10th International Conference on Short and Medium Span
Bridges
Quebec City, Quebec, Canada,
July 31 – August 3, 2018
PERFORMANCE OF GFRP COMPOSITE SLAB-ON-CONCRETE GIRDER BRIDGE –
10 YEARS AFTER CONSTRUCTION BASED ON LOAD TESTS
Au, Alexander1 and Mermigas, Kris
Bridge Office, Ontario Ministry of Transportation, Canada
1 [email protected]
Abstract: The 1st edition of the Canadian Highway Bridge Design
Code (CSA 2000) did not permit the use of glass-fibre-reinforced
polymer (GFRP) for the main reinforcement in the bridge deck.
However, this limitation was removed in the 2nd edition (CSA 2006),
based on field observations of GFRP performance in concrete (Mufti
et al. 2007). The rehabilitation of the 3rd Concession Road
Underpass in 2008 took advantage of this material (Lee et al.
2010). The four-span superstructure consists of a composite
concrete slab-on-CPCI girder system built in a semi-continuous
sequence. The entire deck is reinforced with GFRP reinforcement. In
order to assess the structural performance of this material under
field conditions, the deck was not protected with the customary
waterproofing system and was left with an exposed concrete surface,
and the bridge is monitored visually and through behavioural load
tests. The first behavioural load test of the bridge was performed
in July 2010 (Au and Lam 2010). Strain gauges were installed on the
GFRP reinforcement during construction while displacement
transducers were installed at other locations. The purpose of the
first load test was to confirm the short term behaviour of the
bridge and provide base data against which future performance could
be compared. The bridge was re-tested in July 2017, nine years
after the rehabilitation and seven years after the first load test.
The paper compares the performance of the deck and the GFRP
reinforcement from the tests in 2010 and 2017.
1. INTRODUCTION
The bridge deck is an early MTO structure to be completely
reinforced by GFRP bars. MTO planned to monitor the long-term
performance of this bridge. During the deck construction in 2008,
24 strain gauges were installed on the GFRP bars. The initial
behavioural load test was in July 2010 as close as practically
possible to the bridge’s initial construction. The observations
from this load test indicated that the bridge performed very well
(Au and Lam 2011). The bridge is inspected regularly with the
latest inspection in early 2017. The second load test was performed
in July 2017. More external gauges were installed on the bridge
deck and more load steps were applied to the bridge. Dynamic tests
were also carried out. Two additional accelerometer sets were used
to monitor the bridge’s performance.
1 BRIDGE DETAILS
The Highway 401/3rd Concession Road Underpass (MTO Site# 6-236)
is a four-span (10.67 m end spans and two 19.20 m main spans)
composite slab-on prestressed concrete girder bridge carrying
traffic on 3rd Concession Road over Highway 401 in Western Ontario.
Its location is on Highway 401 at Lakeshore Road 113, about 30 km
east of Windsor. Originally constructed in 1967, the deck system
consisted of 5 prestressed concrete girders. This bridge was
rehabilitated in 2008 with a superstructure replacement. The new
superstructure consists of semi-integral abutment connections, 5
new CPCI 900 beams, and a GFRP-reinforced concrete deck with new
parapet walls, also reinforced with GFRP bars. The deteriorated
concrete on the pier caps was removed and replaced with new
concrete. The 215 mm thick new deck has an exposed concrete
surface. Figure 1 shows the bridge details and Figure 2 shows
photos of the GFRP reinforcement in the deck and in the parapet
wall. Details of the bridge design features are found in Lee et al.
(2010).
(a) Elevation
(b) Deck GFRP rebar details
Figure 1: Details of the Hwy401/3rd Concession Underpass
(a) GFRP Bar in Deck
(b) GFRP Bar in Barrier
Figure 2: Photos of GFRP reinforcement
2 INSTRUMENTATION
A total of 47 gauges were installed on the bridge. At a section
near the mid-span of the end span as shown in Figure 3(a), five
LVDTs and five strain gauges were installed. At a section near the
north pier as shown in Figure 3(b), 10 strain gauges were
installed. There were three strain gauges installed on top of the
concrete deck. During the rehabilitation of the bridge deck in
2008, MTO installed 24 strain gauges on the GFRP bars. Figure 3(c)
indicates the strain gauges on two longitudinal and two transverse
GFRP bars. The instrumented longitudinal GRFP bars were over the
north pier and the transverse GFRP bars were near the mid-span of
the north end span. Figure 4 shows photos of typical gauges. Also,
two sets of accelerometer were used to monitor the dynamic
performance of the deck during dynamic test runs.
