Long-Term Seismic Performance of Rehabilitated Reinforced Concrete by juanagui

VIEWS: 30 PAGES: 28

									Long-Term Seismic Performance of
Rehabilitated Reinforced Concrete
Columns Using Advanced Carbon
Composites



Wilkins Aquino
PI: Prof. Neil Hawkins
University of Illinois at Urbana-Champaign
                     Motivation
   Columns that were built in the 1950’s in Justice,IL
    deteriorated significantly due to corrosion.
   These columns were retrofitted in the 1980’s using glass
    fiber composites.
   By the mid 1990’s it was found that these columns had
    experienced severe distress and some of the composites
    jackets had split longitudinally.
   The problem was attributed to lack of moisture
    dissipation coupled with freeze-thaw cycles.
Statement of the problem
   It has been established that carbon composites can be
    used to improve the mechanical behavior of reinforced
    concrete members.
   Yet, there is not enough information on the long term
    durability of concrete-advanced composite systems.
   In cold regions, retrofitted bridge structures very often
    are exposed to high humidity, freeze-thaw cycles, and
    deicing chemicals.
   How do these environmental conditions affect the
    mechanical response of advanced composite-concrete
    systems?
Objectives
 Explore the structural behavior of columns
  containing corroded reinforcement and
  retrofitted using advanced carbon composites.
 Determine the suitability of a banded layout of
  carbon composite versus a full jacket to avoid
  problems related to moisture encapsulation
  and freeze-thaw damage.
Research Approach
 Field investigation
  • 12 columns retrofitted using carbon fiber
    composites in East St. Louis beneath I-70
  • Relative humidity behind composite material
    monitored over time
 Laboratory tests and Modeling
Moisture Transport Modeling

                      =water content per
  R    100
     s                unit volume
 R                    s=Saturated water
       D( R)R
 t                    content per unit volume
                       R=Relative moisture
                       content in %
Non-linear diffusion
equation.              D=Diffusion coefficient
Moisture Transport Modeling

                            =unit vector normal to
 Boundary and
                            the surface.
 initial conditions:
                            Ho=Relative humidity of
 R = Ri                     the environment.

   R                       Hs =Relative humidity at
 D      m H 0  H s    the surface.
   
                            m =Surface coefficient
                            Ri =Initial moisture
                            content.
 MODELING DRYING OF CONCRETE ENCLOSED WITH
 ADVANCED CARBON COMPOSITES

 The finite element method was used to solve the
  non-linear diffusion equation under the
  prescribed boundary and initial conditions.
 MSC Patran and ABAQUS were used as pre/post-
  processor and solver respectively.
 The following parameters were used:

    •  = 50%   Ho = 60%
MODELING DRYING OF CONCRETE ENCLOSED WITH
ADVANCED CARBON COMPOSITES

   Different combinations of width and spacing were used to
    study how these two parameters affected moisture drying
    in concrete.

          Case        Width (cm)    Spacing (cm)
                         (w)             (s)
          w3s6            3              6
          w3s12           3             12
          w6s6            6              6
          w6s12           6             12
          open           ----           ----
MODELING DRYING OF CONCRETE ENCLOSED WITH
ADVANCED CARBON COMPOSITES



             m=3.333
             H0=60%




            Drying
            direction
                         MODELING DRYING OF CONCRETE ENCLOSED WITH
                         ADVANCED CARBON COMPOSITES

                       100                                                                  100

                       95                                                                   95
Moisture Content (%)




                                                                                            90




                                                                      Moisture Content(%)
                       90
                       85                                                                   85

                                                                                            80
                                                                                                          s=12 w=6
                       80                    s=12 w=6
                                                                                                          Open
                       75                    Open                                           75
                                                                                                          s=6 w=6
                                             s=6 w=6
                       70                                                                   70            s=6 w=3
                                             s=6 w=3
                       65                    s=12 w=3
                                                                                            65            s=12 w=3
                       60                                                                   60

                       55                                                                   55

                       50                                                                   50
                             0          5         10        15   20                               0              5                 10   15
                                              Time (days)
                                                                                                                     Time (days)


                                 Moisture variation at the                                            Moisture variation at
                                 surface                                                              2.5 cm into the concrete
MODELING DRYING OF CONCRETE ENCLOSED WITH
ADVANCED CARBON COMPOSITES

   The width of the composite bands is the controlling factor
    on the moisture transport in concrete enclosed with
    advanced composites.
   Spacing has minimal impact on drying. This opposes
    empirical recommendations of leaving 50% of the
    repaired area exposed.
   The effect of the width of the composite bands becomes
    less pronounced with depth into the concrete.
Measurement of Moisture Distribution
Using Relative Humidity
                        Measurement of Moisture Distribution
                        Using Relative Humidity

