This document discusses methods for extending the service life of existing bridges, including: 1. Better calculation methods such as improved shear capacity formulas, probabilistic analysis, and non-linear finite element models. 2. Better inspection methods like non-destructive testing and proofloading to assess bridge condition. 3. Better rehabilitation techniques like using carbon fiber sheets, external prestressing, and jacketing to strengthen bridges in need of repair.

1. 30-01-2015
Challenge the future
Delft
University of
Technology
Extending the service life
of existing bridges
Eva Lantsoght

2. 2Extending the service life of existing bridges
Overview
• Introduction
• Better calculation methods
• Better inspection methods
• Better rehabilitation methods
• Summary

3. 3Extending the service life of existing bridges
Introduction
Problem Statement
Bridges from 60s and 70s
The Hague in 1959
Increased live loads
heavy and long truck
(600 kN > perm. max = 50ton)
End of service life + larger loads

4. 4Extending the service life of existing bridges
Introduction
Highway network in the Netherlands
• NL: 60% of bridges built before 1976
• First checks since mid-2000s
• 3715 structures to be studied
• 600 slab bridges shear critical
• But: checks according to design
rules
• => Residual capacity???
• Hidden reserves of the bearing
capacity Highways in the Netherlands

5. 5Extending the service life of existing bridges
Introduction
Aging infrastructure in Europe

6. 6Extending the service life of existing bridges
Principle of Levels of Approximation
Model Code 2010
• Approach from fib Model
Code 2010
• Solution strategy = different
levels of approximation
• Eg: Shear capacity in Model
Code 2010

7. 7Extending the service life of existing bridges
Better calculation methods
• Shear capacity
• Testing elements
• Better understanding of
behavior
• Fatigue life of concrete in
compression
• Probabilistic analysis
• Improved live load factors
• Advanced analysis
• Non-linear finite element
models

8. 8Extending the service life of existing bridges
Shear capacity
Importance of shear behavior
Shear failure of the de la Concorde bridge, Laval
=> five people killed, six others seriously injured

9. 9Extending the service life of existing bridges
Shear capacity
Beam shear and punching shear
• Design: shear capacity of slabs
• Flexural failure before shear failure
• Punching shear formulas
• Beam shear formulas over effective width
Beam shear, one-way shear Punching shear, two-way shear

10. 10Extending the service life of existing bridges
Shear capacity
The riddle of shear failure
• Since 1899 (Ritter)
• 1955: collapse of
warehouse
• Most experiments:
• Beams
• Heavily reinforced
• Slender (a/d ≥ 2,5)
• Small size
• Basis for design codes
amount of shear experiments done

11. 11Extending the service life of existing bridges
Shear
Mechanisms of shear transfer

12. 12Extending the service life of existing bridges
Shear
Mechanisms of shear transfer
Concrete in compression
zone
Dowel action
Aggregate interlock
Stirrups

13. 13Extending the service life of existing bridges
Shear capacity
Distance between load and support
Shear span to depth ratio: Kani’s valley
Influence of the support

14. 14Extending the service life of existing bridges
Shear capacity
Influence of reinforcement ratio

15. 15Extending the service life of existing bridges
Shear capacity
Size effect in shear

16. 16Extending the service life of existing bridges
Shear capacity
ACI Formula 318-11 11-5

17. 17Extending the service life of existing bridges
Background
Design codes for Shear
0
500
1000
1500
2000
2500
1 1,2 1,4 1,6 1,8 2 2,2 2,4 2,6 2,8 3a/d
Pu(kN)
Regan SS
NEN SS
ACI SS
EN
Different design codes – different approaches

18. 18Extending the service life of existing bridges
Shear failure

19. 19Extending the service life of existing bridges
Testing elements – slabs in shear
Size: 5m x 2,5m (variable) x 0,3m = scale 1:2
Continuous support, Line supports
Concentrated load: vary a/d and position along width

