NO20141466A1 - Pipe section for floating bridge - Google Patents

Description

The present invention relates to the design of a pipe section to form a bridge girder for a floating bridge for a transport lane between two attachment points across a strait or a fjord, towards land, where the bridge girder is composed of a number of mutually joined pipe sections end to end, as is evident from the introduction in the subsequent claim 1.

Furthermore, the invention relates to a method for manufacturing a bridge girder for a floating bridge for a transport lane between two attachment points across a strait or a fjord, towards land, where the bridge girder is assembled from a number of pipe sections, end to end, as stated in the introduction to claim 8.

Furthermore, the invention relates to a raft which is used during the assembly of the bridge girder, as stated in the introduction in claim 1.

More specifically, the invention deals with a floating bridge that can be installed between moorings at each end, and operate in both calm and weather-resistant areas with large waves and sea swells, at the same time that, if desired, it can be combined with ship passage and can also cross very wide fjords and straits, preferably with a width of up to 10-20 km.

A floating bridge means a structure that can be arranged with a roadway, with for example several lanes of carriageway, for the transport of people and vehicles, and possibly a rail passage for train operation.

By a bridge girder is meant a hollow body designed as an elongated hollow box shape of plates mounted around a structural framework. The roadway is arranged either directly on top of the bridge girder, on a viaduct that is supported by columns on top of the bridge girder or inside the hollow part of the bridge girder. Such a hollow bridge girder is normally composed of a number of pipe sections.

In the further description, it is stated that the bridge girder has a largely horizontal course above the water, but this also includes that the bridge girder must to some extent be able to be bent slightly upwards in the vertical plane to follow the roadway, if the vertical distance down to the water surface over a part of the bridge is desired to be increased, for example because ships must be able to pass directly under the roadway or that the exit towards the landing is desired higher up in the terrain. Such a vertical deflection of the bridge girder will preferably follow the roadway, i.e. with a typical gradient of 1 - 6%.

A float means a float or pontoon in the sea that supports the hollow bridge girder along the length of the floating bridge. The floats for a floating bridge are preferably designed in concrete, but can also be built in steel. The floats are placed with a calculated mutual distance to ensure the necessary buoyancy and stability in the floating bridge, while at the same time the influence of environmental forces on the floating bridge is minimised. A typical distance between the floats can be 50 - 150 metres.

The floating bridge according to the invention is designed to span fjords and straits where the water depth can be from approx. 5 meters to approx. 2000 meters water depth.

The anchorage points for the floating bridge can either be shore anchored at each end, or on another bottom-fixed installation. The attachment points preferably form a continuation of the roadway in extension of the floating bridge.

The invention includes a floating bridge consisting of a closed bridge beam that rests on the floats above the waterline and which binds the floating bridge between the attachment points, so that a continuous floating bridge is formed between the attachment points. If desired, parts of the bridge girder can also be arranged with, or possibly replaced by, a ship passage for larger ships at a desired location along the floating bridge, where road traffic can either pass over the ship passage or by the bridge girder being arranged with a movable floating bridge segment that can occasionally be opened to let through shipping traffic across the bridge, while road and train traffic is stopped at the same time.

If desired, the ship passage can also be arranged by an underwater structure forming an integrated structural part of the floating bridge between the attachment points. This underwater structure can have a different design to the bridge girder, for example as a truss. The purpose is that ship passage in this case can take place over this underwater structure, across through the floating bridge.

For very long distances over fjords or lakes, floating bridges can be a cost-effective and safe alternative. Floating bridges have been known for a long time and are currently in operation in several places in the world.

Crossing fjords, straits and lakes with bridges has been a challenge since time immemorial. Different types of bridges have been developed depending on the span, foundation possibilities and sailing heights, and reference should be made to the patent publications US-1852338, SE-458850, NO-113404 and GB-2135637.

A number of floating bridges are built with lateral anchoring regularly along the entire length of the floating bridge, and preferably to both sides, to keep it in position.

The environmental forces on a floating bridge can be significant, especially during storms where current, wind and waves can come sideways and from the same direction. In addition, one has tidal forces that arise from varying water levels such as ebb and flow. This can cause bending forces on the floating bridge near land. It is therefore important that it is designed so that the impact from the environment is minimized.

