1. FAILURE MECHANISMS OF WIDENING
REINFORCED CONCRETE DECK SLABS
WITH EXTERNAL PRESTRESSING
Tokyo, June 24th, 2016
Fakhruddin
13D51340
Supervisor: Prof. Junichiro NIWA
Graduate School of Science and Engineering
Department of Civil Engineering
Tokyo Institute of Technology
Doctoral Thesis Presentation
東京工業大学
Tokyo Institute of Technology

2. No. 2
Shinjuku line, Tokyo metropolitan expressway
Common technique:
Existing PC tendon should
be connected to new slab.
Existing structure
New technique is
proposed.
Traffic capacity reached the design limit  Widened
16 m
Widening structure
21 m
2.5 m
Limitations:
High effect on traffic, great
time and cost
Background

3. No. 3
Demolished
concrete
Existing PC
tendon Sleeves
New PC
tendon
New slab
Mortar
anchorage
1000 mm
Drawbacks
 The existing PC tendon should be
connected to the new slab.
 High volumes of cast-in-place
concrete and formwork are required.
Proposed method
Advantages
 The existing PC tendon does not
need to be connected to the new slab.
 Precast ribs and PC slabs 
decrease cast-in-place concrete.
New
rebar
New
slab
Old rebar Connection
Precast rib
PC cables
Demolished concrete
Existing slab
Existing PC
tendon
Precast
PC slab
Rapid construction can be achieved.High effect on traffic, great time and cost
Conventional vs new method
Conventional method

4. No. 4Construction method
1. Remove the barrier rail
2. Install precast ribs and introduce
prestressing force
Precast rib
PC cable
3. Put precast PC slab on precast rib
4. Expose and connect rebars
5. Cast-in-place new deck slab
6. Introduce prestressing force
Precast slab
New rebarsOld rebars
Connection
Cast-in-place
new deck slab
Interface
Barrier rail
Existing structure

5. No. 5
Precast rib PC cable Precast slab
Cast-in-place slabExisting slab
PC deck slab test
Cast-in-place
new deck slab
Old slab
Vehicle loadInterface
1. To investigate the behavior of
the interface between old and
new deck slabs
2. To evaluate the equation in
recent design guidelines
1. To investigate the behavior of
PC deck slabs
2. To investigate the behavior of
the interface
3. Proposal of predictive equation
Objectives

6. No. 6
Chapter 7:
Conclusions and recommendations
Chapter 2: Literature review
Chapter 1: Background and objectives
Outline of thesis
Behavior of interface between
new and old deck slabs
Chapter 3:
Experimental study on shear
behavior of the interface between
old and new deck slabs
Chapter 4:
Failure mechanisms of interface
between old and new deck slabs
Behavior of widening PC deck
slabs under concentrated load
Chapter 5:
Experimental study on behavior
widening PC deck slabs under
concentrated load
Chapter 6:
Shear resisting mechanisms and
affecting factors

7. Chapter 2:
Literature review

8. No. 8Previous studies (1)
Surface PC rod Rebar
Interlocking
force
Friction
Dowel action
Resistance mechanism of the interface results from interlocking force,
frictional force and dowel action.
Vertical load (V)
Joint opening (w) and displacement
(d) occur at the interface
PC rod and transverse rebars
responds by a tensile force (Asss)
Interlocking force, tc is developed at
the interface
Shear slip along interface inducing
bending stress to the transverse
rebars, Asts (dowel action)
Maekawa et al. 1997: Behavior of RC interface
(Stress transfer across interfaces in RC due to aggregate interlock and dowel action, J. Materials, Conc. Struct.,
Pavements, JSCE)
Mechanical characteristic of RC interface

9. No. 9Previous studies (2)
Nie et al. 2012: Behavior of composite joints
(Mechanical behavior of composite joints for connecting existing concrete bridges and steel-concrete composite
beam, Journal of Construction Steel Research)
Old
concrete
New concrete
Test results
Shear
failure
Specimen designProposed bridge widening technique
 Shear capacity was greatly affected by reinforcement ratio and
surface roughness.
 Influences of prestressing have not been discussed.
Specimen
Embedded
steel bars
Surface
roughness
Vu
(kN)
Failure mode
1 D16@200 Rough 1981.0
Shear failure of the
interface between old
and new concrete
2 D16@200 Smooth 745.5
3 D16@400 Rough 961.0
Failure mode
Old
concrete
New concrete

