Recent NYSDOT Bridge Failure Investigations

Transcription

1 Bridge Failures - Lessons learned Recent NYSDOT Bridge Failure Investigations George A. Christian, P.E. Director, Office of Structures New York State Dept. of Transportation Bridge Engineering Course University at Buffalo March 29, 2010

2 I Dunn Memorial Bridge Interchange Albany, NY partial collapse at pier 11- August 2005 I-787 Ramp NB to South Mall Expressway WB (BIN A) 2

3 BIN A 3

4 Structure Layout (looking east) 4

5 Overview of Failure 5

6 High Rocker Bearings 6

7 History of Misalignment of High Rocker Bearings at Pier Inspection Inspection 70 7

8 2003 Inspection Span 12 East Bearing 45 F Lifted 0.25 ft.(3 in.) - Eccentricity = 3.4 in. 8

9 How did the bearings get misaligned? Superstructure Displacements: Survey of adjacent piers (w/ fixed bearings) Pier 10 displaced north 1.6 inches. Pier 12 displaced north 1.0 in (avg.) 1.7 inches on east side. History of Pier 13 joint Joints reset (vertical) in 1990 Joint was closed in 1990 Closed in 1995 thru present Longitudinal forces due to braking, centrifugal force 9

10 Condition of Rocker Bearings Susceptible to corrosion, debris when continually tilted Corrosion, debris prevents rocking back toward vertical Under rocker Pin corrosion Contact surfaces flatten or dish Result: Bearings become resistant to horizontal movement, especially back toward being plumb. Transfers longitudinal forces to substructure 10

11 Corrosion & Flattening 11

12 Frozen Pins 12

13 Rocker and Pintle Corrosion Span 11 Bearing 13

14 Pier 11 Height: 82.3 feet 13.9 x 6.44 at base 9 x 4 at top of stem Stem rebar: 46 - # 8 bars 14

15 Pier 11: Lack of Elastic Range Cracks 40 ft. up north face Rebounded 51/2 in. when released The pier failed in flexure 15

16 Comparison of Adjacent Piers PIER NO. HGT. BASE REINFORCING STEEL No.-Size Bars Area BEARINGS FIX OR EXP x # Fix - Exp x # Fix x # Exp - Exp x # Fix x # Exp - Exp 16

17 Pier 11 Design Check Designed per 1965 AASHO code Meets strength req. for code assumptions Allowable / Actual ratio = 0.98 =1.0 (OK) No provision for large flexural displacements Equivalent Column with 1% reinforcing. 17

18 Longitudinal Pier Cap Force [kips] Results of Pier Analysis Old Pier 11 (AC-12) f c= Longitudinal Pier Cap Displacement [in.] Limited elastic range - yields at 5.5 deflection psi Cracking at 2.5 deflection No capacity increase beyond cracking 18

19 Forces Needed for Failure Thermal: limited by resistance of bearing Up to 0.58 x Dead Load if sliding assumed: approx. 200 kip from Span 12 only Limited range of movement Corrosion Build-up: Develops horizontal component of vertical dead, live load reactions Larger range of movement 19

20 Probable Failure Sequence Bearings tilted to north > 20 years ago Bearings begin to resist horizontal mov t. Superstructure longitudinal displacements began to move pier instead of Span 12 bearings Bearings resist movement moving back toward vertical Increased southward tipping of Span 12 and 11 bearings Instability point reached bearings tipped Forces (displacements) sustained to deflect pier 16 + in. (bearings tipping and spans falling on tipped bearings) 20

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33 Underlying Cause of Failure 1. Rocker bearings becoming misaligned 2. Rocker bearing not functioning properly 3. Pier 11 was flexible in direction longitudinal to the bridge 4. Pier 11 stem was lightly reinforced, and not elastically ductile 1, 2 and 3 were required for failure to occur. 4 may have been required, but contributed to extent of failure 33

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36 Follow up actions Reviewed all high rocker bearings with low inspection ratings (CR 3 or less) Inspected those overextended Preventive interim retrofits bolsters Technical Advisory: INSP

37 Follow up actions Bolsters installed as an extraordinary precautionary measures on 10 bridges Alerted other owners of bridges not under DOT s inspection jurisdiction Corrective action: Dunn Complex, bearing replacements 37

38 Marcy Pedestrian Bridge Collapse October 2002 Span = 171 ft. South Abutment Bracket Field Splice North Abutment

39 Acknowledgements Sponsored by New York State DOT P.I. Weidlinger Associates, Inc. Material testing and weld inspections by ATLSS Research Engineering Center, Lehigh University

40 Outline 1. Collapsed Bridge 2. Review of Bridge Design 3. Analysis of Bridge Failure 4. Demolition 5. Laboratory Testing 6. Conclusions 7. Recommendations 8. NYSDOT Actions 9. Applications Tub girders and beyond

41 6.3 ft (1.93 m) Tub Girder Cross Section 14.0 ft (4.27 m) 4.3 ft (1.3 m) Intermediate Diaphragm

42 Collapsed Bridge South Abutment Screed North Abutment

43 Collapsed Bridge Exp. Bearing South Abutment

44 Collapsed Bridge North Abutment Fixed Bearing

45 2. Review of Bridge Design Objective: Evaluate the adequacy of the bridge design

46 2.1 Design Codes NYS Standard Specifications for Highway Bridges with provisions in effect as of April AASHTO Standard Specifications for Highway Bridges, 16th Ed. LFD (1996) with 1997, 1998 & 1999 interim AASHTO Subsection Composite Box Girders (LFD). This section pertains to the design of bridges of moderate length supported by two or more single cell composite box girders..

