end region detailing of pretensioned concrete bridge … · end region detailing of pretensioned...
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End Region Detailing of Pretensioned Concrete Bridge Girders
End Region Detailing of Pretensioned Concrete Bridge Girders
Trey Hamilton, PE, PhD, Univ. of FloridaBrandon E. Ross, PE, PhD, Clemson Univ.
Technical Coordinator: Sam Fallaha, PEFDOT Contract BDK75 977-05
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Presentation Outline
Prestressing basics
Background on end region reinforcement
FIB54 Test Program – Service and Ultimate
FIB63 Test Program – Service
Findings
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Prestressing-Hoyer Effect
Flame-cut
Unstressed strand expands back to original diameter
Girder
strand
Girder
strand
Concrete restrains expansion of strandResult: tension stress
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Prestressing-Transfer Length
Transfer Length (60ds)
TendonForce
Effective prestress force in tendon
Tendon FBD
Girder FBD
Bond Stress
Bond Stress
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Prestressing-Transfer Length
Transfer Length (60ds)
TendonForce
Effective prestress force in tendon
Tendon FBD
Girder FBD
Bond Stress
Bond Stress
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Prestressing Effect-Splitting
ez
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Prestressing Effect-Partial Debonding
Excerpt:
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Ultimate Strength-Strut and Tie
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Ultimate strength-Strut and Tie
ConsiderationsFactored Load
Flange GeometryBearing
GeometryStrand Locations
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Lateral-Splitting Failure
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Research Approach
FIB54: Flange Cracks & Ultimate CapacityFIB63: Web Cracks
Finite Element Analysis
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FIB54 10 Specimens (5 beams)
Fabrication Strain data Crack data
Load tests Behavior Capacity
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FIB54 Reinforcement and Prestressing Scheme
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FIB54 Reinforcement and Prestressing Scheme
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FDOT Confinement
Modified Confinement No Confinement (2)
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No Bearing Plate
Bearing Plate
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FIB54 Debonding
45% debonded
13% debonded
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FIB54-ResultsFlange Splitting Cracks
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44.0
99.0
219.5
134.0
104.0
41.5
107.0
0
50
100
150
200
250
Tota
l len
gth
(in.)
Length of flange-splitting cracks
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Analytical Program
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FEA + Experimental-Transfer Length
Stage 1 – outer strands released Stage 2 – all strands released
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FEA + Experimental-Web Stresses
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Shear-span = 10 ft.a/d ~ 2
FIB54 w/ 8 in. deck50 ft. long44 ft. span
62 in.
0.6in. Dia. strands
FIB54-Test Setup
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FIB54-Test Procedures
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Lateral-Splitting(4) specimens
Failure Modes
Web-Shear(4) specimens
Bond-Shear(2) specimens
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Displacement / Slip (in.)
Supe
rimpo
sed
Shea
r (ki
p)
0 0.25 0.5 0.75 1 1.250
100
200
300
400
500
600
700
FNFB WN
WB
Vn = 454kACI
Vn = 528kAASHTO
Bond-shear
Lateral-splitting
Ultimate Capacity
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766
666 698635
508
612
375409
753703
0
100
200
300
400
500
600
700
800
900
HC HU VC VU WN WB FN FB DC DM
Max
imu
m S
hea
r (k
ip)
Lateral-splitting failure
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Ultimate Capacity-Transverse Strain
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14.0
4.4
10.0
29.8
13.1
35.8
12.8
0
5
10
15
20
25
30
35
40
WN WB FN FB
Ave
rag
e st
ress
(ks
i)
V = 375 kip
Ultimate
Includes stress from loading & prestressing
Ultimate Capacity-Transverse StrainSt
ress
in
conf
inem
ent
rein
forc
emen
t
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Ultimate Capacity-Transverse Strain
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75.978.8
74.9
44.2
72.178.5
70.773.070.1
63.9
37.0
57.9 59.7 60.3
0
20
40
60
80
100
HC VC WB FB DC DM Avg.
% of tran
sverse (x‐x) force
carried by bearing plate
V=375
Ultimate
Ultimate Capacity-Transverse Strain
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FIB63 4 specimens (2 beams)
Monitor cracks after release
Load test
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FIB63 Reinforcement and Prestressing Scheme
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FIB63 Test Specimens
SL
CN
LB
PT
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2 ksi
0 ksi
-2 ksi
-4 ksi
-6 ksi
Release Stresses
CalculatedAllowable
0ft. 5ft. 10ft. 15ft. 20ft. 25ft. 30ft. 35ft. 40ft. 45ft. 50ft.
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SL
CNLB
PT
FIB63 Test Specimens
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Conclusions-Ultimate Strength
Horizontal reinforcement – Negligible
Bearing plate - 9% to 21% improvement
FDOT confinement reinforcement-13% increase over no reinforcement
Bonded Strand - 43% increase for strands placed under web
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Conclusions–Flange Splitting
Tension stress Outer strands Hoyer effect
Strategies Bonded strand arrangement Confinement reinforcement Bearing plate Partial debonding
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Conclusions–Web Splitting
Post-tensioning (PT) Promising Additional research
Large diameter bars (LB) Reduce crack width No effect on crack length
45% strand shielding (SL) Shorter, smaller cracks Affects strength
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Report BDK75 977-05
End Region Detailing of Pretensioned Concrete Bridge Girders
Available on theFDOT Research Website
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Thank You Experimental work conducted at
M. H. Ansley Structures Research Center Many thanks to Sam Fallaha and the Center’s
staff! David Allen Adam Brennan Frank Cobb Steve Eudy Tony Hobbs Will Potter Paul Tighe David Wagner Chris Weigly Steven Nolan, P.E., FDOT Structures Design Office
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Wish List
Bottom Flange
Flange Strands
Flange Strands
Web Strands