10. No. 10Previous studies (3)
Pirayeh et al. 2014: Behavior of full-scale bridge deck slab
(FRP slab capacity using yield line theory, J. Compos. Constr.)
Panel-to-
panel seam
Prestressing
Loading
point
 The modified yield line theory demonstrated a very good accuracy.
Specimen design
5490
Unit: mm
4880
Joint / seam
Compound shear-flexural mechanism
Application of yield line
  yypyxxpx lMlMIWD 
   vvpyypyxxpx lVlMlMIWD d
Since the failure mechanism might be influenced by panel-to-panel seam, the yield
line analysis was modified.
Modification due to
panel-to-panel seam
*IWD : Internal Work Done

11. Chapter 3:
Experimental study on shear behavior of the interface
between old and new deck slabs

12. No. 12
Top View
f'c=40
MPa
500
Specimen design and parameters
1. Prestressing level (si)
2. Connection between steel bars
si = 0.25, 0.5,
1.0 and 2.0 MPa
Mortar grouted
sleeves
Enclosed
welding
3. Reinforcement ratio (r)
r = 0.51 and 0.79% r = 1.01%
4. Surface roughness
Total = 9 specimens
Experimental parameters
: Strain gauges
Unit : mm Front View
Old slab New slab
200
Old slab
250 900 250
PC
rods
: Transducers
si
Rough surface Smooth surface
f'c=40
MPa
f'c=30 MPa

13. No. 13Fabrication procedures
Preparing rebars connection
(mortar grouted sleeves)
Setting rebars in to
the formwork
Casting the old slab
(f’c=40 MPa)
Surface treatment
(using retarder)
Casting the new slab
(f’c=30 MPa)
Double-shear test

14. No. 14Series I - Effects of prestressing level
- The ultimate load tended to be increased as the initial prestressing
level increased.
- The increment of strain at the bottom PC rods became significant
after the diagonal tension crack occurred at the interface.
100 205 2515
200
400
600
800
1000
1200
Strain (x10-3)
Load (kN)
Diagonal
tension crack
EW-P0.25
EW-P0.5
EW-P1.0
EW-P2.0
Comparison of ultimate loads Load-strain curves
0
200
400
600
800
1000
1200
Load (kN)
Specimens (enclosed welding)
+11.8%
+22.2%
EW-P0.25
EW-P0.5
EW-P1.0
EW-P2.0
-2.9%
Bottom PC rod

15. No. 15Series I- Crack and failure pattern
 Specimens generally failed by
interface cracking between old and new
deck slabs.
 When specimens reached the
ultimate load, concrete crushed at the
compression zone.
Old slab
(f’c=40 MPa)
New slab
(f’c=30 MPa)
(3)
(1)
(2)
Loading test
started
(1) Flexural crack occurred
in constant moment region
(3) Diagonal tension crack
occurred
Crack width
increased
The interface failed
(Concrete crushed)
(2) Joint opening on the
interface
Crushed

16. No. 16Series II – Effects of connection method
Connection method
- By using enclosed welding and mortar
grouted sleeves, the ultimate load decreased.
- The reduction rate of mortar grouted
sleeves was smaller than enclosed welding.
EW-P1.0 SS-P1.0
Comparison of ultimate loads
0
200
400
600
800
1000
1200
NC-P1.0
EW-P1.0
SS-P1.0
-11.2%
-2.3%
Load (kN)
Specimens
Welding
NC-P1.0
Enclosed welding Mortar grouted sleeves
Sleeve
Inlet hole Outlet hole
Rebar
Mortar
Sealing
Cross section
of interface
Mortar grouting
135 mm 135 mm
Due to single test specimen, it cannot be
concluded that mortar grouted sleeves is
better than enclosed welding.

17. No. 17Series III – Effects of reinforcement ratio
Specimens
r
(%)
si
(MPa)
Load (kN)
Pc Pu Vu
EW-P1.0 0.51
1.0
401.7 1011.4 505.7
EW16-P1.0 0.79 412.0 979.0 489.5
EW13-S125 1.01 740.0 866.2 433.1
r: reinforcement ratio, si: initial prestressing level Pc: the
first joint opening load, Pu: ultimate load, Vu : shear capacity.
r = 1.01% (4D13)
With the increase in reinforcement ratio:
 The stiffness and the first cracking
load of the interface increased.
 The ultimate load decreased.
5 100 15 20
200
400
600
800
1000
1200
Displacement (mm)
Load (kN)
EW13-P1.0
EW16-P1.0
EW13-S125
25
0.79%
0.51%
1.01%
Cross section of interface
Load-displacement curves
As the reinforcement ratio increases, the
ultimate load increases significantly.
This study:
Previous research (Maekawa et al.)
125r = 0.51% (2D13)
and 0.79% (2D16)