(a) Mid-span location
(b) Near the north pier
(c) Strain gauges at GFRP bars
Figure 3: Instrumentation on the Hwy401/3rd Concession
Underpass
(a) Strain gauge on GFRP bars
(b) LVDT and strain gauge on girder
Figure 4: Photos of typical gauges
3 APPLIED LOADS
The test loads were applied on the bridge using two test trucks,
each consisting of a three-axle tractor and a two-axle
semi-trailer. The trucks were loaded with concrete blocks, each
weighing approximately 1 tonne, and carrying a maximum load of 36
concrete blocks each. The first truck (Volvo Auto-car) had a
maximum gross weight of 539.5 kN and the second one (Western Star),
548.7 kN (see Figure 5)
The test trucks were loaded incrementally to three different
load levels i.e. with12, 24 and 36 concrete blocks. For each load
level, the trucks were moved longitudinally on the bridge in four
pre-set combinations, referred to as load lines 2 to 5 (Figure 6).
Load lines 2 and 3 were single truck cases while load lines 4 and 5
involved both trucks. It can be seen that load line 4 is
effectively a combination of load lines 2 and 3. To obtain the
bridge response under static conditions, each truck was positioned
at 17 pre-determined locations or steps along each load line, as
shown in Figure 7. For each truck step, the readings from all the
instrumentation devices were recorded by a computerized data
acquisition system. The truck steps were selected in order to
generate maximum theoretical responses in the bridge.
A dynamic test was performed after the static load test. Dynamic
runs were provided by a test truck loaded with 24 concrete blocks,
running with 40 km/hr across the bridge. The time variation of the
responses was measured together with data collected by two
accelerometers on the deck.
Figure 5: Test truck loads and dimensions
Figure 6: Transverse locations of the test trucks
Figure 7: Step locations of the test trucks
4 TEST RESULTS
4.1 Girder Deflections
The deflections from 2010 and 2017 load tests match closely.
Figure 8(a) shows deflections vs load steps. The truck steps were
indicated in Figure 7 (over three spans). The deflection patterns
(positive and negative) are similar for all test truck steps.
Figure 8(b) shows deflections vs load levels. Linear relations were
observed for both 2010 and 2017 deflections. The comparison for the
exterior girders was similar. Therefore, it could be concluded that
there is no change in the deflection performance within this
period.
(a) Deflections(Line 5) vs Steps
(b) Deflections (Line 5 Step 5) Vs Load Levels
Figure 8: Comparison of girder deflections
4.2 Girder Strains
The measured longitudinal strains from 2010 and 2017 load tests
are very close, as shown in Figure 9 at the bottom of the middle
girder. Figure 9(a) shows strains vs load steps. The strain
patterns (positive and negative) are similar for all test truck
steps. Figure 9(b) shows strains vs load levels. Linear relations
were observed for both 2010 and 2017 measured strains. This is also
the case for exterior girders. Therefore, it could be concluded
that there is no change in the girder strain response within this
period.
(a) Interior girder (Line 5)
(b) Linearity of girder strain (Line 5 Step 7)
Figure 9: Comparison of girder strains
4.3 Strains in GFRP Bars
24 strain gauges were installed on the GFRP bars during the
bridge deck construction in August 2008 (see Figure 3(c)). Figure
10 shows the comparison of the longitudinal GFRP bar strains under
load line 5. It indicates that the measured GFRP strains from 2010
and 2017 load tests are very close. The GFRP strain patterns are
similar for all test truck steps. Figure 10(b) shows longitudinal
GFRP bar strains vs load levels. The GFRP strains were linear with
the applied load for both 2010 and 2017 measurements. Therefore, it
could be concluded that the longitudinal GFRP bar strain response
didn’t change in this period.
Figure 11 shows the comparison of the transverse GFRP bar
strains. It also indicates that the measured GFRP strains from 2010
and 2017 load tests are very close. The strain patterns are similar
for all test truck steps shown in Figure 11(a). Figure 11(b) shows
transverse GFRP bar strains vs load levels. It was observed that
for both 2010 and 2017 measured strains were linear and very close.
Therefore, it could be concluded that the transverse GFRP bar
strain response also didn’t change in this period.
