Twin Bridges Strand Replacement and Rehabilitation...-- FSdClForces on Strand Clamps-- Traffic...

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