                        100                                                                             100

                         95                                                                              95

                         90                                                                              90




                                                                                Relative Humidity (%)
Relative Humidity (%)




                         85               w6s6                                                           85
                                          w6s12
                         80               Expon. (w6s12)                                                 80
                                          Expon. (w6s6)                                                                   W6S6
                         75                                                                              75               W12S6
                                                                                                                          OPEN
                         70                                                                              70

                         65                                                                              65

                         60                                                                              60
                              0.0   5.0       10.0         15.0   20.0   25.0                                 0.0   5.0      10.0      15.0     20.0   25.0   30.0
                                               Time (Days)                                                                          Time (days)


                                             Measurements taken at 1.25 cm into
                                             the material.
Durability of systems strengthened using
Carbon composites

•Even if a composite
material is completely
resistant to certain
environmental conditions,             Gap: Location of
the concrete-composite                possible water
                                      infiltration.
system may be susceptible
to environmental damage.          Carbon composite

•Damage might be caused
by accumulation of
moisture, development of
pressures due to freeze-
thaw, and off gassing
under the composite.
LARGE SCALE LABORATORY TESTING

   Six laboratory columns of 1/3 scale of field columns
    were built.
   Columns are 50 cm in diameter and 245 cm in height.
    They have 12 #8 longitudinal reinforcing bars and
    circular hoops at 20 cm centers.
   Five of the columns were deteriorated using external
    currents to accelerate corrosion. The additional
    column was kept as a control specimen.
   Four of the five deteriorated columns were repaired and
    one was kept as a damaged control specimen.
LARGE SCALE LABORATORY TESTING

     Accelerated Corrosion Test setup
LARGE SCALE LABORATORY TESTING
LARGE SCALE LABORATORY TESTING

   The repair process encompassed:
    •   Removal of deteriorated concrete
    •   Abrasive blasting of reinforcing bars
    •   Installation of strain gages and thermocouples
    •   Casting new concrete (35 MPa, 13 mm max. agg. size)
    •   Wrapping of columns with various patterns of
        carbon composite.
LARGE SCALE LABORATORY TESTING
LARGE SCALE LABORATORY TESTING

   Three columns with different band
    schemes were exposed to 50
    freeze-thaw cycles
   Small cylinders cast and exposed
    to same freeze-thaw shedule
   Coupon samples of carbon
    composites exposed to same
    environmental conditions
LARGE SCALE LABORATORY TESTING

   Impulse response used to
    detect damage behind
    composite material in
    columns
   Resonance frequency
    equipment used to detect
    damage in small
    cylinders
LARGE SCALE LABORATORY TESTING
                  LARGE SCALE LABORATORY TESTING

                                  Load vs Displacement                                                         Load vs top displacement

                                            50                                                                            50
                                            40                                                                            40
                                            30                                                                            30
                                            20                                                                            20




                                                                             Load (kip)
Load (kip)




                                            10                                                                            10
                                             0                                                                             0
             -5    -4   -3   -2     -1     -10 0         1   2   3   4   5                -5   -4    -3   -2       -1    -10 0         1   2   3   4   5
                                           -20                                                                           -20
                                           -30                                                                           -30
                                           -40                                                                           -40
                                           -50                                                                           -50
                                     Top Displacement (in)                                                         top displacement (in)




                        Control Column                                                              Corroded Column
Ultimate Load and Displacement


 1.2


  1


 0.8
                                                     Control
                                                     Corroded
 0.6


 0.4


 0.2


  0
                Pmax (KN)                  Du (in)

       * Quantities normalized with respect to control
       specimen results
Preliminary Results

   Width of band is the controlling factor in moisture
    migration from columns wrapped with carbon
    composites.
   Impulse response tests: No damage in concrete-
    composite interface after 50 freeze-thaw cycles
    regardless of band scheme used.
   Resonance frequency test: No damage in small cylinders
    after 50 freeze-thaw cycles
   Corroded column exhibited a significant reduction in
    strength and ductility when compared to as built column.
    It seems that the corrosion process affects the ductility
    capacity of the column to a larger extent.
Preliminary Results

   Field measurements showed moisture built up behind
    continuous wraps in columns located directly under
    bridge deck joints.
Ongoing work
   Cyclic testing of retrofitted specimens
   Closed-loop compression tests on small cylinders
   Tensile tests on composite coupons
   Analysis of experimental data and report

								
To top