Knowledge Experience Innovation Regional Operations and Engineering Services Directorate Bridge Engineering Bridge Assessment & Evaluation Section Octagon Building Level 6, Pod F 110 George St PARRAMATTA NSW 2150 Phone: 8837 0840 Fax: 88370059 Email: [email protected]Prepared for: REGIONAL OPERATION and ENGINEERING SERVICES DIRECTORATE ASSET MANAGEMENT SECTION RTA SYDNEY REGION AUGUST 2006 Perfomance Load Testing of Bridge over Hawkesbury River at WIndsor (BN415)
Transcript
Knowledge
Experience
Innovation
Regional Operations and
Engineering Services Directorate
Bridge Engineering Bridge Assessment & Evaluation Section Octagon Building Level 6, Pod F 110 George St PARRAMATTA NSW 2150
REGIONAL OPERATION and ENGINEERING SERVICES DIRECTORATE ASSET MANAGEMENT SECTION RTA SYDNEY REGION AUGUST 2006
Perfomance Load Testing of Bridge over Hawkesbury River at WIndsor (BN415)
EXECUTIVE SUMMARY The bridge over Hawkesbury River at Windsor consists of eleven spans with span length ranging from 9.8 to 13.5m and was completed in 1931. The superstructure is of reinforced concrete beam and there is a footway on the downstream side. The piers and Abutment A consist of two and three Monier RC cylinders respectively, while at Abutment B it has a mass concrete retaining wall. The bridge was inspected in detail and load rated in 2005. The beams were found to be in deficient in terms of rating factors due to its poor condition. Hence, the performance load testing and monitoring of ambient traffic were recommended. The testing was carried out on 19th and 21st April 2006 and continued for two weeks with the monitoring of ambient traffic. The objective of the testing was:
• to determine the strains in the reinforced concrete beams to the test truck with three different load levels travelling over the bridges at crawl speed
• to compare the recorded strains versus estimated strains • to determine the dynamic response and a appropriate value of dynamic load allowance for the
deck to the fully laden semi-trailer (ST43.14) • to monitor the response of RC beams to the ambient heavy vehicle traffic for two weeks • to determine the Load Factor for the critical RC beams from performance load testing.
The scope of works is:
• to instrument and conduct performance load testing of the Bridge • to conduct dynamic load testing to determine the dynamic response and a appropriate value of dynamic load allowance for the bridge • to carry out health monitoring of the bridge for two weeks • to prepare test report
The performance load testing was carried out with RTA dedicated test vehicle loaded up to three levels on tridem (20.6, 23.8 & 27t). The findings from the performance load testing and health monitoring are summarised below:
The maximum relative positive peak strain of up to 122με was recorded in concrete beam number 2 for RTA test truck with 20.6t on tridem travelling at a crawl in southbound, normal lane
The effect of load on maximum strain for beams is near linear The deck is behaving as an integral unit since the strains are recorded in all beams for test
travelling in both directions The recorded strains are near similar to estimated values for test truck with 20.6t on tridem The maximum dynamic load allowance is 17% for test truck travelling in southbound direction at
a speed of 40km/hr. Maximum strain of 124με was recorded in beam 2 for test truck travelling in northbound direction at 20km/hr
The maximum relative positive peak strain of 159με was recorded in concrete beams 2 & 6 during health monitoring for ambient traffic
Performance Load Testing & Health Monitoring of: ii Bridge over Hawkesbury River at Windsor
The available live load strain for 43.1t GVM test vehicle is greater than the minimum strain for a six axle articulated truck ST42.5, after deducting approximately 200με for dead load. The rating factor is found to be greater than 1.0 after allowing for 25% DLA.