20. 20Extending the service life of existing bridges
Testing elements
Slabs in shear
• 2nd
series experimental work:
• Slabs under combined loading
• Line load
• Preloading
• 50% of strength from slab strips
• Concentrated load
• loading until failure
• Conclusions from 1st
series valid
when combining loads?
• Total: 26 experiments, 8 slabs

21. 21Extending the service life of existing bridges
Testing elements – slabs in shear

22. 22Extending the service life of existing bridges
Testing elements – slabs in shear
BS = 0,5m wide BX = 2,0m wide

23. 23Extending the service life of existing bridges
Testing elements – slabs in shear
• Transverse load redistribution
• Geometry governing in slabs
• Location of load
• result of different load-carrying paths
• Mid support vs end support
• influence of transverse moment
• Wheel size
• more 3D action

24. 24Extending the service life of existing bridges
Testing elements – slabs in shear
5000 1000 1500 2000 2500
b (mm)

25. 25Extending the service life of existing bridges
Testing elements – slabs in shear
45° load spreading - Dutch practice 45° load spreading – French practice
Or: fixed value (eg. 1m)

26. 26Extending the service life of existing bridges
Testing elements – slabs in shear
Modified Bond Model (1)
• Based on Bond Model
(Alexander and
Simmonds, 1990)
• For slabs with
concentrated load in
middle

27. 27Extending the service life of existing bridges
Testing elements – slabs in shear
Modified Bond Model (2)

28. 28Extending the service life of existing bridges
Testing elements – slabs in shear
Modified Bond Model (3)
• Adapted for slabs with concentrated
load close to support
• Geometry is governing as in
experiments
• Determine factor that reduces capacity
of “radial” strip
• Maximum load: based on sum
capacity of 4 strips

29. 29Extending the service life of existing bridges
Testing elements
beams in shear
• Beams from existing
bridges
• Beams cast in the
laboratory
• Different combinations of
load
• Comparison with Eurocode
• Recommendations for
M/Vd

30. 30Extending the service life of existing bridges
Testing elements
Beams in shear
• Changing position of load
• Effect of moment distribution on shear
capacity
• Photogrammetry + LVDTs

31. 31Extending the service life of existing bridges
Testing elements
Time dependent effects
• Time dependent effects
• Speed of loading vs direct
tensile capacity
• Beams under sustained load
in shear

32. 32Extending the service life of existing bridges
Testing elements
Transversally prestressed decks
• Bridge decks cast in
between girders
• Compressive membrane
action => increased capacity

33. 33Extending the service life of existing bridges
Testing elements
Prestressed beams

34. 34Extending the service life of existing bridges
Application of test results to analysis
Live load models
Truck load, AASHTO
Tandem loads, EC

35. 35Extending the service life of existing bridges
Application of test results to analysis
• Loading at edge
• Asymmetric effective width

36. 36Extending the service life of existing bridges
Application of test results to analysis
Effective width per axle instead of per wheel print

37. 37Extending the service life of existing bridges
Application of test results to analysis
• Larger effective width
• Smaller shear stress
• More economic design
• Sharper assessment

38. 38Extending the service life of existing bridges
Improved fatigue models
Reference fc,mean,max (MPa) Influence fc?
Petkovic et al., 1990 95 MPa No
Kim & Kim, 1996 103 MPa Yes
Hordijk et al., 1995 78,2 MPa No
Lohaus et al., 2011
Lohaus & Anders, 2006
170 MPa
(fibers)
MC 90 too
conservative
Tue & Mucha, 2006 65 MPa Yes
 Effect of high strength concrete?
 Conclusion fib task group 8.2: lower fatigue strength
for high strength concrete
 Linear S-N curve starts at+- 100 cycles
 Effect of few heavily loaded trucks?

