The present invention relates to bridge structures, in particular integral bridges.

As illustrated in Figure 1, a conventional integral bridge comprises a deck 1, which comprises a slab or beams, or a combination of the same, abutments 3a, 3b which are connected monolithically to the respective ends of the deck 1 without any mechanical joints, and an intermediate supporting pier 7 for supporting the deck 1 at a central location therealong. The abutments 3a, 3b serve simultaneously to support the traffic loading from the deck 1 and retain a backfill 5, typically granular soil, which is disposed between the abutments 3a, 3b and the respective roadway embankment or virgin ground away from the bridge. Integral bridges of this kind may be formed of steel or concrete, or be of a composite steel and concrete construction.

With this kind of bridge construction, the interaction at the interface of the abutments 3a, 3b and the backfill 5, which results from thermal expansion and contraction of the bridge deck 1, is an important design consideration. In service, daily and seasonal air temperature changes cause the bridge deck 1 to expand and contract in a cyclical manner. These movements, which are dependent upon the length and the material of the bridge, and the temperature change, impose cyclical horizontal displacements on the abutments 3a, 3b and hence the backfill 5 at the interfaces with the abutments 3a, 3b. This horizontal displacement of the backfill 5 causes two important changes to occur in the backfill 5, these being : (i) a progressive stiffening of the backfill 5, which results in progressively increasing horizontal stresses being created at the faces of the abutments 3a, 3b, and (ii) vertical settlement of the backfill 5 close to the abutments 3a, 3b, which results in road surface settlements and surface water ponding in wet weather conditions. These particular problems associated with the conventional integral bridge designs lead to high design and construction costs and the need for frequent maintenance to reinstate the required

surface profile of the roadway. In addition, current design constraints restrict integral bridges to a maximum length of 60 metres.

Recently, attempts have been made to reduce the abutment loading by interposing a layer of a soft, yielding material between the faces of the abutments 3a, 3b and the backfill 5.

Whilst this modification has been partially successful, this modification does not address the problem of settlement, which in the long term may even prove to have been worsened,

It is an aim of the present invention to provide bridge structures which exhibit reduced thermal displacement of the backfill abutments, such as to reduce horizontal stressing of the abutments, reduce road surface settlements, and also enable the construction of long-length integral bridges.

In one aspect the present invention provides a bridge structure, in particular an integral bridge, comprising: a deck for supporting a load thereon; first and second abutments which support respective ends of the deck and bear a compressive load from backfill at the respective outer sides thereof; and at least one displacement compensation unit which is configured such as to accommodate longitudinal thermal displacement of the deck and maintain a predeterminable longitudinal force between the abutments.

In one embodiment the deck comprises a plurality of deck parts.

In one embodiment the deck comprises first and second deck parts which are monolithically formed with respective ones of the first and second abutments, and the at least one displacement compensation unit is disposed between opposed ends of the first and second deck parts.

In one embodiment the opposed ends of the first and second deck parts include a respective one of a projection and a recess which receives the

projection, such that the projection and the recess allow for relative movement of the deck parts and define a shear transfer joint.

In another embodiment the deck comprises first and second deck parts which are monolithically formed with respective ones of the first and second abutments, and a third, suspended deck part which defines a central span between the opposed ends of the first and second deck parts, and comprising: first and second displacement compensation units which are disposed between opposed ends of the first and second deck parts and the third, suspended deck part.

In one embodiment the bridge structure comprises: a plurality of displacement compensation units.

In one embodiment the bridge structure further comprises: at least one supporting pier for supporting the deck.

In another embodiment the bridge structure further comprises: a plurality of supporting piers for supporting the deck.

In another embodiment the deck comprises a single deck part.

In one embodiment the bridge structure comprises: a plurality of displacement compensation units, with the displacement compensation units being disposed between opposite ends of the deck and the respective abutments.

In one embodiment the abutments each comprise a supporting member on which the respective ends of the deck are slideably disposed.

In one embodiment the bridge structure further comprises: at least one supporting pier for supporting the deck.

In another embodiment the bridge structure further comprises: a plurality of supporting piers for supporting the deck.

In one embodiment the deck and the one or more supporting piers are monolithically formed.

