Adrian Kollias, P.E. Philadelphia District Bridge Program
Manager US Army Corps of Engineers Philadelphia District
Introduction
Slide 3
Overview Present problem Previous repair attempts Modeling
Final solution
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MARYLAND DELAWARE NEW JERSEY 301 13 40 1 95 295 Baltimore
Philadelphia Wilmington C&D Canal Dover DELAWARE MARYLAND
Slide 5
Chesapeake Bay Delaware Bay Chesapeake & Delaware Canal
Crossings MarylandDelaware Chesapeake City Bridge 2 Lanes Summit
Bridge 4 Lanes St. Georges Bridge 4 Lanes Reedy Point Bridge 2
Lanes N Conrail DE Rte US Rte MD Rte DE Rts 806 71 US 9 13 213
301
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Terminology Fracture Critical Members: tension members or
tension components of members whose failure would be expected to
result in the collapse of partial collapse of a bridge Fatigue: the
tendency of a member to fail at a lower stress when subjected to
cyclical loading than when subjected to static loading. Fatigue
crack any crack caused by repeated cycle loading. Fatigue life the
length of service of a member.
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Chesapeake City Bridge Tie Girder Floorbeam Arch Pier
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Tied-arch structure Two traffic lanes, Maryland Rte. 213 3,954
feet in length Two-girder, fracture critical structure ADT = 14,825
(2004) ADTT = 2,635 (2006) Constructed 1947-1948 Overall structural
condition is fair Design live load: HS20-44 Description
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Cracks at 3 Locations: L0, L0, L1
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Bridge Floor System Sliding Bearings Cracked Connection Angle
Locations Stringers Floorbeam Deck Tie Girder
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Crack Location Track Crack Propagation with Bi-weekly
Inspections
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Crack Location Track Crack Propagation with Bi-weekly
Inspections
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Crack Location Track Crack Propagation with Bi-weekly
Inspections
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Chesapeake City Bridge Reason for Concern Public Safety
Potential for partial bridge failure if corrective measures are not
taken Major traffic thoroughfare connecting both northern and
southern Delmarva Peninsula in Maryland Connects Northern and
Southern Chesapeake City
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Attempt #1 Drilling Holes
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Attempt #2 Replace Top Portion of Cracked Angles New Angle
Section
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After failed Attempt #2, developed numerical models to
investigate the cracking and analyze bridge behavior. Determine
that frozen stringer bearings are causing the cracks and must be
replaced.
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Original Bronze Bearings Stringer Floorbeam Top Flange Sole
Plate Bearing Plate Bronze Plate Filler Plate
New Neoprene Bearings Sole Plate Bearing Plate Neoprene Bearing
Pad
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Repairs performed in 2003 - Replaced 72 bearings out of 180
total - Repaired connection angles for 6 floorbeams out of a
possible 16 total Cost: $945,000 Duration: 210 calendar days
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Cracks reappear at the angle connections 1-year after bearing
repair. Need to re-evaluate numerical models and design a repair
retrofit for the angles to prevent future cracking.
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Global Model
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Global Modeling: Details and Assumptions Modeled using
STAAD.Pro 2005 Created using beam and shell elements All members
modeled as beam, except deck slab which is modeled using shell
elements Rigid elements and offsets to account for differences in
c.g. locations of members New elastomeric stringer bearings modeled
as tri-directional linear springs Remaining original stringer
bearings are modeled as restrained in 3 directions South main arch
bearings free to expand longitudinally and rotate about transverse
axis North main arch bearings fully fixed Deck is continuous (i.e.,
can transfer axial force from one panel to another)
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Calibration of the Global Model Calibrated to measured global
deflection data Calibrated to measured strains from two previous
diagnostic tests Overall goal of the calibration Capture the key
features of the global response in terms of global deflection and
floorbeam stress Strive for realistic agreement in magnitudes,
given very complex behaviors and small magnitudes of measured
deflection and stress
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Initial Findings a. Cracking is Due to Relative Rotation
between Tie Girder & Floorbeam b. Cracking is Due to Fatigue
not Strength b. Continuous Deck Model Best Predicts Floorbeam
Stresses Matching Actual Field Measurements c. Frozen Stringer
Bearings and Stiff Deck Joints are both Contributing to the
Cracking
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Deflection Under Test Vehicle
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Model Results DiscontinuousSlightly Continuous Completely
Continuous
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Remove Sample of Rubber Deck Joint Material to Test
Stiffness
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Deck Joints
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Deck Joint
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Original Deck Joint Design - 1977 Rubber Seal x Steel Support
Bars
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Fused Steel Bars Deck Joint Deck Joints are Restrained from
Movement
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Fused Steel Bars Typical Deck Joint
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Fused Steel Bars Typical Deck Joint
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Joint Busters I Double Click to See Video
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Joint Busters II Double Click to See Video
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High-Pressure Power Washer
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Models indicate existing FTGC angles do not achieve infinite
fatigue life even with bearings and deck joints repaired.
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Retrofit Design Process Obtain Design Forces Global Model
Develop Preliminary Retrofit Designs (2 Stiffened + 2 Softened)
Incorporate Retrofit Local Model Verify Retrofit Effects - Global
Model Finalize Retrofit Design
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Local Model
Slide 44
Fatigue Analysis Fatigue life is function of stress range
Conducted using actual traffic data (cycles) and vehicle weight
crossing bridge Fatigue category C for out-of-plane displacement
behavior Criteria from AASHTO Guide Specifications and LRFD
Specifications
Slide 45
Current Repair Contract Replace top portions of FTGC angles
with thicker angle members at L0 to L5 and L1 to L5. Replace all
deck joint compression seals Replace neoprene bearings at exterior
stringers at Floorbeams L1 to L3 and L1 to L3. Restore bronze plate
bearings at Floorbeams L4 to L7 and L4 to L7. Cost: $1.3
million