characteristics of a bridge

Field of the invention

The invention relates to the field of traffic bridges. More particularly, the invention relates to a bridge construction and a method for modifying the strain characteristics of a bridge. The invention may have particular application to girder bridges of steel or concrete, or combinations thereof with a steel deck in the form of an orthotropic plate floor.

Background

Figure 1 shows a partial view of an example of a traffic bridge 100 to which the present invention may be applied. The traffic bridge is a girder bridge with an orthotropic plate floor.

The traffic bridge 100 includes a plurality of uprights 1 (one only shown) and cross girders 2 (again one only shown) extending between the uprights 1. The uprights 1 and cross girders 2 may be I beams or another suitable structure. Trough beams 4 provide longitudinal support for the traffic bridge 100. The trough beams 4 extend between and are welded to the cross girders 2.

A steel deck plate 3 is welded to the trough beams 4. An epoxy coating 5 may be provided over the steel deck plate 3. A layer of asphalt (not shown) may be provided over the epoxy coating 5 as a wear layer.

Over time, girder bridges suffer from fatigue. As a result, fatigue cracks may develop, often at the trough beam to cross girder connection and/or at the deck plate to trough beam connection. Repairing fatigue cracks may be a complex and costly process, that may involve partially or fully closing the bridge to traffic. Summary of the invention

Viewed from one perspective, the invention generally relates to a method of modifying strain characteristics of a bridge construction having a support structure for a deck plate, the support structure and deck plate defining respective parts of a mutual sealed internal cavity, the method comprising actively evacuating the internal cavity to create a negative pressure in the internal cavity. The method may be applied to a plurality of the support structures for the deck plate, up to all or substantially all of the support structures.

Viewed from another perspective, the invention generally relates to a bridge construction including a deck plate and a support structure connected to the deck plate. The support structure and deck plate both form part of a mutual sealed internal cavity that has been actively evacuated to create therein a negative pressure differential with the environment of the internal cavity. In some embodiments the negative pressure differential is at least 50 kilopascals (kPa). In other embodiments greater negative pressure differentials may be present, induing negative pressure differentials of at least 60 kPa, at least 70 kPa, at least 80kPa, at least 90 kPa, about 95 kPa and about 100 kPa. In some embodiments, the negatige pressure differential is in the range of 95kPa and 100 kPa.

In some embodiments, the bridge construction is a girder bridge and the support structure is a trough beam extending longitudinally along the girder bridge. The support structure may extend between two cross girders and the sealed internal cavity may extend along substantially the entire longitudinal length of the support structure.

In some embodiments, a pressure detector monitors the negative pressure differential in each said internal cavity, the pressure detector communicably connected to a controller that receives an output from the pressure detector and communicates or outputs detection of a loss of negative pressure differential in one or more of the internal cavities. The bridge construction may include a plurality of the support structures, each at the specified negative pressure differential. In some embodiments, each support structure is isolated from the other support structures whereby a loss of negative pressure in one support structure does not result in a loss of negative pressure in the other support structures. Individual pressure detectors may be provided for each support structure and the controller may receive an output from each of the pressure detectors and communicate or output an indication of which of the support structures has lost negative pressure.

Also disclosed is a bridge construction including a deck plate and a support structure connected to the deck plate, the deck plate and support structure both forming part of a mutual internal cavity that is at a negative pressure, the bridge construction further including a pressure sensor and a controller monitoring the negative pressure of the internal cavity, the controller outputting or communicating a loss of negative pressure in the internal cavity. In some embodiments, the bridge construction includes a plurality of support structures, each forming part of a mutual internal cavity with the deck plate, wherein the pressure sensor and controller monitor the pressure in internal cavities of each of the plurality of support structures. In some embodiments, the internal cavities of each of the plurality of support structures are isolated from each other so that loss of negative pressure in one internal cavity does not result in loss of negative pressure in another of the internal cavities.

Also disclosed is a method of monitoring a bridge construction for fatigue cracks, the bridge construction having a deck plate and a deck plate support structure together defining a mutual sealed internal cavity, the method comprising creating a negative pressure within the internal cavity and monitoring for a loss of negative pressure within the internal cavity.

Also disclosed is a method of producing a bridge construction, including welding a deck plate to a plurality of deck plate support structures to create a plurality of sealed internal cavities defined in part by the deck plate and in part by the support structures, and actively creating a negative pressure within the internal cavity of each of the plurality of support structures.

Also disclosed is a method of modifying a bridge construction to reduce the rate of oxidation of a part thereof, the bridge construction having a steel deck plate and a plurality of steel deck plate support structures together defining respective parts of a mutual sealed internal cavity, the method comprising creating a negative pressure within the internal cavity of each of the plurality of support structures.