18. No. 18Series IV – Effects of surface roughness
Load-displacement curves
Rough surface Flexural crack and combination of diagonal and shear crack
Smooth surface Shear crack
Crack pattern
Ultimate load of the smooth surface extremely decreased by 64% as compared to
that of rough surface.
Surface roughness significantly affected the behavior of the interface.
Ultimate load
2. Intentionally roughened by using retarder.
1. Without further treatment after de-molding.
Load (kN)
Displacement (mm)
0
200
400
600
800
1000
1200
0 5 10 15 20 25
Rough surface
Smooth surface
Crack pattern
Shear crack
EW-Smooth
Old slab New slab
Flex. crack
EW-P1.0 (Rough)
Shear
crack
Old slab New slab

19. No. 19Summaries of Chapter 3
1. The increase in the initial prestressing level increases the first
joint opening load and the shear capacity of the interface.
However, its increment did not proportional with the initial
prestressing level.
2. The connection method between steel bars does not affect the
shear capacity of the interface significantly, as the location of the
connection is sufficiently far from the interface.
3. The increase in the reinforcement ratio from 0.51% to 1.01% tends
to decrease the shear capacity of the interface. However, the
stiffness and the first cracking load increased with the increase in
the reinforcement ratio.
4. The surface roughness of the interface shows a significant
contribution on the behavior of the interface, including the crack
pattern and the shear capacity.

20. Chapter 4:
Failure mechanisms of the interface between old and
new deck slabs

21. No. 21Effect of prestressing level on failure behaviors
Height of joint opening (hop) decreased with increasing the prestressing level
: Flexural crack
: Diagonal crack
: Shear crack
113.3 71.8
0.25 MPa 2.0 MPa
AJO
Aeff.
AJO
0.25 MPa
Aeff. = effective area; AJO = area of joint opening
Aeff.
2.0 MPa
With decreasing the hop :
The effective area of the interface
(Aeff) substantially contributing to
the shear stress increased.
Shear capacity increased.
Failure portions

22. No. 22Effect of reinforcement ratio (r) on failure behaviors
: Strain gauges
r = 0.51% r = 1.01%
Compression arch was formed in r = 0.51% following diagonal crack.
Comparison of concrete strain at the top fiber
0
400
800
1200
-1000 -500 0 500
Strain (x10-6
)
Load (kN)
Diagonal crack
Compr. Tension
: Flexural crack
: Location of
concentrated flow
: Diagonal crack
: Shear crack
: 0.51%
: 1.01%
0.51% Compression zone still formed until
failure.
1.01% Compression zone gradually reduced
and formed the tension zone.
When diagonal tension occurred:
Reinforcement ratio greatly affected failure behavior.
Failure portions

23. No. 23Effect of surface roughness on failure behaviors
Rough
Diagonal crack was formed in the rough interface Compression arch
: Flexural crack
: Location of
concentrated flow
: Diagonal crack
: Shear crack
Smooth
In a rough interface, a high
normal stress was applied to the
interface.
Normal stress > tensile strength
of concrete
Diagonal tension crack
Compression arch was formed
Failure portions
0
200
400
600
800
1000
1200
0 500 1000 1500 2000
EW-P1.0
EW-Smooth
Strain increment (x10
-6
)
Load (kN)
Load-PC rod strain The formation of
diagonal crack

24. No. 24Bending moment effect
Prestressing level increased and affected the shear capacity of interface.
Large moment and high shear  diagonal tension cracks occurred.
Joint opening and displacement increased significantly  greater elongation
and increased the inner force of PC rods.
Bending moment effect
Bending moment effect
Joint opening
si
si
si
si
scr scr
scrscr
1. At the beginning of load
si : Initial prestressing force
2. Diagonal tension cracking load
scr : Prestressing force at the cracking load
Diagonal
tension crack
0
200
400
600
800
1000
1200
0 1000 2000 3000
Strain increment ()
Load (kN)
Load-strain increment at
PC rod
Diagonal
tension

25. No. 25
0
100
200
300
400
500
600
0 100 200 300 400 500 600
JSCE
AASHTO
MC2010
V
EXP
(kN)
V
CAL
(kN)
0
100
200
300
400
500
600
0 100 200 300 400 500 600
JSCE
AASHTO
MC2010
V
EXP
(kN)
V
CAL
(kN)
Calculation-I (Initial prest.) Calculation-II (Ultimate prest.)
  cysc ApfpV tt cossinsin 2

  b
ny
b
cc pff


1
' st t /08.0 ys f
  yn fp /7.110175.0 s 
Where:
- JSCE Standard Specification (2007) - AASHTO-LRFD 2007
- fib Model Code 2010
 cyvfc PfAcAV  
  ycubecyncu fff ,21 rrstt 
Accuracy of design guidelines
Accuracy of all design guidelines improved if the bending moment
effect was considered.

