project team...• steel stiffening truss installed in 1940’s • not included in previous load...

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Project Team

• NYSDOT Region 9 Local Projects Unit

• Federal Highway Administration (FHWA)

• Delaware County Dep’t of Public WorksOwner

• Modjeski & Masters, P.C.Design Engineer, Construction Inspection, Construction Support

• R. DeVincentis Construction, Inc.General Contractor

3• Located in Hamlet of Corbett, NY• Town of Colchester, Delaware County

Location

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Bridge Description

• Suspension bridge (170 ft. main span)• Only one side span – not suspended

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Bridge Description

• Single lane (11 ft. wide)• AADT of 477 vehicles (DCDPW 2004)

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Bridge Description

• Load posted for 8 tons• Controlled by truss bottom chord

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Bridge Description

• South: Side span not suspended• Through-girder (42 ft. simple span)

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Bridge Description

• North: Intersection with NYS Rt. 30• Backstay crosses Rt. 30 (22 ft. clear)

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Bridge Description

• Steel stiffening truss• Open grid deck

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Bridge Description

• 2 inch diameter wire rope main cable• 1-1/2 inch diameter suspender rods

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Bridge Description

• Suspenders attached using cable clips• Cable clamps at saddles

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Bridge Description

• North anchorage2-3/4 inch diameter U-bolt (original)

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Bridge Description

• South anchorage2-1/2 inch diameter U-bolt (new)

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Bridge History

“Styled after the famousBrooklyn Bridge”

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Bridge History

Hint: Brooklyn is the one on the left

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Local History• Hamlet of Corbett, NY built in 1921 by the firm

of Corbett & Stuart

• Wood acid factory and mill town

• Reported to have largest wood acid plant ever built (used to make wood pulp for paper)

• Plant closed in 1934 when new production method developed not requiring wood acid

• Mill remained in operation until 1948

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Bridge History

• Original Construction – 1926• Built by John A. Roebling’s Sons Co.

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Bridge History

• Featured in Roebling’s Sons publication

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Bridge History

• Original construction photos – 1926

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Bridge History

• Original construction photos – 1926• Note original pier and tower

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Bridge History

• Original pier upstream of currentlocation

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Bridge History

• Original timber stiffening truss• Removed 1945 (replaced with steel)

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Bridge Rehabilitation

Blaise A. Blabac, PEModjeski & Masters

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Bridge Rehabilitation

• Objective: Restore and Maintain 8-ton load posting

• Level 1 Load Rating performed in 2004 resulted in lowering posting to 4-tons

• Structural Deficiencies– Stiffening truss angles– Anchorage U-bolts

• Other Ancillary work– Cleaning and Painting– Substructure concrete repairs– Miscellaneous steel repairs

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Bridge Rehabilitation

• Award Date: April 25, 2006

• Start Date: June 1, 2006

• Completion Date: December 14, 2006

• Final Acceptance Date: January 8, 2007

• Engineer’s Estimate: $565,000.00

• Final Cost: $626,453.90

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Bridge Rehabilitation

• Cleaning and Painting• Class A containment

BeforeAfter

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Bridge Rehabilitation

• Guide rail improvements• Bridge and intersection with Rt. 30

Before

After

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Bridge Rehabilitation

• South abutment repairs• Install stone bank protection

Before

After

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Bridge Rehabilitation

• Concrete pier repairs• Install stone bank protection

BeforeAfter

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Bridge Rehabilitation

• North abutment repairs• Install stone bank protection

Before

After

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Bridge Rehabilitation

• North anchorage protection

Before

After

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Bridge Rehabilitation

• South anchorage protection• Drainage improvements

Before

After

It is in there!

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Bridge Rehabilitation

• South anchorage “protection”

Before

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Bridge Rehabilitation

• South anchorage retaining walls

Before

After

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Bridge Rehabilitation

• South anchorage U-bolt replacement

Before

After

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Bridge Rehabilitation

• Stiffening Truss strengthening

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Bridge Rehabilitation• Structural Deficiencies

– Stiffening Truss members– Anchorage U-bolts

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Stiffening Truss

• Buckling of single angle diagonals• NO evidence of vehicle impact

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Stiffening Truss

• Only end diagonals were bent• Improperly ascribed to vehicle impact

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Stiffening Truss

• Original timber truss designed for 15-ton truck

• Steel stiffening truss installed in 1940’s

• Not included in previous load ratings

• End connections consist of two (2) ¾ inch diameter rivets in single shear

• Analysis indicated L 2-1/2 x 2-1/2 x 5/16 buckle, rivets overstressed due to H-15 truck

• Lowered posting to 4-tons from 8-tons

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Stiffening Truss

• Change single angles to double angles• Dome head TC bolts to match rivets

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Stiffening Truss

• Lessons learned:

– Single angle compression members are vulnerable to buckling about z-axis (low rz)

– Importance of rating connections

– Proper assessment of structural behavior

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Anchorage U-Bolts

• Section loss of U-bolt dueto corrosion

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Anchorage U-Bolts

• Unfortunate location

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Anchorage U-Bolts

Water!

Ice!

• Inadequate drainage• 80 years worth of exposure

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Anchorage U-Bolts

• Area prone to flooding

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Anchorage U-Bolts

• Area prone to flooding

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Anchorage U-Bolts

• Area prone to flooding

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Anchorage U-Bolts

• Original 2-3/4 inch diameter U-bolts• Corrosion had reduced diameter to 2-1/8 inch

up to 1/4 inch pitting (1-7/8 inch remaining)• Section loss of 54%!• Original capacity = 190 kips• Reduced capacity = 88 kips• Max. cable force = 63 kips (with H-15 truck)• Inventory level rating of H 17

– Did not control posting (!)

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Anchorage U-Bolts

• How do you replace U-bolts?

• Need to off-load anchorages

• Use Jacking System to transfer cable reaction:– Cable clamps to grip main cable– Helical anchors driven into embankment– Jacking frame to transfer loads

• Bridge closed to traffic

• Completely designed, detailed on plans– Constructed per design

51• Install helical anchors• 60 kips ultimate capacity each

Jacking System

52• Install helical anchors• 60 kips ultimate capacity each

Jacking System

53• Install jacking frame

Jacking System

54• Install jacking frame• Install cable clamp

Jacking System

55• Jack until anchorage is off-loaded• Jacking load was 56 kips per cable

Jacking System

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Helical Anchors

• Installed with conventional skid-steerwith hydraulic torque head driver

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Helical Anchors

• Anchor is advanced until a specifictorque value is attained

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Helical Anchors

• Anchor is tested in place to verifyrequired capacity (60 kips ultimate)

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Jacking Frame

• Placement of Jacking Frame

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Jacking Frame

• Jacking beam connected to extensionrods from helical anchors

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Jacking Frame

• Center-hole hydraulic jacks connectedto extension rods

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Jacking Frame

• Jacking beam transfers jacking loadsto cable clamp

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Jacking Frame

• Cable clamp (tested for 88 kips)• Grips cable using 4 Crosby clips

64• Looks good on paper… will it work?• Contractor played it safe…

Jacking System

65• Cutting existing U-bolts

Jacking System

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Jacking System

• Success!

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Jacking System

• New U-bolts installed

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Questions?Questions?