, the operation service must have a schedule for passing live loads on the bridge, taking into account their weight and dimensions.

When passing cars whose weight is close to the norm, it is necessary to strictly control the distance between these cars, and also to ensure the passage of single especially heavy cars in the middle of the bridge in one-way traffic. After the passage of heavy vehicles, it is necessary to inspect all bridge structures. On floating bridges, sudden braking, as well as the deployment of vehicles, are prohibited. To regulate traffic on the floating bridge, there should be barriers on both banks and the duty of the most experienced workers should be established.

For quick and clear wiring of the span and its return after the passage of ships, it is necessary to equip the adjustable device with electric motors of sufficient power. Electric motors are installed on the shore in a special room or on the first floating support of the draw span.

Usually, with the help of one mechanism, the wiring and the reverse installation of the adjustable link are made (Fig. 158). In this case, a traction mechanism is installed on the shore, consisting of an engine, two drums rotating in different directions and two cables (from the drums) connected to the first floating support of the draw span of the floating part of the bridge. Sometimes two traction mechanisms are installed on the first floating support of the adjustable

link, while one works on the wiring of the bridge, the second - on the tip.

In some cases, when the intensity of traffic on the highway and the river is small, the bridge is drawn and its input is provided with the help of a gate installed on the first floating support of the adjustable link.

In most cases, floating bridges are operated when the river is ice-free, and in winter they are bred and removed to a place safe from spring ice drift, for example, in backwaters on the river in which there is no ice drift, or the water level in which is 25 cm below the draft of the floating support from their own weight, or they are pulled ashore above the level of the largest ice drift. In this case, the movement of vehicles in the winter period is carried out along the ice crossing.

Rice. 158. Scheme of wiring and pickup of a span of a floating bridge: 1 - block; 2 - winch; 3 - draw span

With the approach of cold weather, as well as before the passage of floods and ice drift, it is necessary to organize, taking into account the characteristics of the river regime, observation posts that have a connection with the bridge. More often, such observation posts to obtain information about the movement and accumulation of ice, the appearance of sludge and fat are installed upstream by 5-10 km, and sometimes even further.

With a weak current, the sludge easily accumulates near the pontoon bridge, freezing to piles, floating supports, ropes, clogging the free section of the bridge, forming blockages, creating additional load and thereby reducing the carrying capacity of the bridge. The resulting jams and ice jams hamper the riverbed and increase (sometimes by several times) the pressure on the floating supports, damaging them.

During the period of the first frosts, thin ice forms on the river from small pieces (lard) moving with the flow (autumn ice drift). Thin young ice damages the plating of floating supports, easily cuts even steel ropes with its edges. Salo, especially with a weak flow of the river, freezes to the floating supports and creates a risk of congestion.

Special measures are needed to keep the bridges in good condition.

When sludge, fat, sneshura appear on the river, it is necessary to systematically (with shovels, crowbars or ice picks) clean the sides and bottoms of floating supports, anchor ropes from freezing ice. In some cases, when large ice floes appear, blasting is carried out at a distance that guarantees safety. To protect the side plating of wooden floating supports from cutting through with thin ice, their additional lining with boards is effective either only from the bow or along the entire perimeter of the floating support. In this case, additional skin is given within the limits between the waterlines corresponding to the unloaded and maximum loaded state of the bridge. To pass accumulations of sludge, lard and sneshura, as well as large ice floes, the size of which exceeds the clear distance between the floating supports, it is necessary to breed the spans of the floating part of the bridge.

If not all floating supports enter the drawbridge, then to protect the remaining ones, it is necessary to install floating booms to direct the ice floes into the opening of the bridge. Booms, arranged from single or paired logs, must be securely fastened.

During the freezing period, the water level fluctuates. The lowering of the level causes the ice to sink, its separation from the coast, and if at this time the floating supports are frozen into the ice, they can be crushed. A sharp fluctuation in ambient temperature can also lead to crushing of floating supports. To prevent the destruction of floating supports during this period, it is necessary to systematically break the ice around the supports and anchor ropes during the entire winter period.

To increase the productivity of work on breaking ice, pipes with holes for air passage are laid at the supports along the bottom of the river. Air through the holes enters the water, rises and breaks the ice. This device has great performance.

There are known cases of floating supports freezing into ice on large navigable rivers, where the water level is most stable, and the floating supports are metal. During the operation of floating bridges with frozen-in floating supports, it is necessary to ensure timely ice fragmentation around the floating supports with the onset of spring thaws.