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A paradigm shift in building bridges
Five countries endorse Canadian-led
design concept
Achieving consensus on the Winnipeg Principles indicates
a paradigm shift in how new bridges could be designed and
built and how old ones might be repaired or rehabilitated.
Forty-two internationally renowned bridge designers met at
the International Workshop on Innovative Bridge Deck Technologies
in Winnipeg in April to reach a consensus on the future design
of bridge decks.
The result: the ISIS Canada Winnipeg Principles – endorsed
by representatives from Canada, the United States, Japan,
Switzerland and India – will go into the Canadian Highway
Bridge Design Code, for use by civil engineers.
The agreement is nothing short of a paradigm shift for how
new bridges could be designed and built, and for how old ones
might be restored and rehabilitated. It represents almost
a decade of work by ISIS Canada – the Network of Centres
of Excellence on Intelligent Sensing for Innovative Structures.
The ISIS mandate is to advance Canadian civil engineering
to a world leadership position through the development and
application of fibre reinforced polymers (FRPs) and integrated
intelligent fibre optic sensing (FOS) technologies.
"ISIS has been working on bridge deck design principles
collectively for nine years," says Dr. Aftab Mufti,
the Scientific Director of ISIS, explaining the lead-up to
Winnipeg. "Four project leaders and approximately 30
researchers and staff all came to the same conclusion for
change. The next progression was to present them to the international
group."
For more than 75 years, steel has been used inside the concrete
to support the weight of heavy cars and trucks. The problem
is, steel is heavy, expensive and it corrodes over time, especially
with exposure to the extreme climate conditions in Canada.
Dr. Aftab Mufti, Scientific Director of the ISIS Canada,
a Network of Centres of Excellence, and other international
researchers have found that the arching action of bridge decks,
similar to Roman Arches, provides sufficient strength without
steel reinforcement to bear the load.
"Over time, designing bridge decks based on arching
action will significantly save on material costs estimated
in the billions because steel will not be required for strength,
and corrosion of steel will be eliminated," says Dr. Mufti.
The Winnipeg Principles also give the option of reinforcing
the concrete slabs with FRPs, which are extra strong, last
longer and require less maintenance than traditional construction
materials. They are also more durable than steel.
The Canadian Standards Association, through the Technical
Standard Committees, has issued an addendum to the code that
includes the Winnipeg Principles, with final approval anticipated
later this year.
The Canadian Highway Bridge Design Code is the only code
in the world that permits the use of FRPs for strengthening
and reinforcement on both new and rehabilitated bridges and
structures made of concrete or wood. Incorporating the principles
into the code will not only have an impact on the design of
civil structures in Canada, but it will also influence the
updating of similar codes worldwide.
Introducing these design principles into the code is just
the first of several changes that will be championed by ISIS
to promote innovations in bridge design and construction,
says Dr. Mufti.
ISIS Canada has further broadened the scope for innovative
bridge design concepts through structural health monitoring,
using the “Civionics” concept that combines electronics
with civil engineering.
"It has been shown in both the lab and the field that
these technologies work," says Dr. Mufti.
| The Winnipeg Principles
The new principles are as follows:
- That inherent arching action is present in
concrete bridge deck slabs in the transverse
direction, and that in consequence, relevant
deck slabs, such as those in composite slab
on girder bridges, should preferably be designed
in accordance with such arching action, whereby
the top reinforcement is no longer required
for strength and the arching action is achieved
by one of:
- internal bottom reinforcement in the concrete,
which may be steel or FRP, and which should
be designed by stiffness consideration and
for concrete crack control; or
- stay in place formwork, which may be of
steel, concrete or FRP, which is designed
by stiffness considerations and by proper
connections to the girders
- external straps, designed by stiffness considerations
and by proper connections to the girders,
along with a limited amount of steel or FRP
reinforcement placed as a bottom grid for
concrete crack control.
- suitably placed diaphragms between girders
provided they are properly connected.
- It has been demonstrated that inherent arching
action is of benefit when designing for fatigue,
and it is therefore recommended that, with the
help of research on full-scale models and/or
prototypes, one or more methods should be developed
for designing deck slabs for fatigue.
- That new provisions should be adopted into
codes of practice to reflect the enhanced state
of design knowledge relating to the use of FRP
in concrete deck slabs.
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