Post-EQK Damage Assessment of Bridges

Transcription

1 Post-EQK Damage Assessment of Bridges Marc J. Veletzos, Ph.D., P.E. Merrimack College Post-Earthquake Reconnaissance Workshop 2015 EERI Annual Meeting April 3, 2015

2 Some Questions for You Who is An Undergraduate Student? A Graduate Student? Who has taken EQK Engineering Class? Bridge Design Class? Concrete Design Class? Steel Design Class? Who is from West coast? East coast? Middle states?

3 Outline Current State of Practice Reinforced Concrete Bridge Behavior Inspection and Assessment Protocol of RC Bridge Columns Questions

4 Current State of Practice A Broad Perspective

5 ATC-20 (Buildings) Three placard postings: No apparent hazard Hazardous condition exists Extreme hazard present Source: ATC, 2005

6 Assessment Procedures (Bridges) Indiana DOT Kentucky DOT and Pre-investigation,, and procedures Mississippi DOT New York DOT,, and Aerial reconnaissance,,, and Oregon DOT (multi-hazard) First look,,, and Utah DOT Initial reports,,, and Washington DOT Level I investigation,,, and ATC-20 equivalent

7 Washington DOT Emergency Response Inspection Procedure Event Level I Collapsed Not Collapsed Level II (Rapid Evaluation) Unsafe (red) Unsafe (orange) Limited Entry (yellow) Safe (green) Level III (Detailed Evaluation) Unsafe (red) Limited Entry (yellow) Safe (green) Forensic Investigation Repair/ Rebuild End (Engineering Evaluation) Legend: : Inspection procedure : Inspection rating Source: Reed and Wang, 1993.

8 NY DOT Damage Assessment Types - Aerial Reconnaissance

9 NY DOT Damage Assessment Types

10 NY DOT Damage Assessment Types - Preliminary Bridge Damage Assessment

11 NY DOT Damage Assessment Types - Special Post-EQK Bridge Inspection

12 NY DOT Damage Assessment Types - Further Investigation

13 NY DOT Process Flowchart (Mobilization of Assets) EVENT * In RL1, RSE receives notification If you have a M w =4, do you inspect every bridge in your state? RE receives text message and/or notification from USGS* Mw 3.5? Reports of damage? Yes Affected residency conducts Preliminary Bridge Damage Assessment (PBDA) starting with state bridges on priority routes and reports findings to RSE. No Response Level I: As directed by RSE. Damage found? Uncertain? No Yes RSE arranges for inspection of any critically important bridges within radius of concern (R). Response Level II: 3.5 Mw < 4.5 R = 40 miles Response Level III: 4.5 Mw < 5.5 R = 60 miles Response Level IV: Mw 5.5 R = 80 miles Inspect damage bridges found in PBDA and seismically vulnerable bridges in 40 miles radius. Inspect bridges with VR = 1 or VR =2 Inspect damage bridges found in PBDA and seismically vulnerable bridges in 60 miles radius. Inspect bridges with VR = 1 or VR =2 Conduct Aerial Reconnaissance Inspect all bridges in 80 mile radius, starting with damaged and seismically vulnerable bridges Flag bridges per DOT policy. Call for further investigation if necessary STOP Sources: O Connor, 2010.

14 Reinforced Concrete Bridge Behavior A more detailed perspective

15 Possible Location of Plastic Hinges in Bridge You need to know where to look for damage!

16 Longitudinal Bar Buckling of Pre '71 Design

17 Pull Out Failure of Pre '71 Design

18 Flexural Damage at Base of Column. Note spalling of concrete

19 Flexural Failure of Post '94 Design

20 Shear Failure of Pre '71 Design

21 Shear Failure in Hinge Region

22 Column Lap Splice Failure

23 Shear Failure Below Flare

24 Flexural Failure of Flared Column (Note: Research columns are tested upside down for convenience)

25 Connection/Joint Shear Failure

26 Abutment Shear Key Failure

27 Bearing Failure due to Sliding

28 Inspection and Assessment Protocol of RC Bridge Columns An approach proposed to Caltrans

29 PHASE I DETERMINE PERFORMANCE CURVE How is your column likely to respond? D - Response X Lateral Force X X SD - Response B - Response Lateral Displacement