39. 39Extending the service life of existing bridges
Fatigue testing

40. 40Extending the service life of existing bridges
Fatigue testing

41. 41Extending the service life of existing bridges
Existing codes for fatigue
Model Code 2010, fck in formules, γc = 1,5
EC 2-2: very conservative
EC 2-2 + NB: jump at Ni = 106
γc = 1,35
Kim & Kim: influence fc’ , γc = 1,5

42. 42Extending the service life of existing bridges
Database of test results fatigue
• 429 test results
• 234 no fibers
• ≤ 145 MPa
• 195 with fibers
• ≤ 226 MPa

43. 43Extending the service life of existing bridges
Improved fatigue model for analysis
• Proposed replacement
for Dutch National Annex
• k1 = 1
• γc,fat = γc = 1,5
• At 1 cycle: Smax = 1
• Iterative, but stable
• 1st iteration, try Smax = 1
• Converges at 3rd
iteration
( ) 66 1
log for 10
1
max
i i
max,EC
S
N N
S
−
= ≤
−
3
1 1 1 *
250 7
ck
max,EC i
f
S R
  
= − − − ÷ ÷
  
* min
i
max,EC
S
R
S
=
( ), 1 0 1
400
ck
cd fat cc cd
f
f k t fβ
 
= − ÷
 

44. 44Extending the service life of existing bridges
Improved fatigue model for analysis
• Comparison to test results forSmin = 0,05

45. 45Extending the service life of existing bridges
Probabilistic analysis
Full reliability analysis
• Full reliability calculation
• Variability of material
properties
• Variability of load effects
• Variability of dimensions
• Combination with finite
element models
• Spatial variability of material
properties
• Result: chance of failure

46. 46Extending the service life of existing bridges
Probabilistic analysis
Improved live load factors
• Data of real traffic
• WIM campaign
• Probabilistic analysis
• Different levels
• Analysis not same as
design
• Load factors for levels:
• Repair level
• Unfit for use level
• Code: NEN 8700
Steenbergen, R. D. J. M. et al., 2011

47. 47Extending the service life of existing bridges
Non-linear finite element models
• Advanced models
• Improved material models
• Tensile capacity of concrete
• Fracture mechanics
• Requires computational
power
• LoA IV method
• Better estimate for critical
infrastructure

48. 48Extending the service life of existing bridges
Non-linear finite element models
Link with experiments
(Doorgeest, 2012)
Models of 1,5m wide
a = center-to-center distance
between load and support
Effective width from shear stress
distribution over support

49. 49Extending the service life of existing bridges
Non-linear finite element models
Link with experiments
Models of 2,5m wide
a = center-to-center distance
between load and support
Effective width from shear
stress distribution over support

50. 50Extending the service life of existing bridges
Non-linear finite element models
Link with experiments
Models of 3,5m wide
a = center-to-center distance
between load and support
Effective width from shear
stress distribution over support

51. 51Extending the service life of existing bridges
Non-linear finite element models
Link with experiments
• French load spreading
method gives safe estimate
of beff
• NLFEA: beff depends slightly
on slab width
• NLFEA: influence of a/d less
than in French method
• French method
sufficient for LoA 1

52. 52Extending the service life of existing bridges
Better inspection methods
• Non-destructive test
methods
• Proofloading
• Bridge management
systems

53. 53Extending the service life of existing bridges
Non-destructive test methods
• Electrical resistivity
• Gives idea of corrosion rates in
concrete decks reinforced with
steel

54. 54Extending the service life of existing bridges
Non-destructive test methods
• Ground penetrating radar
• Objects inside depth of
concrete
• Reinforcement
• Wire meshes

55. 55Extending the service life of existing bridges
Non-destructive test methods
• Infrared thermography
• Detect concrete defects:
• cracks
• delaminations
• concrete disintegration

56. 56Extending the service life of existing bridges
Non-destructive test methods
• Combine methods to get
overview of condition of bridge
• More info: NDToolbox
• www.ndtoolbox.org

57. 57Extending the service life of existing bridges
Proofloading
Case Ruytenschildtbrug
• Proofloading to assess
capacity of existing bridge
• Study cracks and
deformations for applied
loads
• Crack formation: acoustic
emissions measurements
• Ruytenschildtbrug: testing to
failure

58. 58Extending the service life of existing bridges
Proofloading
Case Ruytenschildtbrug