An example of a floating bridge that has been built and adapted to sheltered waters is the Nord-Hordlandsbrua in Norway, which is only anchored at the two land moorings. With its 1,246 meter roadway, the bridge is Europe's longest floating bridge without lateral anchorage. The floating bridge itself does not allow the passage of ships, but passage for ship traffic is solved by the addition of a bottom-fixed high bridge close to land with a sailing height of 32 meters and a sailing width of 50 metres. On the Nordhordlandsbroen, the roadway has a width of 16 metres. The floats are designed as barges and built in concrete, where the dimension in the widthwise direction of the roadway is equal to 40.0 meters and in the longitudinal direction of the roadway is equal to 20.5 meters. The free distance between these floats is approx. 110 meters. As the floats lie with the longest side across the direction of the roadway, current forces on the floating bridge are minimized and the surface water flows almost unimpeded under and between the floats.

In addition to anchoring at the end points, floating bridges can also be held in place using lateral anchor lines.

The floating bridge's movements are a direct function of the floaters' response to incoming environmental forces in the 6 known degrees of freedom. The structural stresses in the bridge girder are a function of the movement response of the floats, of the design of the bridge girder and the individual distance between the floats.

With this type of technique, a floating bridge can be designed with constructive solutions so that the dynamic response of the floats from waves is minimized at the same time that the structural stresses in the bridge girder become acceptable, preferably as columnar structures with a small waterline area.

Weather statistics collected over many years indicate dominant and likely directions for environmental forces such as wind, waves and currents. When planning the design of the floating bridge, this information can be used.

The spread of floating bridges has been limited due to the lack of opportunities for ship passage. For the Nordhordlandsbroen, this has been solved by connecting it to a land-based high bridge that allows ships to pass close to land. However, ship passage close to land is often not desirable and in patent application NO 20101273 a solution for a floating ship passage is indicated which allows the ship's passage to pass through the floating bridge far from land.

The term "tube section" refers to the hollow modules of which the floating bridge's girder is assembled, which may include hollow steel structures with a typical length of 50-150 metres, designed as an elongated hollow box shape of plates assembled as a closed box structure, with internal beams and struts in truss frames that can support the roadway or support columns for a viaduct with roadway.

It is an object of the invention to produce a new construction for joining such hollow pipe sections.

Furthermore, it is an aim to produce a new method for assembling such a floating bridge span based on the joining of pipe sections, across a fjord or a strait between two moorings, as well as a completely new method for carrying out said assembly.

Normally, the connection of pipe sections to a bridge girder is carried out largely just above water and is a demanding, extensive, expensive and risky operation because the connection will take place with the use of a number of floating bodies, consisting of both the floating bridge's floats and, in addition, temporary barges and crane vessels, and where these floating bodies will constantly be in natural movements on the sea and which must be controlled continuously by means of tugboats, propulsion systems or temporary moorings. At the same time, joining the pipe sections must be done with great precision since they have large dimensions (length/width/height) and are heavy.

Known floating bridges are mainly a connection of pipe sections by welding, but this takes a long time since such welding processes necessitate a number of sequential, time-consuming operations in the open air, such as preparation of welding joints, hydraulic joining of the large and heavy pipe sections, adaptation of the facing welding joints, welding operations, finishing, X-ray and NDT control, sandblasting, priming, painting, etc. Many of these welding operations must take place under temporary protection from the weather, which varies with both sun, wind, precipitation and temperature, which requires provisional rigging of welding tents or other protection, where these must be constantly moved since new joints are constantly being welded together.

Bolting of pipe sections is a well-known technique in the construction of most types of bridges, but one of the disadvantages of bolting on bridges is that the bolts are often located on the outside of the structure exposed to wind, weather and salt spray, are difficult to access for later inspection and repair, at the same time that over the years more and more layers of paint accumulate, which makes it difficult to properly inspect the surface qualities and replace the bolts.

In the following, the term bolts and flanges is also intended to cover other types of mechanical joining techniques that have the same effect, such as riveting, hydraulic presses, prestressing rods, etc.

An object of the invention to produce a new joining method of pipe sections for the assembly of floating bridges which enables the bridge girder pipe sections to be quickly and precisely joined by placing them flange to flange and joining them using screws, flanges or other known techniques (forces) with great precision and speed.

It is further an object to produce a new construction for orientation of an annular end flange, with which each open end of a pipe section is provided for the mutual joining of two adjacent pipe sections.

It is also an object of the invention that all the bolts are easily accessible for inspection, control and replacement, where one has easy access with mechanical equipment, i.e. even when the bridge girder of composite pipe sections is underwater.

It is also an object of the invention that the air environment in the space around the bolts can be kept controlled with low humidity using known techniques in order to reduce corrosion and the need for expensive surface treatment.

