Risk-based management of the bridge stock

1. Risk-based management of the bridge stock Børre StensvoldBridge DirectorNorwegian Public Roads Administration World Road Association (PIARC) Report Issue 4.3.3:

2. PIARC report Issue4.3.3 Background • Technical committee 4.3 «Road bridges» • Report on bridge management systems, “Management of bridge stock” - 2011 • Advise a review based on risks • Survey of risk-based analyses in several countries • Informal and formal approaches • Report: Risk-based management of the bridge stock - 2015 • Methods • Applications and examples, including climate change

3. Risk management embedded in bridge management Background • Common goal • Ensure the safety and serviceability of bridges at a minimum cost • Implicit or explicit integration in management activities • Design, inclusion of feedback • Evaluation, prioritization, and programming operation and maintenance • Inspection strategy, surveillance and monitoring • Responses to vulnerabilities and hazards • Operating measures, structural assessment, investigationsand operation/maintenance

4. Examples of applications in different countries Background • Belgium • Optimal frequency of detailed inspections • France • A system of enhanced surveillance for complex of defective bridges • Prioritization with respect to specific hazards or structures • Japan • Prioritization of bridges for mitigation of seismic risk • Korea • Prevention of accidents due to fire and crosswind on expressway bridges • In all cases • Formal or informal risk-based analyses interfering the bridge management system

5. Risk-based analysis Background • A systematic approach to analyze sequences and interrelations in potential accidents • Identify weak points and possible improvements • A variety of approaches, methods and models • Qualitative or quantitative • Performance-based approach to safety • Sétra methodology (France) • Screen out a large number of structures facing a set of risks to select those in need for further investigation

6. Risk Terminology • «A potential hazard or threat, more or less predictable, which may affect the performance of a structure» • A combination of the hazard and the magnitude of consequences • The expected value (cost) of the consequences • May be assessed by three factors • Hazards • Vulnerability • Consequences

8. Hazard Terminology • The source of a risk • A possible event, not a reality • Uncertain realization • Four types • Internal damage due to aging of materials • Fatigue loads, aggressive agents, etc. • Initial internal defect • Design or construction errors, defective materials, etc. • External natural phenomena • Earthquakes, floods, avalanches, rock fall, etc. • External phenomena of human origin • Fire, traffic impact, industrial explosion, etc.

9. Hazards Terminology

10. Vulnerability Terminology • The sensitivity of a structure to hazards • Depends on the structure and the hazard itself • E.g., a light steel structure is vulnerable to fire, but not earthquakes • Intrinsic with respect to unknown hazards • Ability to resist unknown impact • (Almost) opposite of robustness • Low intensity hazards do not lead to disproportionate consequences

11. Consequences Terminology • The costs of an exceptional event on the structure • Human lives • Repair costs • Environmental damage • Economic and social disruption due to road closures • Should be determined in a broader context • Entire route and socio-economic activity

12. The Skjeggestad bridge on the E18 Highway near Holmestrand suddenly sagged on Monday 2rd of February 2015

13. Expert panel report on Monday 9th February; Pillar in the axis 5 on bridge west has dropped about 2.5 m and shifted horizontally 2.5 meter in top and 3-5 in bottom. Piles therefore has no bearing capacity and foundation are in the landslide masses. There are high and increasing risk of collapse of the bridge west. Because of the danger of total collapse, were all working on or near the bridge performed by robots or long range cranes. Inspections conducted using drones with HD camera. https://www.youtube.com/watch?v=mVifg1TKvgY

14. The Commission ofInquiry: It is highly probable that it was the completing work on the grounds of the Golf Club, time prior to the event, which has been the triggering cause of the landslide.

15. Three step process, Sétra methodology, (France) Simplified methodology • Data collection • Simplified risk analysis • Assess and quantify hazards • Quantify vulnerability with respect to each hazard • Assess the consequences of structural dysfunction • Further investigations or detailed risk analysis

16. Step 2: Simplified risk analysis Simplified methodology • Criticality matrix • Hazards + vulnerability

17. Step 2: Simplified risk analysis Simplified methodology • Risk matrix • Criticality + consequences

18. Risk evaluation Simplified methodology • Evaluate acceptability of risk • Red, yellow, or green zone • Propose measures to reduce risk to an acceptable level AND/OR • Conduct more detailed analysis to take further action (step 3) • Monitoring program • Reinforcement or repair works

19. Post-tensioned concrete girder bridges (VIPP) Application of simplified methodology • 117 Isostatic precast post-tensioned concrete girder bridges (France) • Insufficient bearing capacity due to corrosion of pre-stressing steel • Hazard criteria • Initial error: a) Design; b1) Initial pre-stressing; c) Construction • Internal hazards: b2) Current pre-stressing condition; d) Maintenance and operation; e) Environment; f) Condition • Scoring + 0 Not relevant + 1 Moderate + 2 Medium + 3 High + 4 Very high

20. Post-tensioned concrete girder bridges (VIPP) Application of simplified methodology • Primary concern: Corrosion of tendons • Initial pre-stressing quality • Cables protection • Steel characteristics • Duct type • Injection products • Overall hazard rating • Total of scores for a given criterion • Criteria weights