26. No. 26Summaries of Chapter 4
1. The failure behavior of the interface is greatly affected by the initial
prestressing level, reinforcement ratio and surface roughness of the
interface.
2. Due to the opening of joint, a remarkable increment of the tensile
stress at the prestressing rod is observed. Furthermore, it affects
the value of bending moment applied to the interface between the
old and new deck slabs.
3. The predicted shear capacity proposed by JSCE Specifications,
AASHTO and fib Model Code 2010 underestimate the ultimate shear
capacity of the experimental results because the bending moment
effect has not been considered.

27. No. 27
Chapter 7:
Conclusions and recommendations
Chapter 2: Literature review
Chapter 1: Background and objectives
Outline of thesis
Behavior of the interface between
new and old deck slabs
Chapter 3:
Experimental study on shear
behavior of the interface between
new and old deck slabs
Chapter 4:
Failure mechanism the interface
between new and old deck slabs
Behavior of widening PC deck
slabs under concentrated load
Chapter 5:
Experimental study on behavior
of widening PC deck slabs under
concentrated load
Chapter 6:
Shear resisting mechanisms and
affecting factors

28. Chapter 5:
Experimental study on widening PC deck slabs with
unbonded tendon under concentrated load

29. No. 29Background
1. Connection between new and old
deck slabs
2. RC slab and precast
PC slab
Double-shear
test
Slab test supports
on three sides
Connection between the new
and old deck slabs
RC slab and precast PC slab
1. To investigate the behavior of connection between old and new slab
2. To investigate the behavior of prestresssed concrete deck slabs
3. Proposal of predictive equation
Objective:

30. No. 30Experimental program
No. Parameters Specimens
Prest. level,
si (MPa)
Concrete strength,
f’c (MPa)
Surface
roughness
Old slab New slab
1. Control specimen SL-P1.0 1.0 50 50 Rough
2. Effect of initial
prest. level
SL-P0.5 0.5
50 50 Rough
3. SL-P2.0 2.0
4. Effect of concrete
strength
SL-C30
1.0 50
30
Rough
5. SL-C70 70
6.
Effect of surface
roughness
SL-Smooth 1.0 50 50 Smooth
Interface:
rough and smooth
Smooth surfaceRough surface
SL-P1.0 / 30 / smooth
Slab Prest. level
Concrete strength
Smooth surfaceOld slab
50 MPa
New slab
30, 50 and 70
Load
si = 0.5, 1.0
and 2.0 MPa

31. No. 31Details of specimen
NewslabOldslab
725
9D6 @150mm
1700
1225
500
A A'
B'
B
Long. rebars 9D16
100 550
Long. rebars 9D10
PC rod f17
100475 475
1500
Tested span
100
50
625 500
Old slab New slab
Transv. rebars 9D6
PC rod f17Transv. rebars 9D6
100
Reinforcement layout
Section A-A’ Section B-B’
Fixed support
Fixed support
Fixed support
Unit : mm

32. No. 32Fabrication procedures
1. Fabricating formwork
and rebars for old slab
2. Coating formwork at
location of interface with
retarder
3. Casting old slab
part
4. Spraying concrete
surface with high
pressure water
6. Casting new slab part5. Fabricating new slab
rebars
Rough

33. No. 33Picture of loading test
PC rods
Fixed
Old slab
New slab
Bolt
Deck slabs were restrained at the supporting steel beam and fixed with
high strength steel bolts along the three edges.