It is also an object of the invention that the temperature in the air environment in the space around the bolts can, if desired, be kept at a desired, almost constant level, in order to reduce stress variations in the entire structure of the bridge girder as a result of external temperature variations, so as to be able to increase the lifetime of the whole the floating bridge construction, especially in geographical areas with large temperature variations.

It is also an object of the invention that the bolts should be protected against salt spray from the sea.

It is also an object of the invention that the bridge girder can be dismantled by unscrewing/unscrewing the bolts and separating the hollow tube sections, so that all or parts of the floating bridge can be moved and reused elsewhere, or damaged parts replaced.

It is also an object of the invention to produce a rational method for manufacturing a bridge girder for a floating bridge.

The pipe section construction according to the invention is characterized by the fact that each end of a pipe section comprises an inwardly directed annular flange with means for forming abutment against and assembly with a corresponding flange form in an adjacent pipe section in the bridge girder.

Preferably, the opposing flange surfaces are oriented across the longitudinal direction of the pipe section, and extend internally around the entire periphery of the pipe section at its end.

Preferably, the means comprise sets of bolts with tightening nuts around the entire circumference, where the bolts extend through mutually flush bores through the flanges in the longitudinal direction of the pipe section, and where the flange surfaces are clamped together by means of the tightening nuts, or with forcing constructions that grip and tighten against the rear sides of the flange surfaces.

It is particularly preferred that each bore on the inside of the flange is designed as a sleeve-shaped seat with a bolt channel that aligns with an associated bolt channel in the bore in a corresponding seat construction in the adjacent flange construction.

Furthermore, it is preferred that when the end part of the pipe section comprises a transverse beam, it also has a flange surface which faces and is connected together with a corresponding flange surface on the opposite pipe section.

Furthermore, it is preferred that the flange installation surfaces comprise a film to form a seal in the joint between two pipe sections, which sealing film is of a softer metal such as copper, or a rubberized or felt-like material.

According to a preferred embodiment, the bottom part of the beam-cavity comprises a transport track, such as a rail passage for advancing means with inspection and maintenance equipment.

The method according to the invention is characterized by the following steps being produced: a) a number of pipe sections are produced to form the bridge span over the strait/fjord, where each pipe section comprises an inwardly directed annular flange for

fitting to an adjacent pipe section in the bridge span, and that

b) a first pipe section is placed at a land side for connection to a land transport system, after which a next pipe section is placed on a floating

assembly float which is arranged in a suitable position and adjusted to flush the flanged end of the second pipe section into contact with the corresponding flanged end of the first pipe section in a controlled manner,

c) that the first and second pipe sections are connected by fitting fastening bolts and associated tightening nuts through respective flush bores in

the two opposing flanges, said connection being carried out from the inside of the pipe sections, and

d) whereupon the mounting raft is suitably maneuvered to set a third pipe section resting on the raft flush with the projecting end of said

second pipe section, and

e) the remaining pipe sections to complete the floating bridge over to the other land side are assembled in turn in the corresponding manner as described under

method steps c) - d).

It is preferred that a sealing film is arranged between opposing flange surfaces to form a tight joint between two adjacent pipe sections.

Furthermore, it is preferred that the assembly raft (50) is positioned in the sea via cables that extend from the respective assembly raft end towards land, and the cables are winched to move the assembly raft successively across the sea surface as the pipe sections are assembled, with the assembly raft being stabilized laterally via transverse cables that extend out each side of the mounting raft across the longitudinal direction.

It is particularly preferred that the assembly fleet is maneuvered with incorporated propulsion machines in the fleet hull and a number of azimuth propellers that can be brought down into the sea below the fleet and operated, the propeller system being operated based on automatic positioning via satellite navigation, such as a GPS system.

Furthermore, it is preferred that each pipe section is placed successively on a substrate on the raft deck which enables a simple horizontal displacement of the pipe section to create the correct flush position between the two pipe sections to be connected, which substrate includes, for example, a transport roller. This shift can also occur if the top cover includes smooth sliding surfaces (sliding bearings) with, for example, the use of Teflon or lubricating oil on the sliding surfaces.

Furthermore, it is preferred that the pipe section's horizontal movement on the transport roller is regulated by the rollers being driven by motor operation and can be stopped via a brake.

The assembly raft according to the invention is characterized by the fact that the raft deck comprises a transport means which enables a simple horizontal displacement of a loaded pipe section, which transport means in the form of a conveyor roller or belt which is connected to a motor and a brake to control the movement of the pipe section on the raft deck during assembly, and the assembly fleet includes a device for controlled movement in the sea during assembly.

