BRIDGE-WIM AS AN EFFICIENT TOOL FOR OPTIMISED BRIDGE ASSESSMENT Aleš Žnidarič, ZAG Ljubljana
Content What is Bridge WIM? Structural parameters in BWIM Influence lines Load distribution factors Soft load testing Dynamic Amplification Factors Conclusions
WHAT IS BRIDGE WIM?
What is BridgeWIM? B-WIM is anaccurate accurate high-speed weigh-in- motion system that uses existing instrumented bridges as weighing scales. It does not only provide the same traffic data as the pavement WIM systems, but also some additional, measured structural parameters that can be used for optimised bridge assessment.
BWIM shema SiWIM Bridge Weigh-in-motion system
History of bridge WIM developed by F. Moses (CWRU) in 1979, as an alternative to the pavement WIM systems in Australia CULWAY since 1986 in Slovenia since 1991 in Ireland since 1995 in WAVEproject from 1996 to 1999 since 2000 SiWIMsystem, used in 12 countries on 4 continents also in Japan, Taiwan
B-WIM advantages Full portability High accuracy Ease of installation No interference with traffic Provides not only traffic but also structural data Data can be checked
B-WIM disadvantages Accuracy and efficiency depends on: Type of bridge Qualifications of personnel Bridges are not available everywhere
B-WIM developments Extensive implementation of FAD (Free-of-Axle Detector) approach New technologies: Cameras Solar power and fuel cells Mobile connectivity New applications: Pre-selection of overloaded vehicles Bridges
B-WIM developments To involve new types of bridges: To improve FAD efficiency To deal with multiple-presence presence events To increase accuracy Theoretical studies: Dynamic algorithms Tikhonov regularisation Moving Force Identification ADR Assessment Dynamic Ratio
B-WIM SYSTEM INSTALLATION
Strain transducer ST-500 S.N. 10122150100001 R ST500 SN 10122150100001 220mm
Installation with axle detectors
Installation with axle detectors
Installation without axle detectors
Installation with axle detectors
Installation withoutaxle detectors
Installation withoutaxle detectors >70% of European installations in 2007
SOME TYPICAL INSTALLATIONS
2.5+3.0 m integral slab bridge Canada
9 m long, integral-type type slab bridge France
7 m long, simply-supported supported slab bridge India
186 m long, 5-span beam-deck bridge Slovenia
530 m long, 6-span orthotropic deck bridge Poland
530 m long, 6-span orthotropic deck bridge Poland
B-WIM FOR OPTIMISED BRIDGE ASSESSMENT
B-WIM for optimised bridge assessment Objective: To use structural parameters: Influence lines Load distribution factors Dynamic Amplification Factors measured by B-WIM in optimised structural (bridge) analyses.
Influence lines In first generation of B-WIM calculated analytically -> this does not work Influence lines must be determined from measurements 2 methods: UCD, using a vehicle of known characteristics ZAG, using random vehicles (in SiWIM WIM)
Construction of influence line
Construction of influence line
Construction of influence line
Construction of influence line
Construction of influence line
Construction of influence line
TRAFFICLOAD MODELLING
Truck histograms from Europe 10% 10% Frequency 5% Frequency 5% 0% 0 10 20 30 40 50 60 0% 0 10 20 30 40 50 60 GVW (Tonnes) GVW (Tonnes) 10% 10% Frequency 5% Frequency 5% 0% 0 10 20 30 40 50 60 0% 0 10 20 30 40 50 60 GVW (Tonnes) GVW (Tonnes)
Traffic load modelling calibrated notional load models (loading schemes) for: design and assessment (rating) static and dynamic loading, incl. fatigue site specific modelling based on traffic data: Monte Carlo simulation simplified models (convolution)
Traffic load modelling Q = a W.95 H m I g where: a = constant W.95 H = expected loading m = vehicle factor I = impact factor (DAF) g = load distribution factor 3 19% 2 1.3 m 5.3 m 26% 17% 3.5 m
Traffic load modelling
SOFT LOAD TESTING
Soft load testing Introduced in the SAMARIS project (5 th FW programme) Studied further within ARCHES project (6 th FW Programme) Objective: To optimise bridge assessment by finding reserves in load carrying capacity and loading
Load testing -Knowing bridge behaviour on bridges that seem to carry out normal traffic satisfactorily, but fail to pass the assessment calculation the available model of the bridge likelydoes not match the real bridge to supplement and check the assumptions and simplifications made in the theoretical assessment To optimise bridge assessment by finding reserves in load carrying capacity and loading
Load testing benefits: less severe rehabilitation measures less traffic delays tremendous savings drawbacks: costly danger of damaging the bridge best candidates: difficult modelling lack of documentation (drawings, calculations ) when savings are greater than the cost of load test
Load testing Types of load test: proof diagnostic soft
Soft load testing -advantages uses B-WIM to provide: normal traffic data information about structural behaviour of the bridge: influence lines statistical load distribution impact factors from normal traffic. quick & cost-effective : no need for pre-weighed vehicles no need to close the traffic no risk of overloading and damaging of structure
Soft load testing limitations not intended to predict ultimate state behaviour if higher traffic loading is expected, measurements should be extended or replaced by a normal diagnostic load test only tested and used on bridges < 40m requires an experienced engineer
