VT/FHWA Center of Excellence for Polymer Composites & Adhesives in by KLNS4Q

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									   Development of
Product Design Guides
        John J. Lesko & Thomas E. Cousins,
          Department of Engineering Science & Mechanics
        Department of Civil and Environmental Engineering,
                            Virginia Tech
                      Blacksburg, VA 24061


        Dan E. Witcher & Glenn P. Barefoot
                          Strongwell, Corp
                          Bristol, VA, 24203


2003 Technical Conference on Construction, Corrosion and Infrastructure
                      Las Vegas, NV, 22-25 April 2003
Where is Virginia Tech?



                   Hawthorne St. Bridge


                                            That Other
                                              Univ.
                 Troutville Weigh Station

           Tom’s Creek Bridge
                                                         Tangier Island

  Dickey Creek Bridge
                                                         Rt. 601 Bridge
Barriers to Routine use of FRP
        Administrative                                Technical
   Fragmentation of the industry           Lack of design
   Lack of interdisciplinary training       specifications
    for design engineers                    Performance vs. Material
   Cost (first vs. life cycle)              specification
                                            Lack of sufficient long-term data
   Limited commercial capital for           and experience
    development of new systems
                                            Plethora of new materials, additives
   Incremental - piecemeal                  & combinations
    approach to FRP                         One-for-One material substitution
    implementation in designs               Lack of confidence in adhesive
                                             bonding
Barriers to Routine use of FRP
        Administrative                                Technical
   Fragmentation of the industry           Lack of design specifications
   Lack of interdisciplinary training      Performance vs. Material
    for design engineers                     specification
   Cost (first vs. life cycle)             Lack of sufficient long-term data
   Limited commercial capital for           and experience
    development of new systems              Plethora of new materials, additives
   Incremental - piecemeal                  & combinations
    approach to FRP                         One-for-One material substitution
    implementation in designs
                                            Lack of confidence in adhesive
                                             bonding
Barriers to Routine use of FRP
        Administrative                                Technical
   Fragmentation of the industry           Lack of design specifications
   Lack of interdisciplinary training      Performance vs. Material
    for design engineers                     specification
   Cost (first vs. life cycle)             Lack of sufficient long-term
   Limited commercial capital for           data and experience
    development of new systems              Plethora of new materials, additives
   Incremental - piecemeal                  & combinations
    approach to FRP                         One-for-One material substitution
    implementation in designs
                                            Lack of confidence in adhesive
                                             bonding
Barriers to Routine use of FRP
        Administrative                                Technical
   Fragmentation of the industry           Lack of design specifications
   Lack of interdisciplinary training      Performance vs. Material
    for design engineers                     specification
   Cost (first vs. life cycle)             Lack of sufficient long-term data
   Limited commercial capital for           and experience
    development of new systems              Plethora of new materials,
   Incremental - piecemeal                  additives & combinations
    approach to FRP                         One-for-One material substitution
    implementation in designs
                                            Lack of confidence in adhesive
                                             bonding
 Mil Handbook 17
            Mission Statement
Develop world-class engineering
handbooks for structural applications of
composite materials. These handbooks will
include standards for test/characterization
methods, statistics and databases, as well
as guidelines for processing, design and
analysis.


                      http://www.mil17.org/
                                Modified LRFD
                                  Approach
                                             Resistance, R
                                   Load, Q




                           8” & 36” DWB Design Guide
                              •Deflection (A&B Allowables)
                              •Strength (A&B Allowables)
Reliability based approach    •Stability
to assessing A & B basis      •Bearing
Allowables, as described      •Connections
through Weibull Statistics    •Fatigue & Long Term
Extren™ 8” Double Web Beam
(DWB) Characteristics
               Pultruded Hybrid Glass &
               Carbon/Vinyl Ester Shape

               Ixx = 129 in4   Iyy = 31.8 in4
               Sx = 32.2 in3   Sy = 10.6 in3
               rx = 3.07 in    ry = 1.52 in

               A = 13.7 in2
               A2 webs = 5.36 in2
               A2 flanges = 7.44 in2
               Weight/foot = 11lbs/ft
Extren™36” Double Web Beam
(DWB) Characteristics
Pultruded Hybrid Glass &
Carbon/Vinyl Ester Shape

Ixx = 15291 in4      Sx = 849 in3
Iyy = 2626 in4       Sy = 292 in3
rx = 12.9 in         ry= 5.37 in

A2w = 50.1 in2
Asf = 34.0 in2
Weight/foot = 75 lbs./foot



                                    Dimensions in inches
 Load Resistance Factor
 Design (LRFD)
                             Resistance, R
                   Load, Q



Rn     Q
          i   ni




        AASHTO (1998) LRFD based design
DWB Design Guide Approach
                                             Resistance, R
 User supplies loads and level
 of acceptable risk based on
 change in Resistance                           Cumulative Probability
                                   B-Basis


                            A-Basis




                   Level of Risk
Design Guide
  Material Specification
  Weibull Statistics & Reliability
  8” & 36” Deep DWB Design Guide
     Deflection (A&B Allowables)
     Strength (A&B Allowables)
     Stability
     Bearing
     Connections
     Fatigue & Long-term
Stiffness & Capacity