It is preferred that the device for holding and changing the assembly raft's position during assembly comprises an adjustable mooring system connected to the raft comprising a set of ropes connected to separate motor-driven winches which can either be mounted on the shore sides or preferably on board the raft.

Furthermore, it is preferred that the assembly raft comprises a winch-operated first cable set towards the shore from each end of the raft aligned approximately in the longitudinal direction of the bridge girder, and possibly a second set of winch-operated cables that extend out from each side of the assembly raft across said longitudinal direction.

Furthermore, it is preferred that the assembly raft comprises a winch-operated cable set towards the shore from each end of the raft arranged approximately in the bridge girder, the assembly raft is stabilized laterally via transverse cables which extend out from each side across the longitudinal direction of the assembly raft.

As an alternative to the use of mooring lines, the assembly raft can include propulsion machinery in the raft hull in the form of a number of azimuth propellers which, according to known techniques from oil drilling rigs, are organized as an integrated dynamic positioning system and which can be brought down into the sea under the raft and is operated, as the propeller system is operated based on automatic positioning via satellite navigation, such as a GPS system or by means of a number of electronic transponders which are temporarily placed on the seabed or on land

A third alternative is to combine the use of ropes and propulsion, which can be advantageous on bridge routes where there is a large difference in water depth, which is known from offshore drilling rigs and which in the technical language is often referred to as "mooring-assisted dynamic positioning". In shallow water it is natural that mooring lines are in use, while in deeper water you can let the propulsion system maintain the position of the assembly raft.

The device according to the invention shall be explained in more detail in the following description with reference to the accompanying figures, in which: Figure 1 shows a horizontal section of a floating bridge comprising an elongated bridge girder that rests on a number of floats, and which continuously spans a fjord or a strait between two mooring points. Figure 2 shows an end view of a pipe section according to the invention. In general, the pipe section has an adapted cross-section, it is preferably rectangular, preferably with rounded edges. Figure 3 shows a partial view of the flange construction for joining two opposing tube sections of the bridge girder, while Figure 4 shows an enlargement from Figure 3 to illustrate a preferred flange joining with a row of bolts. Figure 5 shows an initial part of the assembly of the floating bridge from one land side, and shows a floating assembly raft with maneuvering cables to assemble the pipe sections for the floating bridge. More specifically, the figure shows the second pipe section ready to be joined with the first section connected to the land side. Figure 6 shows the continuation from Figure 5, where the second section is now connected to the first section. Figure 7 shows yet another step in the assembly, where a fourth section is ready for assembly to the preceding third section, and furthermore that the two previously formed pipe section joints rest on respective floats.

Figure 8 shows a side view of the mounting setup according to Figure 7.

Figure 9 shows a plan view of the assembly setup according to Figure 7, and also shows a service fleet which supplies the assembly fleet with pipe sections for assembly. Figure 10 shows an interior section of two interconnected sections where a longitudinal rail passage is arranged which can advance a service trolley to carry out internal inspection and maintenance of the pipe joints and of the inner walls of the assembled pipe sections.

Identical construction details are given the same reference numbers in the various figures.

The invention will now be explained in more detail by referring first to figure 1.

Figure 1 shows a floating bridge 10 that spans a fjord or a strait between two moorings 11 and 13. The floating bridge consists of a bridge girder 12 that floats above the water line 21 resting on a number of floats 17 across the bridge span. The bridge girder 12 is composed of a number of pipe sections 14,16,18,20 ... which are joined together as according to this invention to form the bridge girder 12. The seabed is shown at 15 in the figure. In Figure 1, the joints between two adjacent pipe sections are shown at 19.

Figure 2 shows an end view of a pipe section 14 in the row according to the invention. The pipe section is shown with a rectangular cross-section, and comprises side, bottom and top surfaces, where the top surface 20 itself constitutes or forms the base for a transport/roadway across the floating bridge. An annular flange 30 is arranged facing inwards around the entire inner circumferential cross-section, so that it forms an outward facing flange surface for installation in a vertical plane against a corresponding flange surface at the end of the adjacent section 16 (figures 1-5). Each end of a pipe section 14,16,18,20... is designed with such a flange surface. To reinforce the hollow pipe section, there is a centrally arranged bracing post 22 between the pipe section's inner bottom and top at the opening surface. The forward-facing part of the post 22 forms a flat surface which forms part of the flange surface which must rest against the neighboring section's corresponding flange surface 31 (figure 4).