In one embodiment at least one of the at least one displacement compensation unit comprises at least one resilient unit which expands or is compressed in response to longitudinal displacement of the deck.

In one embodiment the at least one displacement compensation unit has a non-linear load-displacement characteristic.

In one embodiment the at least one displacement compensation unit is configured to maintain the longitudinal force within a predeterminable range.

In one embodiment the at least one displacement compensation unit provides for a substantially uniform longitudinal force with expansion or compression of the at least one resilient unit.

In one embodiment the resilient unit comprises a resilient element which expands or is compressed in response to longitudinal displacement of the deck.

In one embodiment the resilient element comprises an elastomeric component.

In another embodiment the resilient element comprises a compression spring.

In a further embodiment the resilient element comprises a plurality of conical spring washers.

In one embodiment the resilient unit comprises a casing which encloses the resilient element.

In another embodiment at least one of the at least one displacement compensation unit comprises at least one hydraulic unit which expands or is compressed in response to longitudinal displacement of the deck.

In one embodiment the at least one displacement compensation unit provides for a substantially uniform longitudinal force with expansion or compression of the at least one hydraulic unit.

In one embodiment the hydraulic unit comprises a hydraulic actuator which is actuatable, under control of a controller, to maintain a predeterminable longitudinal force between the abutments with longitudinal displacement of the deck.

In one embodiment the controller is an active pneumatic or hydraulic pressure control system.

In another embodiment the controller is a passive dead-weight control system.

In one embodiment at least one of the at least one displacement compensation unit comprises a single displacement compensation element which extends across substantially a full width of the deck.

In another embodiment at least one of the at least one displacement compensation unit comprises a plurality of displacement compensation elements which extend across substantially a full width of the deck.

In one embodiment the at least one displacement compensation unit accommodates a displacement of at least about 25 mm per 100 m length of the deck.

In one embodiment the at least one displacement compensation unit accommodates a displacement of at least about 50 mm per 100 m length of the deck.

In one embodiment the bridge structure has a length of at least about 100 m.

In one embodiment the bridge structure has a length of at least about 200 m.

In one embodiment the bridge structure is formed of concrete.

In another embodiment the bridge structure is formed of steel.

In a further embodiment the bridge structure is formed of concrete and steel.

In one embodiment the bridge structure supports a road surface.

In another aspect the present invention provides a bridge structure, in particular an integral bridge, comprising: a deck for supporting a load thereon; first and second abutments which support respective ends of the deck and bear a compressive load from backfill at the respective outer sides thereof; and at least one displacement compensation unit which is configured such as to accommodate longitudinal thermal displacement of the deck and maintain a longitudinal force between the abutments.

In a further aspect the present invention provides a method of constructing the above-described bridge structure, comprising the steps of: installing the deck and the first and second abutments; compressing the at least one displacement compensation unit with a predeterminable longitudinal force; backfilling the opposite outer sides of the abutments with backfill, such that the backfill has a predeterminable compressive state; and releasing the at

least one displacement compensation unit, such that the backfill is compressed with the predeterminable longitudinal force.

In one embodiment the backfill is backfilled to a compressive state which is less than an isotropic stress state of the backfill,

In another embodiment the backfill is backfilled to a compressive state which exceeds an isotropic stress state of the backfill.

In a further embodiment the backfill is backfilled to a compressive state which is substantially an isotropic stress state of the backfill.

In one embodiment the predeterminable longitudinal force corresponds to a force required to maintain the backfill substantially in an isotropic stress state, such that, on releasing the at least one displacement compensation unit, the backfill attains substantially the isotropic stress state.

