New San Francisco-Oakland Bay Bridge Self Anchored Suspension Bridge By: Brian Maroney, PE, Dr. Engr. Deputy Toll Bridge Program Manager California Department of Transportation
Objective Carry out an open and transparent and technical meeting on the A354BD fasteners in order to offer an opportunity for the public to see and hear: What the TBPOC and its partners are doing Who is involved What t is being planned Before final decisions are made 2
3 New East Bay Bridge Span
Self Anchored Suspension Bridge (SAS) 4 Total Number of Fasteners Assemblies: 1,367,300
Bolts and Rods on SAS A307: 1,000 (Multiple Suppliers) A325: 1,250,000 (LeJeune Bolt Company) A490: 100,000 (LeJeune Bolt Company) A354BC: 13,000 (Dyson Company) A354BD: 2,306 (Dyson / Vulcan Threaded Products) Total Number of Fastener Assemblies: ~ 1.4 Million 5
AASHTO Definitions for Fracture Critical and Redundancy 6 C1.3.4 The Manual for Bridge Evaluation (2008) defines bridge redundancy as the capability of a bridge structural system to carry loads after damage to or the failure of one or more of its members. System factors are provided for post-tensioned segmental concrete box girder bridges in Appendix E of the Guide Manual. System reliability encompasses redundancy by considering the system of interconnected t components and members. Rupture or yielding of an individual component may or may not mean collapse or failure of the whole structure or system (Nowak, 2000). 4.11 Fracture-Critical Members Fracture-critical members or member components (FCMs) are steel tension members or steel tension components of members whose failure would be expected to result in a partial or full collapse of the bridge.. After the crack occurs, failure of the member could be sudden and may lead to the collapse of the bridge. For this reason, bridges with fracture-critical critical members should receive special attention during the inspections. C4.11 Steel bridges with the following structural characteristics or components should receive special attention during the inspections: One- or two-girder I- or box girder systems, Suspension systems with eyebar components, Steel pier caps and cross girders, Two truss systems, Welded tied arches, and Pin and hanger connections on two- or three-girder systems. The above examples are not a comprehensive list of FCMs or fracturecritical bridge structure types and shall not serve as a checklist.
What is an A354BD SAS Bolt? Steel fasteners, designated on the plans as A354, Grade BC, and A354, Grade BD, shall conform to the requirements ASTM Designations: A354. Steel fastener components for steel fasteners designated as A354 shall include a bolt, nut and hardened d washer. ASTM A354BD Strength, Hardness & Galvanization Blasting cleanliness to protect against internal hydrogen (similar to ASTM F2329) ASTM A143 Safeguard against hydrogen embrittlement Other factors to protect bolts from external environment (e.g., paint, dehumidification, encased in grouted tubes) 7
March 2013 A354 BD Rod Failure: Shear Keys S1 & S2 B1 S1 B3 21 of 48 rods broke at S1 S3 S4 B2 S2 B4 11 of f48 rods broke at ts2 8
A354BD Rods at E2 Break Locations 2010 24Rods 2008 48 Rods 2010 24 Rods Location of Breaks March 2013 9
March 2013 Fasteners Were Observed to be Broken Immediate observations: All fastener connections are between Pier E2 bent cap and the two shear keys directly over the two columns All are same type of fasteners A354BD All galvanized All large diameter 3-inch All from same supplier delivered at the same time in 2008 All from the same inspection protocol All installed at the same time and exposed to the same environment All stressed at nearly the same time in 2013 All stressed to 0.70Fu (minimum specified ultimate tensile strength) All fasteners broke at the base 10
What is Different About the A354BD Bolts Immediate observations: Different size diameter Different supplier Different inspection Different manufacturer process even different Contract Different construction stage/exposure Different stress levels Different environmental conditions 11
12 ASTM A354 Grade BD Rods Across SFOBB-SAS
ASTM A354 Grade BD Structural Components and Bolt Tension in Service 13 Failure has ONLY occurred in the 2008 Anchor Rods; 2006 and 2010 rods have been in service and under tension from 7 months to 3 years
Fabrication Dates and Status of A354 Grade BD High-Strength g Steel Rods Item # Fabricator End of Fabrication Tension or Loading Complete # of Rods Installed # of Fractured Rods After Tensioning Days Under Tension Through July 1, 2013 1 Dyson Sept 2008 Mar 2013 96 32* Rods began failing after 3 days of tensioning 2 Dyson Mar 2010 Apr 2013 192 0 91 3 Dyson Mar 2010 Sept 2012 320 0 295 4 Dyson Mar 2010 Sept 2012** 224 0 292 5 Dyson Aug 2009 Jun 2009** 96 0 1,429 6 Dyson Dec 2009 Jan 2010 336 0 1,245 7 Dyson Nov 2011 Sept 2012 274 0 278 8 Dyson Jul 2010 Jul 2012 25 0 351 9 Dyson Jan 2011 Jul 2012 108 0 351 10 Dyson Jan 2011 Mar 2013 90 0 97 11 Dyson Oct 2011 Jul 2012 4 0 334 12 Vulcan Threaded Products Feb 2007 Mar 2011 388 0 821 13 Vulcan Threaded Products Feb 2007 Mar 2011 36 0 821 14 Dyson Jun 2010 May 2010** 32 0 1,125 15 Dyson May 2010 Apr 2012 18 0 443 16 Dyson Oct 2012 Feb 2013 24 0 142 17 Dyson Jun 2009 N/A*** 43 N/A * Caltrans reduced d the tension on the remaining i unfractured rods on March 15, 2013. Additional rods might have fractured if not detensioned. d ** Rods were tensioned in the fabrication shops, Item #4 in PA, Item #5 in Korea and Item #14 in Japan, prior to the assembly being delivered to SAS Bridge site. Items #7, 8, 12, and 13 were adjusted as part of Load Transfer in October 2012. *** Details for bike path support frame being redesigned to improve consistency with other design features of SAS. 14