34. No. 34Series I - Effect of initial prestressing level
0
40
80
120
160
SL-P0.5
SL-P1.0
SL-P2.0
+30.6% +33.3%
Load (kN)
Increase of initial
prestressing level
Comparison ultimate loads Load-joint opening curves
0
40
80
120
160
0 0.5 1 1.5 2 2.5
SL-P0.5
SL-P1.0
SL-P2.0
Joint opening (mm)
Load (kN)
Pcr=53 kN
Pcr=77 kN
 The ultimate load and the first joint opening load increased as the
initial prestressing level increased.
 At similar load level, the joint opening decreased.
Pcr=63 kN
*Pcr= First joint opening load
π-gauge

35. No. 35Series I - Deflection distributions
 Deflection at the same load level decreased.
 Due to crack opening and displacement which shear cannot be
further transferred, the interface affected the deflection distributions.
362.5 412.5 200 200
Old slab New slab
Transverse direction
475 275 475275
Longitudinal direction
P = 109 kN
-40
-30
-20
-10
0 0 250 500 750 1000 1250 1500
SL-P0.5
SL-P1.0
SL-P2.0
Deflection(mm)
Distance (mm)
-40
-30
-20
-10
0 0 250 500 750 1000 1250 1500
SL-P0.5
SL-P1.0
SL-P2.0
Distance (mm)

36. No. 36Series I - Crack pattern
(2)
(3)
(5)
(4) (4)
(1)
(6)
Shear
failure
Loading test started
(1) Flexural crack occurred
near the free edge
(3) Joint opening initiated at
the interface
Shear failure at the interface
(2) Propagated toward the
loading point
(4) Diagonal tension crack at
the bottom of new deck slab
(5) Tensile crack on the top
surface of the new deck
(6) Concrete near the free
edge crushed
Bottom surface
Free edge
Top surface

37. No. 37Series II - Effect of concrete strength
Specimens
fc’ (MPa)
si
(MPa)
Load (kN)
Old
slab
New
slab
Pcr Pu
SL-C30 50.7 33.7
1.0
55.0 136.0
SL-P1.0 53.4 56.5 63.0 141.0
SL-C70 52.3 69.6 69.0 153.0
Old slab
50 MPa
New slab
30, 50 and 70Load
si: initial prestressing level Pcr: the first joint opening
load, Pu: ultimate load.
Load-deflection curves
0
40
80
120
160
0 10 20 30 40
SL-C30
SL-P1.0
SL-C70
Deflection (mm)
Load (kN)
 The first joint opening load increased.
 Deflection at ultimate load decreased.
 The ultimate load increased.
With increase of the concrete strength:
Pcr
Load-deflection behavior:
 Similar behavior up to first yielding of
the lower transverse rebars
First yielding
of transverse
rebars

38. No. 38Series III - Effect of surface roughness
SmoothRough
Load-deflection
Specimen Surface
du
(kN)
Pcr
(kN)
Pu
(kN)
SL-P1.0 Rough 22.9 63.0 141.0
SL-Smooth Smooth 27.7 55.0 139.0
du : displacement at Pu, Pcr : the first joint opening
load, Pu : the peak load
0
40
80
120
160
0 10 20 30 40
Deflection (mm)
Load (kN)
Smooth
Rough
Joint opening
propagates along
the length
First joint opening
load, Pcr
Rough surface Smooth surface:
 First joint opening load and
deflection decreased.
 Ultimate load slightly decreased.
Load-deflection behavior:
 Similar behavior up to prior to failure
 Prior to failure, the stiffness of
smooth surface decreased due to
shear slips.

39. No. 39Summaries Chapter 5
1. The increase in the initial prestressing level and concrete strength
of the new deck slab increase the shear capacity of the widening PC
deck slabs. However, the ultimate shear capacity does not increase
proportionally with the initial prestressing level and the concrete
strength.
2. The variation of surface roughness at the interface does not show
any remarkable influences on the shear capacity of the deck slabs,
as long as the amount of prestressing force is sufficiently
introduced to the interface.
3. Due to excessively large crack opening and shear displacement, the
interface cannot transfer the shear stress to the adjacent deck slab.
Thus, the deflection distribution of the deck slab is modified
significantly.

40. Chapter 6:
Shear resisting mechanisms of the widening PC deck
slabs under concentrated load

41. No. 41Failure mode (1)
Failure modes How to identify?
Punching shear Punching occurred before yielding of reinforcement.
Flexural failure All reinforcement yielded before the occurrence of
compression failure.
Shear failure at the
interface
Shear failure occurred at the interface before yielding of all
tensile reinforcement.
Shear-flexural failure Shear crack occurred after yielding of all reinforcement.
Certain potential failure modes:
Bottom surfaceTop surface
Typical shear failure at the
interface
Typical flexural yield line pattern of
the slabs supported under three fixed
1. Crack pattern

42. No. 42Failure modes (2)
Some transverse rebars were not
yielded at failure.
Failure mode was shear failure at the interface between old and new slabs.
0
40
80
120
160
-1000 0 1000 2000 3000
LL-1 LL-2 LL-3
Load(kN)
Strain (x10
-6
)
0
20
40
60
80
100
120
140
160
-1000 0 1000 2000 3000
TL-1
TL-2
TL-3
TL-4
TL-5
TL-6
Load(kN) Strain (x10
-6
)
Longitudinal rebars Transverse rebars
All longitudinal rebars yielded.
y y
2. Strain of rebars