Preferred embodiments of the present invention will now be described hereinbelow by way of example only with reference to the accompanying drawings, in which:

Figure 1 illustrates a longitudinal elevational view of a conventional integral bridge;

Figure 2 illustrates a longitudinal elevational view of an integral bridge in accordance with a first embodiment of the present invention;

Figure 3 illustrates a perspective view of a displacement compensation unit in accordance with one embodiment of the present invention;

Figure 4 illustrates a vertical sectional view (along section I-I in Figure 3) of the displacement compensation unit of Figure 3;

Figure 5 illustrates a vertical sectional view of a displacement compensation unit in accordance with another embodiment of the present invention;

Figure 6 illustrates a vertical sectional view of a displacement compensation unit in accordance with a further embodiment of the present invention;

Figure 7 illustrates a vertical sectional view of a displacement compensation unit in accordance with a still further embodiment of the present invention;

Figure 8 illustrates a perspective view of a displacement compensation unit in accordance with a yet further embodiment of the present invention;

Figure 9 illustrates a first vertical sectional view (along section II-II in Figure 8) of the displacement compensation unit of Figure 8;

Figure 10 illustrates a second vertical sectional view (along section III-III in Figure 8) of the displacement compensation unit of Figure 8;

Figure 11 illustrates a fragmentary longitudinal elevational view of an integral bridge in accordance with a second embodiment of the present invention;

Figure 12 illustrates a fragmentary longitudinal elevational view of an integral bridge in accordance with a third embodiment of the present invention;

Figure 13 illustrates a fragmentary longitudinal elevational view of an integral bridge in accordance with a fourth embodiment of the present invention; and

Figure 14 illustrates a fragmentary longitudinal elevational view of an integral bridge in accordance with a fifth embodiment of the present invention.

Figure 2 illustrates an integral bridge in accordance with a first embodiment of the present invention.

The bridge comprises a supporting deck 11 for supporting a load, in this embodiment a road 12, first and second abutments 13a, 13b which are monolithically formed with the respective ends of the deck 11 and act to support the same and bear a compressive load from backfill 15, typically granular soil, and at least one, in this embodiment a single supporting pier 17 for supporting the deck 11 at a location intermediate the abutments 13a, 13b, in this embodiment at a central location between the abutments 13a, 13b.

The deck 11 comprises a plurality of, in this embodiment first and second deck parts 11a, lib, which are movable relative to one another, such as to accommodate displacement of the deck parts 11a, lib, typically as caused by thermal expansion and contraction.

In this embodiment the first and second deck parts 11a, lib are supported on the supporting pier 17 by a low shear resistance packing 19, such as to facilitate displacement of the deck parts 11a, lib over the supporting pier 17.

In one embodiment the deck 11 can have a length of at least about 100 m, and preferably at least about 200 m. As will be appreciated, these lengths are considerably greater than can be achieved with existing integral bridge designs.

The bridge further comprises at least one, in this embodiment a single displacement compensation unit 21 which is disposed between the opposed ends of the deck parts 11a, lib, and which is such as to allow for displacement of the deck parts 11a, lib and operative to maintain a longitudinal force F on the abutments 13a, 13b, against the compressive loading of the backfill 15, which is within a predeterminable range and

significantly reduced as compared to conventional integral bridges which have no displacement compensation unit 21.

In one embodiment the displacement compensation unit 21 comprises a resilient element which expands or is compressed in response to longitudinal displacement of the deck parts 11a, lib and exhibits a load-displacement characteristic which maintains a longitudinal force F within a predeterminable range.

In one embodiment the resilient element has a non-linear load-displacement characteristic, which provides for an increasing longitudinal force F with compressive longitudinal displacement of the deck parts 11a, lib. In this embodiment the resilient element is configured such that the average value for the longitudinal force F corresponds substantially to an isotropic state of the stresses in the backfill 15.

In another embodiment the resilient element provides for a substantially uniform longitudinal force F with longitudinal displacement of the deck parts 11a, lib. In this embodiment the resilient element is configured such that the longitudinal force F corresponds substantially to an isotropic state of the stresses in the backfill 15.

In one embodiment, as illustrated in Figures 3 and 4, the displacement compensation unit 21 comprises a pair of loading members 27a, 27b, in this embodiment compression plates, and a resilient element 29, in this embodiment an elastomeric component, for example, a rubber block, which is disposed between the loading members 27a, 27b, such as to provide for the transmission of the longitudinal force F therethrough.

In this embodiment the displacement compensation unit 21 comprises an elongate unit which extends across the full width of the deck 11. This unitary configuration is advantageous, in providing for a structure which is less susceptible to the ingress of water and other environmental agents.

In an alternative embodiment a plurality of displacement compensation units 21 can be arranged across the width of the deck 11.