21. Post-tensioned concrete girder bridges (VIPP) Application of simplified methodology • Vulnerability • Simplified strength calculations (ULS, SLS) • Local vulnerability indicators scored from 1-5 • Level 1 (low vulnerability) • Level 5 (high vulnerability) • Final score equals maximum local level • Consequences • Socio-economic indicator • Three levels

22. Post-tensioned concrete girder bridges (VIPP) Application of simplified methodology Risk-based management of the bridge stock • Criticality level • Hazard + Vulnerability • Risk level • Criticality + Consequence • Three categories: from low (R1) to high (R3) risk • Results • 30 out of 117 bridges ranked as R3 • All bridges built before 1960 were R3 • Actions required for R2 and R3 • Modification of surveillance programs • Advanced calculation of structural performance

23. Climate change Application of simplified methodology • Hazards • Temperature rise, cyclones, rainfall, sea level rise, etc. • Costs of considering these in design vary considerably! • Vulnerability • Parameters related to technical and cultural evolution • Analysis of climate trends, updating regulations and constant monitoring of data • Consequences • Economic impact is huge and largely underestimated • Impossible to estimate a cost on all factors

24. Climate change Application of simplified methodology • Adaptation to climate change • Limit exposure to natural events, e.g. location • Auxiliary structures for protection, e.g. dikes • NB: may generate new risks • Redundancy of road connections • Consider all phases of the service life • Design • Construction • Maintenance • Uncertainty is the fundamental challenge

26. Japan methodology for seismic risk Other applications • Hazard characterized by dual level design ground motions • Level 1: High probability ground motion • Level 2: Low probability ground motion (Type I and II) • Seismic performance level (SPL) depends on importance • Type-A bridges, standard • Type-B bridges, important

27. Japan methodology for seismic risk Other applications • Level 2 earthquake ground motions given by acceleration response spectra • 3 soil conditions • 5 zone factors

28. Japan methodology for seismic risk Other applications • Seismic design for new bridges • Seismic performance level (SPL) 2: damage should be limited and controlled • Different levels of resistance between components to induce damage where investigation and repair is easy • Seismic retrofit of existing bridges • Prioritization of highway routes • Prioritization of bridges and components • Reinforced concrete piers design before 1980 and with vertical reinforcements that are terminated at mid height: Steel plate, reinforced concrete or CFS jacketing • Steel single piers designed before 1980: prevention of fracture at weld seams or filling of piers with concrete • Curved bridges, skew bridges or liquefaction of ground: Unseating prevention structure

29. South Korea methodology for fire risk Other applications • Three steps • Preliminary risk analysis • Screening based on vertical clearance and accessibility • Simplified risk analysis • Calculation of risk factors • Determination of risk as low (RL), moderate (RM), or high (RH) • Detailed risk analysis • Refined bridge fire analyses for RH-bridges

30. South Korea methodology for fire risk Other applications Fire risk analysis procedure

31. South Korea methodology for fire risk Other applications Step 1: Preliminary risk analysis

32. South Korea methodology for fire risk Other approaches • Step 2: Simplified risk analysis • Calculation of occurrence, vulnerability, and importance • Each consists of several sub-factors and is scored on a scale from 1(best) to 3 (worst) • Occurrence • Geographical location, traffic conditions, and road type under the bridge • Vulnerability • Structural characteristics, material, and redundancy • Importance • AADT, repair/reconstruction costs, transportation systems under the bridge

33. South Korea methodology for fire risk Other applications • Determination of risk level • Criticality matrix: Occurrence + vulnerability • Risk Matrix: Criticality + importance • Classification of risk level • Low risk (RL): negligible • Moderate risk (RM): acceptable • High risk (RH): Perform detailed risk analysis

34. South Korea methodology for fire risk Other applications • Step 3 Detailed risk analysis • Re-evaluate the probability of bridge fire based on field data, e.g., hazardous material transportation, AADT, and traffic accidents • Repeat step 2 • If risk level is not lowered, re-evaluate vulnerability using advanced fire analysis • Device countermeasures to mitigate bridge fire, if necessary

35. Conclusion of the report Risk-based management of the bridge stock • Survey of risk-based methodology in bridge management in several counties • Implicit integration in BMS, e.g., surveillance policies • Formal methodologies for risk-based analysis (some countries) • Ensure safety and serviceability at a minimum cost • Identified risks • Overloading vehicles, avalanches, flood, scour, earthquake, fire, cross-winds, collision, deterioration and structural failure • A formal explicit risk-base methodology was combined by; • Hazards; - events that may happen • Vulnerability; - behavior of structure facing hazards • Consequences; - of partial or total structural failure • Application to corrosion of pre-stressing cables, seismic risk, scour, wind (for traffic safety) and fire hazards • Limited application due to climate change • Difficulty in assessing the increase of natural phenomenon • Included in other unpredicted natural hazards

36. Thank you for your attention https://www.youtube.com/watch?v=mVifg1TKvgY PIARC TC 4.3 Road Bridges