4.4 Uncracked Condition over the Pier
In the negative moment area, the crack control for the GFRP
design is 0.5 mm against the traditional steel design of 0.25 mm
(Lee et.al. (2010)). GFRP design allows higher concrete crack width
over the pier. Figure 12 shows the distribution of longitudinal
strain at a section near to the north pier. The strains at the
girder bottom and at the girder web were plotted at all the load
levels. The strains in the girder were negative indicating a
negative moment region. Figure 12 also shows the location of the
theoretical neutral axis (NA) for the naked girder and the
uncracked section. The neutral axis projected from the measured
strains is somewhere above the theoretical neutral axis of the
uncracked section. It indicates that the girder-GFRP reinforced
deck remains in an uncracked condition in the negative moment
region. It is in agreement with the bridge inspection where no
crack was observed at the negative moment region.
(a) Longitudinal GFRP bar (Line 5)
(b) Linearity of strain in longitudinal GFRP bar (Line 5 Step
11)
Figure 10: Comparison of strains in longitudinal GFRP bars
(a) Transverse GFRP Bar (Line5)
(b) Linearity of strain in transverse GFRP bar (Line 5 Step
11)
Figure 11: Comparison of strains in transverse GFRP bars
Figure 12: Strain distribution in a girder section near the
north pier (2017 data - Line 5 Step 11)
4.5 Dynamic Behaviours
(a) Longitudinal GFRP bars
(b) Transverse GFRP bars
Figure 13: Dynamic measurement of the GFRP bars (2017 data)
Figure 13(a) shows the longitudinal GFRP bar strains measured in
the dynamic test. It shows similar responses at 4 different gauges
along the same longitudinal GFRP bar. It could be concluded that
the GFRP bar performed well under the live load and the GFRP bars
were perfectly bonded to the concrete. Figure 13(b) shows the
transverse GFRP bar strains at 4 gauges along the same transverse
GFRP bar. It clearly shows the individual axle effect from a
five-axle truck. Therefore, the GFRP bars are working under dynamic
loads. Figure 14(a) shows the vibration velocity of the deck during
a test truck run. It could be observed that the vibration velocity
changes sign a few times due to the effect of a moving truck on a
4-span bridge. Figure 14(b) shows the bridge acceleration vs time.
The maximum acceleration at the deck was 0.03g. Detailed analysis
of the acceleration vs time and the prediction of the vibration
measurement will be presented in a future publication.
(a) Vibration Velocity vs Time
(b) Acceleration vs Time
Figure 14: Dynamic measurement of the deck (2017 data)
5 CONCLUSIONS
Based on the observations from 2010 and 2017 load tests, the
following conclusions could be deduced:
· There is no change in the girder performance (deflection and
strain) within this period.
· There is no change in the GFRP bar performance (longitudinal
and transverse) within this period.
· The girder-concrete deck remains in an uncracked condition in
the negative moment region.
· There has been no loss of elastic stiffness in positive and
negative moment regions, based on an applied live load.
· The GFRP reinforced deck performing very well in the first ten
years in the service.
Acknowledgements
The instrumentation on the GFRP bars was designed by Dr.
Clifford Lam, former Head of Bridge Research, Bridge Office. He
also worked on the load test in 2010. His contribution is
gratefully acknowledged. Both load tests were performed with the
hard work of the MTO technical staff, Ping Kang and Nebojsa Lukic.
Their efforts are greatly appreciated. The authors also like to
thank the contribution of a summer student from McMaster
University, Patrick Wilkon, for his work on the load test in
2017.
References
Au, A. and Lam, C. 2011. Testing of Hwy 401/3rd Concession Road
Underpass. Bridge Office Report (BRO-054), Bridge Office, Ministry
of Transportation, Ontario, Canada.
CSA. 2000. Canadian Highway Bridge Design Code CAN/CSA-S6-00.
Canadian Standard Association (CSA) International, Toronto,
Ontario, Canada.
CSA. 2006. Canadian Highway Bridge Design Code CAN/CSA-S6-06.
Canadian Standard Association, Mississauga, Ontario, Canada.
Mufti,A.A., Onofrei, M., Benmokrane, B., Banthia N., Boulfiza,
M., Newhook, J.P., Bakht, B., Tadros G.S. and Brett, P. 2007. Field
study of glass-fibre-reinforced polymer durability in concrete.
Canadian J. Civil Engineering, 34(3), 355-366.
Lee, J., Craig, B., Loh P. and Dimitrovski, V. 2010. Working
towards maintenance-free bridge decks using glass fibre-reinforced
polymer reinforcing bars. Proceedings of 8th International
Conference on Short and Medium Span Bridges, Niagara Falls,
Ontario, Canada, 165: 1-10.
014-1
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CONCRETE PARAPET
WALL WITH RAILING
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SOUTH ABUTMENTBEARINGS
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GUIDERAIL ANDCHANNEL ANCHORAGE
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155.927.95
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Line 5
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