Around the circumference, the flange is pierced with a number of axial bores 32 with approximately the same distance from each other. Each bore is internally formed as a sleeve-shaped seat 34 which forms a longer bolt channel flush with the associated bore 32. Each flange on the ends of a pipe section includes such seats 34 for the placement of bolts. Figure 3 shows that upper and lower bolt-horizontal rows with 11 bolts in each row have been installed. Correspondingly, the vertical flange surfaces (also the additional support surface 34) are shown to comprise 6 - 7 bolts in height.

Dimensioning of bolts and the flange connection is carried out according to traditional methods and available software. Traditional bolts used for bridges often have a diameter of 15-27 mm, where a large number of bolts are used. For floating bridges according to the invention, calculations show that it can be advantageous that the number of bolts is somewhat reduced by using coarser dimensions of the bolts, preferably with a diameter of up to 50-70 mm diameter. The bolts are attracted and tightened according to well-known techniques by, for example, hydraulic force where the pre-tensioning force is measured. Other mechanical connections can also be used, for example pre-tension cables that are bolted or cast in place. However, traditional bolt and screw connections are preferred due to simple and well-known replacement procedures.

Before the two end flanges of two opposing pipe sections 14 and 16 are inserted against each other and screwed together using said bolts around the circumference, a thin sealing film is placed on the contact surfaces to form a secure seal in the joint 19 between two pipe sections. This film can be a sealing film of a softer metal such as copper, or a rubberized or felt-shaped film. This is not shown in the figures.

Figure 3 shows a partial view of the flange construction for joining two opposing pipe sections of the bridge girder, while Figure 4 shows an enlargement from Figure 3 to illustrate a preferred flange joint with a series of through bolts.

Reference should now be made to figures 5 and 9 which show a floating assembly raft 50 which is used to assemble the bridge girder from the pipe sections.

In a preferred embodiment, the raft comprises a deck for placing a pipe section 16 (figure 2). On the top deck there is a sliding track for the pipe sections, for example as shown by a series of parallel rotatable rollers (as on a transport roller) 52 on which the pipe section is placed, so that it can be easily moved to its mounting position. Horizontal movement of the pipe section can be carried out, for example, by means of jacking mechanisms or hydraulic cylinders, or by the installation barge being moved with the help of the ropes and the connected pipe section being dragged to a new position. Instead of rollers, adapted sliding surfaces can also be used based on known techniques, for example sliding surfaces fitted with Teflon sheets which reduce the horizontal friction. The raft is moored to both land sides 11 and 13 respectively by means of suitable cables 60,62,64,66 mainly along the length of the bridge span, and side cables 65,67 (crosswise) which contribute to the lateral stability of the raft 50. Harnesses 60-68 are shown as harness pairs.

Each pair of winches is maneuvered via separate motor-driven winches which can either be mounted on the shore sides or on board the fleet 50. The maneuvering of all the winches is synchronized and controlled via a computer unit not shown, for example based on automatic positioning via a GPS system, so that the fleet gradually and can be pulled in a controlled manner from one land side 11 and over towards the other land side 13 in order to carry out the assembly of the pipe sections into a complete bridge girder as according to the invention. In the figure it is indicated two exemplary winches with cable winding drums 70 and 71. The system also includes the control with a brake system associated with the rotatable rollers 52, so that these are stationary and do not allow the section to move on the raft until it is brought to the assembly itself . To perform the maneuver, the deck of the fleet 50 may include a wheelhouse for an operator to control and monitor the process.

The ropes are kept in a certain pre-tension to secure the position on the assembly raft/barge. The winches are computer-controlled and linked together so that the entire assembly fleet can be moved via a joystick, for example, while the line tension and the fleet's position are monitored by the operator.

According to another preferred solution, the assembly raft 50 is moved by means of incorporated propulsion machines in the hull, and comprises a number of azimuth propellers which project into the sea below the raft. The propeller system is operated based on automatic positioning, for example via a GPS system. In this solution, mooring ropes are unnecessary, although it can also include ropes as mentioned above and which are brought as extra security to hold the raft in place for each pipe section that is installed. The submersible propeller systems and rotatable "thrusters", which have suitable redundancy to ensure reserve capacity in the event of failure, maintenance, accidents, etc. These are known techniques and are regularly used in other types of offshore well operations, where the positioning requirements are strict, even during storms. The advantage of this variant with automatic positioning is that you don't have to lay out lines, while the assembly fleet moves with equal accuracy to exact positions (parks on the sea) as needed.

