A Survey of Bridge Practitioners to Relate Damage to Closure Keith Porter

1. A Survey of Bridge Practitioners to Relate Damage to ClosureKeith Porter Bridge Testbed Meeting 21 Oct 2003

2. Bridge DVs • DVs measure performance in terms of • collapse • closure • repair duration • speed limitations • load limitations • other?

3. Small pilot study of current practice • Probabilistic relationship between what bridge inspectors see and what decision they make • What they would do, not should do • Cases with inconclusive safety evidence • Bridge category: “like Humboldt” • AASHTO-Caltrans girder bridge • Multi-span, single-column bent • Modest traffic demand • If successful, I-880, other categories later

4. 25 Feb 2002 Caltrans meeting • How do post-earthquake inspectors characterize performance? (What are the DVs?) • What are the possible outcomes of a post-earthquake inspection? (What values can DV take on?) • What evidence do inspectors consider when making their performance evaluation? (What are the DMs?) • How is damage evidence assessed to result in a decision? (How is DV related to DM?)

5. DVs • Primary concern: collapse potential • DV1: collapsed, not collapsed • Post-earthquake, if not collapsed, inspectors have 2 alternatives: open or closed; if open, keep open? • DV2: inspector closure decision: if not collapsed, open or close? • Assessment protocol • Inspectors report inspections to Caltrans EOC • EOC compiles database of observed damage; bridge open or closed; recommended repair, repair cost estimate. • DV2 = “closed” subdivided into closed briefly, closed longer • DV3: cost • Inspectors & traffic engineers decide which routes to open first. Can important be opened after shoring? • Construction engineers or design engineers design repairs

6. DMs • Settlement • Misalignment • Large roadway gaps • Physical evidence of structural distress • Permanent deformation • Plastic hinging • Fracture or buckling of flexural steel • X-cracking and other evidence of shear failure

7. Qualitative DM-DV2 relationship • Can bridge stand up to live load? • Likely to collapse in an aftershock? • If there is any question of the capacity of the bridge, it is closed • Repair vs. replacement: time is the deciding factor, not cost • Cost is a less-important DV • Expert system in development • If widely adopted, present results may become outdated • Mean time, how to encode DM-DV practice

8. Surveying practitioners on DM-DV2 • DV2: inspector’s closure decision • meaningful only for no collapse; doesn’t address cost (Thanks, Eberhard, Conte, Kunnath, Mahin, DesRoches)

9. Survey form • Instructions • Provide summary info • Review the damage measures (2 blanks) • Consider the decision values (2 blanks) • Judge the max DM consistent with DV2 • Comment

10. Survey form (ver. 1) summary info • Name • Agency or affiliation • Area of expertise • Geotech, design, inpect/maint, traffic • Bridge category (Humboldt) • Level of familiarity (1-5)

11. Settlement of approach Vertical offset at abutment Horizontal offset at abutment Vertical offset at expansion jt Horizontal offset at expansion jt Max. beam or column flexural crack width Max. beam or column shear crack width Concrete beam or column spalling (y/n) Beam or column rebar buckling, fracture, pullout (y/n) Shear key or backwall shear cracking or spalling (y/n) DMs (rows; 2-4 ranges)

12. DV2 values (ver.-1 columns) • No closure • Close 1-3 days • Close > 3 days • Reduced speed Not examining closure duration as continuum—not an issue for the judgment of the inspector

13. Administering survey • 1st Tri-center Workshop on Earthquake Loss Estimation Methodologies for Transportation Systems; June 2003 • 15-20 DOT engineers from around US • Administered the survey in 2 of 3 breakouts • 12 responses • 6 self-rate as 4 or 5 on 1-5 scale Is 6 adequate?

14. Analyzing survey 6 of 6 say, “If DM1 > 6 in, then we would close at ≥ 1 day” 4 of 6 say, “If DM1 > 3 in, then close ≥ 1 day” 1 of 6 say, “If DM1 > 1 in, then close ≥ 1 day” Let X = capacity to resist ≥ 1 day closure in terms of DM1 mX = 3.67 in. mlnX = 1.17 sX = 1.97 in. slnX = 0.50

15. Creating a fragility function LN(mX=3.7 in; slnX=0.5)

16. Results • Parameters of 13 functions • b values 0.3 ~ 0.7

17. Combining results for different DMs • Problem: • Survey did not test vector DMs • How to combine P[DV | DMi]? • Possibilities • Independent decisions? P[DV ≥ dvj|DM] = 1 – Πi(1 – P[DV ≥ dvj|DMi]) • Worst DM controls? P[DV ≥ dvj|DM] = maxi(P[DV ≥ dvj|DMi]) • Must still account for correlation in DM • Check w/survey using sample vectors DM?

18. Problems & next steps • Larger survey: 2nd round in ~Nov; web survey ~Dec • Revise DVs • closed >0, >3, >30 days to regular traffic • ditto, emergency vehicles • Rephrase questions: “What is the minimum DM causing this decision?” • Include pictures • Explore I-880 DM-DV as well • Test clarity of questions

19. Discussion • DMs & their ranges • Ditto, DVs • Combination of p[DV2] values • Combination with other DVs

21. Simulation of DV P[DV = dvj|DM] = 1 – P[DV ≥ dv1|DM] j=0 = P[DV ≥ dvj|DM] – P[DV ≥ dvj+1|DM] 1 ≤ j < n = P[DV ≥ dvn|DM] j = n FDV|DM(DV = dvn|dm) = Sj=1..n P[DV = dvj|DM] u ~ U(0,1) DV* = F-1DV|DM(u)