Performance Load Testing & Health Monitoring of: iii Bridge over Hawkesbury River at Windsor
TABLE 1. MAXIMUM RECORDED STRAINS FOR RTA TEST VEHICLE WITH THREE LEVELS OF LOADING TRAVELLING AT A CRAWL SPEED ALONG CENTRE OF THE BRIDGE AND IN NORMAL TRAFFIC LANE .................................... 10
FIGURE 1. PARTIAL ELEVATION ...........................................................................................................................2 FIGURE 2. ABOVE DECK ....................................................................................................................................3 FIGURE 3. LOCATION OF INSTRUMENTED SPAN .....................................................................................................4 FIGURE 4. INSTRUMENTATION LAYOUT................................................................................................................4 FIGURE 7. INSTRUMENTATION OF CONCRETE BEAM NUMBERS 1 & 2 (U/S) OF SPAN 4-ALL FSGS ...................................5 FIGURE 8. INSTRUMENTATION OF CONCRETE BEAM NUMBERS 3 (FSG), 4 (DSG) & 5 (FSG) OF SPAN 4 .........................5 FIGURE 9. DEFINITION OF OFF, PR-, PR+, PK- AND PK+ ....................................................................................6 FIGURE 10. RTA DEDICATED TEST TRUCK ........................................................................................................7 FIGURE 11. RTA TEST VEHICLE (43.14 TONNE GVM)............................................................................................8 FIGURE 14. TEST VEHICLE (20.6T TRIDEM) CRAWL ALONG BRIDGE CENTRELINE IN SOUTHBOUND DIRECTION..................9 FIGURE 16. EFFECT OF WEIGHT ON MAXIMUM STRAIN IN BEAMS FOR TEST VEHICLE, CRAWL IN S/B NORMAL LANE ......... 11 FIGURE 17. EFFECT OF WEIGHT ON MAXIMUM STRAIN IN BEAMS FOR TEST VEHICLE, CRAWL IN N/B NORMAL LANE ........ 11 FIGURE 18. PERCENTAGE OF STRAIN DISTRIBUTION IN GIRDERS FOR 43.1T TEST VEHICLE ........................................... 12 FIGURE 19. STRAIN DISTRIBUTION IN GIRDERS FOR 43.1T TEST VEHICLE................................................................... 12 FIGURE 26. DYNAMIC LOAD ALLOWANCE VERSUS SPEED FOR 43T TEST VEHICLE ...................................................... 13 FIGURE 12. SCATTER PLOT OF RELATIVE POSITIVE PEAK STRAINS VERSUS TIME.............................. 15
Performance Load Testing & Health Monitoring of: 1 Bridge over Hawkesbury River at Windsor
The report details the Performance Load Testing and Health Monitoring of Windsor Bridge over Hawkesbury River at Windsor is in response to the request made by the Sydney Maintenance Planner dated February 2006. The bridge was inspected for category Level 3 and analytical load assessed in 2005 and was found to be deficient in terms of rating factors due to its poor condition in RC longitudinal beams. And from the meeting for Windsor Bridge Strategy held on 24 May 2005 it was agreed to carry out monitoring. The testing was carried out on the nights of 19th and 21st of April 2006 and continued for the next two weeks with the health monitoring of the bridge. 2. BRIDGE DESCRIPTION
The RC Beam bridge consists of eleven spans and was built in 1931. The span sequence is 12.83/2x13.35/3x13.5/13.28/3x13.41/9.78m. The bridge has a carriageway width of 6.1m between kerbs and carries two lanes of traffic. There is a footway of 1.22m on the downstream which is attached to the Pier headstocks with RSJ stringers spanning between the piers. It is structurally independent from the main deck and was constructed in late 60’s. The deck has eight longitudinal beams with spacing of 1.05m between centres and there is no transverse beam. The beams are fixed to RC Pier headstock on both sides with dowels. The piers consist of two Monier RC cylinders and concrete headstock. The cylinders are transversely braced with concrete bracing at the top and steel bracing at the bottom. At Abutment A (Windsor end), it consists of three Monier RC cylinders and the cylinders are braced with concrete wall. While at Abutment B, it consists of a mass concrete retaining wall.
