FRP composites are becoming a material of choice in an increasing number of rehabilitation and retrofitting projects around the world. Depending on the design objectives, these materials can be used to improve one or more of the structural member characteristics, such as the load capacity, ductility and even durability. Design of structural strengthening applications using externally bonded FRP composites is usually based on conventional design approaches with improvement to account for the presence and characteristics of the FRP material. Non-conventional design issues that are specific to the type of application require special considerations for their proper inclusion in the design process. One such design issue is the debonding problems in externally bonded FRP strengthening applications that have been a concern and a research challenge since the initial development stages of the strengthening method. End-peeling has governed a large interest and several debonding models have been presented. However, interfacial peeling at flexural cracks has not attained the same focus – even though this debonding failure is most likely more common. This paper presents laboratory tests of concrete beams strengthened in flexure with CFRP epoxy bonded plates. Wrapping with CFRP sheets was applied in order to try to localize the failure initiation. Concrete cracking as well as debonding initiation and propagation was possible to observe with help of advanced optical measuring system and high speed camera.
ACI 440.2R-02. (2002). Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures, ACI Committee 440.
2.
Ali-AhmadM.SubramaniamK. and GhosnM. (2006). “Experimental investigation and fracture analysis of debonding between concrete and FRP sheets”, Journal of Engineering Mechanics, ASCE, Vol. 132, No. 9, pp. 914–923.
3.
BonacciJ.F. and MaalejM. (2000). “Externally bonded fiber-reinforced polymer for rehabilitation of corrosion damaged concrete beams”, ACI Structural Journal, Vol. 97, No. 5, pp. 703–711.
4.
CasasJ.R. and PascualJ. (2007). “Debonding of FRP in bending: Simplified model and experimental validation”, Construction and Building Materials, Vol. 21, pp. 1940–1949.
5.
ChenJ.F. and TengJ.G. (2001). “Anchorage strength models for FRP and steel plates bonded to concrete”, Journal of Structural Engineering, ASCE, Vol. 127, No. 1, pp. 784–791.
6.
ChenJ.F. and YuanH. (2007). “Debonding failure along a softening FRP-to-concrete interface between two adjacent cracks in concrete members”, Engineering Structures, Vol. 29, pp. 259–270.
7.
DaiJ.G.YokotaH. and UedaT. (2007). “Hybrid bonding system for optimizing structural performance of FRP flexurally strengthened concrete beams”, Proceedings of the First Asia-Pacific Conference on FRP in Structures (APFIS 2007), SmithS. T., ed., The University of Hong Kong, Hong Kong, China, 12–14 December, pp. 785–791.
8.
fib (2001). Externally Bonded FRP Reinforcement for RC Structures, Bulletin 14, pp. 51–58.
9.
GardenH.N.QuantrillR.J.HollowayL.C.ThorneA.M. and ParkeG.A.R. (1998). “An experimental study of the anchorage length of carbon fibre composite plates used to strengthened reinforced concrete beams”, Construction and Building Materials, Vol. 12, pp. 203–219.
10.
HarmonT.G.KimY.J.KardosJ.JohnsonT. and StarkA. (2003). “Bond of surface-mounted fiber-reinforced polymer reinforcement for concrete structures”, ACI Structural Journal, Vol.100, No. 5, pp. 557–564.
11.
JSCE (2001). “Recommendations for upgrading of concrete structures with use of continous fiber sheets”, Concrete Engineering Series 41, Japan Society of Civil Engineers, pp. 31–34.
12.
KarbhariV.M. and EngineerM. (1996). “Investigation of bond between concrete and composites: Use of a peel test”, Journal of Reinforced Plastics and Composites, Vol. 15, No. 208, pp. 208–227.
13.
LiuI.S.T.OehlersD.J. and SeracinoR. (2007). “Study of intermediate crack debonding in adhesively plated beams”, Journal of Composites for Construction, ASCE, Vol. 11, No. 2, pp. 175–183.
14.
LuX.Z.TengJ.G.YeL.P. and JiangJ.J. (2007) “Intermediate crack debonding in FRP-strengthened RC beams: FE analysis and strength model”, Journal of Composites for Construction, ASCE, Vol. 11, No. 2, pp. 161–174.
15.
MalekA.M.SaadatmaneshH. and EhsaniM.R. (1998). “Prediction of failure load of R/C beams strengthened with FRP plate due to stress concentration at the plate end”, ACI Structural Journal, Vol. 95, No. 1, pp. 142–152.
16.
MazzottiC. and SavoiaM. (2007). “Intermediate debonding of FRP strengthened RC beams”, Proceedings of the First Asia-Pacific Conference on FRP in Structures (APFIS 2007), SmithS. T., ed., The University of Hong Kong, Hong Kong, China, 12–14 December, pp. 877–883.
17.
NiuH.KarbhariV.M. and WuZ. (2006). “Diagonal macro-crack induced debonding mechanisms in FRP rehabilitated concrete”, Composites: Part B, Vol. 37, pp. 627–641.