Also disclosed is a method of evaluating the integrity of a bridge construction, the bridge construction having a deck plate and a plurality of deck plate support structures together defining respective parts of a mutual internal cavity, the method comprising actively creating positive pressure within the internal cavity of each of the plurality of support structures and monitoring for a loss of negative pressure within the internal cavity. This method may be completed as a pressure test to evaluate whether the internal cavity can withstand a negative pressure sufficient to modify the stain characteristics of the bridge construction.

Various aspects of the invention and further embodiments of the aspects described in the preceding paragraphs will become apparent from the following description and/or from the accompanying drawings.

Brief description of the drawings

Figure 1 (prior art) shows an example of a girder bridge to which the present invention may be applied.

Figure 2 shows a portion of a girder bridge construction between two uprights including a negative pressure system.

Figure 3 shows a trough beam with strain gauges. Detailed description

A description of embodiments of the invention is provided with reference to the accompanying Figures in which like reference numerals represent like components.

Referring to Figure 2, a girder bridge 200 is partially shown. The girder bridge 200 is of the same type described as the girder bridge 100 with reference to Figure 1. The girder bridge 200 includes uprights 1, cross girders 2 extending between the uprights 1 and trough beams 4 extending between the cross girders 2. The surface of the bridge includes a steel deck plate 3, an epoxy coating 5 and a layer of asphalt 6.

Each trough beam 4 defines an internal cavity 7. The internal cavity 7 is closed at its ends by the cross girders 2 and the welds connecting the trough beam 4 to the cross girders 2. A hole 8 is formed in each trough beam 4, for example by drilling and tapping. The hole 8 may be suitably formed in its trough beam 4 at a central location between the cross girders 2. The holes 8 are connected to a vacuum pump 10 via valves 9 and pipe and/or hose connections 11. Figure 2 shows a single pump 10 used to provide a negative pressure (i.e. a pressure below atmospheric pressure) to the cavities 7, but in other embodiments there may be a plurality of pumps. For example the trough beams 4 may be split into n groups corresponding to n pumps, with each pump responsible for a group of trough beams. The pumps may apply the same or different pressures to different trough beams. The groups of trough beams may each comprise a single trough beam, two trough beams or three or more trough beams. The groups may have an equal number or different pumps may be responsible for differing numbers of trough beams.

The vacuum pump 10 is operated to evacuate air from the internal cavities 7. Pressure gauges 12 provide an indication of the negative pressure created in each of the internal cavities 7. One or more pressure gauges 12 may also indicate the negative pressure within the pipe and/or hose connections 11. By providing a negative pressure within the internal cavities 7, the welds connecting the trough beam 4 to the deck plate 3 are compressed, relative to the compression extant prior to application of the negative pressure. This modification of ^' the strain characteristics of the bridge construction may reduce the fatigue stress about these welds. The welds connecting the trough beam 4 to the cross girders 2 may similarly be compressed.

The negative pressure applied to the internal cavities may vary, depending on requirements. However, approximately 90 to 95 kPa negative pressure or higher may be suitable. Lower negative pressures may also be useful, for example ranging from about about 50 or 60 kPa, depending on the requirements and the structure of the bridge to which the invention is to be applied. Again, the reference to negative pressure is made with reference to atmospheric pressure for bridges of the type shown in Figures 1 and 2. For other bridges that have a plurality of cavities, for example nested cavities where the joints requiring compression are in an internal cavity, then the reference to negative pressure is made with reference to the pressure surrounding the cavity. In other words, the invention creates a differential pressure between inside and outside the relevant cavity.

In some embodiments, the negative pressure within the internal cavity 7 may be set to achieve a required strain change. For this purpose, strain gauges 13 (see Figure 3) may be provided about the trough beam 4. Figure 3 also shows the welds 14 between the trough beam 4 and the deck plate 3. The pump 10 may then be operated to, over a period of time, increase the magnitude of the negative pressure in the internal cavity 7, until the strain gauges 13 measure a required change, or a practical or set maximum negative pressure is reached. The change may be an average change, for example measured over a period of hours, part days or days, so that for instance the negative pressure may start at a negative pressure of about 50 or 60 kPa and step or ramp up over a period of hours or days or a longer period until the required change in average strain is detected. The change in micro-strain at one or more of the sensors may be about 50 or more. In other embodiments the change in micro-strain may be 70 or more, 100 or more, 150 or more or about 250. The strain gauges 13 may also be used to detect a loss of the modified strain characteristics, in addition to or instead of detecting a loss of negative pressure differential between an internal cavity 7 and its environment. In addition to the compression of the welds around the trough beam 4, the application of a negative pressure to the internal cavity 7 may provide a warning of the development of fatigue cracks. The pressure gauges 12 measure the pressure within the internal cavity 7. A reduction in the magnitude of the negative pressure beyond that attributable to thermal effects may indicate the development of fatigue cracks. A controller 50 may be provided, for instance a simple microprocessor based device, microcontroller or programmable logic device that receives a signal from each of the pressure gauges 12 and controls a transmitter 51 (or other communication device such as a modem) to send a signal indicating the loss of negative pressure within one or more of the trough beams 4. For the purposes of clarity, in Figure 2 the controller 50 is shown connected to one only of the gauges 12, but the controller 50 may be connected to any or all of the gauges 12, depending on the monitoring requirements. The connection between the gauges 12 and the controller 50 may be wired or wireless. In the embodiment shown the controller 50 is local to the bridge 50 and the transmitter 51 provides for transmission or broadcast of signals. In alternative embodiments, the gauges 12 may include a modem or other device enabling communication onto a network, for example a telecommunications network or interrogation through the network.