Bolt Failure Histogram After Tensioning Num ber of Fa iled Anch hor Bolts 7 6 5 4 3 2 1 0 Bolt Failure Histogram S1 and S2 6 55 3 32 broken rods (out of 96), Multiple l Heats At 14 days, pre-tension reduced to.45fu No further failures of rods after that. 1 1 1 1 4 2 2 3 4 5 6 7 8 9 10 11 12 13 14 Number of Days after Tensioning Shear Key S1 Shear Key S2 1 15
Specific Requirements For Hydrogen Embrittlement 16
Shear Key S1 and S2: 2008 Rod Testing Program I. Visual Examination/Observations II. Scanning Electron Microscopy III. Microstructural Examination IV. Hardness Testing a. Knoop Microhardness b. Rockwell C Hardness V. Tensile Test VI.Charpy V-Notch Impact Test VII.Chemical Analysis (Spectrochemical) Bearing and Shear Key Test Specimens: S1 G1 S2 A6 Anchor Rod LD. Key: B1 E8 Bearing/Shear Key Piece Mark Rod Grid Number Rod Grid Letter 17
18 Boroscope Images in 2008 Pipes
Scanning Electron Microscope Equipment 19
Purpose of Analysis of 2008 Fractured Rods Identify the failure mechanism and determine level of confidence in remaining 2008 rods 20
Tests Performed on 2008 Fractured Rods Visual Examination Mechanical Testing (Tensile / Yield Strength, Reduction of area, Elongation) Spectro Chemical Analysis Hardness / Microhardness Charpy V-Notch Scanning Electron Microscopy Metallurgical analysis Microstructural Examination 21
Summary of Findings of 2008 Fractured Rods Hydrogen embrittlement was likely the cause of failure. Hydrogen was present at the time of tensioning i Source of hydrogen could be internal OR environmental Inhomogeneous microstructure Material is susceptible 2008 rods abandoned (Retrofit) Further analysis is ongoing 22
Authors of 2008 Fractured Rods Report Rosme Aguilar, PE Masters in Metallurgical Engineering Chief of Caltrans Structural Materials Testing Branch 30 years of experience as an engineer Salim Brahimi, PE Chair of ASTM Fastener Committee 24 years of experience in fastener industry Conrad Christensen, PE Licensed Metallurgical Engineer 32 years of experience in metallurgy 23
Pier E2 2008 Rods vs. 2010 Rods 2008 (32 Failed Rods) 2010 (Rods in Service for 10 months) No Vacuum Degassing g Vacuum Degassing g Double Heat Treatment Single Heat Treatment No Magnetic Particle Testing (MT) Water removed from base of Rod several times during construction MT of threads Through Bolts, No standing water issue Fabricated & Installed in 2008 Tensioned in March 2013 Installed and Tensioned in April 2013 +/- Hardness Range: 26-39 Hardness Range: 27 38 (< HRC 39 required at R/2) (< HRC 39 required at R/2) CVN @ 40F : 13.5 18 ft.lb CVN @ 40F : 36 39 ft.lb Elongation: 12.5% to 15% Elongation: 14% to 17% (14% min required) (14% min required) UTS: 159 171 ksi UTS: 153 158 ksi 24
A354BD Testing Program GOAL: Determine acceptable levels for sustained pre-tension loads for existing galvanized A354 BD for the Design Life of the Bridge. This goal will be reached through a combination of: I. In Situ Hardness test of all accessible rods (100% +/-) II. Laboratory hardness test of sample cut from field installed rods and spares III. Destructive testing/chemical analysis/metallurgical analysis of a representative sample (15 +/-) IV. Stress Corrosion (Townsend) Test of a representative sample (11 +/-) Post-Fracture Analysis to include SEM V. Small Sample Stress Corrosion (Raymond) Test (16 +/-) VI. SCC Threshold Verification Testing In addition, the 2008 bolts are being tested (same as above) for comparison. 25
26 Tension Test
27 Hardness Tests Lab & On-Site
28 Charpy Tests for Toughness
29 Test Setup for: Stress Corrosion (Townsend) Test
30 Townsend Test 1975
31 Test IV Preliminary Results: Stress Intensity Factors vs. HRC
32 Test Setup for: Raymond Test (Incremental Load Step) ASTM F1624
33 Test Setup for: Raymond Test (Incremental Load Step)
Comparison of 3" Diameter E2 Rods Material Heat Treat Method Elongation (%) Mechanical Testing Reduction of Area (%) Fu (ksi) Other Testing NDT Manufacturing Embrittlement Hardness CVN @ Tension Range 40F In Field (+/-) (HRC) (ft-lb) (kips) ASTM A354BD Requirements 14 min 40 min 140 min supplemental 31 39 no max if specified 1 at R/2 2008 3 4140 Furnace/ Oven 12.5 15 40-50 159 171 not tested Bend Test 2 (ASTM A143) 26 39 13.5-18 @Surface 585 Fabrication Ye ear 2010 4140 2013 4340 Induction Coils Vacuum Degassing Induction Vacuum Coils Degassing 14 17 40-53 153 158 19 21 55-5959 160 163163 MT of Threads 1 Specification recommends using same as ASTM A490 when tensioning in excess of 50% Fu Bend Test 2 (ASTM A143) MT of Bend Test Entire Rod (ASTM A143) 27 38 30 3838 36-39 @Surface 49-56 @Center 47-52 @Surface 585 585 2 Not performed 3 Water was pumped out multiple times between 2008 and 2013 34
Thank You! 35