Performance Load Testing & Health Monitoring of: 2 Bridge over Hawkesbury River at Windsor
The objective of the testing program was to: • determine the strains in the reinforced concrete beams to the test truck with four different load
levels travelling over the bridges at crawl speed and high speed • compare the recorded strains versus estimated strains • determine the dynamic response and a appropriate value of dynamic load allowance for the deck to
the fully laden semi-trailer • monitor the response of RC beams to the ambient heavy vehicle traffic for two weeks • determine the Load Factor for the critical RC beams from performance load testing. 4. SCOPE OF WORKS
The scope of works included the followings: • Instrument and conduct performance load testing of the Bridge • Conduct dynamic load testing to determine the dynamic response and a appropriate value of
dynamic load allowance for the bridge • Carry out health monitoring of the bridge for two weeks • Prepare test report
Performance Load Testing & Health Monitoring of: 4 Bridge over Hawkesbury River at Windsor
5.1 Instrumentation Layout The concrete beam span numbers 4 and 5 were instrumented. The location of these spans relative to other spans on the bridge is shown below in Figure 3. From Windsor To Wilberforce
Spans 1 to 3
Span 4 (tested span)
Span 5 (tested span)
Spans 6 to 11
Figure 3. Location of instrumented span The locations of the instrumentation are illustrated in Figure 4. Figures 7 and 8 show photos of the instrumentation installed on the span. The girders 1 to 4 are in northbound direction.
Figure 4. Instrumentation Layout
The instrumentation installed on the spans included the followings: 1. Demountable Strain Gauges (DSG) • on concrete beams 4, 6, 7 & 8 of Span 4 • on concrete beams 1, 2, 6 & 7 of Span 5 2. Foil Strain Gauges (FSG) • on concrete beams 1 to 3 an 5 of Span 4 All transducers were installed at midspan to measure flexural strain. Description of Instrumentation Examples: F-4-G1 FSG Foil Strain, Span 4, Girder 1 S-5-G7 DSG Demountable Strain, Span 5, Girder 7 Legend Type of gauges: F- FSG-Foil Strain Gauge, S-DSG-Demountable Strain
5.2 Nomenclature and Sign Convention A typical waveform is shown in Figure 9. This figure is used to define the nomenclature that is used to refer to particular summary results. The Nomenclature and extended definition are as follows: Pk+ positive peak or maximum Pk- negative peak or minimum Off offset Pr+ relative positive peak (=Pk+ - off) Pr- relative negative peak (=Pk- - off) PkP peak to peak (=Pk+ + Pk-) The Pr+ and Pr- are most relevant to this report. For all of the transducers, positive recorded values indicate tension strains and negative recorded values indicate compression strains.
Figure 9. Definition of Off, Pr-, Pr+, Pk- and Pk+
-50
0
50
100
150
200
250
300
350
400
-4.99 5 15 25
Time (s)
S-D
-S2
(Mic
rost
rain
)
OffPr-
Pr+Pk+
Pk-
Performance Load Testing & Health Monitoring of: 7 Bridge over Hawkesbury River at Windsor
Performance load test is a serviceability limit state test. Under the Performance type test, the bridge is carefully and incrementally loaded in the field to a pre-determined live load level, marginally higher than the legal load current at the time. Generally, this pre-determined load level is determined by multiplying the pre-determined live load by the dynamic load allowance and the serviceability limit state live load factor as given in the ’96 ABDC. As the load levels are lower in performance load testing, this test is both less costly and risky than a proof (ultimate) load test. Its responses are compared to some pre-determined/predicted values. The effects of the applied loads on critical members of the bridge are measured by strain gauging these members. The resulting field measured effect, such as load-strain is recorded and from these results the actual strength of the bridge to carry live loads is determined by making allowance for the serviceability live load factor and the dynamic load allowance factor. 6.1 Test Vehicles The performance load testing was conducted by using the RTA dedicated test loading vehicle as shown in Figure 10 The RTA test vehicle consisted of a Prime Mover and an extensively modified Low Loader in a six axle articulated vehicle with a Gross Vehicle Mass (GVM) of 43.14 tonnes as shown in Figure 11.
