REHABILITATION OF A PRESTRESSED CONCRETE BOX BEAM BRIDGE

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					  REHABILITATION OF A
PRESTRESSED CONCRETE
   BOX BEAM BRIDGE

     Curtis Wood, P.E.
             Introduction
6,000+ prestressed box beam bridges in
the state of Ohio

Current rehabilitation methods are limited
– ODOT standard operating procedure is to
  monitor and replace entire superstructure
MOT-35-1.55 (Montgomery Co.)
  Box Beam bridge with 2 deteriorated
  interior beams
  Move beyond the research of FRPC and
  into implementation
 – Project conducted under ODOT standards
 – Determine if FRPC is a viable option
 – If FRPC is not an option, to determine the
   best method of rehabilitation
                  Outline
Description of MOT-35-1.55 bridge
Bridge Assessment
– Inspection Techniques
– Existing Capacity

Possible Solutions
Decision
Construction
Conclusions
               MOT-35-1.55
– Span: 60 ft 0 in. center to center of bearings
     Width: 40 ft 0 in. Beams: (10) ODOT B33-48 adjacent box
     beams
     Concrete Strength: Prestressed Reinforcement: (16) ½ in.
     diameter strands (As=0.153 in2, fy=270 ksi).
– Non-prestressed Reinforcement: (4) #5 epoxy coated
  bars (fy=60 ksi).
– Required Live Load: HS-20
– Date Constructed: Early 1980’s
– Initial Construction Sequence:
     Phase 1: Beams 1-6
     Phase 2: Beams 7-10
MOT-35-1.55 Existing Plans
MOT-35-1.55 Existing Plans
MOT-35-1.55 Existing Plans
       Bridge Assessment
Visual Inspection

Hammer Testing

Chloride Testing

Pull-off Adhesion Testing
Visual Inspection
Visual Inspection
Visual Inspection
Hammer Testing
Hammer Testing
                Chloride Testing
Corrosion of steel reinforcement typically occurs at a level
of 1.0 to 1.4 pounds of chloride per cubic yard of concrete
Collected samples with a drill for testing in the lab
      Drill bit penetrated between 1-2 inches into beam


        Sample #         Chloride (lb cl- / cubic yard)
            1                        8.77
            2                        10.24
            3                        4.94
            4                        6.77
            5                        1.15
            6                        3.16
   Pull-Off Adhesion Testing
Followed ACI 503R
A minimum of 200 psi is required to prevent
premature failure of FRP laminates
     Location   Beam   Stud A   Stud B   Stud C    Average
        #               (psi)    (psi)    (psi)   Stress (psi)
        1        6      139      112     116.5       128
        2        5      186      122      209        198
        3        6      357      248      295        326
        4        6      184      389      373        381
        5        5      319      391      311        355
        6        6      419      448      421        434
        7        6      156      62       207        181
        8        5      320      101      358        339
        Existing Capacity
Used Conspan

Assumed 11 Remaining Strands
– 18% Overstressed in Ultimate Moment
  Capacity
       Possible Solutions
Do Nothing
Replace Entire Superstructure
Replace Beam 5 and Beam 6 only
Repair Waterproofing and Patch Concrete
Repair Waterproofing, Patch Concrete,
Add Sacrificial Zinc Anodes
Repair Waterproofing, Patch Concrete,
Add Sacrificial Zinc Anodes, Strengthen
with FRP
                     Cost Estimates
                                           Preliminary   Estimate with
                Option
                                            Estimate       Inflation

  New Non-Composite Superstructure          $174,606       $221,565


     New Composite Superstructure           $200,286       $254,151


         Replace Beams 5 and 6              $54,433        $69,072


         Repair Beams 5 and 6               $55,266        $70,129

Repair and Strengthen Beams 5 and 6 with
                                            $77,000        $97,709
                 FRPC
                Decision
Major Criteria for Decision

– Cost

– Durability and effects weathering

– Constructability

– Degree of certainty with regard to long term
  performance
                             Decision

     Option         Cost           Advantages            Disadvantages


                               Life of repair        Unexpected
Replace Beams 5              predictable            Construction Delays
                   $69,072
and 6                          30% less expensive   Possible
                             than FRP option


Repair and                    None apparent          Unknown life of repair
Strengthen Beams   $97,709                           Brittle failure mode
with CFRP Plates                                     Possible construction
                                                    defects
                  Decision
Remove and Replace Beams 5 and 6
– Removal Sequencing was detailed
– Construction Sequencing was detailed
    Attempted to use as close to standard construction
    details as possible
     – Used Sleeve Nuts from phase construction detail
     – Used modified B33-48 box beams
     Removal Sequencing
Remove existing backwall behind beams 5 and 6.
Core two holes at each end close to abutments and at
midspan of beams to install lifting devises.
Core out around dowels at each end of beams.
Saw cut keyway joints down through tie rods. Special
care shall be taken not to damage the transverse tie
rod sleeve nut between Beams 6 and 7.
Remove beams. Beams shall be supported at both
ends and centerspan during removal.
Remove grout and clean keyways by grinding. Use of
pneumatic hammer is prohibited.
Clean connection in existing tie rod from Beam 7.
Cut off anchor dowel and core out dowels from both
abutments.
Removal Sequencing
Removal Sequencing
Removal Sequencing
Removal Sequencing
Removal Sequencing
Removal Sequencing
Removal Sequencing
Removal Sequencing
  Construction Sequencing
Thread the end of existing tie rod 4A.
Place sleeve nut on tie rod 4A.
Clean the connection on the existing transverse tie rod in Beam 7 to be
reused.
Place transverse tie rods in Beam 6.
Place nuts on all ends of both tie rods in Beam 6.
Place Beam 6.
Connect tie rod 6A to existing tie rod from beam 7 using sleeve nut.
Torque tie rod 6A from the north side.
Place tie rod in Beam 5.
Place Beam 5.
Place Beam 5 connect tie rod 5 to tie rod 4A and tie rod 6B.
Torque tie rod 6B from the nut on the south side of Beam 6.
Grout tie rods, keyways, and joints.
Install anchor dowels in beam seats.
Construction Sequencing
Construction Sequencing
Construction Sequencing
Construction Sequencing
Construction Sequencing
Construction Sequencing
Construction Sequencing
Construction Sequencing
Construction Sequencing
Final Product
Final Product
1 Year Later
        Concluding Remarks
Use of FRPC for rehabilitation of concrete bridges is still
in question.
– Bridges for which FRPC is considered for use should not have
  damaged concrete.
– Research shows non-ductile and catastrophic manners of failure.
– For this type of application, FRP could not have been efficiently
  or effectively used.


Details used to replace interior box beams can be copied
for future box beam rehabilitation projects

– Under 1 week total closure

– Approximately $100,000 for construction costs
    QUESTIONS?
       THANK YOU

curtis.wood@dot.state.oh.us