strengthening of rc beams with externally bonded and anchored frp laminate

188 Pages·2012·2.29 MB·English

by  Ryne Cameron

STRENGTHENING OF RC BEAMS WITH ANCHORED FRP LAMINATE
STRENGTHENING OF RC BEAMS WITH EXTERNALLY BONDED AND ANCHORED
FRP LAMINATE

By RYNE CAMERON, B.ENG.

A Thesis Submitted to the School of Graduate Studies in Partial Fulfillment of the Requirements
for the Degree Master of Applied Science

McMaster University © Copyright by Ryne Cameron, June 2012
McMaster University MASTER OF APPLIED SCIENCE (2012) Hamilton,
Ontario
TITLE: Strengthening of RC Beams with Externally Bonded and Anchored FRP
Laminate AUTHOR: Ryne Cameron, B.Eng. (McMaster University)
SUPERVISOR: Professor A. Ghani Razaqpur NUMBER OF PAGES: xi, 176
ii
ABSTRACT
Premature debonding of externally bonded FRP laminate from retrofitted
reinforced concrete (RC) members can lead to inefficient use of FRP and can limit
the level of strength increase that can be achieved. In this investigation, novel
carbon FRP anchors were used in an attempt to delay the onset of premature
debonding and to achieve superior strength. Nine double shear tests were
performed on small scale concrete prisms to determine the most suitable epoxy
for bonding the anchors to the laminate and the concrete. One type of epoxy
increased the ultimate load of the prism retrofitted with two anchors at each
end of the laminate 83.7% over the control specimens without anchors. The
second phase of the investigation consisted of testing six large scale T-beams
with a 4500 mm span, 400 mm height and 500 mm flange width under four point
bending. Two beams were tested without FRP reinforcement as control beams,
one beam was tested with FRP only epoxy bonded and the remaining three
beams were tested with the FRP epoxy bonded and anchored. One of the beams
with 30 anchors exhibited a 46% increase in the debonding load over the beam
without anchors while the FRP laminate attained a maximum strain equal to 80%
of its ultimate strain capacity, a 94% increase over the beam strengthened with
only epoxy bonded FRP. The results demonstrate the anchoring system’s
effectiveness and a feasible way to efficiently utilize the FRP laminate.

iii
ACKNOWLEDGEMENTS

I would like to sincerely thank my supervisor, Dr. A. Ghani Razaqpur, for sharing
his knowledge, guidance and patience throughout this process. His continued
support led me through this process and I will always be grateful for this
wonderful opportunity to work with him.
I would also like to thank all those who helped me complete my experimental
work in the Applied Dynamics Laboratory. Most notably, I am very grateful for
the help from lab technicians Kent Wheeler and Dave Perrett. Only with their
help and patience could my experimental investigation have been completed.
Special thanks to former McMaster student Ahmed Mostafa, PhD and current
student Kevin Simonds. I am very grateful for Ahmed’s guidance with the
manufacturing of the anchors and with FRP application techniques. Thank you
also to Kevin who helped with the construction of the concrete prisms.
I would also like to thank my parents for encouraging me to continue my
education and showing me the value of hard work through their own example.
Finally, I’d like to thank everyone who helped me in any way, big or small,
through this process, especially, Zach Cameron, Anneke Cameron, Alec Cameron,
Darren Bos, Mark Campbell, Craig Marentette, Matt Bradbury, Eric Durrant, Niel
Van Engelen and Sabrina Gismondi.
Ryne Cameron
Department of Civil Engineering
McMaster University
iv
TABLE OF CONTENTS
Chapter 1 - Introduction ......................................................................................... 1
1.1 General .......................................................................................................... 1
1.2 Problem and Study Motivation ..................................................................... 4
1.3 Research Methodology ................................................................................. 5
1.3.1 Objective and Scope ............................................................................... 6
1.4 Thesis Layout ................................................................................................. 7

Chapter 2 - Literature Review ................................................................................. 8
2.1 General .......................................................................................................... 8
2.2 Predicting Laminate Debonding .................................................................. 17
2.2.1 Closed-Form Analytical Solution........................................................... 18
2.2.2 Chen and Teng Model (2001) ............................................................... 20
2.2.3 Teng et al. (2003) .................................................................................. 22
2.2.4 American Concrete Institute (ACI) 440.2R-08 Guidelines (2008) ......... 23
2.2.5 Said and Wu (2008) .............................................................................. 24
2.2.6 International Federation for Structural Concrete (fib) Bulletin No.14
(2001) ............................................................................................................. 25
2.2.7 CNR-DT 200/2004 (2004) ...................................................................... 27
2.2.8 Rosenboom and Rizkalla (2008) ........................................................... 28
2.2.9 ISIS Canada Design Manual .................................................................. 31
2.2.10 Summary ............................................................................................. 31
2.3 Anchor Comparison ..................................................................................... 32
2.3.1 Mechanically-Fastened (MF) Anchors .................................................. 33
2.3.2 Fan Anchors .......................................................................................... 35
2.3.3 Ductile Anchor System ......................................................................... 37
2.3.4 Hybrid Bonded FRP ............................................................................... 38
2.4 Summary ..................................................................................................... 41