In another embodiment, as illustrated in Figure 5, the displacement compensation unit 21 comprises a pair of loading members 37a, 37b, in this embodiment compression plates, a resilient element 39, in this embodiment a compression spring, which is disposed between the loading members 37a, 37b, such as to provide for the transmission of the longitudinal force F therethrough, and a casing 41 which encloses the resilient element 39 such as to support the same and also protect the same from the environment.

In this embodiment a plurality of displacement compensation units 21 are arranged across the width of the deck 11.

In this embodiment the displacement compensation unit 21 has a substantially circular section, but in other embodiments could have other shaped sections.

In a further embodiment, as illustrated in Figure 6, the displacement compensation unit 21 comprises a pair of loading members 47a, 47b, in this embodiment compression plates, which are movably disposed relative to one another, a support member 49, in this embodiment a guide rod, which is disposed to one loading member 47a and over which the other loading member 47b is slideable, a resilient element 51, in this embodiment comprising a plurality of conical spring washers, which is disposed on the support member 49, such as to provide for the transmission of the longitudinal force F therethrough, and a casing 55 which encloses the resilient element 51 such as to protect the same from the environment. In this embodiment the load-displacement characteristic of the displacement compensation unit 21 is non-linear, such as to provide for a small rate of change in the longitudinal force F with displacement of the deck 11, and determined by the size and number of the spring washers.

In this embodiment the displacement compensation unit 21 has a substantially circular section, but in other embodiments could have other shaped sections.

In a yet further embodiment the displacement compensation unit 21 could comprise a hydraulic unit which is operative to expand or contract in response to longitudinal displacement of the deck parts 11a, lib, such as to maintain a longitudinal force F between the abutments 13a, 13b within a predeterminable range, and preferably at a constant value.

In one embodiment the hydraulic unit has a substantially constant load- displacement characteristic, which maintains a substantially uniform longitudinal force F with longitudinal displacement of the deck parts 11a, lib. In this embodiment the hydraulic unit is configured such that the longitudinal force F corresponds substantially to an isotropic state of the stresses in the backfill 15.

In one embodiment, as illustrated in Figure 7, the displacement compensation unit 21 comprises a pair of loading members 63a, 63b which are movable relative to one another and a hydraulic actuator 65 which is actuatable, under the control of a controller 67, to maintain a substantially uniform longitudinal force F with displacement of the deck parts 11a, lib and hence the loading members 63a, 63b.

In one embodiment the controller 67 is an active pneumatic or hydraulic pressure control system.

In another embodiment the controller 67 is a passive dead-weight control system.

In a further embodiment, as illustrated in Figures 8 to 10, the displacement compensation unit 21 comprises a pair of loading members 77a, 77b, in this embodiment compression plates, a first displacement compensation element 79, in this embodiment a resilient element, as an elastomeric component,

for example, a rubber block, which is disposed between the loading members 77a, 77b and includes a plurality of lateral through bores 81 at locations along the length thereof, and a plurality of second displacement compensation elements 83 of the kind of the embodiments of any of Figures 5 to 7 which are housed in respective ones of the through bores 81 and extend between the loading members 77a, 77b, with the displacement compensation elements 79, 83 being such as to provide for the transmission of the longitudinal force F therethrough.

In this embodiment the displacement compensation unit 21 comprises an elongate unit which extends across the full width of the deck 11. This unitary configuration is advantageous, in providing for a structure which is less susceptible to the ingress of water and other environmental agents.

In an alternative embodiment a plurality of displacement compensation units 21 can be arranged across the width of the deck 11.

In the above-described bridge structure configurations, the displacement compensation units 21 accommodate most, and in a preferred embodiment substantially all, of the thermal length changes in the bridge deck 11, thereby reducing, and in a preferred embodiment eliminating, the displacement of the abutments 13a, 13b, which would otherwise be transferred to the backfill 15, as described hereinabove. As a consequence, the abutments 13a, 13b experience less horizontal stressing, and the backfill 15 undergoes less cyclic straining, and hence less progressive stiffening due to this straining, which, significantly, leads to less settlement of the roadway 12.

