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ENGINEERING
newspix / andrew tauber
Opened in 1978,
the West Gate Bridge
was widened in a project
completed last year.
Anchors of cloth
“We developed an anchorage system that is added to the carbon-fibre laminates
but also uses carbon-fibre material. This anchoring system increased the efficiency
of the fibres by up to 260 per cent. What this really meant was that we reduced the
overall amount of fibre we needed to use,” Professor Al-Mahaidi says.
The anchorage system is simple and cheap. A 25 centimetre-wide strip of
carbon-fibre fabric runs across the end of all the carbon-fibre beams, like a line
of super-strong sticky tape.
The fabric anchor is a different weave so the strength-bearing threads run in
two directions. It anchors the laminates and spreads their load to surrounding
concrete to increase the overall strength of the system.
The strength, delicacy, ease and versatility of the
West Gate Bridge
stats
Opened:
15 November 1978
Total length:
2582 metres
Maximum width:
37 metres
Longest span:
336 metres
Clearance below:
58 metres
Strengthening
complete:
June 2011
Number of Lanes:
5 inbound
5 outbound
Daily traffic:
160,000 vehicles
Strengthening Cost:
$347 million
Strengthening
materials:
38km of carbonfibre
laminate,
12,000m 2 of carbon
fibre fabric,
400,000 bolts and
1600 tonnes of
steel fabricated
into 80,000 pieces.
techniques. And they did, if we could prove the
efficiency of another system experimentally.”
Traditionally bridges are strengthened by reinforcing
them to resist strains by glueing steel plates or
jacketing sections with additional concrete that act
in the same way as a splint or putting a cast on a
broken limb. But over the past two decades engineers
have been investigating alternative bracing materials
like carbon-fibre reinforced polymer (CFRP). CFRP
is a strong, lightweight fabric of interlocking carbon
threads with up to 10 times the strength of steel, twice
the stiffness, yet only one-seventh the weight.
Furthermore, it is very durable, with none of the
corrosion problems experienced with steel and
concrete.
Prefabricated carbon-fibre laminate beams can be
fixed with epoxy to structures like external ribs. In the
case of the West Gate Bridge, however, only around
20 per cent of the CFRP’s strength would have been
harnessed using these standard design guideline
approaches.
CFRP laminate and fabric system recently took
Professor Al-Mahaidi to Karbala city in Iraq. The
system was used in the repair of Al-Abbas ibn Ali
shrine masonry dome, which was damaged by artillery
and tank fire in 1991.
Mimicking a bridge
At Monash University and then at Swinburne,
Williams, Professor Al-Mahaidi and his team tested
possible anchoring solutions to the point of failure
using concrete blocks to mimic bridge sections
and the position of areas prone to delamination
(stress fractures).
“During tests we monitored the blocks using
surface sensors to measure the level of stress and
strain, and used photogrammetry, two cameras
continually recording any surface deformation,”
says Professor Al-Mahaidi.
“In addition, computer simulation gave us a deeper
understanding of what was happening within these
zones. These computer models also correlated with
the physical evidence from the lab testing.”
This work was commissioned by The West Gate
Bridge Strengthening Alliance comprising SKM,
VicRoads, John Holland and Flint & Neill, with funding
from the federal and Victorian governments.
Strengthening the curriculum
The scale of the West Gate Bridge strengthening
project, the novelty of the solution and importance
of these maintenance processes have created a body
of knowledge Professor Al-Mahaidi feels is worth
codifying and sharing.
“The research over the past 10 years has
encouraged us to introduce a new unit of study to the
curriculum, which is the first of its kind in Australia:
‘Strengthening and monitoring of structures’.”
The unit relates many findings from the West Gate
Bridge and is suitable for fourth-year and masters
engineering students. l
“We developed an
anchorage system
that is added to the
carbon-fibre laminates
... This anchoring
system increased the
efficiency of the fibres
by up to 260 per cent.”
Professor Riadh Al-Mahaidi