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Twin Bridges Strand Replacement and RehabilitationRehabilitation
Tom Hoffman, P.ER-1 Structures Engineer
Contractor: Piasecki Steel Construction CorpEngineering Consultant: WSP-Sells
•Built in 1958- Strands are Original Construction
Background Data
O i i l C t ti Bid $4 959 515 00•Original Construction Bid was $4,959,515.00
•(2008 price ~ $42,000,000)( p )
•Main Span Length = 600’
•Total Bridge Length = 779’
T t l S 7•Total Spans = 7
•Condition Rating = 3.625g
Background Data
Each Bridge has 21 floorbeamsEach Bridge has 21 floorbeamsSpaced at 25’ Centers
4 2” Di B id St d Fl b4 – 2” Dia. Bridge Strands per Floorbeam
Total of 168 Strands
Each Strand is Made up of 97 Wires
F.S. (original = 3.55, 2.6 as inspected in 2007)
• 104,000 Vehicles per Day• Limited Lane Closure Windows• Narrow Shoulders
Design Parameters and Early Considerations
Work Could not Disrupt “Rush Hour” Traffic
Closures only Late at Night (10 min from 12 5a m )Closures only Late at Night (10 min from 12-5a.m.)
Crossovers for Nighttime Work were Considered
A Support Method Would be Provided in the Plans
No Live Loads for Tensioning Operations, Measuring o e oads o e s o g Ope at o s, easu gProfiles, Jacking and other Operations
Budgeted at $10,000,000
Necessary Steel and Paint Associated with Strands
Floorbeam Connection(Top Flange not Shown)(Top Flange not Shown)
Multiple Support Schemes Investigated
Initial Regional Preference was to Replace O f T Fl b St d t TiOne of Two Floorbeam Strands at a Time, Relying on One Strand to Support the Floorbeam(Design Determined This Was Not Prudent)
Sells Developed Alternate SchemesSells Developed Alternate Schemes
Structural Lifting Item 585.xxP t P id d t All C t t t D l Lift PlParameters Provided to Allow Contractors to Develop own Lift Plan –Special Notes in Proposal
All bl D fl ti d Diff ti l D fl ti (A id D k C ki )-- Allowable Deflections and Differential Deflections (Avoid Deck Cracking)-- Minimum Loading under Various Scenarios-- Maximum Jacking Forces on Floor Beams
F S d Cl-- Forces on Strand Clamps-- Traffic Restrictions-- Value Engineering Change Proposals (VECP) Needed for Traffic Pattern
ChangesChanges
Site AccessSite Access is a Key
Factor for ProductionProduction
Avoiding TrippingTripping Hazards
As requested, strand breakage:
9-11-08 9-15-08 9-18-08 9-25-08 9-29-08 10-2-08 10 6 0810-6-08
N / S N / S N / S N / S N / S N / S N / S 1) SBE, PP 22 30 / 13 NC NC Supported Supported Supported ) pp pp ppSupported 2) NBE, PP 2 0 / 38 Supported Supported Supported Completed Completed Completed 3) SBW PP 2 3 / 25 NC @ NC NC NC Supported3) SBW, PP 2 3 / 25 NC @ NC NC NC Supported Supported 4) NBE, PP 21 0 / 30 NC Supported Supported Completed Completed Completed 5) SBE, PP 2 ** 18 / 0 NC NC 19 / 0 ^ NC Supported 6) SBE, PP 4 ** 19 / 0 NC NC NC NC NCNC 7) NBW, PP 3 ** ** 12 / 17 NC NC NC NC 8) NBE, PP 22 ** ** 16 / 0 NC NC NC NCNC 9) NBE, PP 3 ** ** 15 / 0 NC NC NC Supported
Jacks Tension Rods and Lift FloorbeamFloorbeam
What They’re Supposed to Look Like!Like!
Additional Work
Yellow Flag for Stringer Cracks
Finite ElementModel withwith Stiffening Plates
Lessons for a Local Bridge Owner (or what I learned on my excellent trip to Syracuse):
• Floorbeams Spaced Greater Than 12’ are Considered “Fracture Critical”, and Require Special Steel Testing and Certification
• Using a Strongback Beam is an Effective Way to Stage or Repair a Through-Girder Bridge, or Trussor Truss
• Wire Diameters May Vary or be Uniform Throughout the Cross Section of a BridgeThroughout the Cross Section of a Bridge Strand
Lessons for a Local Bridge Owner (continued):
• Keep Costs Down by Allowing Flexibility inKeep Costs Down by Allowing Flexibility in Construction
• Red Flags Require Attention Within 6 Weeks g qof Discovery
• Don’t be Distracted by the Worst Looking y gFeatures, Other Problems May Need Addressing
• Painting and Cleaning are Essential for Longevity of the Structure