In a preferred embodiment the displacement compensation units 21 are pre- compressed with a predeterminable force, which corresponds to the force required to achieve a state of isotropic stress in the backfill 15, such that, where the backfill 15 is backfilled to a stress which is lower than the isotropic stress of the backfill 15 and the compensation units 21 are

subsequently released, the backfill 15 subsequently attains this optimal isotropic stress state.

Figure 11 illustrates an integral bridge in accordance with a second embodiment of the present invention.

The integral bridge of this embodiment is very similar to the integral bridge of the above-described embodiment, and thus, in order to avoid unnecessary duplication of description, only the differences will be described in detail, with like reference signs designating like parts.

The integral bridge of this embodiment differs from that of the above- described first embodiment in the construction of the opposed ends of the deck parts 11a, lib and the arrangement of the at least one supporting pier 17. In this embodiment the end of the first deck part 11a includes a projection 84 and the end of the second deck part lib includes a recess 85 which receives the projection 84, such that the projection 84 and the recess 85 allow for relative movement of the deck parts 11a, lib and define a shear transfer joint, and displacement compensation units 21 are disposed between each of the opposed end sections of the deck parts 11a, lib. Also, in this embodiment the integral bridge comprises first and second supporting piers 17a, 17b which are spaced from the shear transfer joint and support respective ones of the deck parts 11a, lib.

Figure 12 illustrates an integral bridge in accordance with a third embodiment of the present invention.

The integral bridge of this embodiment is very similar to the integral bridge of the above-described first embodiment, and thus, in order to avoid unnecessary duplication of description, only the differences will be described in detail, with like reference signs designating like parts.

The integral bridge of this embodiment differs from that of the above- described first embodiment in that the deck 11 includes a third, suspended

deck part lie, which defines a central span between the opposed ends of the first and second deck parts 11a, lib, and in the arrangement of the at least one supporting pier 17.

In this embodiment the ends of the first and second deck parts 11a, lib each include a supporting projection 87 at a lower edge thereof and the third, central deck part lie includes supporting projections 89a, 89b at upper edges of the respective ends thereof, which, through low shear resistance packings 19, engage the supporting projections 87 at the lower edges of the first and second deck parts 11a, lib, such that the third, central deck part lie is suspended by the first and second deck parts 11a, lib and the first and second deck parts 11a, lib are movable relative to one another, and displacement compensation units 21 are disposed between each of the opposed end sections of the first and second deck parts 11a, lib and the third, central deck part lie. Also, in this embodiment the integral bridge comprises first and second supporting piers 17a, 17b which are spaced from the suspended deck part lie and support respective ones of the first and second deck parts 11a, lib.

Figure 13 illustrates an integral bridge in accordance with a fourth embodiment of the present invention.

The integral bridge of this embodiment is quite similar to the integral bridge of the above-described first embodiment, and thus, in order to avoid unnecessary duplication of description, only the differences will be described in detail, with like reference signs designating like parts.

The integral bridge of this embodiment differs from that of the above- described first embodiment in the construction of the deck 11 and the abutments 13a, 13b, and in the omission of a supporting pier 17.

In this embodiment the deck 11 comprises a single part which is formed separately of the abutments 13a, 13b, with the abutments 13a, 13b each including a supporting member 91 on which the respective ends of the deck

11 are movably supported, through respective packings 19, and displacement compensation units 21 are disposed between the respective ends of the deck 11 and the abutments 13a, 13b.

Figure 14 illustrates an integral bridge in accordance with a fifth embodiment of the present invention.

The integral bridge of this embodiment is similar to the integral bridge of the above-described first embodiment, and thus, in order to avoid unnecessary duplication of description, only the differences will be described in detail, with like reference signs designating like parts.

The integral bridge of this embodiment differs from that of the above- described first embodiment in that the abutments 13a, 13b comprise retaining walls which are formed separately of the deck 11, the deck 11 comprises a single part which is supported by first and second supporting piers 17a, 17b which are monolithically formed at the respective ends thereof, and displacement compensation units 21 are disposed between each of the opposed ends of the deck 11 and the respective abutments 13a, 13b.

Finally, it will be understood that the present invention has been described in its preferred embodiments and can be modified in many different ways without departing from the scope of the invention as defined by the appended claims.