Unsupported Spans: 8, 14, and 20 feet
Instrumentation: S – Shear, B – Bending, D - Deflection
8” DWB




                                                36” DWB
     Top flange failure due to delamination




                Support failures at spans shorter than 30’
Moment Capacity & Material
                   Moment capacity
                   controlled by carbon/glass
                   interlaminar interface



               2
        1
DWB: Strength vs. Span
                        200                                      3
                                                 3                   Pad conditions
                        180       36”                            2   for bearing
                                  DWB                                failures
                        160
                                  Bearing        2               1
Shear Capacity (kips)




                        140       Failures
                                                 1
                        120

                        100                                     36” DWB
                                                                Bending Failures
                        80

                        60

                        40                                       8” DWB Bending
                                                                 Failures
                        20

                         0
                              0              5       10   15    20         25         30
                                                          L/d
Shear Deformation: 36” DWB
             100
              90
                                            kGA 2.00E+07
              80                            kGA 4.00E+07
              70                            kGA 8.00E+07
                                            kGA 1.00E+08
              60
  % shear




              50                       B-basis Allowable
              40                       E = 6.1 Msi
              30
              20
              10
               0
                   0   10   20   30    40       50   60    70
                             Span Length, ft.
Assessing Stiffness Allowables

 Bending modulus is determined in the constant moment section
 from axial strains
                                  Mxx c
                         E zz   
                                   zzIxx
 kGzyAv is not independent of Ezz And is therefore determined from
 deflection under the 4 point loading condition


                          7 PL3     PL
                 max          
                          216 EI 3 kGxy A
Development of Allowables
    Using Median Rank and Weibull statistics we develop  and 
                                                                           
                   xi - 0.3                                        x 
            Pi =
                   n + 0.4                     
                                    F( x )  f ( x )dx  1  exp   
                                            0
                                                                    
                                                                   

    Establish the lower (5% confidence interval) and the A and B
    basis allowables based on the desired reliability
                                         1                                        1
            ~             2n                             ~        1         
            lower                        A Allowable = lower ln      
                       (2n) 2 0.05                                 0.99 
~                                                                                 1
lower                                                        ~      1 
                                              B Allowable = lower ln     
                                                                                   


                                                                     0.90 
 FRP Design Allowables
                                             Resistance, R


                                        1
                      ~        1     
                                                 Weibull Cumulative Probability
                      lower ln      
                                0.90                                              
                                                                               x 
                         1
                                  B-Basis               
                                                F( x )  f ( x )dx  1  exp   
                                                        0
                                                                                 
                                                                                
       ~        1     
       lower ln      
                 0.99  A-Basis
                          




                Level of Risk
Design Stress
Weibull Statistics on
Modulus, Ezz
         1

        0.9

        0.8

        0.7
                    Weibull mean = 6.21 Msi ± 0.27
        0.6
                    A allowable = 5.29 Msi
f (E)




        0.5         B allowable = 5.75 Msi

        0.4

        0.3

        0.2

        0.1

         0
              5.0              5.5                   6.0     6.5   7.0
                                             modulus (Msi)
    8” DWB Hybrid Beam
    A-basis Allowables
             Ezz = 5.66 x 106 psi        kGzyAV = 1.8 x 106 psi-in2
                              Mmax = 36.1 kip-ft.
             Strength                           Deflection
                        L/180   L/240   L/300     L/360       L/420   L/500   L/600   L/800
Span (ft.)
   8          4513      2970    2228    1782      1485        1273    1069    891     668
  10          2888      1703    1277    1022      851         730     613     511     383
  12          2006      1054    791     632       527         452     379     316     237
  14          1473      693     520     416       346         297     249     208     156
  16          1128      478     358     287       239         205     172     143     107
  18          891       342     257     205       171         147     123     103     77
  20          722       253     190     152       127         109      91     76      57

                                                   Based on a simply supported
             Shear Deflection                      beam under distributed load
                30% @ 8’                                        5wL4        wL2
                                                     max               
                7% @ 20’                                       384 E xx I 8 kGxy A
     36” DWB Hybrid Beam
     B-basis Allowables
             Ezz = 6.10 x 106 psi           kGzyAV = 46.2 x 106 psi-in2
               Mmax = 1139 kip-ft @30’ Span & 916.7 kip-ft 40-60’ Span
             Strength                           Deflection
                        L/360   L/400   L/500     L/600      L/700   L/800   L/900   L/1000
Span (ft.)
   30         10124     2051    1846    1477      1231        1055    923    820      738
   35          6712     1536    1382    1106       921         790    691    614      553
   40          4584     1173    1055     844       704         603    528    469      422
   45          3622     911      820     656       547         468    410    364      328
   50          2933     719      647     517       431         370    323    287      259
   55          2424     575      517     414       345         296    259    230      207
   60          2037     466      419     335       279         239    210    186      168


                                                    Based on a simply supported
             Shear Deflection                       beam under distributed load
               15% @ 30’                                        5wL4        wL2
                                                     max               
                5% @ 60’                                       384 E xx I 8 kGxy A
Lateral Torsional Buckling
8” DWB
                          4x Lateral Supports @ 9’ (2.7m) off-center
                          w/1” (25mm) clearance



Rotation & lateral
displacement
allowed at mid-span
                      2x Lateral-Torsional restraints to
                      satisfy Mottram boundary conditions


                      Unsupported Spans Tested:
                      40, 36, 32, 28, 24, 20 feet
                      To L/90
                      No LTB observed!