Chapter 3 - Experimental Program ....................................................................... 43
v
3.1 Phase One – Double Shear Tests ................................................................. 43
3.1.1 General ................................................................................................. 43
3.1.2 Material Properties ............................................................................... 49
3.1.3 Fabrication of Specimens ..................................................................... 55
3.1.4 Instrumentation .................................................................................... 58
3.1.5 Test Setup ............................................................................................. 62
3.1.6 Summary of Test Specimens ................................................................ 63
3.2 Phase Two – Large-Scale T-Beams .............................................................. 63
3.2.1 General ................................................................................................. 63
3.2.2 Material Properties ............................................................................... 66
3.2.3 Fabrication of Specimens ..................................................................... 69
3.2.4 Instrumentation .................................................................................... 73
3.2.5 Test Setup ............................................................................................. 76
3.2.6 Summary ............................................................................................... 77

Chapter 4 - Experimental Results ......................................................................... 78
4.1 Phase One.................................................................................................... 78
4.1.1 Control Specimens ................................................................................ 78
4.1.2 Specimens with One Anchor on Each Face .......................................... 83
4.1.3 Specimens with Two Anchors on Each Face ......................................... 98
4.1.4 Summary of Phase One Results .......................................................... 104
4.2 Phase Two ................................................................................................. 105
4.2.1 Control Beams .................................................................................... 106
4.2.2 Epoxy Bonded Beam ........................................................................... 107
4.2.3 Beams with Epoxy Bonded FRP with Anchors .................................... 111
4.2.4 Summary of Phase Two Results .......................................................... 125

Chapter 5 - Analysis ............................................................................................ 127
5.1 General ...................................................................................................... 127
5.2 Phase One.................................................................................................. 127
5.2.1 Average Ultimate Shear Stress ........................................................... 127
vi
5.2.2 Ultimate Load ..................................................................................... 129
5.2.3 Observed Failure Modes..................................................................... 132
5.2.4 Load-Elongation Curves ...................................................................... 133
5.2.5 FRP Laminate Strain Distribution ........................................................ 135
5.3 Phase Two ................................................................................................. 143
5.3.1 Ultimate Flexural Load ........................................................................ 143
5.3.2 Observed Failure Modes..................................................................... 153
5.3.2 Load-Displacement Curves ................................................................. 154
5.3.4 Ductility ............................................................................................... 156
5.3.5 FRP Strain at Debonding ..................................................................... 158
5.3.6 Anchor Efficiency Factor ..................................................................... 160
5.3.7 Predicted Laminate Debonding .......................................................... 162
5.3.8 Summary ............................................................................................. 163

Chapter 6 - Summary and Conclusions ............................................................... 165
6.1 Summary ................................................................................................... 165
6.1.1 Phase One ........................................................................................... 166
6.1.2 Phase Two ........................................................................................... 167
6.2 Conclusions ............................................................................................... 168
6.2.1 Phase One ........................................................................................... 168
6.2.2 Phase Two ........................................................................................... 170
6.3 Recommendations for Future Work ......................................................... 171

References .......................................................................................................... 173

vii
LIST OF FIGURES
Figure 1.1: Anchors for delaying FRP debonding .................................................... 5

Figure 2.1: Shear-Slip Models for Plate to Concrete Bonds ................................. 13
Figure 2.2: Typical tri-linear response of FRP strengthened RC beams/slabs ...... 17
Figure 2.3: Theoretical load-displacement curve ................................................. 19
Figure 2.5: Mechanism of HB FRP anchor debonding .......................................... 39