Figure 10. RTA dedicated Test Truck
Performance Load Testing & Health Monitoring of: 8 Bridge over Hawkesbury River at Windsor
6.2 Test Loading The lengths for the tested spans are 13.5m. It was found that the tridem of RTA dedicated test truck is critical loading for short span bridges. Hence, the following loading levels were used for RTA test vehicle travelled at crawling speed against the kerbs and at centre of bridge: Performance Load Testing
Level 3: 20.67t on tridem or 43.14t Gross Mass Vehicle (GMV) Level 4: 23.8t on tridem or 46..34t GMV Level 5: 27t on tridem or 49.54t GMV
Dynamic Load Testing For dynamic load testing on the Bridge, the test vehicle was loaded to Level 3 (that is 20.67t on tridem) and travelled at speed up to 60km/hr in 10 km/hr increments in both directions. 7. TEST RESULTS
The testing involved recording the response of each transducer versus time as the test vehicle travelled over the bridge. The data were sampled at 100Hz for the static (crawl) load testing, and 200Hz for the dynamic load testing (high speeds) and health monitoring (ambient traffic). The static and dynamic load testings of the bridge were carried out on the night of 19th April which covered all girders in Span 4 and girders 1 & 2 in Span 5. The performance load testing of and health monitoring of the bridge (girders 1-5 & 8 of Span 4 & girders 6 & 7 of Span 5) was conducted on the night of 21st April and continued over the next two weeks with the collecting of ambient traffic. 7.1 Performance Load Testing (Crawl) The maximum recorded strain for test vehicle with load of 20.6t on tridem (or 43.14t GVM) travelling in southbound normal lane is 122με in girder number 2 as shown in Table 1. The estimated strain in an internal girder is 117με.for ST42.5 at 0.6m from kerb. A typical plot of flexural strain at midspan versus time for test vehicle with load level 1 (20.6t on tridem) travelling at crawl speed along centreline of bridge in southbound direction is shown in Figure 14. It
Tandem 16.66t
1.27m 1.27m
5.81t Tridem 20.67t
6.96 m 3.22m
Performance Load Testing & Health Monitoring of: 9 Bridge over Hawkesbury River at Windsor
shows the highest flexural strain of 117με was recorded in girder number 5. More waveforms for test vehicle with different load levels travelling in different locations and directions are shown in Appendix B. The effect of imposed load on maximum strain for concrete girders is near linear as shown in Figures 16 and 17 for test vehicle travelling in southbound and northbound lanes respectively. The recorded strains for test vehicle with different load levels travelling in different locations and directions are shown in Table 1. The recorded strain distribution in all girders for test vehicle with 43.1t GVM is shown in Figure 18. The strains are recorded in all girders for test vehicle travelling in normal lane for any direction. This shows that the deck is behaving as an integral unit rather then two independent structures, as previously unsure of the connection/continuity between girders 4 and 5. For test vehicle travelling in northbound normal lane, the girder number 2 has a highest strain distribution of 21.3% and then girder 3 has 20.7%. The average total recorded strain in all girders for one span is approximately 588με. The recorded strains in concrete girders for test vehicle with load of 43.1t GVM are near similar to the estimated value as shown in Table 1. However, for a steel reinforcement bar with a yield stress of 210MPa, the available live load strain is greater than the minimum strain for six axle articulated truck of ST42.5t, after deducting approximately 200με of dead load. The maximum recorded strain for test vehicle with load level 1 of 43.1t GVM (ie 20.6t tridem) travelling at crawl speed is 122με. With the dynamic load factor of 1.25, the Rating Factor is found to be greater than 1.0.
Strain vs Time for test vehicle (200.6t tridem) travelling along centre in S/B direction
Table 1. Maximum recorded strains for RTA test vehicle with three levels of loading travelling at a crawl speed along centre of the Bridge and in normal traffic lane
Strain (µe) Span 4 Span 5
Load Level (tridem)
Location /Direction
Gird 1 F-4-G!