Soft Load Testing Soft load testing Simply supported Bending moment due to a 3-axle vehicle Measured
ARCHES Load testing experiment 12.4 msimply supported bridge nearljubljana: obsolete : low resistance (1 layer of reinforcement) insufficient serviceability reassessment: 4 or 5 layers of reinforcement likely safe 49
Soft Load Test - SiWIM 50
DLT experiment 51
PLT experiment
PLT in the laboratory 53
PLT in the laboratory 54
Load distributionfactors normally guestimation SiWIM evaluates it statistically
DYNAMIC AMPLIFICATION FACTOR
Dynamic Amplification Factor DAF in design codes are high: OK for design but too conservative for bridge assessment DAF 1.7 1.6 1.5 1.4 1.3 1.2 1.1 4 Lanes 1 Lane Moment 1 Lane Shear 2 Lanes 5 10 15 20 25 50 100 Bridge Length (m)
Dynamic amplification
Dynamic amplification
Dynamic amplification
Dynamic amplification
Dynamic amplification
Dynamic amplification
Dynamic amplification 1 hour = 387 vehicles
Dynamic amplification 1 day = 4120 events
Dynamic Amplification Factor Before resurfacing
Dynamic Amplification Factor After resurfacing
Dynamic Amplification Factor Average value Coefficient of variation 112% 110% 108% Before resurfacing After resurfacing 12% 10% 8% Before resurfacing After resurfacing 106% 6% 104% 4% 102% 2% 100% 0% 0 5 10 15 20 25 0 5 10 15 20 25 Strain (V) Strain (V)
ARCHES site 1 2,4 DAF Single 2 MP Light MP 2,2 2,0 DAF 1,8 1,6 1,4 1,2 1,0 0,8 0 20 40 60 80 100 120 140 160 180 200 Total strain (m/m 10-6) 69 220 240 260 280 300 320
DAF Vransko 70
ARCHES site 2 71
ARCHES site 2 2,4 DAF Single 2 MP Light MP 2,2 2,0 DAF 1,8 1,6 1,4 1,2 1,0 0,8 0 10 20 30 40 50 Total strain (m/m 10-6) 72 60 70 80 90
Lifetime Traffic Dynamics SAMARIS: WIM 10-year static simulations 3D FE model to derive total load effect from critical load effects Results statistically modelled using Bivariate Extreme Value Theory Extrapolations performed using parametric bootstrapping
Conclusions B-WIM well established WIM technique Used for all standard applications, incl. bridges: Load modelling (for codes, site-specific) specific) Updating of structural models soft load tests (IL, DAF, LDF) Room for improvements Developments continue: SiWIM3 Theoretical and practical work in Ireland, Austria, France, Netherlands, Canada
Thank you for your attention!
Multiple Presence Events a problem until a few years ago final solution is an influence sufrace solved to great extent by using strips: simplified 2D influence lines: cross-influence lines 1 value per lane advantages: can use normal calibration procedure considerably improved results
Calibration
Bridge applications safety assessment of existing bridges: for normal traffic for special transports assessment of dynamic effects bridge monitoring
Safety assessment of bridges the common basic requirement to be fulfilled: R G γ + Q γ + A G Q γ A Capacity Dead loads + Traffic loads + Other loads safety factor RF: Safety = Capacity Dead loading Traffic loading 1
Example of bridge safety assessment
Existing traffic regime 4 heavy corroded tendons Beam 4 Beam 3 Beam 2 Beam 1 1.75 3.15 3.15 3.15 1.95 13.15 m
Proposed temporal traffic regime Safety calculation using traffic load model based on design WIM results code RF = 0.84 1.14 < > 1.00 4 heavy corroded tendons Beam 4 Beam 3 Beam 2 Beam 1 1.75 3.15 3.15 3.15 1.95 13.15 m
Application for special transport
Application for special transports Objective: To assess bridges for special transports in an optimal way only onceand then to perform safety calculation instantly for any loading scheme (special transport), using the SiWIM influence lines and load distribution factors.
Application for special transports Objective: To assess bridges for special transports in an optimal way only onceand then to perform safety calculation instantly for any loading scheme (special transport), using the SiWIM influence lines and load distribution factors.
B-WIM as a tool for improved knowledge about bridges
B-WIM forbridges B-WIM provides: True influence lines Load distribution factors DAF (Dynamic Amplification Factors)
Safety assessment to verify that a structure has adequate capacity to safely carry or resist specific loading levels: R>S Rating FactorRF: S k Rk γs γ R RF = Φ R γ d Q γ G G Q G n
Carrying capacity characteristics of concrete: from design assumed (conservatively) or based on NDT testing steel reinforcement: from design NDT (profometer/ferroscan) samples dimensions taken conservatively calculation of capacity
SiWIM system installation and set-up
Verification of measured strains
Application of B-WIM results B-WIM results are used for: Road planning Road maintenance Bridge applications Pre-selection
Annual measurements in Slovenia + around30 othermeasurements With 6 SiWIM systems
Loading -WIM and specifications 202% 178% 229% 191% 179% 169% 172% 150% 216% 267% 268% 378% 400% 350% Actual loading Without overloading 300% 250% 200% 150% 100% ESALWIM/ESALSpec 163% 160% 235% 193% 222% 191% 170% 155% 196% 170% 136% 227% 191% 230% 181% 142% 102% 231% 138% 163% 113% 153% 135% 223% 166% 161% 139% 188% 158% 182% 120% 156% 145% 168% 154% 214% 137% 213% 130% 192% 128% 222% 145% 132% 131% 118% 50% 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 It is useless to use counting data Spec.factors with counting data and generalised factors from specifications!
SiWIM for pre-selection PO D6-307