Figure 3.1: Typical Phase One specimen .............................................................. 44
Figure 3.2: Typical specimen without anchors (a) Elevation view, (b) Top view and
(c) End view ........................................................................................................... 45
Figure 3.3: Typical specimen with one anchor per face (a) Elevation view, (b) Top
view and (c) End view ........................................................................................... 46
Figure 3.4: Typical specimen with two anchors per face (a) Elevation view, (b)
Top view and (c) End view .................................................................................... 47
Figure 3.5: Schematic of CFRP anchors (a) Elevation view, (b) Side view and (c)
Plan view ............................................................................................................... 53
Figure 3.6: CFRP Anchors (a) Carbon fibre fabric and tow for anchor, (b)
Aluminum moulds for making anchors and (c) Finished anchors ........................ 55
Figure 3.7: Cross-section of Phase One specimens .............................................. 56
Figure 3.8: Location of centre north and south strain gauges ............................. 59
Figure 3.9: Location of strain gauges on specimen DS1 (north side) ................... 59
Figure 3.10: Location of strain gauges on specimen DS2 (north side) ................. 60
Figure 3.11: Location of strain gauges and anchors on specimen DS6 (north side)
............................................................................................................................... 60
Figure 3.12: Location of strain gauges and anchors on specimen DS7 (north side)
............................................................................................................................... 61
Figure 3.13: Location of strain gauges and anchors on specimen DS8 (north side)
............................................................................................................................... 61
Figure 3.14: Location of strain gauges and anchors on specimen DS9 (north side)
............................................................................................................................... 62
Figure 3.15: Typical specimen within testing device ............................................ 63
Figure 3.16: Phase Two beam (a) Cross-section and (b) Elevation view .............. 65
Figure 3.17: Loading and support dimensions ...................................................... 65
Figure 3.18: Layout of FRP reinforcement ............................................................ 70
Figure 3.19: Soffit of beams EBA1 and EBA2 ........................................................ 72
Figure 3.20: Soffit of beam EBA3 .......................................................................... 72
Figure 3.21: Location of strain gauges on tensile steel reinforcement ................ 73
Figure 3.22: Location of string potentiometers .................................................... 74
viii
Figure 3.23: FRP strain gauge locations of EB1 ..................................................... 75
Figure 3.24: FRP strain gauge locations of EBA1 .................................................. 75
Figure 3.25: FRP strain gauge locations of EBA2 .................................................. 75
Figure 3.26: FRP strain gauge locations of EBA3 .................................................. 75
Figure 3.27: Typical setup of Phase Two beams ................................................... 77

Figure 4.1: Failure plane of (a) Bottom south side of DS1 and (b) Top south side
of DS2 .................................................................................................................... 80
Figure 4.2: Load-elongation curve for control specimens DS1 and DS2 .............. 81
Figure 4.3: DS1 load-strain curves ........................................................................ 82
Figure 4.4: DS2 Load-strain curves ....................................................................... 82
Figure 4.5: Strain profile in FRP at half and full debonding load of specimen DS1
and DS2 ................................................................................................................. 83
Figure 4.6: (a) Failed specimen DS3, (b) Initial debonding of specimen DS4 and (c)
Failure of specimen DS4........................................................................................ 85
Figure 4.7: Comparison of amount of epoxy used on (a) South side of DS3 and (b)
North side of DS4 .................................................................................................. 86
Figure 4.8: Load-elongation curves for DS3 and DS4 ........................................... 87
Figure 4.9: Load-strain curve for specimen DS3 and DS4 ..................................... 88
Figure 4.10: Failure of DS5 (a) Bottom north face and (b) Failure plane ............. 89
Figure 4.11: Load-elongation curve for DS5 ......................................................... 90
Figure 4.12: Load-strain curve for specimen DS5 ................................................. 91
Figure 4.13: Debonding of DS6 (a) Top north face and (b) Bottom south face .... 93
Figure 4.14: Failure planes of DS7 (a) Bottom south face and (b) top north face 94
Figure 4.15: Load-elongation curves of DS6 and DS7 ........................................... 95
Figure 4.16: DS6 load-strain curves ...................................................................... 96
Figure 4.17: DS7 load-strain curves ...................................................................... 97
Figure 4.18: Strain profile within FRP at half and full debonding load of specimen
DS6 and DS7 .......................................................................................................... 98
Figure 4.19: Failure plane of (a) DS8 and (b) DS9 ............................................... 100
Figure 4.20: Load-elongation curve for DS8 and DS9 ......................................... 101
Figure 4.21: DS8 load-strain curves .................................................................... 102
Figure 4.22: DS9 load-strain curves .................................................................... 102
Figure 4.23: Strain profile within FRP at half and full debonding load for DS8 and
DS9 ...................................................................................................................... 103
Figure 4.24: Typical concrete compression failure of control beams from Mostafa
(2011) .................................................................................................................. 106
Figure 4.25: Load-deflection curves of control beams ....................................... 107
Figure 4.26: Failure plane of east side EB1 ......................................................... 108
Figure 4.27: Load-displacement curve of EB1 .................................................... 109
Figure 4.28: EB1 load-strain curves .................................................................... 110
ix