The present invention relates to a clamped-down bridge comprising a superstructure supported by pon¬ toons, each end of said bridge being fixedly secured to the bottom by means of anchors and anchor cables and clamped down to the expected maximum load by means of sinkers and sink cables, the anchor cables and the sink cables being wound in pairs onto a common shaft in such manner that winding up of the sink cables causes unwinding of the anchor cables, and vice versa. Bridges or loading platforms are previously known, the outer end of which is clamped down to different le¬ vels to correspond to the changes in level of a vessel relative to the water surface in loading or unloading, or to stabilise the bridge against heeling moments when the load is uneven. Such bridges are, however, freely floating or provided with complicated means for adjust¬ ing and maintaining the bridge at a correct level rela¬ tive to, for example, a vessel.

The object of the present invention is to provide a clamped-down bridge which normally acts as a freely floating bridge but, when loaded or in case of transitory changes of the water level, such as when subjected to wave action, is automatically locked, and which allows vertical adjustment of the bridge as the water level rises or sinks. This object is achieved by means of a bridge having the features as stated in the characteris¬ ing clause of claim 1.

The invention will now be explained by means of examples, reference being had to the accompanying draw- ings in which:

Fig. 1 is a top plan view of a bridge according to the present invention, the superstructure being shown merely by dash-dot lines;

Fig. 2 is a side view of the bridge shown in Fig. 1;

Fig. 3 is an end view of the bridge shown in Fig. 1;

Fig. 4 is an enlarged view of part of the bridge, showing an automatic locking device which is included in the bridge shown in Fig. 1 ; Fig. 5 is a top plan view of the locking device according to Fig. 4;

Fig. 6 illustrates the principle of the function of the locking device, when subjected to wave action;

Fig. 7 shows the principle of the function of the locking device as the water level rises;

Fig. 8 shows the principle of the function of the locking device as the water level falls or the bridge is loaded; and

Fig. 9 illustrates in principle the stress occurring under different conditions.

With reference to Figs. 1-3, the bridge comprises a superstructure 1 which is supported by pontoons 2 which preferably are arranged in each of the corners of the bridge. The bridge is secured to the bottom by means of an anchor 3 arranged in each corner. The anchors 3 are connected with the bridge by anchor cables which are wound in pairs onto pulleys 4 mounted on a shaft 6 which is common to each such pair. On each shaft 6, there are further arranged pulleys 5 for sink cables connected with sinkers 10 which clamp down the bridge to the ex¬ pected maximum load. To avoid uneven load of the anchor cables and oblique floating of the bridge, the sinkers should be centred on the shafts 6. The anchor cables on the pulleys 4 and the sink cables on the pulleys 5 are wound in opposite directions, so that unwinding of the anchor cables causes winding up of the sink cables, and vice versa. The two shafts 6 are, by means of chain gears 7, chains 8 and cables 9, rotatably connected with one another and with an automatic locking device 11 ac- cording to the invention.

The automatic locking device 11 is shown in more de¬ tail in Figs. 4 and 5. The locking device comprises two

toothed ratchet wheels 12, the teeth of one wheel being opposed to the teeth of the other wheel, and the ratchet wheels being mounted side by side on a shaft 27 which is supported by two bearings 26. On the shaft 27 there are further mounted two chain gears 13 which by means of chains 25 are connnected with .the cables 9 and, thus, with the chain gears 7 on the shafts 6. Thus, rotation of one of the shafts 6 causes rotation of the ratchet wheels 12. Moreover, the locking device 11 comprises lock means 14 which are mounted on a common locking bar 15 on vertically opposite sides of the ratchet wheels 12. The locking bar 15 is connected with a float 16 which is provided with a weight 17, such as a metal plate, to give the float the correct buoyancy. The float 16 is mounted in a float casing 18 which by means of suspension mountings 23 is suspended in the superstructure 1 of the bridge. The float casing 18 further contains a pipe 19 which is adapted to ventilate the float casing and provided with guide means 20 for the locking bar 15. The lower part of the pipe 19 is provided with an inlet and outlet pipe 21 which extends vertically downwards and is provided with a sieve 22. An abutment 24 is ar¬ ranged to absorb the locking pressures occurring in the locking device. The function of the locking device will now be ex¬ plained with reference first to Fig. 6 which shows the conditions when the bridge is freely floating, the bridge being loaded only by its own weight in which also the weight of the sinkers is included, or being subjected to wave action. When the bridge is freely floating, the lock means are in one of the positions shown in the upper part of the Figure. As soon as the bridge is sub¬ jected to an outer load, i.e. a force which can be di¬ rected upwards or downwards, the shaft 6 will be rotated due to the winding or unwinding of the anchor cables onto or from the pulleys 4. The rotary motion of the shaft 6 is transferred by means of the chain gears 7,

the chains 8, the cables 9 and the chains 25 to the chain gears 13 on the shaft 27 and, thus, to the ratchet wheels 12. Since the lock means 14 engage with the teeth of the ratchet wheels 12, the bridge is automatically locked against vertical movements and functions as a clamped-down bridge. Under the action of waves, the di¬ rections of force and motion change continuously. If the lock means are in the position shown in the left- hand upper part of Fig. 6 when the wave motion starts, the ratchet wheels will therefore always rotate so that the lock means take the position shown in the right-hand upper part of the Figure. As a result, the bridge is locked against motions in both directions. The inlet and outlet pipe 21 should be of such length that its lower end is always positioned under the water surface. The dimension of the pipe should be so small that water in such amounts that the locking positions change, does not manage to flow out or be pressed into the casing of the float in the time it takes for a wave to pass. The function as the water level rises is illustrat¬ ed with reference to Fig. 7. The upper part of the Figure shows from left to right first how the bridge is freely floating and there is no engagement between the lock means and the teeth of the ratchet wheels. It is then shown how the water surface rises. The upward pressure under the pontoons causes rotation of the shaft 6 and, thus, the ratchet wheels 12, such that the upper lock means is brought into engagement. As the water surface rises, the float raises the lock means, until the upper lock means is moved out of engagement and the ratchet wheel can begin to rotate. The next part of the Figure shows how the bridge together with the float casing is raised during rotation of the ratchet wheels. The float remains on its level of altitude, since the lower lock means is fed downwards by the lower tooth to the same extent as the ratchet wheel rises. Since the float casing rises but not the float, the water in the float casing will