Gird 2 F-4-G2
Gird 3 F-4-G3
Gird 4 S-4-G4
Gird 5 F-4-G5
Gird 8 S-4-G8
Gird 6 S-5-G6
Gird 7 S-5-G7
S/B centre 33 77 106 93 117 36 96 36 N/B centre 33 79 103 95 117 39 104 38 S/B normal 21 37 50 74 91 103 115 86
(*) Estimated strain of internal beam is 117με for GAV ST42.5 based on uncracked section due to triden at midspan by positioning test truck 0.6m from kerb
Performance Load Testing & Health Monitoring of: 11 Bridge over Hawkesbury River at Windsor
The dynamic load allowance was calculated using the following equation:
static
staticdynamicDLAε
εε −=
The response from the crawl tests on Bridge for test vehicle travelled at centre of bridge was used for the static strain in the calculation of the dynamic load allowance. The dynamic load allowance was calculated for transducers on girders 1 to 5 of Span 4 for speed at increment of 10km/hr as shown in Figure 25. The maximum strain of 124με was recorded in girder 2 for test vehicle travelling in northbound at 20km/hr. The highest dynamic load allowance is 17% in girder 1 for test vehicle travelling in the southbound direction as shown in Figure 26. While for northbound direction, the highest dynamic load allowance is 13% in girder 4 at speed of 40km/hr. The highest average dynamic load allowance for the four girders is 3%, which is very low. The likely reasons for low values are poor deck condition, poor road geometry at the southern approach and had not taken into account of the other three girders. The maximum speed achieved was 60km/hr in the northbound.
-0.20
-0.15
-0.10
-0.05
0.00
0.05
0.10
0.15
0.20
-60 -50 -40 -30 -20 0 20 30 40 47
Speed
Dyn
amic
Incr
emen
t
F-4-G1 F-4-G2 F-4-G3 F-4-G4 F-4-G5Average
NorthboundSouthbound
Figure 26. Dynamic Load Allowance versus speed for 43t test vehicle
Performance Load Testing & Health Monitoring of: 14 Bridge over Hawkesbury River at Windsor
9.1 Introduction The health monitoring system (HMX) monitors the bridge response induced by the ambient heavy vehicle traffic crossing the bridge. A statistical distribution of the bridge’s response to the actual traffic is obtained. The bridge was monitored for heavy vehicles for two weeks starting from 21st April 2006. However, the data for 2nd week is poor due to problem with hardware. Therefore recorded data given below is for one week from 21st to 27 April 2006. The data gives an indication of expected ultimate limit state strains for single vehicle events. 9.2 Monitoring Statistics Start Time 21/04/06 12:55 End Time 27/04/06 07:58 Duration 5.79 days Number of events 312 Events Per Day The trigger threshold was set at 60με. 9.3 Results A typical scatter plot of positive strain versus time (hours) for health monitoring is shown in Figure 12. The maximum relative positive peak strain is 160με in girder 1 of span 4. The maximum relative positive peak strains for members from health monitoring are shown in Table 1. A comparison of maximum relative peak strains from dynamic load testing and health monitoring is shown in Table 2.
Performance Load Testing & Health Monitoring of: 15 Bridge over Hawkesbury River at Windsor
This report detailed the background of the bridge, program and results of the performance load testing and health monitoring of the concrete beam Bridge over Hawkesbury River at Windsor. The test vehicle with up to 3 load level was used for testing. The recorded strains in all beams have been summarised in this report.
The maximum strain of 122με was recorded in beam number 2 for test vehicle with load of 20.6t on tridem travelling at crawl speed in southbound normal lane.
The effect of load on maximum strain for concrete beams is near linear. The strains are recorded in all beams for test vehicle travelling in both directions. This indicates
that the deck is behaving as an integral unit which resolved doubt of connection/continuity between beams 4 and 5.
The recorded strains in concrete beams are near similar to estimated values for test vehicle with 20.6t on tridem.
The maximum dynamic load allowances (DLA) is 17% for test vehicle travelling in southbound at a speed of 40km/hr.
The available live load strain for test vehicle with 20.6t on tridem (43.14 GMV) is greater than the minimum strain for a six axle articulated truck ST42.5, after deducting approximately 200με for dead load. It is also found that the Rating Factor is greater than 1.0 after allowing 25% for DLA.
The maximum strain of 124με was recorded in beam 2 for high speed test with test vehicle travelling in northbound at 20km/hr
The bridge was monitored for ambient heavy vehicles for one week and the maximum relative positive peak strain of 159με was recorded.
11. RECOMMENDATION
It is recommended that::
the six axle articulated truck with maximum GVM of 42.5t (ST42.5) be continued to cross the bridge
the bridge be inspected annually.
Performance Load Testing & Health Monitoring of: 17 Bridge over Hawkesbury River at Windsor