To make maneuvering easier, a raft with room for a single pipe section placed on the rollers is preferably used, this is because a pipe section can have a different weight (in tonnes), which can affect how easily the raft can be maneuvered in the sea. To supply the raft deck 50 with pipe sections 14,20...one by one, a separate supply raft 80 can be loaded with a number of pipe sections, floated forward and moored alongside the assembly raft 80. The supply raft 80 includes a crane 90 conveniently located on the raft 80 (shown placed in a corner) and dimensioned to lift one section at a time from the supply raft 80 and carefully place it down on the deck (rollers) 52 of the assembly raft 50. Alternatively, the new pipe sections can be transferred to the assembly barge by adapted sliding devices which are also mounted on the supply raft 80 .

As mentioned, the bridge beam rests across the span on a number of floats 17 to keep the bridge beam stable in operation when it carries traffic, and to withstand the prevailing weather forces to which it is exposed. More specifically, each joint between two adjacent screwed together pipe sections rests on a float 17, which keeps the joint area extra stable.

The great advantage of the invention is that the series of bolts that hold the pipe sections 14,16,18,20... together are placed inside the bridge girder. The hollow part of the bridge girder has such large dimensions that the maintenance of the row of bolts and the inside can be carried out by personnel from the inside. In order to facilitate the introduction of inspection and maintenance equipment, the bottom/floor of the cavity, with reference to figure 10, is equipped with a transport track, such as a rail passage 100 which can advance a carriage 102 with inspection and maintenance equipment. It is an advantage to have a rail mounted on top of the flanges, since the bottom is not even but includes transverse flange sections that rise up. The carriage 102 comprises a personnel basket 104 mounted to a movable arm 104. Figure 10. The cavity can be accessible via entrance doors for the passage of equipment and personnel, preferably located at the shore side 11 or 13. Instead of the entire bridge girder having a continuous hollow part from shore side to shore side, it must be divided into several hollow sections by means of tight walls. If a bridge girder, for example, consists of 10 flanged pipe sections each of 120 metres, the closed internal space will be approx. 1200 m.

Joining the pipe sections to form the overall bridge girder. The assembly of the sections to form the bridge girder can be carried out as follows, with reference to figures 5-9.

The first pipe section 14 is mounted with one end on the land side as indicated in Figure 5, to form a transport connection further to a road system on the land side which shall not be discussed in more detail here. This is done by the section 14 placed on the raft deck 52 being slowly brought in over the land side 11 and assembled. The next pipe section 16 is then brought over to the mounting raft 50 which is then maneuvered so that the two opposing flanges 30 and 31 with attached sealing films on the ends of the pipe sections 14 and 16 are brought in towards each other and aligned, on which all screw bolts 40 are mounted and screwed to the section appropriately together. In order to obtain good precision in the joining of the two flange surfaces, the two surfaces can then be fitted with guide devices, for example of the male/female type to facilitate the joining and alignment of the flanges to the two opposite pipe sections.

Calculation of the number of bolts and the design of the flanges, their dimensioning and the mutual position of the bolts along the flange surfaces can be calculated according to known techniques, and is adapted to the forces that arise in the tube sections of the bridge girder. The aforementioned leveling of two opposite pipe section ends 14 and 16 can be carried out by the support for the transport rollers 52 being connected to a lifting/lowering drive so that the section on the raft can be freely raised and lowered on the raft. Alternatively, the raft itself can be equipped with ballasting tanks for air/water filling to regulate the raft's draft.

When the first sections 14 and 16 (figure 5) have been positioned, all the fastening bolts 40 are inserted through the flange bores and the associated tightening nuts 42 are screwed so that the flange surfaces 30 hh1 on the two opposite sections and with intermediate gaskets/seals are clamped against each other so that the gap /joint 19 (figure 1) becomes completely tight.

After the two sections 14,16 have been joined (figure 6), a support float 17 is maneuvered under the bridge girder and positioned so that the bridge girder rests with the joint on the float. This is shown in Figure 7. Furthermore, the raft 50 is pulled away to the right so that only the end of the outermost pipe section rests on the raft 50. Jr. figure 5 which shows that the end of the section 14 rests on the left side of the raft 50, while the next section 16 is ready.

Shown in Figure 7, the three pipe sections 14, 16 and 18 are interconnected while the fourth, No. 20, is in turn. The end of the pipe section 18 still rests on the raft to carry out the next connection.