on the one hand be pressed out of the pipe 21, but since this is narrow, the water will, on the other hand, also be pressed upwards above the float. During the rotation, the lower lock means will thus be pressed against the lower teeth. When the lower lock means has passed the edge of the teeth, the float is unprevented from rising to the surface, while the excess water in the float casing flows out. The right-hand part of the Figure shows how the float has risen to its balanced position and the water surface in the float casing has taken the same position as the surrounding water surface. The bridge is again freely floating but on a level which has risen by the height of a tooth. As the water surface rises further, the procedure will be repeated. With reference to Fig. 8, the function as the water level sinks is illustrated. The left-hand upper part of the Figure shows again how the bridge is freely float¬ ing and there is no engagement between the lock means and the teeth of the ratchet wheels. The next part of the Figure shows how the water surface sinks. The pulling force of the sinker causes rotation of the ratchet wheels such that the lower lock means is brought into engage¬ ment. As the water surface sinks, the float pulls down the lock means until the lower locks means is moved out of engagement and the ratchet wheels can begin to rotate. The bridge together with the ratchet wheels and the float casing sink during the rotation of the ratchet wheels, as shown in the next part of the Figure. The float remains on its level of altitude, since the upper lock means is fed upwards by the upper teeth to the same extent as the ratchet wheel sinks. Some water will then be sucked into the float casing. During the rotation, the upper lock means is pressed against the upper teeth, but when the lock means has passed the edge of the teeth, the float is unprevented from sinking, while the water level rises. The right-hand upper part of the Figure shows how the float has sunk to its balanced

position and the water surface in the float casing has taken the same position as the surrounding water surface. The bridge is again freely floating, but on a level which has fallen by the height of a tooth. If the water surface continues to sink, the procedure will be re¬ peated.

Under effective load, i.e. when a load is applied to the bridge, the bridge will be pressed down, i.e. the same case of load as shown in the lower part of Fig. 8. The pressing down of the bridge implies that an upward pressure is exerted on the float. The ratchet wheels will rotate such that the lock means takes the position shown in the right-hand upper part of Fig. 6. The lock means remains in this position until the bridge has been unloaded.

Fig. 9 shows schematically the forces acting on the bridge under different conditions of load. The upper part of the Figure shows from left to right how the bridge is anchored, the locking device first being locked. The upward pressure exerted on the pontoons, i.e. the lifting force, is P and the downwardly directed force, i.e. the weight of the bridge and the sinkers, is also P, which means that the tension in the anchor cable is 0. Subsequently, the locking means is released and the bridge is clamped down and the pontoons sink until they support the load 2P, whereupon the sinkers are locked in their new position, as shown in the right-hand upper part of the Figure. The centre row in the Figure shows to the left how the load P is applied to the bridge. As the load is applied to the bridge, the tension in the anchor cables is reduced. When the tension is 0, the maximum load P has been applied. The further parts of the Figure in the centre row show what happens as the water level rises. The rising water level supplies the addition Δ P to the lifting force of the pontoons, and the bridge automatically takes its new level of altitude in the manner shown in Fig. 7. The two left-hand

lower parts of the Figure show in a corresponding manner what happens as the water level sinks. Finally, the right-hand lower part of the Figure shows schematically how the anchors can readily be hoisted, for example to prevent the bridge from being damaged by moving ice in winter. Additional pontoons are inserted between the upper side of the ordinary pontoons and the lower side of the superstructure. As a result, the bridge can follow the motions of the ice. The weight which is to be hoisted constitutes the difference between the weight of the anchors and the weight of the sinkers, and therefore a minor amount of power is required.

The bridge according to the invention is, of course, not restricted to the embodiment described above and shown in the drawings, but can be modified in various ways. Thus, in the embodiment shown the pulleys 4 for the anchor cables are as large as the pulleys 5 for the sink cables. For a certain load, a fixed tension in the anchor cables is required which yields a corre- sponding torque in the pulleys of the anchor cables. The necessary torque is produced by the weight of the sinkers and depends on the radius of the pulleys of the sink cables. If the pulleys are designed with the same diameter, the bridge will move to the same extent as the water level rises or sinks, but the sinkers will move twice this difference in height, since the sink cables are wound up or unwound to the same extent as the bridge moves upwards or downwards. When the bridge is laid in deep water, the pulleys of the sink cables can, however, be made considerably larger than the pulleys of the anchor cables. The motion of the sinkers will then to a corresponding degree be much bigger than the motion of the bridge. This means that the weight of the sinkers can be reduced. The portion of the pontoons which is used to support the sinkers can then also be reduced to the same extent. When the bridge is laid in shallow water, the condition will be reversed, i.e.

the pulleys of the sink cables must be smaller than the pulleys of the anchor cables. This means heavier sinkers and larger pontoons than if the pulleys are of the same size. A more complicated design is to provide the pulleys of the sink cables with a gear, e.g. a plane¬ tary gear, which may give a ratio in the available space, which is higher than if the diameters of the pulleys are changed.