Evaluation of a High-Performance Steel Bridge Using by hat20206

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									Evaluation of a High-Performance Steel Bridge
             Using Field Test Data

                  Kelsey Miner

             NSF Research Experiences for
          Undergraduates in Bridge Engineering
                University of Delaware
Intro
 Location / History of Churchman’s Bridge
 Previous Research
 Bridge Model
 Strain Gage Data
 Results / Discussion
Location - Map
University of Delaware   Churchman’s Road Bridge
Location - Pictures
 New bridge looking from the east.
 Aerial view of old bridge (notice skew).


                        27º
History of Churchman’s Bridge
 Work began in 2004
 to replace existing
 overpass
 773’ long steel bridge
 with five spans
 Sharply skewed at an
 angle of 27º
 Cross frames (to
 connect the girders)
 are parallel to the
 abutments (with the
 skew and not normal
 to the girders)
Previous Research
 Eight girders and two cross frames have been
 instrumented with Geokon vibrating wire strain
 gauges.
 Gauges have been continuously recording data
 since before construction began.
 Data has been removed from the data loggers
 approximately every two weeks, and then
 stored as text files.
Previous Research – Strain Gauges
                                   Two cross
   Cross Frame Detail              frames have
                                   gauges on all
                                   members.
                                   All eight girders
                                   have strain
                                   gauges on the
                                   bottom flange
                                   and two also
                                   have them on
                        End View   top.
Research Objectives and Importance
 Very few skewed steel bridges have been
 instrumented before construction.
 Currently they require significant design
 experience due to cross-frame and girder
 rotation issues.
 This project aims to increase the understanding
 of dead load stresses in these bridges.
Modeling
 Modeling Program: STAAD 2003
    Easy to learn, available and
    recommended




                                                                                                              2
                                                                                        1




                                                                                                             n
                                                  Girder Details - Side View




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                                                                                                       Se
                                                                                 Se
 Using STAAD, a line model was
                                                             G2 to G7          PL16'x13 4"          PL20'x118"
                                         Top Flange          G1 & G8
                                                                               PL16'x15    8"       PL20'x118"

 created.
    Members are treated 2-d lines,
    as compared to a 3-d model in        Web
                                                      7
                                               PL72"x 8" (TYP.)
                                                                                 110'

    which they are solids.
 Girder cross-sections produced in                                                              Field Splice 1


 Section Wizard and imported into                                 G2 to G7     PL16'x13 4"          PL20'x118"
                                         Bottom Flange
 STAAD.                                                           G1 & G8
                                                                               PL16'x15    8"       PL20'x118"


    AutoCad used to organize the 26
    different sizes of girders on this
    bridge.
Modeling - Simplifications
 Cross-frames modeled as single members.
 Models were created in STAAD and their
 effective areas determined.




 W-sections with the same area were then
 chosen to represent these cross-frames.
Modeling - Cross-Frames, Utility Supports
  By modeling the cross-frames as single members,
  their true weight was not being represented.
  The utility supports were not modeled, and
  instead loads were added to represent them.
                                                                         Gir
            r                                                               der
      Girde
                Cro
                      ss-f
                          ram
                              e
                                       Girder

                                                     Cros
                                                            s-fra
                                                                    me

                                  Utility Supports
Modeling - Supports and Errata
  Middle pier modeled as fixed support, with all other piers being
  modeled as rollers.
  Modeled this way since k-values for springs would be difficult to
  determine.
  Also, STAAD has a node limitation of 500 nodes, so only the west
  half of the bridge was analyzed, although entire model was
  created.
                        Model of Entire Bridge




                    Model of West Half of Bridge
Modeling - Construction Process
  Each step in the construction process was
  modeled, with one shown below.




  Done so that the evolution of stresses in the
  girders could be analyzed.
Strain Gage Data
 Strain data was plotted versus time for months
 before construction to weeks after construction



                                                  Girder placement

        In High Steel’s    In transit /
        fabrication yard   At construction site
Strain Gage Data – Three Types
Three types of strains were determined.
  1. Overall                                        Strain on Bottom Of Girder 1 During Construction


  2. Construction                 250

                                  150
                                                                                                            Maximum Strain
  3. Maximum                       50

                                   -50
                                                                       Construction
                    Microstrain                                                                                           Extreme
                                                                                                                          Maximum Strains
                                                                                                                           Construction Strains
                                  -150                                 Strain                                              Overall Strains

                                  -250              Overall
                                                    Strain
                                  -350

                                  -450

                                  -550
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Results
 Stresses from gages compared to the results from the
 models.                West End of Bridge Stresses
 Agreed on stress
 development, such as
 both having largest
 stresses after girder
 six was placed.
 Did not agree on magnitude of stresses with gages
 reading 12-14 KSI and model predicting 5 KSI
Discussion
 Discrepancy in stresses is most likely due to
 loads not being taken in account.
 From plan drawings and bridge visits it is not
 clear what these loads would be.
   Possibly welds, safety devices, stiffener plates
 Results could also be improved by better
 modeling of supports and of cross-frames.
   Determine k-values for all the supports
   Take into account other properties besides effective
   area for the frames.
Further Research
 3-D modeling of the bridge.
   Would allow accurate modeling of the cross-
   frames, since could attach members to the
   tops and bottoms of girders
 Relationship between temperature and
 strain in the girders, since temperature
 causes significant strain variation.
Acknowledgements
 Professor Chajes
 Gary Wenczel
 Jason Winterling
 National Science Foundation
   This material is based on work supported by the National
   Science Foundation under Grant No. EEC 0139017 “ Research
   Experiences for Undergraduates in Bridge Engineering” at the
   University of Delaware.

								
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