47 2.3 Finished Bridge Design assumption: Two I-girders Conclusions: The bridge, as designed, would have been sufficient to resist its design loads if it had survived its construction.

48 2.4 During Construction Top Flange Intermediate Diaphragm Failure Modes: b/t of top flange; Top flange buckling (between intermediate diaphragms) Global Torsional buckling

49 3. Analysis of Bridge Failure Objective: To find and prove the cause of failure

50 3.1 Deck Construction Facilities: C.L. Bridge Screed Operator Engine Form/Catwalk Web Concrete Drum West Tie-rod (4' apart) Hanger Angle Top Flange Metal Form Web Bottom Flange Bracket (3' apart) East

51 3.3 Elastomeric Bearings Top Steel Plate Bottom Steel Plate Elastomer Steel Plates Top Steel Plate Bottom Steel Plate Steel Pin Y k EC k k ES ES X Z a). Expansion Bearing Top Z k EC k FS Y F D Nonlinear Spring X k BRG =k ES +k PIN b). Fixed Bearing k PIN

52 94mm Force, N 3.4 Fixed Bearing Steel Pin Model 36 mm dia Applied Force Fixed Boundary Steel Plate Deformation, mm Force-Deformation Curve

53 3.5 Global Model Top Flange Web Strut Diaphragm End Diaphragm Top Flange

54 Girder Rotation, Degree 3.6 Analysis Results North Abutment Concrete Screed SW+DL (rebar, form, etc.) Steel girder As-designed (ideal) As-built ' Concrete Pour Length, m 105' Y Rotation

55 3.7 Corrugated Metal Form Edge Screw Location Middle Screw Location Top Flange Form Thickness = 1.2 mm (3/64 in.)

56 3.9 Form Connection Model a Fixed Boundary F Weak Form: a=1/2" (12 mm) Fy = 40 ksi (275 MPa) Strong Form: a=3/4" (20 mm) Fy = 45 ksi (310 MPa)

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58 Girder Rotation, Degree 3.11 Force-Rotation Curve Y As-designed (ideal), No form Rotation As-built No form Weak form, as-built 42' 82' Strong form, as-built 95' 105' Concrete Pour Length, m

59 4. Demolition Objectives Remove debris safely; Sample materials; Preserve evidence Cut Location Temp. Support

60 Objectives: 5. Laboratory Testing Verify Analysis Assumptions Check whether materials conform to contract specifications

61 Force, N 5.1 Form Connection Tests Gage 12 Steel PL Lab Results Strong Form Model Screw Form Form connection test Weak Form Model Lateral Deformation, mm Force-Deformation Curve of Form Connections

62 Force, N 5.1 Form Connection Tests Gage 12 Steel PL Lab Results Strong Form Model Screw Form Form connection test Weak Form Model Lateral Deformation, mm Force-Deformation Curve of Form Connections

63 5.2 Bearing Inspection a. Damaged Fixed Bearing Fixed Boundary b. Bearing Model

64 6. Conclusions The bridge failed in a global torsional mode; Stay-in-place forms greatly delayed the collapse, but were not strong enough to prevent it; Progressive failure of form connections that initiated the failure sequence The bridge would have buckled even if the two deck haunches were identical

65 7. Recommendations Clarify applicable codes; Add a new code provision that requires full length lateral bracing to be installed between top flanges unless proven unnecessary by analysis

66 8. NYSDOT Actions Reviewed similar ongoing projects in NYS. Required bracing systems for similar bridges in NYS (NYSDOT Blue Page ) Sought recommendations from AASHTO regarding code revisions.

67 AASHTO LRFD Specs. 3 rd Edition (2004) Art. 6.11: Provisions for single or multiple closed-box or tub girders Art : Lateral Bracing : Top lateral bracing shall be provided between flanges of individual tub sections. The need for a full-length system shall be investigated If a full length lateral bracing system is not provided, the local stability of the top flanges and global stability of the individual tub sections shall be investigated for the assumed construction sequence

68 Lateral Torsional Stability of Open-tub girders 1/16 Top Plate Shear Izz = 36 in^4 Iyy = 205,817 in^ Shear Izz = 114,870 in^4 Iyy = 212,572 in^4

69 Application to I-Girder Bridges

70 Application to I-Girder Bridges

71 Twin I-Girders: No bottom lateral bracing Iyy = 15,470 in^4 Izz = 472 in^4

72 Twin I-Girders: With bottom lateral bracing Shear Izz = 472 in^4 Iyy = 296,426 in^4

73 Dead Load Factor Twin I-Girders: With bottom lateral bracing LTB with Non-linear Plate Model Transverse Displacement at Midspan [in.]

74 Dead Load Factor Twin I-Girders: No bottom lateral bracing LTB with Non-linear Plate Model No Lateral Bracing Transverse Displacement at Midspan [in.]

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79 Twin I-Girder Behavior--summary More stable than open tub girder. Lateral or lateral-torsional behavior (vs. global torsional) Bottom lateral system effective for lateral resistance Consider top and bottom laterals for long, narrow spans No spec-ready equations for checking global behavior (Single Tubs or Twin-I systems)

80 Dealing with a bridge failure Expect your inspection program to come under scrutiny Expect safety of other bridges to be questioned Expect requests for data on failed bridge and other bridges Establish point of contact for all media questions. Make public info. Easily available

81 Dealing with a bridge failure Work with your lawyers, (but do not expect them to always have the same priorities). Establish protections for privileged material, e.g. ongoing investigations.

82 One Final Lesson The Paradox of Failure When it comes to bridge design, collapse is a most reliable teacher. Henry Petroski Success Through Failure; The Paradox of Design

83 Questions?