How safe are our highway structures? Optimised assessment of bridges Aleš Žnidarič Slovenian National Building and Civil Engineering Institute

1 Contents General about bridge assessment General about bridge assessment Bridge WIM, including French experience Bridge WIM, including French experience SAMARIS project SAMARIS project Load testing Load testing Examples of improved assessment Examples of improved assessment Conclusions Conclusions

2 Why optimised bridge assessment?

3  new bridges are designed conservatively:  uncertainty about increases in loading  inexpensive to add capacity  assessment of existing bridges should be less conservative:  very expensive to strengthen/replace or post a bridge  capacity and current loading can be measured and monitored

4 Design vs. Assessment Bridge design: Bridge design: –high uncertainty of data: conservative analysis for long-term safety conservative analysis for long-term safety design loading schemes design loading schemes –high safety factors –unnecessary: costly rehabilitation measures costly rehabilitation measures load limits load limits Efficient assessment: Efficient assessment: –better defined inputs: carrying capacity realistic, even site- specific loading  –lower safety factors –optimised: cheaper rehabilitation measures posting of bridges

5 Why optimised assessment?  to select optimal rehabilitation measures:  do nothing  protect  repair  strengthen  replace

6 Why optimised assessment?  to select optimal rehabilitation measures:  do nothing  protect  repair  strengthen  replace

7 Assessment of existing bridges factors taken into account: factors taken into account: –condition, level of damage –structural safety: carrying capacity carrying capacity loading (dead, traffic, dynamic loading) loading (dead, traffic, dynamic loading) reliability of data reliability of data –serviceability (clearances, traffic, obsoleteness) –service life, importance of structure 5-level assessment 5-level assessment

8 Questions for assessment 1. What is its carrying capacity (age, condition, drawings…)? 2. How does the bridge really behave: –What are the influence lines? –How the traffic load distributes? 3. What is the real loading: –in a country, type of road, specific bridge –dynamic amplifications (Bridge) WIM measurements

SAMARIS project

10 SAMARIS Project Sustainable and Advanced MAterials for Road InfraStructure Sustainable and Advanced MAterials for Road InfraStructure EU 5 th FW programme EU 5 th FW programme ,5 million € (5,4 million USD) 4,5 million € (5,4 million USD) 23 partners, 16 countries 23 partners, 16 countries 2 subprojects (streams): 2 subprojects (streams): –Pavements (FR) –Structures (SI)

11 SAMARIS Structures Objectives: 1.To develop guidelines and specifications for use of innovative intervention techniques (materials). 2.To provide an updated inventory of highway structures in selected EEA and CE countries and tools for their optimised assessment.

Traffic Loading

13 Traffic loading Design loading schemes Design loading schemes Assessment (rating) loading schemes Assessment (rating) loading schemes Site-specific loading (WIM data) Site-specific loading (WIM data) Dynamic loading Dynamic loading

14 Truck histograms from Europe

15 Truck histograms from Europe

16 Traffic load modelling

17 Comparison of sites in NL and SI

18 Site-Specific Load Assessment Better assessment load models needed:  for more accurate assessment of bridge safety  to save many bridges, particularly on less heavily trafficked roads  to account for number of vehicles and overloaded vehicles

19 There is an urgent need for effective overload enforcement – better compliance with legal limits will greatly reduce traffic loading on bridges. Site-Specific Load Assessment

Dynamic Loading

21 Dynamic loading Problem: combining the extremes of dead load and dynamic effects => (too) high DAF Problem: combining the extremes of dead load and dynamic effects => (too) high DAF SAMARIS experiment: SAMARIS experiment: –31-m long span –to assess influence of pavement unevenness –to evaluate DAF for 1000’s of vehicles –upgraded SiWIM system

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23 Dynamic loading Before resurfacing Before resurfacing

24 Dynamic loading After resurfacing After resurfacing

25 Dynamic loading Reduction of DAP due to resurfacing: SingleHeavy+Light 2 Heavy all events 73,7%60,8%69,9% > 22 ton truck 87,4%67,5%55,8% > 38 t semitrailer 66,7%71,0%49,4%

26 Dynamic loading Reduction of DAP due to resurfacing: SingleHeavy+Light 2 Heavy all events 73,7%60,8%69,9% > 22 ton truck 87,4%67,5%55,8% > 38 t semitrailer 66,7%71,0%49,4%

27 Conclusions on loading  factors from Eurocodes can be lower if used for assessment of existing bridges  factors from Eurocodes can be lower if used for assessment of existing bridges traffic patterns in EU, EEA and CEC are different traffic patterns in EU, EEA and CEC are different dynamic amplification factors for the extreme load cases are considerably lower than specified in the design codes dynamic amplification factors for the extreme load cases are considerably lower than specified in the design codes

Load Testing

29 Load testing on bridges that seem to carry out normal traffic satisfactorily, but fail to pass the assessment calculation on bridges that seem to carry out normal traffic satisfactorily, but fail to pass the assessment calculation the available model of the bridge does not perfectly match with the real bridge itself the available model of the bridge does not perfectly match with the real bridge itself To optimise bridge assessment by finding reserves in load carrying capacity Very different situation around Europe

30 Load testing benefits: benefits: –less severe rehabilitation measures –less traffic delays –tremendous savings drawbacks: drawbacks: –very costly –danger of damaging the structure

31 Load testing best candidates: best candidates: –difficult structural modelling –lack of documentation (drawings, calculations,…) –when savings are greater than the cost of load test

32 Load testing Types of load test: Types of load test: –proof –diagnostic –“soft”

33 “Soft” load testing the lowest level of load application the lowest level of load application to supplement and check the assumptions and simplifications made in the theoretical assessment to supplement and check the assumptions and simplifications made in the theoretical assessment use bridge WIM to provide: use bridge WIM to provide: –“normal” traffic data –information about structural behaviour of the bridge influence lines influence lines statistical load distribution statistical load distribution impact factors) from normal traffic. impact factors) from normal traffic. –no need for pre-weighed vehicles –the bridge need not be closed to traffic –no risk of overloading and potential damaging of the structure

34 Teoretična in izmerjena vplivnica

35 Influence lines 50 years old, no drawings Probably not simply supported but how fixed?

36 SiWIM and Soft Load Testing Soft load testing Simply supported RF = 0,58

37 SiWIM and Soft Load Testing Soft load testing Simply supported RF = 0,58 Measured RF = 1,46 Message: Check, how bridges really behave.

38 SiWIM and Soft Load Testing Simply supported RF = 0,58 Measured RF = 1,46

39 Load distribution normally guestimation normally guestimation bridge WIM can evaluate it statistically bridge WIM can evaluate it statistically

40 Example 13 posted bridges assessed for special transport 13 posted bridges assessed for special transport 11 proved safe even for a 165-tonnes special vehicle with 12 axles 11 proved safe even for a 165-tonnes special vehicle with 12 axles for the rest no reliable data on carrying capacity available for the rest no reliable data on carrying capacity available on shorter bridges normal traffic can be worse than special transports on shorter bridges normal traffic can be worse than special transports

41 Conclusions 1. Bridge WIM systems:  very efficient way of collecting traffic loading data  very useful for collecting structural data:  influence lines  load distribution factors  DAF

42 Conclusions 2. Design conservatively, assess optimally:  very expensive to strengthen/replace a bridge  measurements:  capacity,  traffic (incl. dynamic) loading,  load distributions  load testing  monitoring

43 Conclusions 3. Proper assessment (with monitoring) can:  prove that many existing bridges are safe in their current condition for their current loading  justify optimal rehabilitation measures  save a lot of money

44 Thank you!