43. No. 43Failure modes (3)
0
40
80
120
160
-500 0 500 1000 1500 2000
SL-P1.0
SL-P2.0
SL-C30
SL-C70
SL-Smooth
Load(kN)
Strain (x10
-6
)
y
0
40
80
120
160
-500 0 500 1000 1500 2000
SL-P1.0
SL-P2.0
SL-C30
SL-C70
SL-Smooth
Load(kN)
Strain (x10
-6
)
y
50 mm from the interface 250 mm from the interface
The strain varied along the length of rebars and was the highest at 50 mm
from the interface.
 Specimens tended to be failed just after yielding of the strain gauge at 50
mm from the interface.
Failure was governed by loss of confinement of transverse rebars.

44. No. 44Effect of prestressing on resistance mechanism (1)
0
40
80
120
160
-500 0 500 1000
SL-P0.5 SL-P1.0
Load(kN)
Strain (x10
-6
)
Specimen
Prest. level
(MPa)
Surface
roughness
fps (MPa) Dfp
(MPa)Initial Ultimate
SL-P0.5 0.5
Rough
161.4 240.0 78.6
SL-P1.0 1.0 372.2 436.2 109.0
The frictional force contribution increased with the increase in the
prestressing level.
fps: tensile stress of PC rod, Dfp: Stress increment of the PC rods;
The stress increment increased
When the prestressing level increased
Frictional force which was
transferred to the interface increased
Frictional force contribution

45. No. 45Effect of prestressing on resistance mechanism (2)
0
40
80
120
160
-500 -400 -300 -200 -100 0
SL-P0.5 SL-P1.0
Load(kN)
Strain (x10
-6
)
Interlocking force contribution
 With the higher prestressing level,
the higher compression force can
develop at the top fiber of interface.
 For a compression force smaller
than the one necessary for resisting
the applied load, the shear slip can be
occurred once the joint opened.
Shear slip at SL-P0.5Concrete strains
Interlocking force contribution increased with increasing prestressing level.
Bottom view

46. No. 46
 Friction : sn (P=0.5) < sn (P=1.0)
 Interlocking : tc (P=0.5) < tc (P=1.0)
sn
d
Asss
Asts
Asss
Asts
tc
sn
sn
sn
New slab Old slab
tc
Asss
Asss
Asts
Asts
sn
sn
sn
New slab Old slab
sn
Effect of prestressing on resistance mechanism (3)
SL-P0.5 (rough, sn = 0.5 MPa) SL-P1.0 (rough, sn = 1.0 MPa)
Schematic of concrete interface
tc : interlocking force
sn : compressive stress of PC rod
ss : tensile stress of rebars
ts : shear stress of rebars
d : shear slip
Prestressing level equal to or larger than 1.0 MPa provide better shear
resistance mechanism than that of the prestressing level of 0.5 MPa.

47. No. 47
0
40
80
120
160
-500 0 500 100015002000
SL-P1.0 SL-Smooth
Load(kN)
Strain (x10-6
)
Effect of surface on resistance mechanism (1)
Frictional force and dowel action contributions
0
40
80
120
160
-500 0 500 1000 1500 2000
SL-P1.0 SL-Smooth
Load(kN) Strain (x10
-6
)
Transverse rebars strainsPC rod strains
 Rough interface produced the
higher strain increment.
The measured load in smooth
surface was higher than rough surface.
Rough interface Frictional force contribution increased.
Smooth interface Dowel action contribution more predominates

48. No. 48Effect of surface on resistance mechanism (2)
Interlocking force contribution
Concrete strains
 Rough Compression
Smooth Tension
0
40
80
120
160
-500 -250 0 250 500
SL-P1.0 SL-Smooth
Load(kN)
(compression) (tension)
Joint
opening
propagated
SL-Smooth
Propagation of joint opening
Shear slip (bottom surface)
Behavior of top fiber:
Surface roughness greatly affected the overall resistance mechanism.