                      Impose Limit L/180
 Lateral Torsional Buckling
 36” DWB
                          4x Lateral Supports @ 9’ (2.7m) off-center
                          w/1” (25mm) clearance

Rotation & lateral
displacement
allowed at mid-span

                      2x Lateral-Torsional restraints to
                      satisfy Mottram boundary conditions



                      Unsupported Spans Tested:
                      60 feet To L/180
                      No LTB observed!

                      Impose Limit L/360
Bearing Capacity: Web
Buckling

                     Bearing controlled by web buckling

                                      E12
                         FuCr =             0.55
                                  56 (Kl r )

  Factor of Safety   Total allowed bearing load
          FuCr
     Fa =                     P = 2Fal' t
           3
   Bolt Bearing in Connections
Bolt bearing controlled by                                FpCr = 30 ksi
ultimate bearing strength of the
web material                                                        Fu
                                                           FpCr   =
                                                                    3

                                                         Allowable pin
                                                         bearing load
                                                          P = FPCr t w d


Fastener edge distances: 2 diameters or 1” (25mm) minimum, which ever is greater.
Fastener pitch:4 diameters or 3” (76mm) minimum, which ever is greater.
So what about
durability?
Tom’s Creek Bridge




  Tom’s Creek Bridge
 Tom’s Creek Bridge, June 1997




Deflection = L/490
Wheel Load Distribution Factor = 0.101
Dynamic Load Allowance = 0.9
Beam Removal & Replacement
Two beams having seen 15 months
(Sept 1998) of service were removed to
assess remaining strength and stiffness




                             After 15 months of service...
                               • No residual creep deflection
                               • No reduction in residual strength and stiffness
  Dickey Creek Bridge




Dickey Creek Bridge
Dickey Creek Bridge




 Deflection = L/1100
 Wheel Load Distribution Factor = 0.2
 Dynamic Load Allowance = 0.36
How Does the Resistance
Change?

FRP Life prediction is Resistance, R
required as a function                 A, Residual
                                       Resistance
of load and                            X-years of service
environmental history
                                            B, Residual
to assess the changes                       Resistance
in Resistance                               X-years of service

                                            Initial
                                            Resistance




  “Emphasis on Combined Environments”
  CERF/MDA Durability Gap Analysis
Estimating Remaining Strength
& Stiffness
FRP composites durability is best described by nonlinear cumulative damage
approaches where residual strength and stiffness are tracked during life
              Degradation Processes
                   •Cycle dependent Geometry
                   damage           Constitutive                           Remaining Strength
Initial Strength




                                                      Stress or Strength
                                                                           Of Critical Element
                   •Kinetic

                   •Chemical

                   •Thermodynamic
                                                                            Life        N
  Reifsnider et al. (1975- present)                Stress on Critical Element
    Simulation Approach
 Loads                   Develop estimate on resistance
                          based on stress analysis/material            No       Yes
                         Develop load/environment history
                          based on statistical description
                                                                            ?
                          (Monte Carlo Simulation)



                                                                       Compute
                                                     Life Prediction      & Pf
                                Stress or Strength


Input material
 characteristics (S-N
 curve, stiffness and
 strength reduction as a
 function of environment -
 including statistical
 description)
                                                         Life
Engineering Practice: Example
Element: FRP Pultruded hybrid vinyl ester structural girder
Region: Northeast US (Environmental factors - thermal, moisture & UV)
Rn = X moment capacity (Resistance and inherent resistance variation)
Qn = Operating Moment based on stress analysis from AASHTO HS20,
with ADT 10,000, 30% fully loaded (Load and load variation)
                                    Pf
         5 yrs        10 yrs       20 yrs       30 yrs        40 yrs
.99      .010          .015         .018         .025          .10
.95      .008          .007         .015         .020          .05
.90      .004          .003                                   
.85      .002                                                
.80                                                         
                                                           
                                                           




                  Example NOT meant for design
Conclusions
 FRP design guide
    Materials specification
    Laboratory testing
    Reliability based
    Long-term validity of as received design allowables
 Durability Modified LRFD for FRP: a possibly
  means to gain acceptance among practicing
  engineers
      Suggest inspection cycle
      Phenomenological vs. First Principles
      Material Specification?
      Is this realistic or just academic???
Acknowledgements
 FHWA, Innovative Bridge
  Research & Construction Program
 Virginia Dept of Transportation
 National Science Foundation
 Virginia Center For Innovative
  Technology
 Strongwell, Corp.
QUESTIONS?

								
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