GB2065569A - Floating breakwaters - Google Patents

Abstract

A floating breakwater adapted to be moored with its leading side exposed across the path of waves, comprises at least one pair of shallow buoyant slabs of substantially the same length and a series of slender booms rigidly connecting the slabs in spaced apart parallel relation so that one slab of the or each pair forms the exposed side of the breakwater and the other forms the sheltered side, the breakwater having such trim and buoyancy that it floats with the slabs substantially awash. The slabs are structurally continuous throughout their length and strong in bending and torsion; they may be made of reinforced concrete and the booms may be inverted T-section girders. Where the breakwater comprises several pairs of slabs laid end to end to form two rows of slabs, articulations may be fitted between adjacent slabs. <IMAGE>

Description

SPECIFICATION Floating breakwaters The invention relates to a floating breakwater for limiting the deterioration of a structure or shore resulting from the incidence of surface waves travelling across a contiguous body of water such as the sea.

The structure to be protected may be a fixed installation such as a harbour wall or an oil drilling rig standing on the sea bottom, or a floating object such as an oil tanker moored at a pier for the loading or discharge of cargo.

It is known that a long shallow buoyant slab moored in water transversely to an advancing wave or train of waves will reduce the height of the incident wave by a fraction which depends on the relation of the gross plan area of the buoyant slab per unit length of slab to the wave length of the incident wave and also on the overall breadth of the slab related to the wave length of the incident wave. With long waves of small height, it may thus be advantageous to have a buoyant slab of large overall breadth but small plan area; such a slab may be made up of very slender members.

A breakwater as described, by imposing a horizontal barrier to the orbital motion of particles of water causing the wave motion, attenuates wave action whilst imposing only small forces on the moorings. The moorings can thus be widely spaced provided that the slab is strong enough in horizontal bending to span between them.

It is also known that the effect of short wave length or oblique waves on a long buoyant slab is to set up bending and torsion in the longitudinal direction which may greatly exceed those in the transverse direction.

One form of floating breakwater is described in out prior patent No. 1,293,521.

The present invention provides a floating breakwater comprising a pair of shallow buoyant slabs of substantially the same length, each slab being structurally continuous throughout its length and strong in bending and torsion, and a series of slender booms rigidly connecting the slabs in spaced apart parallel relation, one slab forming the exposed side of the breakwater and the other the sheltered edge.

The breakwater of the invention has the effect of a plan area and breadth which is much greater than the sum of the areas and breadths of the slabs.

The slabs may be made of short lengths joined end to end in known manner dependent on material used and side conditions.

The slabs will be almost awash. They can be made of reinforced concrete having cavities or cast-in expanded polystyrene to give the desired buoyancy. The slabs will be imperforate, or substantially so.

The booms must be of adequate bending strength in the vertical plane but need not be strong in torsion, nor need they be capable of floating. Their structural role is simply to link the two slabs together with such strength and rigidity that neither slab can rotate without imposing an equal (or nearly equal rotation upon the other slab. The slabs can conveniently be secured to the slabs by being laid on top of them with one end bolted down to each slab with sufficient strength to build up the full bending and shear strength of the boom. This arrangement makes it easy to connect the boom to the slabs while afloat and easy to make connections which are strong enough.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a transverse section of a floating breakwater according to the invention; Figure 2 is a partial plan view of the breakwater; and Figures 3, 4 and 5 are partial plan views of modified forms of the breakwater.

Referring to Figs. 1 and 2, the breakwater there shown comprises two similar reinforced concrete slabs 1, 2, as described, secured rigidly in spaced apart relation by booms 3 arranged at intervals along the length of the breakwater. Each slab can be for example 10 m. wide and 100 m. long, with a spacing between the slabs of at least three times the breadth of a slab. The booms 3 are inverted T-section structural steel members. Fixings 4 are built into the slabs 1, 2 near either edge and the booms are bolted down on to these.

The booms may be spaced quite widely apart; they may also be shaped to have a maximum plan area e.g. by broadening the flange.

Fig. 3 shows the booms laid out in an arrangement like that of a lattice girder. This arrangement provides very high strength in a horizontal direction (and thus permits very wide spacing of the moorings) and can increase the longitudinal strength of the breakwater, since the bending strength of the booms has a component in the longitudinal direction when the booms are inclined in this way.

Whichever arrangement is used, a given plan area of slab (plan area being the most significant factor in cost) can be given a very large breadth and thus good performance in attenuating waves of large length, with only the extra expenditure of the booms.

In certain conditions of exposure e.g. when very rare, very severe storms can be expected, there may be advantage in fitting articulations whereby extreme values of bending movement and torsion may be relieved.

Fig. 4 illustrates an arrangement of hinges 5 on both slabs 1, 2 between longitudinal sections A, B, C of the breakwater. The hinges 5 can be of rubber.

Fig. 5 illustrates an arrangement where hinges 6 of ball and socket type connect sections A', B', C' of one slab 1 only. The sections A", B", C" of the other slab 2 are rigidly connected to the corresponding sections A', B', C' of the first slab by boom 4; they are not connected to each other, but merely separated by fenders.

The Fig. 4 arrangement relieves longitudinal bending stresses in the breakwater, but not torsion.

The Fig. 4 arrangement relieves both bending and torsional stresses.

It is emphasised that in normal operation the arrangements of Figs. 4 and 5 function as longitudinally rigid members, and that stress relief is provided only for exceptional conditions.

Claims (11)

1. A floating breakwater adapted to be moored with its leading side exposed across the path of waves, comprising at least one pair of shallow buoyant slabs of substantially the same length, each slab being structurally continuous throughout its length and strong in bending and torsion, and a series of booms rigidly connecting the slabs in spaced apart parallel relation so that one slab of the or each pair forms the exposed side of the breakwater and the other forms the sheltered side, the booms being slender relative to the width of the slabs, the breakwater having such trim and buoyancy that it floats with the slabs substantially awash.

2. A breakwater as claimed in Claim 1, wherein the slabs are spaced apart a distance equal to at least three times the width of a slab.

3. A breakwater as claimed in Claim 1 or 2, wherein the slabs are made of reinforced concrete having cavities or cast-in expanded polystyrene.

4. A breakwater as claimed in any one of Claims 1 to 3, wherein the booms are secured to the slabs by being laid on top of the slabs and bolted at their ends to the slabs.

5. A breakwater as claimed in any one of Claims 1 to 4, wherein the booms are in- verted T-section structural steel girders.

6. A breakwater as claimed in any one of Claims 1 to 5, wherein the slabs are made of short lengths joined together.

7. A breakwater as claimed in any one of Claims 1 to 6, wherein the breakwater comprises several pairs of slabs laid end-to-end to form two rows of slabs with articulations fitted between adjacent slabs.

8. A breakwater as claimed in Claim 7, wherein the articulations comprise rubber hinges.

9. A breakwater as claimed in Claim 7, wherein the articulations comprise ball and socket type hinges between adjacent slabs of one row and fenders separating adjacent slabs of the other row of slabs.

1 0. A breakwater as claimed in any preceding claim, wherein adjacent booms are angled to one another so that, in plan view, the breakwater has an arrangement resembling a lattice girder.

11. A floating breakwater substantially as hereinbefore described with reference to Figs.

1 and 2 or any one of Figs. 3 to 5 of the accompanying drawings.