In some embodiments, a pressure gauge is provided for each trough beam 4. Also, the trough beams 4 may be isolated from each other, for example by the valves 9 shown in Figure 2. In this way localised fatigue monitoring can be achieved and the loss of negative pressure in one trough beam 4 does not necessarily result in all trough beams 4 losing negative pressure. Alternatively, the trough beams 4 may not be isolated or only isolated in groups, in which case a single pressure gauge may suffice to detect fatigue cracks in any one of the trough beams or any one in a group of trough beams.

In some embodiments, the pressure gauges 12 may output a signal , to a pump controller 53, which controls operation of the pump 10 (or pumps 10 if there are more than one under its control) and in the event that the magnitude of the negative pressure reduces below a set point by a threshold amount, the pump controller 53 turns the pump on to increase the negative pressure back to its set point. The frequency of activations of the pump 10 may indicate the progression of fatigue around the trough beams 4, in addition to or as an alternative to any indication that may be taken from direct readings of the pressure gauges 12. The pump controller 53 may be communicatively connected to the gauges 12 by any appropriate mechanism, including a wired or wireless connection. Like the controller 52, for the purposes of clarity, in Figure 2 only one such connection is shown. The controller 50 and pump controller 52 may in some embodiments be implemented in the same physical device.

In some embodiments, the internal cavities 7 of the trough beams 4 are tested before the negative pressure is applied. Testing may be performed by pressurising the internal cavities 7 to a positive pressure and determining whether the pressure holds constant. For example, the internal cavities 7 may be pressurised to 15 kPa above atmospheric pressure and checked for retention of the positive pressure for a period of 24 hours. The pump 10 may be reversible and used to perform the positive pressure testing, either through the pipe and/or hose connections 11 or through a separate connection provided to perform the test, which would allow testing prior to installation of the pipe and/or hose connections 11. Alternatively a different pump may be used for pressure testing. The testing may indicate whether the trough beams 4 are likely to hold the negative pressure when applied. Trough beams 4 that fail the test or are found not to hold the negative pressure despite passing any testing may be omitted. The areas around these trough beams 4 may be left as is, reinforced against fatigue using other methods, or work undertaken to seal the areas of ingress of air.

The evacuation of air from within the trough beams 4 may have the additional benefit of reducing the rate of oxidation of the trough beams 4.

Those skilled in the relevant arts will appreciate that there are different structures of girder bridge. The foregoing description has been provided by way of example with reference to one possible structure. The invention will have application to other bridge structures with an appropriately located and sealed cavity to which a negative pressure can be applied to reduce stress at a connection point by compressing the connection.

For example, a bridge construction may have trough beams of a different shape, for example trough beams that define a rectangular shape instead of the trapezoidal shape shown in the drawings. The trough beams may have internal structures, for added reinforcement or other purposes. A single trough beam may include two cavities sealed from each other, which can either be maintained in isolation and separately maintained at a negative pressure, or which could be shorted together, for example by drilling and tapping holes into each and connecting the holes with pipes and/or hoses.

Also, in the embodiments described the internal cavities are formed in part by the trough beams, in part by the deck plate and in part by the cross girders. In alternative embodiments the ends of the tough beams may be sealed by means other than the cross girders, for example by an additional plate welded to the end of the trough beam (which will therefore terminate short of any cross girders to allow space for the additional plate).

In other embodiments of bridge construction, the trough beams of which the internal pressure is changed may extend transversely across the bridge, in addition to or as an alternative to changing the internal pressure of longitudinally extending trough beams. To the extent that a bridge construction includes trough beams that extend obliquely to the transverse and longitudinal directions, then the invention may also have application to such a bridge construction.

It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.