18.
PanJ. and LeungC.K.Y. (2006). “Debonding along the FRP-concrete interface under combined pulling/peeling effects”, Engineering Fracture Mechanics, Vol. 74, pp. 132–150.
19.
PeaseB.GeikerM.R.StangH. and WeissJ. (2006). “Photogrammetric assessment of flexure induced cracking of reinforced concrete beams under service loads”, Proceedings of the Second International RILEM Symposium: Advances in Concrete through Science and Engineering, Quebec City, Quebec, Canada.
20.
prEN 1992-1-1. (2003). Eurocode 2: Design of Concrete Structures – Part 1–1: General Rules and Rules for Buildings.
21.
RabinovitchO. and FrostigY. (2001). “Delamination failure of RC beams strengthened with FRP strips – A closed-form high-order and fracture mechanics approach”, Journal of Engineering Mechanics, ASCE, Vol. 127, No. 8, pp. 852–861.
22.
SaadatmaneshH. and EhsaniM.R. (1991). “RC beams strengthened with GFRP plates. I: Experimental study”, Journal of Structural Engineering, ASCE, Vol. 117, No. 11, pp. 3417–3433.
23.
SaidH. and WuZ. (2007). “Prediction of load carrying capacity due to intermediate crack-induced debonding in FRP-strengthened flexural members”, Proceedings of the First Asia-Pacific Conference on FRP in Structures (APFIS 2007), SmithS. T., ed., The University of Hong Kong, Hong Kong, China, 12–14 December, pp. 885–891.
24.
SaidH. and WuZ. (2008). “Evaluating and proposing models of predicting IC debonding failure”, Journal of Composites for Construction, ASCE, Vol. 12, No. 3, pp. 284–299.
25.
SebastianW.M., (2001). “Significance of midspan debonding failure in FRP-plated concrete beams”, Journal of Structural Engineering, ASCE, Vol. 127, No. 7, pp. 792–798.
26.
SkočekJ. and StangH. (2008). “Inverse analysis of the wedge splitting test”, Engineering Fracture Mechanics, Vol. 75, No. 10, pp. 3173–3188.
27.
SmithS.T. and TengJ.G. (2001). “Interfacial stresses in plated beams”, Engineering Structures, Vol. 23, pp. 857–871.
28.
StratfordT. and CadeiJ. (2006). “Elastic analysis of adhesion stresses for the design of a strengthening plate bonded to a beam”, Construction and Building Materials, Vol. 20, pp. 34–45.
29.
TengJ.G.SmithS.T.YaoJ. and ChenJ.F. (2003). “Intermediate crack-induced debonding in RC beams and slabs”, Construction and Building Materials, Vol. 17, pp. 447–462.
30.
TengJ.G. and ChenJ.F. (2007). “Debonding failures of RC beams strengthened with externally bonded FRP reinforcement: Behaviour and modelling”, Proceedings of the First Asia-Pacific Conference on FRP in Structures (APFIS 2007), SmithS. T., ed., The University of Hong Kong, Hong Kong, China, 12–14 December, pp. 33–42.
31.
TumialanG.BelarbiA. and NanniA. (1999). Reinforced Concrete Beams Strengthened with CFRP Composites: Failure due to Concrete Cover Delamination, Report No. CIES-99/01, Department of Civil Engineering, Center for Infrastructure Engineering Studies, University of Missouri-Rolla, USA.
32.
TäljstenB. (1997). “Strengthening of beams by plate bonding”, Journal of Materials in Civil Engineering, ASCE, Vol. 9, No. 4, pp. 206–212.
33.
TäljstenB. (1994). Plate Bonding, Strengthening of Existing Concrete Structures with Epoxy Bonded Plates of Steel or Fibre Reinforced Plastics, PhD Thesis, ISSN 0348.8373, Luleå University of Technology, 1994:152D, ISSN 0348-8373, p. 308.
34.
WangJ.L. and ZhangC. (2007). “Nonlinear fracture mechanics of flexural-shear crack induced debonding of FRP strengthened concrete beams”, Proceedings of the First Asia-Pacific Conference on FRP in Structures (APFIS 2007), SmithS. T., ed., The University of Hong Kong, Hong Kong, China, 12–14 December, pp. 871–876.
35.
WuZ.S.KurokawaT.YoshizawaH and HirahataH. (2000). “A study on debonding mechanisms of bonded FRP laminates in beam members”, Journal of Structural Engineering, JSCEVol. 46A, pp. 1469–1478.
36.
YaoJ.TengJ.G. and LamL. (2002). “Debonding in RC cantilever slabs strengthened with FRP strips”, Proceedings of the International Conference on Advanced Polymer Composites for Structural Applications in Construction, Southampton University, UK, 15–17 April, pp. 125–133.
37.
ØstergaardL (2003). Early-Age Fracture Mechanics and Cracking of Concrete, Ph.D thesis, Department of Civil Engineering, Technical University of Denmark, Lyngby, Denmark.