49. No. 49
50
50 50750
500
150
Mesh size
Prestressing
force
Three-dimensional finite element mesh
Three dimensional FEM analysis
DIANA (Ver. 9.5)
1. To determine the proper interface element model
2. To compare the experimental load-deflection curves
3. To compare the experimental crack pattern
Objectives
Unit: mm

50. No. 50FEM vs Experimental failure load
FEM analyses:
 Good agreement to
predict experimental
failure load
0
40
80
120
160
0 10 20 30
EXP
FEM
Load(kN)
Deflection (mm)
SL-P1.0
0
40
80
120
160
0 10 20 30
EXP
FEM
Deflection (mm)
Load(kN)
SL-P0.5
f
kt
kn
(a) Non-cohesive (SL-P0.5)
c f
c / tanfkt
kn
(b) With cohesive (SL-P1.0)
1. Interface model : Coulombian Friction Model
2. Load-deflection curves
Interface model:
Dependent on the
behavior of interface
once the joint opened.
Slabs
Cohesion, c
(N/mm2)
SL-P0.5 0
SL-P1.0 1.931)
1) AASHTO

51. No. 51FEM - The principle tensile strain
Shear slip
Lack of
integrity
SL-P0.5 (Prest. level of 0.5 MPa)
SL-P1.0 (Prest. level of 1.0 MPa)
Prestressing level of 1.0 MPa provided sufficient shear strength for
transfer the shear force to the adjacent deck slab.
No significant
shear slip Rigidly
connected

52. No. 52Design equation for interface shear capacity
  cysc ApfpV tt cossinsin 2

  b
ny
b
cc pff


1
' st t /08.0 ys f
  yn fp /7.110175.0 s 
Where:
- JSCE Standard Specification (2007) - AASHTO-LRFD 2007
- fib Model Code 2010
 cyvfc PfAcAV  
  ycubecyncu fff ,21 rrstt 
Assumption in above guidelines:
 Area of the interface (Ac) the total area of the interface
 Compressive stress (sc) or force (Pc) sc or Pc at initial load
(a) Rough surface (except for smooth) (b) Smooth surface
45o
a0.5h 0.5h
h hh + a
a0.5h 0.5h
2h h + a 2h
h 26.6o
Slabs under concentrated load:
Investigations on:
 Crack pattern
 Principle tensile strain
 Transverse rebars
Trapezoidal shape
Ac Effective area (Aeff)

53. No. 53Accuracy of recent guidelines
 Design guidelines showed a good
accuracy with the experimental shear
capacities.
 For the smooth surface, the fib MC2010
provides the most accurate predictions
because the dowel action which
predominates in smooth surface has been
explicitly taking into account.
Specimen
su
(MPa)
Aeff.
(mm2)
As
(mm2)
VEXP
(kN)
JSCE AASHTO fib MC2010
VCAL
(kN)
VEXP /
VCAL
VCAL
(kN)
VEXP /
VCAL
VCAL
(kN)
VEXP /
VCAL
SL-P1.0 1.10
30,000 126.7
141.0 150.9 0.93 133.5 1.06 132.6 1.06
SL-P0.5 0.60 109.0 118.8 0.92 113.4 0.96 118.4 0.92
SL-P2.0 2.21 144.0 149.2 0.97 152.9 0.94 147.3 0.98
SL-C30 1.30 136.0 140.8 0.97 134.2 1.01 135.1 1.01
SL-C70 1.17 153.0 151.1 1.01 149.9 1.02 143.9 1.06
SL-Smooth 1.01 40,000 190.1 139.2 148.0 0.94 133.6 1.04 137.2 1.01
0
50
100
150
200
0 50 100 150 200
JSCE
AASHTO
MC2010
V
EXP
(kN)
V
CAL
(kN)

54. No. 54Modified yield line analysis (1)
 Yield line theory is an upper bound limit analysis
dedge
do
dedge
dedge≈d
dedge≈d
Interface
do
 Two modifications taking into account the effect of the interface.
Common deflection profiles Modification of deflection profiles
a. Modification due to the deflection distributions
b. Modification due to moment produced at the interface
  cdd AwpEWD dd0   yypyxxpx lMlMIWD =
   xyerfacepyyypyxxpx lMlMlMIWD  int
 Failure might be influenced by the two-way slab interaction, the
failure load was also computed using the yield line analysis.