The longitudinal mooring lines 60 and 66 are shown in the figure and the raft is pulled/slackened in the desired direction by synchronous maneuvering of the winches (70,72 in Figure 5), which can optionally be based on a dynamic positioning of the raft via a satellite navigation system, such as GPS . The adaptation and alignment can of course be controlled by an operator who lives in the fleet, as well as by the assembly personnel who are inside the pipe section and who carry out the screwing.

Further details of the invention.

Typically, each single hollow bridge girder segment can have a length of 50 - 150 metres, a width of 8 - 20 meters and a height of 4 - 8 metres. The mounting raft therefore preferably has a correspondingly greater length. That is that when the pipe segments are 150 meters long and 20 meters wide, the raft should have a length/width of the order of 200/40 metres. The contact surfaces of the adjacent bolt flanges must have such good contact that a satisfactory structural connection is formed that can absorb and transmit the forces occurring around the flanges and bolts, including shear forces, as well as compressive and tensile forces that may occur in this connection during the operation of the bridge .

The pipe sections can be mounted in a straight line in the floating bridge's longitudinal direction or at a smaller angle, preferably less than 6 - 7°, depending on the desired global curvature of the floating bridge or rise in the vertical plane. Each of the bridge girder elements is preferably rectilinear in the axial direction, i.e. in the floating bridge's longitudinal direction, but can also be produced with a slight curvature if desired, preferably with a larger bending radius greater than 1500 metres.

When the pre-assembled bridge girder is finished and attached to the end fasteners 11 and 13, it is preferred that the end walls are also made as tight as possible, so that the pre-assembled pipe sections form a continuous closed space where the air can be conditioned with regard to replacement, temperature and humidity . Experience shows that steel and iron surfaces at low humidity experience minimal corrosion and there is little need for surface treatment in the form of priming and painting, which is cost-saving both for construction and operation.

If the floating bridge is longer than 2000 metres, it should be divided into several mutually separated closed spaces, which will not affect the structural integrity of the bridge girder and the individual pipe sections. By the fact that the bolt flanges and associated bolts according to the invention are located inside a closed room that has moderate cross-sectional dimensions, typically width of 8 - 20 meters, and height of 4 - 8 meters, all bolt flanges and bolts in the bridge girder are easily accessible for inspection and replacement from the inside, and in a completely weather-protected environment.

According to known techniques, the roadway on the floating bridge can be led over any ship passages either on a high bridge or over a movable bridge section.

The floats 17 can be designed according to the local environmental conditions so that they transfer the least possible dynamic forces into the bridge girder. In calm waters, the floats can have a traditional single-hull shape, while in more weather-hardened areas, for example, they can be formed of columnar structures. The buoyancy capacity and stability of the floats are dimensioned for the appropriate carrying capacity of their own weight as well as the weight of bridge girders, bridge equipment, asphalt and traffic, and that they must meet safety requirements for ship collisions and damage stability.

The floating bridge can be without lateral anchoring or anchored in a number of anchor lines to meet the functional requirements set for the floating bridge.

Claims (17)