30 Column Failure Mode and Performance Curve Decision Making Flowchart 1. Column Retrofits Start column jacket Yes F-F column jacket Yes DUCTILE flexure failure End retrofit retrofit Check for Column Retrofits No No P-F Yes column jacket retrofit STRENGTH DEGRADING flexural failure but the column will retain vertical load capacity collapse possible End 2. Aspect Ratio No P Yes column jacket retrofit Check 2. Aspect Ratio and 3. Transverse Reinforcement. This column may be moved to BRITTLE but will be no better than STRENGTH DEGRADING. BRITTLE Shear dominated failure or STRENGTH DEGRADING Flexural failure End End Check Aspect Ratio L/D < 2 Yes BRITTLE Shear Dominated Failure End 3. Column Reinforcement Splices 3a. Check TRANSVERSE Reinforcement for Lap Splices No Are hoops or spirals continuous No BRITTLE Shear Dominated Failure End Yes

31 Column Failure Mode and Performance Curve Decision Making Flowchart Any 3b. Check Yes longitudinal LONGITUDINAL splices in Reinforcement for column Lap Splices No Splicing not an issue. Check Column Transverse Reinforcement 4. Column Transverse Reinforcement Column trans rebar spacing > 8 Yes BRITTLE Shear failure. The column may not retain vertical load capacity End collapse possible STRENGTH DEGRADING Flexure No failure. Regardless of column reinforcement, under extreme cycles the End splice may slip and act more like a strength degrading column. The column may retain vertical load capacity. collapse is unlikely 4a. Check Column TRANSVERSE Reinforcement Spacing 12 (typ. of pre 72) or spacing > 12 Yes BRITTLE Shear Dominated Failure End No 4b. Check Confinement of Plastic Hinge Regions (adjacent to fixed connections at footing and/or bent cap) s >= min(6d b, 8 ) No Yes STRENGTH DEGRADING Flexural failure End s <= min(6d b, 8 ) DUCTILE Flexural failure 5. Comments Check Development of Column Longitudinal Reinforcement l < l d Yes Make note of inadequate development of column long. rebar. Use this information to assess the bridge system End No End

32 PHASE II DETERMINE DAMAGE LEVEL Where is your column on each curve? Lateral Force Level IV Level III X X Level II Level V Level I Level V Ductile Curve X Strength Degrading Curve Brittle Curve Lateral Displacement

33 Performance Classifications (Five Damage Levels) Damage Level I Damage Classification None Damage Description Barely visible cracking II Minor Minor cracking Repair Description No Repair Possible Repair Socio- Economic Description Fully Operational Operational III Moderate Open cracks; onset of spalling Minimum Repair Life Safety IV Major Very wide cracks; extended spalling Repair Near Collapse V Local Failure/Collapse Reinforcement buckling/rupture; Visible structural damage Replacement or substantial retrofit Collapse (Ref. Hose)

34 PHASE II DETERMINE DAMAGE LEVEL Step 1. - Check for diagonal cracks. Step 2. - Check for horizontal cracks. Step 3. - Check for concrete crushing or spalling. Step 4. - Check for longitudinal bar buckling. Step 5. - Check for rupture of transverse reinforcement Step 6. - Determine the damage level based on the observations above.

35 Determination of Extension of Diagonal Cracks D Extension of diagonal cracks

36 Length of Spalled Region D Length of spalled region spalled concrete

37 Performance Assessment Damage Level Performance Level Qualitative Performance Description Quantitative Performance Description I Cracking Onset of hairline cracks Barely visible residual cracks II Yielding Theoretical first yield of longitudinal reinforcement Residual crack width ~ 0.008in III Initiation of Local Mechanism Initiation of inelastic deformation. Onset of concrete spalling. Development of diagonal cracks. Residual crack width 0.04in 0.08in Length of spalled region >1/10 crosssection depth. IV Full Development of Local Mechanism Wide crack widths/spalling over full local mechanism region. Residual crack width > 0.08in. Diagonal cracks extend over 2/3 cross-section depth. Length of spalled region > ½ crosssection depth. V Strength Degradation Buckling of main reinforcement. Rupture of transverse reinforcement. Crushing of core concrete. Lateral capacity below 85% of maximum. Section depth expands to >5% of original dimension. (Ref. Hose)

38 Decision-making Matrix for Damaged Bridge Columns Pronounced Horizontal Cracks Field Observations Pronounced Diagonal Cracks Incipient Concrete Crushing/ Spalling Long. Bar Buckling Conclusions Damage Level Possible Failure Type No Yes No No III Shear Yes or No Yes Yes Yes or No IV or V Shear Yes No No No II or III Flexure Yes No Yes No IV Flexure Yes No Yes Yes V Flexure

