Note: Descriptions are shown in the official language in which they were submitted.
CA 02778354 2012-04-16
WO 2011/044611 PCT/AU2010/001268
1
A bridge construction and method for modifying strain
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 I (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.
CA 02778354 2012-04-16
WO 2011/044611 PCT/AU2010/001268
2
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, incluing 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.
CA 02778354 2012-04-16
WO 2011/044611 PCT/AU2010/001268
3
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
CA 02778354 2012-04-16
WO 2011/044611 PCT/AU2010/001268
4
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.
CA 02778354 2012-04-16
WO 2011/044611 PCT/AU2010/001268
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
5 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
CA 02778354 2012-04-16
WO 2011/044611 PCT/AU2010/001268
6
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.
CA 02778354 2012-04-16
WO 2011/044611 PCT/AU2010/001268
7
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
CA 02778354 2012-04-16
WO 2011/044611 PCT/AU2010/001268
8
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
CA 02778354 2012-04-16
WO 2011/044611 PCT/AU2010/001268
9
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.