55. No. 55Modified yield line analysis (2)
Interface
do
lx lxb1
x
y
d0
Mp
-
ly1
ly2
d0
dedge=d0
y
do
x x
Mx1
Mx2
Mx1
Mx2
Mx1 Mx1
My2
Mx2 Mx2
My2
My2
: positive yield line
: negative yield line
: yield line at the interface
Y
X
Modified equation
M = yielding moment (N-mm)
do = displacement (unit length)
ly1 = width of old slab (mm)
ly2 = width of new slab (mm)
lx = distance fixed-plate (mm)
b = length of loading plate (mm)























1
12
1
21221 2444
y
o
y
y
o
xy
x
o
yx
x
o
yx l
bM
l
lM
l
lM
l
lMIWD
dddd
  yyyxxx lMlMIWD Basic equation

56. No. 56Accuracy of modified yield line analysis
Specimens
PEXP
(kN)
Modified yield line
analysis
PCAL
(kN)
PEXP /
PCAL
SL-P1.0 141.0 149.5 0.94
SL-P0.5 109.0 119.0 0.92
SL-P2.0 144.0 205.6 0.70
SL-C30 136.0 146.5 0.93
SL-C70 153.0 154.0 0.99
SL-Smooth 139.0 148.7 0.93
 The proposed modified yield line analysis demonstrated a good
accuracy to predict the experimental failure load (except for higher
prestressing level).
 For higher prestressing level, the proposed modified yield line analysis
overestimated the experimental failure load.
Failure load of widening PC deck slabs subjected to lower
prestressing force can be evaluated using the proposed equation.
0
50
100
150
200
250
0 50 100 150 200 250
P
CAL
(kN)
P
EXP
(kN)
SL-P2.0
Avg. = 0.90
C.V. = 11.4%

57. No. 57Summaries of Chapter 6
1. Failure mode of widening PC deck slabs is shear failure of the interface
between the old and new deck slabs. It is governed by loss of confinement
of reinforcement crossing the interface.
2. Prestressing level of 1.0 MPa and 2.0 MPa provides sufficient shear stress
to transfer the shear stress to the adjacent deck slabs.
3. FEM model using DIANA system is supposed to be appropriate to simulate
the behavior of widening PC deck slabs supports on three sides. In
addition, a Coulombian friction model with and without cohesion
coefficients are also satisfactorily reproduced the results obtained in the
experimental test.
4. The effective area of the interface (Aeff) for the widening PC deck slabs was
proposed in this study. By using the Aeff instead of the total area of the
interface, the calculation of shear capacity in recent design guidelines show
a good accuracy with experimental shear capacity.
5. The proposed modified yield line analysis demonstrated a good accuracy to
predict the experimental failure load of the PC deck slabs subjected to
lower prestressing force.

58. Chapter 7:
Conclusions and Recommendations

59. No. 59Conclusions (1)
Behavior of the interface between old and new deck slabs
1. When the initial prestressing level increases, the height of the joint opening
decreases. Decreasing the height of joint opening led to increasing the area
to transfer the shear force and compression force across an opened
interface. Thus, the shear capacity of the interface increases.
2. With a greater amount of reinforcement ratio at the interface (equal to
1.01%), the shear capacity decreased. This is caused by a significant
difference between the various prestressing forces in the prestressing rods
as a consequence of the opening of joint.
3. The shear capacity of the interface decreases when the interface between
the old and new deck slabs is changed from rough to the smooth surface.
4. Since the effect of bending moment have not been take into account, the
equation in recent design guidelines underestimated the experimental shear
capacity.

60. No. 60Conclusions (2)
Behavior of widening PC deck slabs under concentrated load
1. The failure mode of the widening PC deck slabs supports on three sides and
subjected to concentrated load was a shear failure of the interface between
the old and new deck slabs.
2. The shear capacity of the PC deck slabs increases with the increase in the
prestressing level and concrete strength of the new deck slab.
3. With the effect of surface roughness of the interface, the shear capacity of
the smooth interface was slightly decreased as compared to the rough
interface.
4. The FEM analysis had a good agreement with the experiment to predict the
ultimate shear capacity of the widening PC deck slabs.
5. The conventional yield line analysis for the cantilever structure was modified
in this study. The results showed that it was found to be capable to accurately
predict the failure load of the widening PC deck slabs, except with the
prestressing level was equal to 2.0 MPa

61. No. 61Recommendations for further research
1. Behavior of the interface between the old and new deck slabs
The variation of the prestressing force in the PC rod due to the effect of size
such as the length of the new deck slab, the area of the interface and
diameter of PC cables have not been covered in this study. Therefore, in
order to develop the equations for predicting the shear capacity of the
interface between the old and new deck slabs in a more general use, the
effect of size needs to be considered in the future work.
2. Behavior of widening PC deck slabs
The parameters which affect the failure mode of the widening PC deck slabs
such as the loading position need to be further studied.

62. Thanks for your kind
attention!
"Study and work hard, be specialist,
be organizer and keep your personality"
[Prof. Niwa]