39 PHASE III ASSESS BRIDGE SYSTEM Remaining Capacity Remaining Capacity Lateral Force x X Level I Level II Level III Level IV Level V Bent 1 Column 2 (Brittle) Bent 1 Column 1 (Brittle) Brittle Curve Lateral Displacement Lateral Force x X Level I Level II Level III Level IV Level V Strength Degrading Curve Bent 2 Columns 1 and 2 (Strength Degrading) Lateral Displacement

40 Thanks! Questions?

41 References ATC Rapid Visual Screening of Buildings for Potential Seismic Hazards: A Handbook. FEMA P-154, Edition 2. ATC ATC-20-1: Field Manual: Procedures for the Postearthquake Safety Evaluation of Buildings, Second Edition. Applied Technology Council, Redwood City, California. Hose, Y.D., Silva, P., Seible, F., Performance Library of Concrete Bridge Components, Sub-Assemblages, and Systems under Simulated Seismic Loads, Structural Systems Research Program, SSRP 99/08, University of California, San Diego, La Jolla, CA, January, O Connor, J. S Post-Earthquake Bridge Inspection Guidelines. Final Report for NYSDOT SPR Project # C Reed, D. A., and J. Wang An Emergency Response Plan for Bridge Management. Report No. WA-RD Washington Department of Transportation. Veletzos, Panagiotau and Restrepo Post Seismic Inspection and Capacity Assessment of Reinforced Concrete Bridges. UCSD Structural Systems Research Project SSRP-06/19.

42 Training Course: Post Earthquake Inspection and Capacity Assessment of RC Bridges Prepared by: University of California, San Diego Department of Structural Engineering

43 Lectures Lecture 1: Introduction, Seismic Design Concepts (A) Lecture 2: Seismic Design Concepts (B) Lecture 3: Performance of Bridge Components (A) Lecture 4: Performance of Bridge Components (B) Lecture 5: Post Earthquake Evaluation Lecture 6: Lessons Learned

44 Lecture 6 Lessons Learned Flexure vs. Shear Design Era Shear vs. Lap Splice Abutments Connections

45 Lecture 6 Lesson 1a. Flexure vs. Shear Lateral Force Level III Level II Level I X Level IV Level IV Level V Ductile Curve X Level V Brittle Curve Flexural behavior (ductile curve) is progressive and gives warning Lateral Displacement Shear behavior (brittle curve) is sudden and compromises gravity load carrying capacity.

46 Lecture 6 Lesson 1b. Flexure vs. Shear Flexure and shear have different crack patterns Level II Flexural Column Horizontal cracks Level II Shear Column Diagonal cracks

47 Lecture 6 Lesson 1c. Flexure vs. Shear Similar level of damage very different amount of remaining capacity Level IV Shear Level IV Flexure Level IV Level III Ductile Curve X Lateral Force Level II X Level V Level V Level I Level IV Brittle Curve Lateral Displacement

48 Lecture 6 Lesson 2a. Design Era Similar level of damage (crack sizes) different amount of remaining capacity Level IV Pre 71 Level IV Post 71 Level III Level IV Ductile Curve X Lateral Force Level II Level I Level IV X Level V Level V Strength Degrading Curve Lateral Displacement

49 Lecture 6 Lesson 2b. Design Era Pre 71 columns typically strength degrading or brittle behavior Level III Level IV Lateral Force X Level II X Level V Strength Degrading Curve Level I Brittle Curve Lateral Displacement

50 Lecture 6 Lesson 2c. Design Era Pre 94 columns with aspect ratio < 4 susceptible to brittle shear behavior

51 Lecture 6 Lesson 2d. Design Era Post 94 columns with aspect ratio >4 typically ductile flexural behavior Note heavy confinement of hinge region

52 Lecture 6 Lesson 3. Shear vs. Lap Splice Shear F- Response Lap Splice F- Response Similar response, but.

53 Lecture 6 Lesson 3. Shear vs. Lap Splice Shear Failure Lap Splice Failure lap splice failure may retain vertical load capacity. Shear failure will not support gravity load.

54 Lecture 6 Lesson 4. Abutments typically characterized by brittle performance curve

55 Lecture 6 Lesson 5. Connections Pre 94 designs typically brittle Note lack of joint reinforcement