1. Construction of tube section (14,16,18,20—) to form a bridge girder (12) for a floating bridge (1) for transport track between two attachment points (11,13) across a strait or fjord, towards land (11 . 30,31) in an adjacent pipe section in the bridge girder (12). 2. Construction in accordance with claim 1, characterized in that the opposing flange surfaces are oriented across the longitudinal direction of the pipe section, and extend internally around the entire periphery of the pipe section at its end. 3. Construction in accordance with claims 1-2, characterized in that the means comprise a set of bolts with tightening nuts around the entire circumference, where the bolts extend through mutually flush bores through the flanges in the longitudinal direction of the pipe section, and where the flange surfaces are clamped together using the tightening nuts, or with forceps - constructions that grip and tighten against the back sides of the flange surfaces. 4. Construction in accordance with one of the preceding claims, characterized in that each bore is on the inside of the flange designed as a sleeve-shaped seat 34 with a bolt channel that aligns with an associated bolt channel in the bore 32 in a corresponding seat construction in the adjacent flange construction. 5. Construction in accordance with one of the preceding claims, characterized in that when the end part of the pipe section comprises a transverse beam 24, it also has a flange surface which faces and is connected together with a corresponding flange surface on the opposite pipe section. 6. Construction in accordance with one of the preceding claims, characterized in that the flange installation surfaces comprise a film to form a seal in the joint 19 between two pipe sections, which sealing film is of a softer metal such as copper, or a rubberized or a felt-like material. 7. Construction in accordance with one of the preceding claims, characterized by the bottom part of the beam cavity comprising a transport track, such as a rail passage (100) for advancing means (102) with inspection and maintenance equipment. 8. Method for manufacturing a bridge girder for a floating bridge (1) for a transport track between two attachment points (11,13) across a strait or a fjord, towards land (11,13), where the bridge girder is assembled from a number of pipe sections (14, 16,18,20—), characterized in that the following steps are produced: a) a number of pipe sections to form the bridge span over the strait/fjord, where each pipe section comprises an inwardly directed annular flange (30,31) for assembly to an adjacent pipe section in the bridge span, and that b) a first pipe section (14) is placed at a land side (11) for connection to a land transport system, after which a next pipe section (16) is placed on a floating installation raft (50) which is arranged in a suitable position and is set so that the flanged end of the second pipe section (16) is flush against the corresponding flanged end of the first pipe section (14) in a controlled manner, c) that the first (14) and second (16) pipe sections are connected by mounting bolts (44) and associated tensioning strap otters (42) through respective flush bores (32,34) in the two opposing flanges, said coupling being effected from the inside of the pipe sections, and d) whereupon the assembly raft (50) is suitably maneuvered to set a third pipe section resting on the raft (50) flush with the protruding end of the aforementioned second pipe section (14), and e) the remaining pipe sections to complete the floating bridge (12) over to the other land side (13) are assembled in turn in a similar manner as described under method steps c) - d). 9. Method in accordance with claim 8, characterized in that a sealing film is arranged between opposing flange surfaces to form a tight joint (19) between two adjacent pipe sections (14,16; 16,18; 18,20;...), 10. Procedure in accordance with claims 8-9, characterized in that the assembly raft (50) is positioned in the sea via cables (60,62 and 64,66) which extend from the respective assembly raft end towards land, and the cables are winch-operated (70,72) to move the assembly raft (50) successively across the sea surface (21) as the pipe sections are assembled, the assembly raft being stabilized laterally via transverse ropes (65,67) which extend out each side of the assembly raft (50) across the longitudinal direction. 11. Method in accordance with one of the claims 8-10, characterized in that the assembly raft (50) is maneuvered with incorporated propulsion machines in the raft hull and a number of azimuth propellers which can be brought down into the sea under the raft and operated, the propeller system being operated based on automatic positioning via satellite navigation, such as a GPS system. 12. Method according to one of the claims 8-11, characterized in that each pipe section is placed successively on a base (50) on the raft deck comprising a sliding track (52) which enables a simple horizontal displacement of the pipe section to create the right flush position between the two pipe sections (14,16) which are to be connected, which surface comprises the transport roller (52). 13. Method in accordance with one of claims 8-12, characterized in that the horizontal movement of the pipe section on the sliding track/transport roller is regulated by the rollers being driven by motor operation and can be stopped via a brake. 14. Raft (50) for positioning and assembly of pipe sections to a bridge girder for a floating bridge (1) for transport track between two attachment points (11,13) across a strait or a fjord towards land sides (11,13), characterized in that the raft deck includes a a sliding track/transport means (52) which enables a simple horizontal displacement of a loaded pipe section, for example in the form of a transport roller (52) or - a belt which is connected to a motor and a brake to control the pipe section's movement on the raft deck during assembly, and the installation fleet includes a device for controlled position and movement in the sea during installation. 15. Raft in accordance with claim 14, characterized in that the device for holding and changing the assembly raft's position during assembly, comprises an adjustable mooring system connected to the raft comprising sets of ropes connected to separate motor-driven winches which can either be mounted on the shore sides or on board the raft 50 . 15. Raft in accordance with claim 14, characterized in that a winch-operated first cable set towards the shore from each end of the raft is arranged approximately in the longitudinal direction of the bridge girder, and optionally a second set of winch-operated cables (65,67) extending from each side of the assembly raft (50 ) across the mentioned longitudinal direction. 16. Raft in accordance with claim 14, characterized in that a winch-operated cable set towards the shore from each end of the raft arranged approximately in the bridge girder's mounting raft is stabilized laterally via transverse cables (65,67) which extend from each side across the longitudinal direction of the mounting raft (50) . 17. A raft in accordance with claim 14, characterized in that the assembly raft (50) comprises propulsion machines in the raft hull in the form of a number of azimuth propellers which can be brought down into the sea below the raft and operated, the propeller system being operated based on automatic positioning via satellite navigation, such as a GPS system.