59. 59Extending the service life of existing bridges
Proofloading
Finding position of test loads
• Skewed viaduct
• Distance for shear av = 2,5dl
• Edge distance
• Tandem loads of Eurocode
• Result: center of axle at
2,5dl

60. 60Extending the service life of existing bridges
Proofloading
Failure mode
• Monte Carlo simulation
( )shear momentfp P= <
( )f shear momentp P uc uc= >
( )
( )
1/3,
1/3
,
, , ,
100
100
Rd c
l ck
Ed c
shear
Rd c
Rd c test l c mean
C
k f
v
uc
Testv C k f
Predicted
ρ
γ
ρ
= =
2
2
s y
Ed
moment
Rd
s u
M
a
A f d
M
uc
Test aM
A f d
Predicted
 
− ÷
 = =
   
− ÷  ÷
   

61. 61Extending the service life of existing bridges
Probability of shear failure
Test/Predicted shear
From slab shear experiments TU Delft Test/Predicted wrt
Eurocode expression

62. 62Extending the service life of existing bridges
Probability of shear failure
Resulting limit state function

63. 63Extending the service life of existing bridges
Probability of shear failure
Results
• Span 1: 85,2% probability failure in bending before failure in
shear
• Span 2: 45,9% probability failure in bending before failure in
shear
• Span 2: 98,2% probability failure in bending before failure in
shear when using from slab shear experiments
V
Test
Predicted
 
 ÷
 

64. 64Extending the service life of existing bridges
Probability of shear failure
Uncertainties
• Effect skew on effective
width
• Material properties?
• Samples after proofloading
• Steel samples
• Concrete cores

65. 65Extending the service life of existing bridges
Analysis Ruytenschildtbrug
With Modified Bond Model
• Using measured average
material properties
• First span
• Ptot =2864kN
• Ptest=3049kN
• Second span
• Ptot = 3816kN
• Ptest= 3995 kN
• Failure in bending before shear

66. 66Extending the service life of existing bridges
Bridge management systems
• For bridge owners
• Better management of data
• Quick access to
• as-built plans
• Inspection reports
• Prioritize inspection and
repair efforts

67. 67Extending the service life of existing bridges
Better rehabilitation techniques
• Carbon fiber sheets
• External prestressing
• Jacketing of columns
• Overlays
• ECC
• UHPC
• Structural health monitoring

68. 68Extending the service life of existing bridges
Carbon fiber sheets
• External reinforcement
• Increases bending moment
capacity
• Problem: delamination of
sheets

69. 69Extending the service life of existing bridges
External prestressing
• Increase prestressing force
• For example, necessary
after loss of prestress from
time-dependent effects
• Creep
• Shrinkage
• Relaxation

70. 70Extending the service life of existing bridges
Jacketing of columns
• Steel jacketing
• Prestressed jacketing
• Place concrete under triaxial
compression
• Larger capacity
• Larger ductility
• In seismic regions

71. 71Extending the service life of existing bridges
Overlays
• UHP = ultra high
performance concrete
• High strength
• High ductility
• ECC = engineered cement
composites
• Higher capacity

72. 72Extending the service life of existing bridges
Structural health monitoring
• Information from sensors
• Real-time updating online
• Bridge warns when
problems arise
• Reality: lots of data,
interpretation sometimes
difficult

73. 73Extending the service life of existing bridges
End-of-life of bridges
• Repair and rehab before
replacing
• When need for replacing:
recover materials as much
as possible
• Recycled aggregates
• Can be reused for foundations
and pavements

74. 74Extending the service life of existing bridges
Sustainability

75. 75Extending the service life of existing bridges
Summary & Conclusions
In order to extend the service life of
existing bridges, combine the
following:
1.Better calculation methods
(Research!)
2.Better inspection techniques
3.Better rehabilitation techniques

76. 76Extending the service life of existing bridges
Contact:
Eva Lantsoght
E.O.L.Lantsoght@tudelft.nl
elantsoght@usfq.edu.ec